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         United States
         Environmental Protection
         Agency
           Water Engineering
           Research Laboratory
           Cincinnati OH 45268
EPA/600/9-86/015a
July 1986
         Research and Development
Proceedings

Tenth United States/
Japan Conference on
Sewage Treatment

and
         North Atlantic Treaty
         Organization/Committee
         on the Challenges of
         Modern Society
         Conference on Sewage
         Treatment Technology
         Volume I. Part A.
         Japanese Papers

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                                                                  EPA/600/9-86/015a
                                                                  July 1986
                                          PROCEEDINGS
                              TENTH UNITED STATES/JAPAN CONFERENCE
                                 ON SEWAGE TREATMENT TECHNOLOGY

                                      OCTOBER 17-18, 1985


                                              AND
>                    NORTH  ATLANTIC TREATY ORGANIZATION/COMMITTEE ON THE
<                    CHALLENGES OF MODERN SOCIETY (NATO/CCMS) CONFERENCE
                                 ON SEWAGE TREATMENT TECHNOLOGY
VJ

                                      CINCINNATI, OHIO
                                      OCTOBER 15-16, 1985
                                           VOLUME I.

                                    PART A.   JAPANESE PAPERS
                              U.S.  ENVIRONMENTAL PROTECTION AGENCY
                               OFFICE  OF RESEARCH AND DEVELOPMENT
                                    CINCINNATI, OHIO 45268
                                   U.S. Environmental Protection Agency
                                   Region 5, Library (PL-12J)
                                   77 West Jackson Boulevacd, 12th F/o»
                                   Chicago, II 60604-3590

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                     NOTICE

This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication.  Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
                         11

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                          FOREWORD
     The maintenance of clean water supplies and the
management of municipal and industrial wastes are vital
elements in the protection of the environment.

     The participants in the Japan-United States-North
Atlantic Treaty Organization/Committee on the Challenges
of Modern Society (NATO/CCMS) Conferences on Sewage Treat-
ment Technology completed their conferences in  Cincinnati,
Ohio, in October 198^.  Scientists and engineers of the
participating countr'es were given the opportunity to study
and compare the latert practices and developments in Canada,
Italy, Japan, The Ne.hcrlands, Norway, the United Kingdom and
the United States.  The proceedings of the conferences comprise
a useful body of knowledge on sewage treatment  which will be
available not only to Japan and the NATO/CCMS countries  but
also to all nations of the world who desire it.
                        Lee M. Thomas
                        Administrator
Washington, D.C.
                              TM

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                              CONTENTS


Foreword	111

Japanese Delegation  	  vi

United States Delegation 	 vii

North Atlantic Treatment Organization/Committee on the
   Challenges of Modern Society (NATO/CCMS) Delegation 	viii

Joint Communique	   1

Volume I.
   Part A.  Japanese Papers	   3

Volume I.
   Part B.  United States Papers	367

Volume II.
   North Atlantic Treaty Organization/Committee on the
   Challenges of Modern Society (NATO/CCMS) Papers 	 633

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                           JAPANESE DELEGATION
DR. TAKESHI KUBO
  Head of Japanese Delegation,
  Counselor, Japan Sewage works Agency

TOKUJI ANNAKA
  Chief, Water Quality Section
  Water Quality Control Division
  Public Works Research Institute
  Ministry of Construction

DR. KEN MURAKAMI
  Deputy Director, Research and
  Technology Development Division
  Japan Sewage Works Agency

DR. KAZUHIRO TANAKA
  Chief Researcher, Research and
  Technology Development Division
  Japan Sewage Works Agency

KENICHI OSAKO
  Chief, Eastern Management Office
  Sewage Works Bureau
  Tokyo Metropolitan Government

SAKUJI YOSHIDA
  Chief, Facility Section
  Construction Division
  Sewage Works Bureau
  City of Yokohama

YUKIO HIRAYAMA
  Director, Planning Division
  Sewage Works Bureau
  City of Fukuoka

MASAHIRO TAKAHASHI
  Extraordinary Participant,
  Researcher, Sewerage Section
  Water Quality Control Division
  Public Works Research Institute
  Ministry of Construction

TAKASHI KI MATA
  Extraordinary Participant,
  Researcher, Research and Technology
  Section, Research and Technology Division
  Japan Sewage Works Agency
                                    VI

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                           UNITED STATES DELEGATION
JOHN J. CONVERY
 General Chairman of Conference and
 Head of Cincinnati  U.S.  Delegation
 Director, Wastewater Research Division
 Water Engineering Research Laboratory
 U.S. Environmental  Protection Agency
 Cincinnai, OH 45268

DOLLOFF F. BISHOP
 Co-Chairman of Conference
 Chief, Technology Assessment Branch
 Wastewater Research Division
 Water Engineering Research Laboratory
 U.S. Environmental  Protection Agency
 Cincinnati, OH 45268

FRANCIS T. MAYO
 Director,
 Water Engineering Research Laboratory
 U.S. Environmental  Protection Agency
 Cincinnati, OH 45268

LOUIS W. LEFKE
 Deputy Director,
 Water Engineering Research Laboratory
 U.S. Environmental  Protection Agency
 Cincinnati, OH 45268

DR. JAMES A. HEIDMAN
 Environmental Engineer
 Innovative & Alternative Technology Staff
 Systems & Engineering Evaluation Br., WRD
 Water Engineering Research Laboratory
 U.S. Environmental  Protection Agency
 Cincinnati, OH 45268

HENRY H. TABAK
 Research Chemist,
 Toxic Research & Analytical Support Staff
 Technology Assessment Branch, WRD
 Water Engineering Research Laboratory
 U.S. Environmental  Protection Agency
 Cincinnati, OH 45268

DR. ALBERT D. VENOSA
 Microbiologist, Ultimate Disposal Staff
 Systems & Engineering Evaluation Br., WRD
 Water Engineering Research Laboratory
 U.S. Environmental  Protection Agency
 Cincinnati, OH 45268
ARTHUR H. BENEDICT, Ph.D.
 Brown & Caldwell  Consulting Engrs
 P.O. Box 8045
 Walnut Creek, CA  94546-1220

DR. WILLIAM C. BOYLE
 Dept. of Civil Engineering
 & Environmental Engineering
 University of Wisconsin
 3230 Engineering  Building
 Madison, Wisconsin 55706

DR. MICHAEL CARSIOTIS
 Dept. of Microbiology
 & Molecular Genetics
 University of Cincinnati
 College of Medicine
 231 Bethesda Avenue
 Cincinnati, OH 45267

DR. CLEMENT FURLONG
 Dept. of Medical  Genetics, SK50
 University of Washington
 Seattle, WA 98195

GILBERT B. MORRILL, P.E.
 McCall, Elingson, Morrill, Inc.
 Consulting Engineers
 1721 High Street
 Denver, CO 80218

DR. GEORGE PIERCE
 Battelle-Columbus Laboratories
 505 King Avenue
 Columbus, OH 43201

DR. JOHN N. REEVE
 The Ohio State University
 Dept. of Microbiology
 484 West 12th Avenue
 Columbus, OH 43210-1292

DR. H. DAVID STENSEL
 Dept. of Civil Engrg, FX-10
 University of Washington
 Seattle, WA 98195
                                     VII

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       NORTH  ATLANTIC  TREATY  ORGANIZATION/COMMITTEE  ON  THE  CHALLENGES
                  OF MODERN SOCIETY  (NATO/CCMS)  DELEGATION


DR. J. DUANE  SALLOUM
 Chairman of  NATO/CCMS Committee
 Director, Technical  Services Branch
 Environmental  Protection Service
 Ottawa, Canada K1A 1C8

DR. B. E. JANK
  A/Director,
  Wastewater  Technology Centre
  Canada Centre for Inland Waters
  P.O. Box 5050,
  Burlington, Ontario  L7R 4A6
  Canada

DR. ROLF C. CLAYTON
  Director,
  Process Engineering
  Water Research Laboratory
  Elder Way,  Stevenage, Herts, SGI  1HT,
  England

DR. IR. WILHELMUS H. RULKENS
  Department  of Environmental  Technology
  Division of Technology for  Society
  MT/TNO
  P.O. Box 342, 7300 AH Apeldoorn
  The Netherlands

DR.ING. BJ0RN RUSTEN
  Aquateam, Norwegian  Water Technology Centre A/S
  P.O. Box 6593
  Rodelrfkka,  N-0501 Oslo 5,
  Norway

DR. MARIO SANTORI
  Institute di  Ricerca sulle  Acque
  Consiglio Nazionale  delle Ricerche
  Rome, Italy 00198
                                  VI 1 1

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  DELEGATES TO THE NATO/CCMS CONFERENCE AND THE TENTH UNITED STATES/
           JAPAN CONFERENCE ON SEWAGE TREATMENT TECHNOLOGY
ANDREW W.  BREIDENBACH ENVIRONMENTAL RESEARCH CENTER,  CINCINNATI,  OHIO

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DR. JOHN H. SKINNER,  DIRECTOR,  OFFICE OF ENVIRONMENTAL  ENGINEERING
 AND TECHNOLOGY,  MR.  FRANCIS T.  MAYO, DIRECTOR,  WATER ENGINEERING
   RESEARCH LABORATORY,  U.S. EPA AND DR.  TAKESHI  KUBO,  HEAD  OF
  JAPANESE DELEGATION AND  COUNSELOR,  JAPAN  SEWAGE WORKS AGENCY
 MR. DOLLOFF F. BISHOP, U.S. DELEGATE AND DR. ROLF C. CLAYTON,
           NATO/CCMS DELEGATE FROM THE UNITED KINGDOM

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   VIEW OF CAPTOR WASTEWATER TREATMENT PROCESS
  TEST AND EVALUATION FACILITY, CINCINNATI, OHIO
   VISIT TO THE MULTIPLE DIGESTION PROJECT
TEST AND EVALUATION FACILITY, CINCINNATI, OHIO
                       XI

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                           JOINT COMMUNIQUE
                 TENTH UNITED STATES/JAPAN CONFERENCE
                    ON SEWAGE TREATMENT TECHNOLOGY

                           Cincinnati, Ohio
                           October 18, 1985
1.   The Tenth United States/Japan Conference on Sewage Treatment
Technology was held in Cincinnati, Ohio, from October 17 to 18, 1985.

2.   The Japanese delegation headed by Dr. Takeshi Kubo, Counselor,
Japan Sewage Works Agency,was composed of two representatives from the
Ministry of Construction, three representatives from the Japan Sewage
Works Agency and one each from the local  governments of Tokyo, Yokohama
and Fukuoka.

3.   Mr. John J. Convery, Director, Wastewater Research Division, Water
Engineering Research Laboratory, U.S. Environmental Protection Agency,
was head of the U.S. delegation,which consisted of seven representatives
of the federal government,  five academia representatives and three repre-
sentatives from consulting engineering firms and scientific laboratories.

4.   The chairmanship of the Conference was shared by Mr. John J. Convery
and Dr. Takeshi Kubo.

5.   During the Conference, papers relating to the joint research projects
on sludge treatment and disposal, including combustion, oxidation and compost-
ing,were presented by both  sides.   Data and findings on the joint research
projects were mutually useful and provided increasing insights into the
nature of the problems and  potential  solutions for each country.  A decision
was made to expand the scope of the joint research projects to include
anaerobic treatment of wastewater.

6.   Principal topics of the Conference were bioengineering applications
in wastewater treatment as  well as sludge management and disposal,
aeration practice, wastewater reuse,  odor control,  small flow sewerage
system, nutrient control and innovative biological  treatment processes.


     The discussions which  followed the presentations were also useful
to both countries.

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7.   Field visits in Lawrence, Marlborough and Hartford,  Connecticut;
Chicago, Illinois; Madison and Milwaukee, Wisconsin;  and  Sacramento,  Cali-
fornia; are planned to inspect wastewater treatment facilities  in these
areas.

8.   Recent engineer exchanges between the two countries  included a two-
week visit in 1985 to Japan by Mr.  James F. Kreissl,  Wastewater Research
Division, Water Engineering Research Laboratory,  U.S. Environmental
Protection Agency,and a fourteen-month visit to the United States by
Dr. Kazuhiro Tanaka, Japan Sewage Works Agency, in 1984 to 1985.  Mr.
Takashi Kimata of the Japan Sewage Works Agency is now staying  at the
above U.S. EPA Cincinnati Research  Laboratory.  Both  parties  agreed  to
continue the engineer exchange program.

9.   It was proposed by the Japanese side that the Eleventh Conference
be  held  in Tokyo, Japan, about September 1987, and the future Confer-
ences in the United States would be held in Cincinnati, Ohio  and also  in
Washington, D.C. as were the past Conferences.

10.  A proceedings of the Conference will be printed  in English and  Japanese.

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                              JAPANESE PAPERS
APPLICATION OF BIOTECHNOLOGY TO WASTEWATER TREATMENT	    5
   Itaru Nakamoto, Head, Sewerage and Sewage Purification
   Department, Ministry of Construction

AUTOGENOUS COMBUSTION OF SEWAGE SLUDGE	19
   T. Murakami, Senior Research Engineer, and K.  Murakami,
   Deputy Director, Research and Technology Development Division,
   Japan Sewage Works Agency

THE PERFORMANCE OF THE CARVER-GREENFIELD PROCESS	67
   Kenichi Osako, Nagaharu Okuno, and Hitoshi Daido, Sewerage
   Bureau, Tokyo Metropolitan Government, Japan

CENTRALIZED SLUDGE TREATMENT IN YOKOHAMA	   91
   Sakuji Yoshida, Chief Engineer, Sewer Designing Division,
   Construction Department, Sewage Works Bureau,  City of
   Yokohama

ODOR CONTROL IN MUNICIPAL WASTEWATER TREATMENT PLANT	127
   Masahiro Takahashi, Research Engineer, Sewage  Works Section,
   and Shigeru Ando, Director, Water Quality Control Division,  Public
   Works Research Institute, Ministry of Construction

SLUDGE DISPOSAL BY COMPOSTING IN FUKUOKA	153
   Ukio Hirayama, Director of Planning Division,  Sewage Works Bureau,
   City of Fukuoka

TECHNICAL EVALUATON OF "ENERGY-SAVING" AERATION DEVICES 	  197
   Tokuji Annaka, Chief, Water Quality Section, and Masahiro
   Takahashi, Research Engineer, Sewage Works Section, Water  Quality
   Control Division, Public Works Research Institute, Ministry  of
   Construction

FULL SCALE EVALUATION OF BIOLOGICAL PHOSPHORUS AND NITROGEN REMOVAL . .  223
   K. Tanaka, Senior Research Engineer, T. Ishida, Research
   Engineer, and T. Murakami, Research Engineer,  Research and
   Technology Development Division, Japan Sewage  Works Agency

PERFORMANCE EVALUATION OF OXIDATION DITCH PROCESS 	  265
   K. Matsui, Research Engineer, and T. Kimata, Research Engineer,
   Research and Technology Development Division,  Japan Sewage
   Works Agency

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PLANNING AND DESIGN MANUAL FOR SMALL-SCALE SEWERAGE SYSTEM 	   303
   S. Ohmori, Research Engineer,  M.  Fukabori,  Research Engineer,  and
   K. Murakami, Deputy Director,  Research and  Technology Develop-
   ment Division,  Japan Sewage Works Agency

EFFLUENT REUSE IN  AN URBAN RENEWAL  DISTRICT IN TOKYO 	   343
   Kenichi  Osako and Yasuo Kuroda,  Sewerage Bureau, Tokyo
   Metropolitan Government, Japan

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                     Tenth United States/Japan Conference
                        on Sewage Treatment Technology
 APPLICATION OF BIOTECHNOLOGY

                 TO

     WASTEWATER TREATMENT
The work described in this paper was
not funded by  the U.S. Environmental
Protection Agency.  The contents do
not necessarily  reflect the views of
the Agency and no official endorsement
should be inferred.
             Itaru Nakamoto

                 Head

 Sewerage and Sewage Purification Department

          Ministry of Construction

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                              TABLE OF CONTENTS
                                                                          Page
1.   STATUS QUO OF SEWERAGE AND SEWAGE PURIFICATION PROGRAMS IN
     JAPAN AND NEEDS FOR WASTEWATER TREATMENT TECHNOLOGY 	      8
 1.1   History and status Quo of Sewerage and Sewage
       Purification Programs 	      8
 1.2   Status Quo and Needs for Wastewater Treatment Technology	     12
2.   DEVELOPMENT OF NEW WASTEWATER TREATMENT SYSTEMS
     EMPLOYING BIOTECHNOLOGY 	     14
 2.1   Outline of Biofocus W.T	     14
 2.2   Joint Research System 	     17

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                         APPLICATION OF  BIOTECHNOLOGY
                                      TO
                            WASTEWATER  TREATMENT

                                Itaru  Nakamoto
                                    Head
                 Sewerage and Sewage  Purification Department
                          Ministry of Construction


                                   PREFACE

     In Japan, secondary treatment of municipal wastewater became real for
the first time using standard-rate trickling filter in Tokyo in 1922.
However, the activated sludge process became the leading one among wastewater
treatment processes since the conventional process was introduced in
Nagoya-city in 1930.  The activated sludge process requires comparatively
high skills and attentive control of  the sludge to perform good treatment,
while it offers an advantage creating the better-quality effluent than any
other secondary processes.

     Despite the long history of success, improvement of the activated sludge
process has been strongly desired since it requires an immense land or
enormous energy for treatment and disposal of excess sludge.  In addition,
the effluent is expected to play a positive role in the prevention of
eutrophication of lakes and oceans, thereby increasing the need for
development of the technology to improve and stabilize the removal rate of
nitrogen and phosphorus which cause eutrophication.   Further, various needs
for technology development are imposed on us, such as the technology to
degradade and stabilize toxic substances when subtley contained in the
influent, decoloring technology which widens the scope of reuse of the
effluent, and energy saving wastewater treatment technology which is the
eternal need of Japan poor in its energy resources.

     To meet such social needs, the Ministry of Construction has decided to
carry out the five-year research project for "Development of new wastewater
treatment systems employing biotechnology", starting from the fiscal year of
1985.

     This project is called "Biofocus W.T.".  Described in this paper are the
status quo of the Sewerage and Sewage Purification Programs in Japan which
helped to set out the biotechnology project and to identify the needs for
wastewater treatment technology (Chapter 1), and the outline of the Biofocus
W.T. (Chapter 2).

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1.   STATUS QUO OF  SEWERAGE AND SEWAGE PURIFICATION PROGRAMS IN JAPAN AND
     NEEDS FOR WASTEWATER TREATMENT TECHNOLOGY

1.1  History and  Status Quo of Sewerage and  Sewage Purification programs

          The Sewerage and Sewage Purification  Programs as public works
     became real  with enactment of the Sewerage Law in 1958.  The first
     Five-Year Plan of Sewerage Construction was started in 1963.  Since
     then, several  Five-Year Plans have been carried out with revisions  until
     the current  5th Five-Year plans.  During such period, the scale of
     investment to  the sewerage programs went through rapid progress.  It had
     once grawn equivalent to the defense  budget.   However, it has been  at a
     standstill these years reflecting the severe  financial situations
     (Fig. 1).
      B    C

"2.0  1.0  10 -




 1.6  0.8  8




 1.2  0.6  6



 0.8  0.4  4
         0.4
             0.2
                            Investment to sewerage programs
                                                      (A) Trillion Yen,
                     	 Investment to sewerage programs/GNP (B)  %

                     	 Investment to sewerage programs/   (C)  *
                            Government Fixed Capital Formation
                                                      •75
                                                                '80
                                                                         '84
                   Note: GW and qi ivi--i nmcn t fixed capital formation of each year before 1964 are
                        bd.s.'d on tliu old SNA.

            Fig.  1   Trends of the investment  to sewerage programs
          The number  of municipalities having  started Municipal Sewerage
     Program is  836 at the end of FY  1984.   This number holds a quarter of
     the total 3,256  Japanese municipal bodies.   Four-hundred and
     eighty-three (483) municipalities out  of  such 836 are currently carrying
     out treatment of their municipal wastewater.  Regional sewerage program
     has been carried out at 81 places in the  41 prefectural divisions, and
     43 wastewater treatment plants are now in operation.  Moreover, the
     Special Environment Protection Municipal  Sewerage Program for
     agricultural/mountain/fishing villages and national parks have  been
     carried out at 94 places, and the Special Public Sewerage Program for

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 the areas containing industrial wastewater over two third (2/3) of the
 total quantity have been practiced  at  8  places (Pig. 2).
      Number of
      places
          1000
          800
          600
          400
          200
Municipal sewerage
Regional sewerage
Storm drainage
Special public sewerage
Special environment protection
                     municipal sewerage
                                                             910
            u     '60        '(,'j       '70       '75        '80     '84

Fig. 2  Trend of the  number  of  cities carrying out sewerage programs
      In spite of such increase in the investment to the Sewerage and
 Sewage purification Programs and in  the  number  of places carrying out
 sewage works, improvement has been slow  in  the  spread of sewerage
 systems.  The fiscal year of 1984 has proved that the number of
 inhibitants in the sewered areas holds no more  than 34% of the total
 Japanese population.  Such percentage held  by designated cities with
 population over one million is as high as 80%,  while general cities show
 such  percentage of only 20%.  This means that there is a big disparity
 in  the service by sewerage systems among areas.  It is urgently demanded
 to  spread sewerage systems to comparatively less-inhibitied local cities
 thereby decreasing the disparity among areas.

      The Ministry of Construction has announced several measures in
 these years,  to let as many people as possible  understand the benefits
 of  sewerage systems and to smoothly  promote the sewerage programs.
 Table 1 presents the list of cities  to which the model project of sewage
 works called Aquatopia (from Aqua Utopia) are applied and the purposes
 of  the project.  In these works, it  is tried to retrieve "rest by the
 water".  In the Aquatopic cities, the sewerage  programs are to be
 promoted with priority.  Besides such works,  the other model projects
 such  as Appeal Sewerage (Table 2) and Idea  sewerage (Table 3) have been
 practiced,  thereby trying to make citizens  recognize the benefit of
 sewage works.

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Table 1  List of aquatopia projects
Prefecture
Hokkaido

Aomori


Yamagata

Ibaraki

Gunma

Gifu


Shizuoka

Osaka


Shimane

Okayama


Yamaguchi

Fukuoka


Kumamoto


City/Town
Ikeda

Hirosaki


Tendo

Itako

Raruna

Takayama


Hamamatsu

Toyonaka


Matsue

Kurashiki


Hagi

Yanagawa


Hitoyoshi


Major water body
Riyomi Nisen
River
Dobuchi River


Kuratsu River

Itako Cannals

Lake Haruna

Miya River


Hamana Lake

In town Rivers


Ohashi River

Kurashiki River


Niihori River

Yanagawa Cannals


Yamada River


Major purpose
Clean water ways in the town and improve water quality of the Kiyomi
Nisen River to create resort places for citizens.
Improve water quality of the streams in the city and stock the
water ways with carp so as to give citizens the opportunities to
familiarize with water.
Clean all water ways in the city so as to offer the citizens the
resort places where carp are stocked.
Clean all cannals in the town so as to improve the environment of
the town of "Iris and Cannals.".
Clean all water ways in the town so as to maintain water quality of
Lake Raruna which is the precious property of the citizens.
Improve water quality of all water ways in the city so as to
maintain the precious environment of the town which is called
" small Kyoto" .
Improve water quality of all water ways in the city so as to offer
the citizens the opportunities to familiarize with water.
Restore the "home of fireflies" at the artificial water way in the
Tokura district as well as to improve water quality of all water
ways in the city so as to offer the citizens the resort places.
Improve water quality of all water ways in the city so as to
restore the Matsue-city as "city of water".
Improve water quality of water ways in the city so as to create the
environment matching the white walls (symbol of the city) and to
offer the citizens the opportunities to familiarized with water.
Improve water quality of all water ways in the city so as to
restore the precious environment of Hagi, a historical castle town.
Improve all water ways in the city so as to restore the environment
of the cannal district which is remembered with connection to
Hakushu (historical Japanese poet) , the property of the citizens.
Maintain water quality of Kuma River (famous for rifting) as well
as to improve water quality of all water ways in the city so as to
offer the citizens the opportunities to familiarized with water.
                  10

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Table 2  List of appeal sewerage projects
Prefecture
Hokkaido
Hokkaido
Saitama
Toyama
Saitama
Osaka
Kyoto
Shiga
Osaka
Okayama
Ehime
Oita
City/Town
Otaru
Lake Akan
Honjo
inani
Kawagoe
Toyonaka
Kyoto
Ohmi-
hachiman
Sakai
Yamate
Imabari
Oita
Project name
Otaru Cannal Clean Project
"Marimo" (Aegagropila Sauteri)
Protection Sewerage System
Friendly to Weaver Fish
(Tittlebat) Sewerage System
Snowless Sewerage
Firefly Fostering Shingashi
River project
Preparation of the Firefly
Dancing sewerage System
Yodo Castle Sight Protection
Sewerage System
The Hachiman Cannal Revival
Sewerage System
Revival of Rikyu's
Intrenchment
Agricultural Villages Waste-
water Reclamation Project
Rivers Revival Project by
Short Cut - Kinboshi River
Polluted by Dyeing
Funai Castle Fresh Dp project
Purposes
The Otaru cannal district along with the stone warehouses, the remainder of Bokkaido pioneering era,
is a resort spot for the citizens. The cannal whose water quality has been deteriorated by domestic
wastewater shall be cleaned via urgent preparation of sewage works so as to protect the historical
legacy.
Water quality of the mysterious Lake Akan where "marimo" (Aegagropila Sauteri) is found has been
deteriorated every year due to urbanization of the peripheral areas. Miscellaneous wastewater from
the hotel district around Lake Akan, which is now discharged into the lake, shall be taken into
sewage so as to protect the precious natural product "marimo" from now on as well as in future.
Hoto-oyama River which is completely polluted by urbanization need be cleaned by preparation of
sewage so as to create a friendly environment for weber fish that used to live therein and to
complete the "Honjo Riverside Combination Park" which links historical remains and sights along
Hoto-oyama River.
Inami-machi has snow over 1 m depth every winter, which affects traffic and civil life in the town.
It is promoted to make the city tough against snowing by providing the snow melting function (Removing
snow from the town) to the Yamami-city sewage system.
The Kawagoe-city municipal sewerage shall be prepared so as to clean water of Shingashi River.
The natural environment, in which fireflies show up as dusk gathers, shall be restored together with
the civil movement for "Firefly Fostering Shingashi River".
Urbanization has been promoted thereby spoiling the natural environment. The natural environment
shall be restored so that fireflies dances in the Tokura district (which used to be famous for
fireflies) and the peripheral districts thereof and to create a cozy city space: Artificial breeding
of fireflies is available now.
The site of Yodo castle is now popular as Yodo castle park. Mixing of miscellaneous wastewater from
the peripheral districts into the moat around the castle and water ways in the peripheral districts
has deteriorated the water quality. Water environment shall be made suitable for the historical
remainings by promptly preparing sewerage in the peripheral districts for improvement of the water
quality.
Rachiman cannal established in the era of Momoyama (1585) has been polluted by accumulated sludge
causing water quality deterioration. Dredging and plantation for scenic purpose have been practiced
in the course of river improvement works and city greening works (by the National Land Agency) with
less effect for water quality maintenance. Therefore, the municipal sewerage shall promptly start
its services so as to maintain water quality of the Hachiman cannal.
Sakai-city had flourished in the era of civil wars. One of the reasons for prosperity is that the
town surrounded itself by intrenchment in fear of invaders and observed strict nutrality in politics
and military affairs. Sewage works shall be prompted in hilly districts so as to revive such
intrenchment, which is noted with connection to Rikyu (historical Japanese poet).
Yamate-mura is hardly benefitted by water resources having small quantity of rain through the year and
no trunk rivers. Accordingly, treated wastewater shall be utilized for the secondary water ways as
well as for agricultural waters.
Imabari-city, whioih is the No. 1 in towel production, has been suffered from water pollution by
dyeing industrial wastewater is discharged directly into rivers. Bypass sewers shall promptly be
prepared so as to decrease water pollution by dyeing and to avoid flood into the town.
More and more domestic wastewater has been discharged into Funai castle internal trench (closed water
area), thereby causing serious pollution these days. Treated wastewater shall be supplied to Funai
castle internal trench so as to clean the historical remaining.

-------
                    Table  3   List of  idea  sewerage FY  1983
Prefecture
Akita
Tokyo
Kanagawa
Yamanashi
Toyama
Shizuoka
Osaka
City/Town
Lake
Tazawa
Each word/
section
Zushi
Takane
Takaoka
Haraaraatsu
Osaka
Project name
Reuse of refuse involving the
residents
Purification of combined sewer
overflows (swirl concentrator)
Energy saving sludge processing
using waste heat generated by
garbage furnace
Aeration-omitting wastewater
treatment (Aerobic, anaerobic
biofilra process)
Energy-saving sludge furnace
project
Simultaneous removal of nitro-
gen and phosphorus by
microorganisms
Countermeasure for local flood
utilizing the underground of
the park - Imazu storage tank
Purposes
By using the refused plastic material (vacant bottles)
collected through the town cleaning movement as
attached media for aerobic contictor the treatment
plant construction cost can be cut while promoting
effective reuse of such refused material.
Wet weather combined sewage drained into rivers and
waters shall be utilized to maintain water quality of
the public waters after being eliminated the polla-
tents such as suspended solids therein through the new
separation method, that is, the swirl
repelator/concentrator .
The sludge drying facility shall be accommodated with
the city garbage furnace: sludge cakes generated from
wastewater shall be dried by the waste heat of the
furnace. Thus, the amount of sludge can be decreased
and stabilized while cutting energy (fuel) and mainte-
nance cost.
The microorganisms which can achieve purification
without air have been adapted for treatment thereby
omitting aeration, that is, the electric power. This
aeration-omitting process is just suitable for small-
scale treatment plants.
Digestion gas generated from the accompanied excreta
disposal facility shall be used as fuel for the sludge
furnace and the deodorizing facility equipment there-
by saving fuel and cutting maintenance cost.
Eutrophication of Lake Ramana shall be avoided
through the removal of nitrogen and phosphorus:
Mixed liquor shall go through repetition of stirring
and aeration thereby removing nitrogen and phosphorus
simultaneously with the help of microorganisms.
An underground storage tank having capacity about
26,000 m3 (W 5.0 m x D 5.3m x 109.3 m x two basins,
W 10.8 m x D 5.3 m x 115.1 m x two basins) shall be
prepared underground of Imazu park in Tsurumi
district. The tank shall temporarily store excess
stormwater thereby preventing lowlands from flooding.
1.2  Status Quo and Needs for Wastewater Treatment Technology

          Five-hundred and twenty-two (522)  publicly owned wastewater
     treatment plants have been in operation by the end of FY 1982.   Table 4
     shows these plants classified based on their treating methods.   This
     table manifests that the overwhelming majority of  treatment plants are
     adopting the treatment method so called activated  sludge process.   There
     is no room to doubt that the activated sludge process is advantageous to
     the earlier treatment methods.  However, the following problems
     resulting from the situations unique to Japan have been pointed out.
                                      12

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             Table  4  Number of plants of  each treatment  process
                                                                        (The end of F.Y. 1982)
\v Treatment
\, process
Planed daily \
maximum dry \
weather flow \
(1,000 m3/day) \
Less than 5
5-10
10 - 50
50 - 100
100 - 500
More than 500
Total
Primary
Sedimen-
tation
process
2
1
2



5
Intermediate
High-
rate
trickl-
ing
filter
2
3
6
1
1

13
High-
rate
aera-
tion
2

14
3


19
Secondary
Conven-
tional
acti-
vated
sludge
process
37
45
121
69
88
10
370
Step
aera-
tion
process
5
6
13
23
21
9
77
Extend-
ed
aera-
tion
process
12
1




13
Contact
stabili-
zation
process
1





1
Pure
oxygen
aera-
tion
process
2

1

2

5
Oxida-
tion
ditch
process
6




•
6
Rotating
biologi-
cal
contac-
tor
process
7
3
2
1


13

Total
76
61
158
96
112
19
522
Notes:   1.  In case two or more treatment processes are employed at a plant, the one treating the largest flow
          is counted.
       2.  Details of the total 522 treatment plants:
          Municipal sewerage 	 460
          Regional sewerage 	  41
          Special public sewerage 	   8
          Special environment protection municipal sewerage —  13
               10.0
                1.0
                0.1
                0.01
                                       O    000
                                      °     °     °
                                                                      10"
                               10s           10'          10-

                               Wastewater flow rate (1,000 m /year)

         Fig. 3   Electric consumption depending  on scale  in activated
                  sludge  process


          The first  problem  is that  the energy efficiency  in the activated
     sludge  process  is deteriorated  as the  scale  of  the  treatment  plant
     becomes smaller.   Fig.  3 shows  electric  power  required for treatment
     (including sludge treatment/disposal)  of 1 m3  wastewater depending on
                                            13

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     the amount of influent to the treatment plant.   As mentioned  before,
     sewerage systems are to be spreaded mainly to comparatively small-scale
     local cities in Japan in the future. With consideration to the limited
     energy available in the whole nation,  the problem of  deterioration of
     the energy efficiency corresponding to  small-scalling shall be  closed  up.

          Secondly, sludge disposal holds much more  significance in  Japan
     than any other countries since it has only a small land.   In  fact,  lack
     of room for sludge disposal has naturally popularized the method of
     expensive sludge incineration and disposal of the outcoming ashes within
     the site of treatment plant.

          In the third place, receiving waters to which the effluent is to  be
     discharged are limited in many cases to rivers  and/or inland  waters
     which have only a small dry weather flow.  For  such cases, advanced
     treatment to eliminate nutrients is required to avoid eutrophication of
     rivers and lakes.  However, nutrients  removal can not be achieved in a
     stable manner in the activated sludge  process.   The chemical  oxygen
     demand (COD) is used as one of the effluent standards in some areas.
     It has turned out that the activated sludge process does not  necessarily
     remove COD to a satisfactory point.

          The fourth problem is that the use of treated wastewater is limited
     due to the remaining refractory substances, color of  water,
     epidemiologic danger, and others.  Some local areas in Japan  suffer from
     water shortage every year.  One of the  effective methods to solve the
     problem of water shortage is to promote the reuse of  treated
     wastewater.  To make the reuse system of the treated  wastewater to solve
     the problem of water shortage with local and seasonal pecuriorities,
     some technical innovation is needed in  the secondary  treatment  processes
     before advanced treatment.

          As for sludge treatment, various needs can be easily listed:
     countermeasures for sludge containing heavy metals, improvement of the
     anaerobic sludge digestion process, and of the  compost process, etc.

          These problems found in the existing systems and/or the  needs
     recognized to be studied have worked as driving force to start  the
     Biofocus W.T. research and development  project.
2.   DEVELOPMENT OF NEW WASTEWATER TREATMENT SYSTEMS EMPLOYING BIOTECHNOLOGY

2.1  Outline of Biofocus W.T.

          Only ten and several years have passed since the term biotechnology
     or bioengineering has started to be used.   Although these terms have not
     yet been defined clearly even at present,  biotechnology shall be
     defined, in a wide sense, as follows.

          "Technology to utilize the life maintenance functions of biological
          organisms for human being"

                                         14

-------
     Biotechnology helps us to benefit our life by utilizing the
functions of  biological organisms or part of such functions  based on the
results obtained from the basic studies of vital phenomena.   We are
employing biological treatment processes for wastewater  treatment:  that
is,  it can  be said that we have already been utilizing biotechnology in
a wide sense.   The first and the most important step  to  apply
biotechnology (including the existing and new) for wastewater treatment
is to precisely identify the characteristics of the existing problems
and  classify  them based on the methods for solution.

     The basic strategy of the Biofocus W.T. begins by classifying  the
existing problems of wastewater treatment as shown in Fig. 4.
The  problems  are identified to be classified as follows:

(1)  The current technology is not economical.

(2)  The current technology is not stable nor effective.

(3)  The problem cannot be solved by the current technology.
      o Removal of heavy metals from sludgn

      o Improvement of sludge dewaterb11ity

      o Stable removal of toxic substances

      o Stable decolorization
   Fig. 4  Problems  in current wastewater treatment technologies
           and their classifications
     Along with classification of the problems, the methods for solution
can also be classified  as  follows:
                                    15

-------
 (1)   improvement  of an existing treatment technology

 (2)   Application  of a technology from a  different field (technology
       transfer)

 (3)   Search for novel microorganisms not prently utilized in  treatment
       and development of the  application  methods thereof

 (4)   Improvement  of microorganisms by genetic alteration

       The definition of the existing technologies differs from country to
 country.  Such definition by field engineers and that by scholars do not
 necessarily conform to each  other within Japan.  Provided that the
 existing technologies are to be understood as those which went through
 historical and spatial selection and those which have been practically
 and widely adopted, the following can be listed: the activated sludge
 process as a suspended growth type of biological wastewater treatment
 process, the trickling filter and the rotating biological contactor as  a
 biofilm process,  and the aerobic and anaerobic sludge digestion as
 suspended growth  types of sludge treatment process.

       The Biofocus W.T. project, leaving  improvement of these  existing
 technologies to other research projects, focuses on study, development,
 and practical application of solution methods classified as  (2)  through
 (4) in  the forementioned category.  Table 5 shows the research subjects
 of the  Biofocus W.T.
Table  5   Research  subjects of  development of new wastewater treatment
          systems employing biotechnology


        I.    Development of immobilization technology  of enzymes and microorganisms
             - Study on immobilization methods
             - Study on bioreactor
             - Study on biosensor

        II.   Development of enzyme and microorganism bank
             - Study on separation and classification  of microorganisms
             - Study on evaluation of enzymes
             - Study on preservation and mass cultivation of microorganisms
        III.  Development of novel bacteria by using genetic alteration
             - Study on needs and feasibility of the genetic control
             - Improvement of novel microorganisms by  recombinant DNA
             - Development of novel microorganisms by  cell fusion

        IV.   Development of combined technology of physical/chemical
             Processes with biological processes
             - Study on evaluation for physical/chemical treatment processes
             - Study on total treatment system

        V.    Application of new technologies to the practical wastewater treatment system
             - Application to the publicly owned wastewater treatment system
             - Application to the single house wastewater treatment
      As for the first subject,  "Development of immobilization technology
 of enzymes and microorganisms", the technology which has already been
 practiced in the  fermentation  industry  and the pharmaceutical industry
 shall  be transferred to the  wastewater  treatment  field.  The fluidized


                                      16

-------
      biological  reactor  utilizing fine  sand or  granular  activated carbon  has
      been  wordly studied and developed.   In this  subject,  the carrier
      themselves  used  in  such a  carrier  bound method  shall  first be
      developed.   The  entrapped  immobilization method shown in Fig. 5 shall
      also  be  studied.
                      i— Pluidized —
     Immobilization—
                    Covalently bound
i—Carrier-bound   \
                    Adsorbed
                    -Mi cr ocaps ula ted
1—Entrapped
                    Matrix-entrapped
                      1—Fixed	Bound

               Fig.  5  Classification of  immobilization methods


          For  the biosensor technology, which is one of the application
     technologies of enzyme immobilization, development shall be done for
     more highly stable sensor for water quality monitoring.

          The purpose of the second subject, "Development of enzyme and
     microorganism bank", is to collect and study unused microorganisms as
     well as to study the application method for wastewater treatment.
     Natural selection of microorganisms, especially those living in the
     extreme environments, is already initiated.  As for the bacteria known
     to have specific abilities such as nitrifying bacteria, methane
     bacteria, and photosynthetic bacteria, the mass cultivation methods with
     the help of immobilization technology are now being studied.

          The third subject, "Development of novel bacteria by using genetic
     alteration", requires to reveal genetic codes responsible for producing
     specific proteins, or enzymes, in the first place.  Much efforts are to
     be intensified in the selection of mutants, because the use of novel
     bacteria produced by recombinant DNA is stricly limited to the reactor
     with the capacity less than 2,000 litters.

          Those three subjects above mentioned are all related to the use of
     microorganisms to the treatment of wastewater.  However,  wastewater
     treatment consists of not only biochemical  processes but also physical
     and/or chemical processes.  The forth and fifth subjects are aiming at
     the development of total wastewater  treatment system followed by
     demonstrative verification in the fields.

2.2  Joint Research System-

          The Biofocus W.T.  is expected to play  a kind of  revolutionary role
     in the wastewater treatment technology for  the next century.  The
     project cannot be achieved only by the Ministry of Construction without


                                      17

-------
     seeing the limit:  the project shall be promoted by several  joint
     researches by the Ministry of Construction,  municipal bodies,  public
     corporations, and private enterprises.  Therefore, the "Regulations on
     Joint Study of the Institutes of Ministry on Construction"  was revised
     in June, 1985.  Primary revision was that the Institutes  became able to
     carry out the joint research with a private  company.

          Methods of joint research shall be classified into two:

     (1)  The Ministry of construction specifies  the joint party:

               The joint party shall be limited to national research
          institutes, municipal governments, public corporations, or
          associations representing the industry.

     (2)  The joint party shall not be specified:

               The Director General of the Public Works Research Institute or
          Building Research Institute of the Ministry of Construction shall
          offer for public subscription for the joint party.  The applied
          enterprises shall be judged and selected in the committee board
          with consideration to their ability to  perform the study.

          As one of the characteristics of the joint research, the  priority
     is given to the joint party to own the right to use the results thereof,
     especially the patents, for no more than five years from  the completion
     date of the joint research.  It is true that there were some refutation
     against this way saying that it stirred up competition among enterprises
     in vain.  On the other hand, many enterprises welcome this  way
     understanding that the Ministry of Construction would like  to  reflect
     the benefits of excellent technologies to the public works.

                                 REFERENCES

1)  Metcalf & Eddy, Inc.: "Wastewater Engineering (Treatment/Disposal/Reuse)"
    2nd ed., 1979, McGraw-Hill, New York

2)  Ministry of Construction:  "Sewage Works in Japan - Current Status/Future
    Needs" Japan Sewage Works Association, Tokyo  FY1984 ed, 1984 (in Japanese)

3)  Fukui, Saburo: What is Biotechnology?  "Chemistry", Vol. 103, 1984,
    KAGAKUDOIN, Kyoto (in Japanese)

4)  Rittmann E. B.: "Needs and Strategies for Genetic Control: Municipal
    Wastes, Genetic Control of Environmental Pollutants" 1984, Plenum Press,
    New York
                                     18

-------
                            Tenth United States/Japan Conference
                               on Sewage Treatment Technology
AUTOGENOUS COMBUSTION OF SEWAGE SLUDGE
       The work described in this paper  was
       not funded by the U.S. Environmental
       Protection Agency.  The contents  do
       not necessarily reflect the views of
       the Agency and no official endorsement
       should be inferred.
                     T. Murakami,
             Dr. Eng., Senior Research Engineer
                     K. Murakami,
                 Dr. Eng., Deputy Director
        Research and Technology Development Division
               Japan Sewage Works Agency
                         19

-------
                              TABLE OF CONTENTS
                                                                          Page
1.   INTRODUCTION	      21
2.   OPERATING STATUS OF INCINERATING FACILITIES 	      23
3.   HEAT CHARACTERISTICS OF DEWATERED CAKE 	      28
 3.1   Outline of Investigations 	      28
 3.2   Results of Measurement	      29
 3.3   The Difference in the Heating Values of Raw Sludge and
       Digested Sludge	      34
 3.4   The Usable Heating Value (H£(W))  of Wet Cake 	      36
4.   EVALUATION OF MULTIPLE HEARTH FURNACE FOR ENERGY SAVING	      38
 4.1   Incinerator Models 	      38
 4.2   General Equations of Mass Balance and Heat Balance 	      39
 4.3   Heat Characteristics Diagram of the
       Multiple-hearth Furnace 	      46
 4.4   Energy-saving Incineration	      47
 4.5   Evaluation of the Existing Multiple Hearth Furnaces by
       the Theoretical Model 	      49
5.   EVALUATION OF THE FLUIDIZED BED FURNACE FOR ENERGY SAVING	      55
 5.1   Features of the Material and Heat Balance 	      56
 5.2   Cake Moisture Content and Auxiliary Fuel Requirement 	      62
 5.3   Cake Organic Content and Auxiliary Fuel Requirement 	      63
 5.4   Capacity of Furnace and Auxiliary Fuel Requirement 	      64
 5.5   Condition for Autogenous Combustion 	      65
                                      20

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1.
INTRODUCTION
          The standard flow of a sewage sludge  incinerator  is  shown in
     Fig. 1.  The flow can be broadly classified  into  two parts,  namely, the
     incinerator main body and exhaust gas  treatment.
                           Standard flow of a sewage s]udge incineratoi i,ybtein


Dewaterud cake
	 ^_


Combustion
air






Auxiliary
fuel




















Flue Gas


















Ash


















	 '
1
1 1






I
f

/\
in
0)
X3
3

to


i
,
1 L.
1
1


Scrubber
water


K
H
J
i
M
§
ri
J

N
H
H
3
H
-1
n
s



o
ostati
itator

P H
U C>
fl) Q>
-H ^
u) ru

                                                Scrubber
                                                water
                                                drat nage
         Fig. 1  standard flow of a sewage sludge  incinerator  system
          Main items reviewed in this paper for energy-conservation are as
     follows:

     (a)   Energy-conservation measures from the viewpoint of  the material
          balance of an overall incinerating process.

     (b)   Energy-conservation measures from the viewpoint of  the heat balance
          of an overall incinerating process.

          In regard to the material balance, factors affecting  energy balance
     from a viewpoint of input and exhausted materials  are  discussed as
     follows.

     (A)   Fuel:   Heavy oil A or kerosene are used.  In  some treatment plants
          digesting sewage sludge, however, digester gas  is used as an
          auxiliary fuel.

          In a standard incinerator, fuel is used as an auxiliary  source of
          heat for burning cake that does not easily burn,  and  for a exhaust
          gas deodorization device (thermal deodorization method).   The
          consumption of auxiliary fuel varies depending  on the
          characteristics of the input cake as fuel (moisture content and
          heating value), temperature, and amount of exhaust  gas.
                                      21

-------
     Consequently,  the following four  measures may be considered to save
     fuel.

     (a)   Improve the characteristics  of  cake as  a fuel,  that is,  reduce
          the cake's water content and improve  its constituents to
          increase the heating value.

     (b)  Minimize the heat loss with  the exhaust gas by  reduction of
          the flow and the temperature of exhaust gas.

     (c)   Provide for an effective use of the exhaust heat.   Among such
         methods are the recovery of  heat from exhaust gas and the
          recurrent use of cooling air for other  purposes.

     (d)   increase the fuel-efficiency in thermal deodorization.

(B)   Water:   The greater part of the water used by the incinerator is
     for  scrubber water for exhaust gas treatment.  Therefore,  the
     following three measures can be considered for water efficiency.

     (a)  Reduce the exhaust gas flow.

     (b)   Lower the exhaust gas temperature.

     (c)   Increase the recirculation of the scrubber  water.

(C)   Chemicals:   The majority of chemicals are for  use in
     desulfurization.   Because the consumption of chemicals varies
     depending on the dewatered cake's sulfide content, chemical  aid for
     dewatering should contain the least  amount of  sulfide.

(D)   Power:   The greater part of power is used for  blowers and  pumps.
     Therefore,  two measures can be considered to reduce  power
     consumption.

     (a)  Reduce the exhaust gas flow.

     (b)  Lower the exhaust gas temperature.

         Taking into account items (A) to (D), the following factors
     need to  be considered as energy-saving measures  for  the  incinerator.

         a)   improve the dewatered cake's fuel characteristics.

         b)   Reduce the exhaust gas flow and lower its temperature.

         c)   increase the efficiency  of  heat recovery.

         d)   Reduce the energy used for  the  exhaust  gas  deodorization.

         e)   Improve  the efficiency in combustion
                                    22

-------
               The following feasibility studies were made to determine how
          these factors can be incorporated into an incinerator and included
          investigations of the actual incinerators in use.
2.    OPERATING STATUS OF INCINERATING FACILITIES

          The total volume of sewage sludge being disposed of in Japan in
     1982 was 2,480,000 (m^/year),  in which the dewatered cake accounts for
     about 80% and the incinerated ash for about 10%.   The majority of sludge
     is disposed of for landfill,  including inland landfill and coastal
     reclamation, which accounted  for about 70% in 1982.
          The potential sludge disposal site must satisfy the basic
     conditions shown in Table 1 in Japan where land is highly utilized.
     Therefore, there has been a tendency for each sewerage authority to
     adapt an incinerating system  which makes it easier to meet the
     conditions shown in Table 1.
              Table 1  Basic conditions of sewage disposal site
Broader
classification
Technical
requirements
Regional
conditions
Economic
conditions
Environmental
conditions
Middle
classification
Requirements
for the sludge
disposal site
The quantity
and property of
sludge to be
disposed
Acquisition of
site
Land use
Final disposal
site
Transpor tation
Surrounding
environment
Contents of basic conditions
o The site must have enough space to be
disposed of planned quality of sludge.
o The ground must be safe after it is
landfUled.
o A step-by-step disposal plan must be clearly
stated.
o The property of sewage sludge must comply
with the disposal standards.
o The consent from the parties with rights to
the land needs to be secured.
o The potential site must conform to the
regulations concerning the use of the land.
o A cencrete plan to utilize the site after
landfill must be formulated in accordance
with city planning.
o The construction and maintenance costs of
the disposal site must be economical (dam,
dike, or shore protection works, sealing
walls and wastewater treatment facilities).
o The shortest possible transportation
distance is desirable, and the transporta-
tion method needs to be optimized.
o proper measures to counter noise, odor, and
scattering can be taken when performing
disposal work.
o The disposal work should not adversely
affect the use of surrounding land.
          Fig.  2  clearly shows the increase in  sewage treatment facilities
     with incinerating system.  As shown in Fig.  2,  the volume of  cake being
     incinerated  has  continuously increased, reaching 1,900,000 (mVyear)
     in  1982.   The  dewatered cake being  incinerated  accounted for  50%  of  the
     total volume of  cake produced.
                                     23

-------
                   4.0
                   3.0
                   2.0
                   1.0
                          Others (Note)
                          Cake disposed of by other ways
                          Incinerated cake
                        1978  1979   1980   1901
                                             1982
                   (Note)  Sludge disposed of  in the form of liquid
                         raw sludge or iliqoalod sludge expressed
                         in terms of dewatered cake

     Fig.  2  The  treated and  disposed  amount of dewatered cake
     The following  types of  incinerators  are used  in Japan for
incinerating sewage sludge:

(i)     Multiple-hearth furnace
(ii)    Fludize bed  furnace
(iii)   Rotary kiln
(iv)    Stoke furnace

     The numbers of incinerators in operation/ classified by types, are
shown  in Fig. 3.  The increase in the number of fluidized bed furnaces
are remarkable.
                                     24

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               1978
                         1979
                                            [2J
             100
Fig. 3  Number of incinerators in operation classified by types of furnaces
         Table 2 shows the summation of incinerators' treating capacities
    (capacity x units) in terms of wet cake.  Among the total number of
    incinerators (148 units) in operation in 1982, the multiple-hearth
    furnace accounted for 57%, and fluidized-bed furnaces accounted for
    24%.  On the capacity base, the total capacity of the incinerators in
    1982 was 10,600 ton/day  (in terms of the wet cake), in which the
    multiple-hearth furnaces accounted for 79% and the fluidized bed
    furnaces accounted 16%.
                                     25

-------
   Table 2   The  total  capacity  of  incinerators  classified  by size
            (capacity  x  units)  (ton wet  cake/day)
rV
cal
Year
1978





1979





1980





1981





1982





Capacity
\
Type of furnace \
Multiple-hearth
furnace
Fluidized-bed furnace
Rotary kiln
Stoker furnace
Others
Total
Multiple-hearth
furnace
Fluidized-bed furnace
Rotary kiln
Stoker furnace
Others
Total
Multiple-hearth
furnace
Fluidized-bed furnace
Rotary kiln
Stoker furnace
Others
Total
Multiple-hearth
furnace
Fluidized-bed furnace
Rotary kiln
Stoker furnace
Others
Total
Multiple-hearth
furnace
Fluidized-bed furnace
Rotary kiln
Stoker furnace
Others
Total
Less than
100
(ton/ day)
31
3
40
8
8
90
31
3
40
8
8
90
22
3
40
8
8
81
22
6
64
8
8
108
22
9
72
8
0
111
10 - 50
(ton/day)
1,131
460
139
207
35
1,972
1,147
555
127
277
48
2,154
1,147
772
78
207
48
2,252
1,302
820
78
257
48
2,506
1,303
968
78
271
48
2,668
50 - 100
( ton/day)
960
0
0
0
55
1,015
1,030
0
0
0
55
1,085
1,150
60
53
0
55
1,318
1,210
320
53
0
55
1,638
1,210
670
53
0
55
1,988
More than
100
(ton/day)
4,840
0
0
0
0
4,840
5,140
0
0
0
0
5,140
5,440
0
0
0
0
5,440
5,790
0
0
0
0
5,790
5,790
0
0
0
0
5,790


6,920
463
179
215
98
7,917
7,348
558
167
285
111
8,469
7,759
835
171
215
111
9,091
8,325
1,146
195
265
111
10,042
8,325
1,647
203
279
103
10,557
     The average capacity per unit of the multiple-hearth furnace is
about 98 (ton/day) and the fluidized-bed furnace about 46 (ton/day).
The maximum capacity of the multiple-hearth furnace per unit is 300
(ton/day).
     Recently, the construction of a fluidized bed furnace with large
capacity has become possible and incinerators with a capacity of more
than 200 (ton/day) are being constructed.  The marked increase in the
number of fluidized-bed furnaces after 1978 was because of the following
reasons:
                                 26

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 (1)   Finding landfill sites  has  become difficult even  in medium-sized
      cities, resulting in the need for incinerators with a  small
      capacities.

 (2)   The intermittent operations of a fluidized bed furnace is
      relatively easy compared with the multiple-hearth furnace.

 (3)   Fluidized-bed furnaces  do not require particular measures  for
      deodorization because the odor of the exhaust gas is much  weaker
      than that of a multiple-hearth furnace.

      Table 3 shows the number of sewage treatment plants with
 incinerators classified by the sludge treatment system.  At the end of
 1982,  the total number of sewage treatment plants in operation  reached
 529,  in  which 89 had incinerators accounting for 17% of the treatment
 plants.
   Table 3  Installation  status of incinerators classified by the
            sludge  treatment system (1982)
^\^Sludge treatment
^^\^ process
Type of furnace ^~^\^
Multiple-hearth furnace
Fluidized-bed furnace
Rotary kiln
Stoker furnace
Others
Combination use
Total
Direct
dewater-
ing
28
19
2
0
1
0
51
Diges-
tion and
dewater-
ing
13
5
1
0
1
1
21
Heat
treat-
ment and
dewater-
ing
1
0
0
5
0
1
7
Others
0
1
0
1
0
1
3
Furnace
not in
operation
5
1
0
1
0
0
7
Total
47
26
4
7
2
3
89
      (Note) 1.  "Combination use" refers to the treatment plants that use more
              than two different types of incinerators.
           2.  "Others" in the sludge treatment process refers to the treatment
              plants with CG process or those with only sludge treatment process.


     The greater part of sewage treatment  plants equipped with an
incinerator(s)  employ raw sludge  dewatering.   in 1982, such sewage
treatment plants accounted for 51, or 62%,  of  the total of 82 treatment
plants equipped with an incinerator(s).
     The fuel consumption of incinerators  is shown in Table 4.  As seen
in this table,  the  incinerator consumes  48.7JL  of heavy oil per 1 m^ of
wet cake on the average.  Improving  the  facilities that consume such a
great deal of energy has become an urgent  problem in energy conservation
for the sewage  treatment plants.
                                    27

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    Table 4  Quantity of the incinerated sludge and the fuel consumption
" — — -____F£scal year
Consumption
Quantity of incinerated
cake
Fuel consumption per
1 (m ) of cake
Number of treatment
plants
1979
85,051 m
1,654,620 m3
51.4 Z/m3
64
1980
81,766 m3
1,592,830 m3
51.3 i/m3
63
1981
86,758 m3
1,730,550 m3
50.1 Vm3
65
1982
91,684 m3
1,881,270 m3
48.7 Z/m3
77
3.   HEAT CHARACTERISTICS OF DEWATERED CAKE

          Because of the change in the quality of sewage and improvement in
     sludge conditioning method, and because of advances of the dewatering
     machines, the property of the dewatered cake has been significantly
     changed.  The following is the result of investigations made on the heat
     characteristics of dewatered cake.

3.1  Outline of Investigations

          The heat characteristics of dewatered cake can be affected greatly
     by the cake's water content, volatile solids and the element composition
     of solids.  Therefore, these properties and higher heating value of the
     cakes collected from 59 sewage treatment plants were measured to grasp
     the heat characteristics of the cake.  As shown in Table 5-(l), the
     samples were taken from wide variety of treatment plants from
     view-points of the collection system, the kinds of sludge supplied to
     the dewatering process (digested sludge or thickened raw sludge), and
     the dewatering machines.   The measured items and the methods of
     measurement are as shown in Table 5-(2).
                                     28

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                   Table 5-(l)  Kind and number of samples
kind of
dehydrator
Centrifuge
Belt press
Vacuum filter
Filter press
Screw press
Collection
system
Combined sewer
Separate sewer
Combined sewer
Separate sewer
Combined sewer
Separate sewer
Combined sewer
Separate sewer
Separate sewer
Kind of sludge
Digested sludge
Mixed raw sludge
Digested sludge
Mixed raw sludge
Digested sludge
Mixed raw sludge
Digested sludge
Mixed raw sludge
Digested sludge
Mixed raw sludge
Digested sludge
Mixed raw sludge
Digested sludge
Mixed raw sludge
Digested sludge
Mixed raw sludge
Mixed raw sludge
Number
of
•samples
7
2
2
4
4
3
4
6
4
4
2
4
2
4
3
3
1
Total
(1)
9
6
1
10
8
6

6
6
1
Total
(2)
15
17
14
12
1
Grand
total
59
            Table 5-(2)   Items of analysis and analytical methods
Item of analysis
Moisture content, ignition loss, higher heating
value
Carbon, hydrogen, nitrogen
Sulphur
Oxygen
Analytical method
Test method for sewage
CHN automatic analyzer
JIS-M-8813
Ignition loss - (C+H+N+S)
3.2  Results of Measurement

     (1)   Heating value of the cake

               Fig. 4 shows a summary of the relations between the higher
          heating value (H^)  and the organic contents (V) classified by the
          dewatered cakes.  The sludge cakes are classified into two
          categories:  one is the sludge dewatered by a centrifuge or a belt
          press with polymer  addition (hereinafter called polymer cake), and
          the other is the sludge dewatered by a vacuum filter or a filter
          press with lime and ferric chloride addition (hereinafter called
          lime cake).
               Equations 1 and 2 show the regression equations between the
          higher heating value and the organic content, expressed by ignition
          loss, for polymer cake and lime cake,  respectively.   In either
          case, a good correlation existed, and the higher heating value
          could be expressed  as a function of the organic content.
                                      29

-------
    !Kcal/kg-DSl

         5000
         2000
         1000
      (Hh)
                 O Polymer :axe

                 • Lirae ca/.e
             0       20        40
                 Organic content
                                            80
                                                    100
                                    (V)
Fig.  4  Relationship between the higher heating value of
        dewatered cake and organic content
 Polymer cake
H.  = 58.3 V - 193
 h
                                                    Equation 1
 Lime cake
H,.
56.4 - 513  	   Equation 2
     In which, Hn is the higher heating  value in Kcal/kg-DS and V
is the organic content expressed by  ignition loss in %.  The higher
heating value of lime cake  is  low  compared with that of polymer
cake even if the organic content is  the  same, and the differences
are 450 to 570  (kcal/kg-DS) within the range of organic contents
from 40% to 70%.  The following factors  are considered to be the
causes of these differences.

(a)  When the inorganic chemicals  (lime  and ferric chrolide) are
     added, these chemicals remain in the cake mainly in the form
     of lime {Ca(OH)2} and  ferric  hydroxide {Fe(OH)3}.  When
     the ignition loss of the  cake is measured, water from these
     compounds evaporates according to the reactions shown by
     equations 3 and 4, resulting  in a greater ignition loss than
     that of the original sludge.

(b)  As shown by Equation 4,  the reaction exhibits a heat
     absorption of  about 350  (Kcal/kg lime)
                                30

-------
              2Fe(OH)       Fe2°3 + 3H2°   	  Equation 3


              Ca(OH)        CaO + HO - 355  (Kcal/kg  lime)   	  Equation 4


              The reason of the smaller correlation  coefficient for lime
         cake than that for polymer cake  is considered to be attributable to
         the  difference in the dose rate  of the coagulant.
              Equations 5 and 6 show the  relations between the lower heating
         values  and the organic contents  of the cakes.   As in the case of
         the  higher heating values, the relationship between the lower
         heating values of polymer cake and lirce cake can be expressed by
         linear  functions of volatile solids as follows:
 polymer cake
E  = 54.0 V - 150  (r  =  0.96)
                                                                   Equation 5
         Lime  cake
        H.  = 51.2  V -  458 (r = 0.87)
                                                          Equation 6
     In which,
Kcal/kg-DS.
                           is the lower heating value of  the  cake in
             Fig.  5  shows the relationship between the higher  and lower
        heating  values of the cakes.  The correlation between  them is quite
        high.  The lower  heating values of the cakes are  0.93  times as much
        as  the higher  heating values for both polymer and lime cakes.
           [Kcal/kg-DS1

                  5000
                  4000
                 2000
              .c
               n
                 1000
                (HID
                           O Polymer cake

                           • Lime cake
                    0     1000     2000     3000
                          Higher neatinc valJe
                                        4000      5000
                                        (Hh) [Kcal/ka-DSl
Fig. 5  Relationship between higher heating value and lower heating  value
                                      31

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(2)   Element composition  of  solids

          As mentioned,  the  heating  value  of  a cake  is  closely related
     to the organic content.   The relationship between  the element
     composition (carbon, oxygen, hydrogen, and sulphur)  of solids and
     the organic content was examined.   Fig.  6 shows the  relationship
     between the content of  each element and  the organic  content of the
     cake.

     (a)   Carbon content

               The carbon content of lime  cake is less  by 3% to 5% than
          that of polymer cake within the  range of organic content of 40
          - 70%.

     (b)   Oxygen content

               The oxygen content of lime  cake is higher  by 4% to 7%
          than that of polymer cake.

     (c)   Hydrogen content

               The hydrogen  content  of  lime cake is  higher by 0.2% to
          0.4% than that of  polymer  cake.
               Both the hydrogen and oxygen contents exhibit different
          tendencies from the carbon content,  and the lime cake has
          higher  hydrogen and oxygen contents than the  polymer cake.
          These are attributable to  hydrogen  and oxygen contained in
          hydroxides,  which  is lost  as  water  during  the measurement of
          ignition loss as shown in  Equations 3 and  4.

     (d)   Inflammable  sulphur content

               The inflammable sulphur  content of polymer cake was found
          to be less than 1.0% and to have no definite  relationship with
          the organic  content.  The  inflammable sulphur,  however, is an
          element that accounts only for a small percentage of ignition
          loss.  Therefore,  the sulphur content of polymer cake was
          regarded as  being  about 1.0%  of  total solids  for reasons of
          simplicity.   Conversely, the  inflammable sulphur content of
          lime cake was found practically  zero.  This may be
          attributable to calcium sulfate  (CaSC^)  produced by the
          reaction of  sulphur and lime  added.
                                   32

-------
                                                                                                 Hydrogen content  (%)
                                                                                                                                                                            Carbon content (% DS)
CO
GO
           0)
           rf
           !-••
           O

           cn

           H-
          •O

           cr
           n>
 n>
 
           o
           ft
                     Nitrogen content (% DS)
                                                                                                 Sulphur content (% DS)
                                                                                    a a

                                                                                  •   %a
                                                                                              StP
                                                                                                                                                                                Oxygen content (% DS)

-------
          (e)  Nitrogen content

                   The nitrogen content of lime cake is less by 0.8% to 1.5%
              than that of polymer cake.
                   The regression equation between each element content and
              the organic content is shown in Table 6.  All the elements
              examined except for sulphur, have good correlations with the
              organic content.  However, correlation between the nitrogen
              content and the organic content is a little worse than the
              other  correlations.  This may be because nitrogen is an
              element which  does not affect the heating value.
         Table 6   Correlation equations  between  element
                  and organic content
constituents
Item
Carbon

Oxygen

Hydrogen

Sulphur

Nitrogen

Cake
polymer
Lime
polymer
Lime
polymer
Lime
Polymer
Lime
polymer
Lime
Correlation equation
C = 0.498-V + 2.46 (r = 0.97)
= 0.534-V
C = 0.479-V = 0.76 (R « 0.83)
= 0.463-V
0 = 0.387-V = 5.44 (r = 0.91)
• 0.307-V
0 = 0.360-V + 2.20 (r = 0.70)
= 0.403-V
H » 0.079-V = 0.79 (r = 0.87)
= 0.068-V
H = 0.095-V - 1.07 (r - 0.88)
« 0.074-V
S = -0.002-V + 0.813 (r = 0.11)
- 0.01-V
_
N » 0.067-V + 0.87 (r =• 0.68)
= 0.079'V
N - 0.066'V - 0.39 (r = 0.76)
- 0.058-V
Item
Carbon

Oxygen

Hydrogen

Sulphur

Nitrogen

Cake
Raw
Digested
Raw
Digested
Raw
Digested
Raw
Digested
Raw
Digested
Correlation equation
C » 0.495-V + 2.73 (r = 0.95)
= 0.533'V
C » 0.501-V + 2.29 (r - 0.97)
= 0.539-V
0 = 0.382-V - 5.09 (r - 0.85)
= 0.311'V
O = 0.389-V - 5.58 (r - 0.91)
= 0.302-V
H = 0.08-V - 0.745 (r - 0.80)
= 0.070-V
H = 0.073-V - 0.435 (r = 0.88)
= 0.065'V
S » 0.005'V + 0.88 (r - -0.23)
= 0.007'V
S • 0.0013-V + 0.009 (r • 0.56)
= 0.013-V
N = 0.049-V + 2.15 (r * 0.48)
- 0.079-V
N = 0.078-V + 0.135 (r - 0.74)
= 0.080-V
3.3  The Difference in the Heating Values of Raw Sludge and Digested Sludge

          The difference in the heating values of cakes due to the
     differences in sludge being supplied to the dehydrating process was
     examined.  The polymer cake, which is least-affected by the coagulant
     addition was selected as the object under the survey.

     (1)  Higher heating value

               The relationships between the higher heating values and the
          organic contents are shown in Fig. 7.

-------
                 5000
                 3000
              t-  2000
                 1000
(T)  Mixed raw sludge
   H. =55.7-V-446
    h
(2)  Digested sludge
                         H =64.4-V-523
                         h
                   o a
                    0
                           20      40     60

                         Organic content (%)
                                                80
                                                      1000
Fig. 7  Relationship between  organic content and higher heating value


           The regression  equations for raw sludge cake and digested
      sludge cake are  expressed by Equations 7 and 8, respectively.
           The differences in the  higher heating values of the raw and
      the digested sludge  cakes are in the range of -40 to +220
      (Kcal/kg-DS) and are not so  large within the range of organic
      contents from 50%  to 80%.
       Thickened Sludge
      H,  = 55.7 V - 466  (r  =  0.92)
       h
       Digested sludge
      Hh = 64.7 V - 523  (r  =  0.98)
 (2)   Element composition
                                          Equation 7
                                          Equation 8
           The regression equation  between the content of each element
      and the organic content  expressed by ignition loss is shown in
      Table 6.  The difference between thickened raw sludge and digested
      sludge is small.  Therefore,  the higher heating value can be
      computed from the organic content by using the respective equation
      mentioned above, regardless the type of feed sludge.
           Sulphur in solids can be separated into inflammable sulphur
      and noninflammable sulphur.   Fig. 8  shows the relationship between
      inflammable sulphur and  total sulphur.   Only very little difference
      exists between the total sulphur contents in the raw sludge and the
      digested sludge.  Total  sulphur is about 1.5 times greater than
      inflammable sulphur.
                                     35

-------
                                          (D Mixed raw sludge
                                           Total S=1.45-X

                                          g) Digested sludge
                                           Total S=1.48-X
                                         JL
                                   1           2

                              Inflammable sulphur content (%)
     Fig.  8   Relationship between total  sulphur  and inflammable sulphur
3.4  The Usable Heating  Value (H£(W))  of Wet Cake

          Cake differs from common fuel because it contains  a  great deal of
     water.  Therefore,  when an evaluation of cake as  fuel  is  attempted,
     moisture content of the cake must be considered.   In such a case, the
     usable heating  value is generally taken to be an  index, which is
     computed by using Equation 9.
                      100
                             600
 w
100
Equation 9
          Lower heating  value based on dry solids
     w;   Moisture content of cake

          A summary of the usable heating values of various  types of cakes
     expressed in terms  of wet cake is shown in Table  7.
       Table 7  Difference in the usable heating value depending on the
                type of dehydrator
Dehydrator
Centrifuge
Belt press
Vacuum filter
Filter press
Average
Range
Average
Range
Average
Range
Average
Range
Moisture
content (%)
80.5
77.4 - 84.8
80.7
73.0 - 84.5
77.6
73.3 - 83.2
59.2
47.3 - 66.9
Organic
content (%)
61.5
39.4 - 80.3
69.3
53.1 - 84.6
49.7
53.5 - 62.4
50.2
35.1 - 58.9
Usable heating value
(Real/
kg-DS)
3,090
2,000 - 4,130
3,650
2,450 - 4,420
2,150
1,440 - 3,300
2,040
1,550 - 2,690
Real/
kg-wet cake)
114
-69 - 506
218
-59 - 606
15
-132 - 375
477
324 - 677
                                        36

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     As seen from this  table,  the  usable  heating value of  the cake
obtained by means of a  filter  press  showed  the  highest average value of
480  (Kcal/kg - wet cake), followed by  220 (Kcal/kg -  wet cake)  of the
cake from a belt-press  filter.  The  cake  obtained by  a vacuum filter
exhibited the lowest value of  20  (Kcal/kg - wet cake).  As shown by
Equations 5 and 6, the  lower heating values based on  dry solids can be
expressed as the functions of  the  organic content.  Therefore, the
usable heating values of both  polymer  and lime  cakes  can be expressed by
Equations 10 and 11, respectively.
 Polymer cake
      •  (54-° v - 150)
  - 6w	  Equation  10
                 100
                  30
               •z  so
                  20
                  50     60      70     80     90


                         Cake moisture content (%)
                                                  100
          Fig.  9   Usable heating value of the polymer cake
 Inorganic cake

H , ,  = (51.2 V - 458)  (1 -
                             w
                            100
•) - 6W  	  Equation  11
     When the moisture content and the organic content of  the  cake are
the same, the usable heating value of polymer cake  is higher than that
of lime cake.  With regard to the usable heating value,  the polymer cake
with moisture content of 80% and the organic content of  70%, is
equivalent to the lime cake with about 3% less moisture  content and 10%
more organic content.  The conclusions can  be summarized as follows:
                                  37

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                              60     70     80      90

                               Cake moisture content (%)
                                                       loo
               Fig. 10  Usable heating value of  the lime  cake
     (a)   No essential difference was observed in the heating value and the
          element composition between the cakes from raw sludge and digested
          sludge.  The heating values can roughly be calculated by the
          organic contents for lime cake and polymer cake respectively.

     (b)   The lower heating value of a cake is about 0.93 times as much as
          the higher heating value.

     (c)   The element compositions of ignition loss of the fed sludge to the
          dehyderating process were about 53% of carbon, about 31% of oxygen,
          about 7% of hydrogen, about 1.0% of inflammable sulphur, and about
          7% of nitrogen.

     (d)   Among the dehyderating machines, the filter press can produce the
          cake with the highest heating value, followed by the belt press
          filter, centrifuge, and vacuum filter.
4.   EVALUATION OP MULTIPLE HEARTH FURNACE FOR ENERGY SAVING

          The two types of multiple hearth furnaces (Model II and Model III)
     that have been improved with respect to heat recovery are compared with
     a conventional furnace (Model I) putting particular emphasis on heat
     balance.

4.1  Incinerator Models

          The following incinerators were selected as the subjects for
     discussion.

     [Model I]  A conventional type of incinerator.  The air used to cool  the
                                      38

-------
     incinerator shaft is discharged to the atmosphere without recovering any
     heat.  The heat is not recovered from the exhaust gas either.

     [Model II]   The air used to cool the shaft is designed to be circulated
     into the furnace to recover the heat.  The heat is not recovered from
     the exhaust gas.

     [Model III]   The shaft-cooling air is circulated to recover the heat,
     and the heat is also recovered from the exhaust gas.  (Although not
     calculated with the model, the unburned materials and lost materials can
     also be reburned).

4.2  General Equations of Mass Balance and Heat Balance

          First, the basic conditions related to input and output of
     materials were determined, and the equations of mass and heat balances
     were formulated.  Next, the equation was modified to calculate the
     deficit of heat which gave the required amount of auxiliary fuel.

     (1)  Heat balance

               The configurations of the three model incinerators illustrated
          in Fig. 11 can be expressed with respect to material balance in a
          block diagram in Fig. 12.
          [Model I]
                                                            [Model III)
                         Fig. 11  Model incinerators
               In Model I, the heat output A-2 was included in the balance.
          In Model II, A-2 became zero because it was recirculated as A-3.
          In Model III, A-2 was zero, too, and A-4 was added to the balance
          as a heat input in proportion to the heat output G-l.
                                    39

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                      A-3
          Fig.  12   Material  flow of  the model  incinerator


(2)   Basic numerical  values  used to  compute  the mass  and heat balances

     (a)   Standard level  of  heat balance

               Atmospheric temperature, and  high-level  standard (Heat
          associated  with moisture in the supplied air  was neglected.)
     (b)   Atmospheric conditions

          Atmospheric temperature   Tc
          Absolute moisture         h

     (c)   Latent heat of  vaporization
20°C
0.01 kg-l^O/kg-dry air
          Latent heat at temperature  TO°C:   L  (Kcal/kg-H^)
          L - 586 (Kcal/kg-H20)  at To = 20°C

     (d)   Average constant pressure specific heat;  Cp (Kcal/kg-eC)

              Cp used in the  calculation  is listed in Table 8.   As an
          average constant pressure specific heat,  the value at  the
          temperature (0 + T)/2*C was used.  Also,  as the dry combustion
          gas specific heat, the specific  heat of nitrogen was used.
                                   40

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  Table 8  The values of constant pressure specific heat  used for
           the computation
Temperature
T (°C)
0 - 100
0 - 300
0 - 500
Dry combustion gas
cre
0.248
0.250
0.253
Vapor
CPH
0.447
0.457
0.470
Dry air
CPA
0.240
0.243
0.247
Range of applicable
temperature
T < 150
150 S T < 400
400 S T
       o The constant pressure specific heat at {(0 + T)/2}°C is used as an
        average constant heat specific heat.
       o The specific heat nitrogen is used as the specific heat of dry
        combustion gas.
     (e)  Composition of dry air  (weight base, and volume  base)

          02;   23.3 weight %, 21.0  vol %
          N2;   76.7 weight %, 79.0  vol %
          Specific gravity;  1.29  (kg/N-m3)

     (f)  Specific heat of ash  (CA)

          CA =  0.3 (Kcal/kg-°C)

(3)   The general properties and basic  numerical value  relating to
     combustion of sludge and auxiliary fuel

     (a)  Properties:  Values shown in Table 9 were used.
           Table 9  Properties of cake and auxiliary fuel
Item

Specific gravity
Water content
Ignition loss
Higher heating value
(Kcal/Kg-DS)
Inflammable
constituents



C (%)
H (%)
N (%)
S (%)
0 (%)
Cake

SG
Stf

SHCV 5'500
Sc 52
SH 7
SN 7
Sg 1.5
so 32-s
Auxiliary fuel
Heavy oil A
FG
Fw
FV
FHCV
Fc
FH
FN
Fs
Fo
0.84
0
0
10,800
85.4
12.6
0.4
0.9
0.7
     (b)  Basic numerical values relating to combustion:

               The basic numerical  values and the equations to calculate
          the values are summarized in Table 10.
                                     41

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Table 10  Basic numerical values relating to combustion of cake and fuel

Theoretical
dry air
Theoretical
dry gas in
the exhaust
gas
Water
generated
on burning
Cake
Height of gas
( kg/kg- VS)
STft 7.03
STA " 
-------
    n_-;   The heat loss (radiation loss)  resulting from the radiation
      L2
           from the incinerator  itself,  which was set as being 6% of the
           total heat input.

    cj     The recovery efficiency of  the  heat in the exhaust gas by the
           heat exchanger,  which was set as being 8% of the sensible
           heat of the exhaust gas at  the  furnace gas outlet.

(5)  The materials balance  at the multiple-hearth furnace

          The quantity and  quality of  sludge input into the furnace are
    defined as follows:

    S;     Cake input into  the furnace (kg-wet cake/hour)

       ;   Water input into the  furnace  (kg/hour)
     S  ;   Solid  input into  the  furnace  (kg/hour)
      Do

     S  ;   Inflammable constituent  input into  the  furnace  (kg/hour)
      VO

     S _;   Mineral  input into the furnace (kg/hour)
      AS

          These parameters can be related by the following equations 12
     to 15.

     S   = S  x  S^/100   .....................................   Equation 12


     SDS = S  -  S^   ........................................   Equation 13
T^    r^
vU    DS
               x  ST/100   ...................................   Equation  14
                  v
     SAS"8DS~SVO   ......................................   Equation 15

          Also,  when  the auxiliary  fuel  supply  and  the  combustion  air
     supply are  define as F (kg/hour)  and A (kg/hour) ,  respectively,  the
     dry gas flow DQ^ and water  output HQJ (kg/hour)  in the exhaust
     gas at the  furnace outlet can  be  expressed by  Equations  16  and 17.
    DG1  = SVO  {STD  + * -  1)>STA  +  F {FTD  +  <« '  1)}FTA
       =  S..,,  {7.4  +  ($ - 1)  7.03} + F {13.97 + /
          vu
       (0 - 1)  14.1}  ......................................  Equation  16
                                  43

-------
    HG1  ' SVO {S™ + «'Vh } + F{FW + *-FTA'h } + SWO
       =  ST_  {0.63 + o x 7.03 x 0.01 } + F {1.13 + jzJ
          V\J
       x  14.1 x 0.01}+ S.~.   	  Equation 17

(6)  The  heat balance at the multiple hearth furnace

          From the material  balance described above, the input and
    output heat of a furnace can be expressed by Equations 18 to 27.

    Heat Input

    The  heat that sludge generates (0^)  (Real/hour)

    Ql = SVO X SHCV = SVO X 5'5°°  	  Equation 18

    The  heat that auxiliary fuel generates (Q_)  (Real/hour)

    Q- = F x F__.r = F x 10,800  	  Equation 19
      &        HL.V

    The  sensible heat of the supplied air (Q ) (Real/hour)

    Q = Q  x e/100 = Q  x 0.08	  Equation 20
      •j    *±             4

     (Q  is added to the heat input only for Model III.)

    Heat Output

    Sensible heat of the gas at the furnace gas outlet (Q4)
     (Real/hour)

    Q4 ' (DGi>crc + "GI^PH*  x (TGI ' V
       =  (D,,, x 0.25 + H.,, x 0.457)  x (300-20)   	  Equation 21
           Gl           Gl

    Latent heat of vaporisation for water in the sludge (Q5)
     (Real/hour)

    Qc = S   x L = S   x 586  	  Equation 22
      j    WO        W\J

    Latent heat of heatable constituent in the sludge and of water
    generated by burning (Q6)  (Real/hour)

    Q, = s._ x S_7 x L = ST_. x 0.63 x 586  	  Equation 23
      D    v\J    *W        \AJ

    Latent heat of auxiliary fuel and of water generated by burning
     (Q7)  (Real/hour)

                                  44

-------
Q  = F x F   x L = F x 1.13 x 586   	  Equation  24


Sensible heat of ash (Qg)  (Real/hour)
Q8 = SAS
                 (TS1 *
   = S._ x 0.3 x (300 - 20)  ..........................  Equation 25
      Ao

Sensible heat of the shaft cooling air (Qg) (Real/hour)

Q9 = (Q1 + Q2) * n/100 = (Q1 + Q2) x 0.02  ............  Equation 26


(Qg is added to the heat output only for Model I.)

Heat loss (QIQ) (Real/hour)

Q
 1Q
          + Q2) x n/100
                              + Q2) x 0.18  ...........  Equation 27
Using Q, to Q,Q mentioned above, a heat balance equation can be
formulated by making [heat input] = [heat output].
Ql + Q2 + Q3 + Q5 + Q6 + Q7 + Q8 + Q9 + Q10
                                                         Equation 28
     The required amount of auxiliary fuel  (Fn kg/hour) for each
model can be expressed by the Equations 29  to 31.

 The required amount of auxiliary fuel for Model I
                                                         Equation 29
' J714SW , 04 (1 *"
A ( 100 ' " v" 10
x v x (3,914 - 5010)
100
The required amount of
(7143,0 S-v,
• _ ) ...+84(1 -
B [ 100 ' " *~ 10
rt
x .v x (4,034 - 5010)
100
The required amount of
f 714SjJ Sy.
) ..,.** i 
-------
4.3  Heat Characteristics Diagram of the Multiple-hearth Furnace

          Based on the heat balance Equations of 29 to 31 for  each Model, a
     characteristic diagram of the amount of auxiliary fuel requirement was
     calculated by taking the combustion air ratio (0), ignition loss of the
     input cake (Sv), and the moisture content of the cake (Sw)  as the
     parameters.

     (1)  Parameter setting

          (a)   The combustion air (0)  were set as being five conditions:
               1.3, 1.6, 2.0, 2.5, and 3.0.

          (b)   In the computation of the heat balance, the heat properties of
               cake that need to be given a numerical value are the higher
               heating value of ignition loss (SHCV), the overall ignition
               loss (Sv) , and the hydrogen content in ignition loss.  Here,
               the higher heating value of ignition loss has been assumed as
               being 5,500 (kcal/kg-VS), and hydrogen content in ignition
               loss being 7% (weight ratio).  Therefore, the only variable
               factor is ignition loss (Sv).  As shown in Table 11, the
               five levels of ignition loss were assumed, and the
               corresponding heating values were calculated.
              Table 11  The relations between ignition loss and
                        the higher heating value of cake


Classifi-
cation NO.


©
©
(D
®
®
Ignition loss

SV


80
70
60
50
40
Ash content

SA


20
30
40
50
60
Higher heating
value based on
ignition loss
SHCV

(Kcal/kg-VS)
5,500




Higher heating
value based on
cake solids
SDCV " SHCV
x Sy/100
(Kcal/kg-DS)
4,400
3,850
3,300
2,750
2,200
          (c)  Five different levels of moisture content (S^) were set:
               60%, 65%, 70%, 75%, and 80%.

                    Fig. 13 shows the amount of auxiliary fuel (calculated in
               terms of heavy oil A) required to burn one ton of dewatered
               cake under the combinations of the moisture content (S^) and
               ignition loss (Sv).  In the diagram, when the amount of
               auxiliary fuel is shown to be negative, it indicates a status
               in which the cake can provide a sufficient heat, and thereby
               needs no auxiliary fuel.
                                      46

-------
                        1.3
                    60   80   100  60  30  100  60  80  100  60   80  100  60   80   100
                                  Moisture content of cake SW (%)
                    Numerals ® to ©  in the diagrams indicate the conditions of calssified
                    numbers in Table  - 11.

      Fig.  13  The relationship  between  the moisture content of cake and
                the amount of auxiliary fuel  (heavy oil A)
                requirement for each model
4.4  Energy-saving Incineration
           To clearly define the situation of  autogeneous combustion,

                                         47

-------
Equations 29,  30,  and 31, were modified to give  the relation between the
moisture content (Sw) and ignition loss  (Sv)  under the condition
that auxiliary fuel requirement  (F) is zero.
In the case of  Model I
       (3,998 -  5010)  Sv
             Too
                  - 84  /  6.3 +
                                          (3,998 - 5010)  Sv
                                                10,000
                                                         Equation 32
In the case of  Model II
(4,118 - 5010) Sv
       100
                          /  6.3
                                    (4,118 -  5010)  Sv 1
                                 + - 10,000      (
                                                         Equation 33
In the case of  Model III
       (4,118 -  4610)  S
                      'V
              100
                          /
                                    (4,118 -  4610)  Sv
                             6.3 + 	——	
                                                         Equation 34
     Fig. 14  shows the relationship between  S^ and Sv by using
Equations 32  to  34.   The line where the auxiliary fuel (F)  becomes zero
is a marginal line of autogenous combustion  under this model.
Therefore,  in Fig. 14, the region above the  curve shows the area where
the condition for  autogenous combustion is satisfied,  and the region
below the curve  is the area in which auxiliary fuel is required.  By  the
use of this diagram,  it is possible to make  an estimation on the
conditions  for Sw, Sy, and 0 that are necessary for autogenous
combustion.   It  should be noted, however, that besides Sw,  Sv, and
0, there are  other factors that may affect autogenous combustion,
including the type of furnace and burning speed.
                    Model 1
                                       Mode 1  Y]
                                          H    EH
4,950


4,400


3,850


3,300


2,750


2 , 200


1,650


1, 100
 90


 80


, 70


> 60
i
i
)
H 50
)
i
j ...

ii
i
 30
                       (Rugion requir-
                        3 mj auxili ary
                        foul]
                                     [ Autogen-
                                     ous com-
                                     bustion )
                                    I Hegj oil rULjul L -
                                     i MCJ tiuxi J i ary
                                     fuel]
                               80  «1O      (ill

                         Moisture content of i,akc ^
                                                 Hi)
                                                 I Autogen-
                                                 ous com-
                                                 bust ion]
       Fig.  14  Limit of autogenous combustion for each model
                                  48

-------
4.5  Evaluation of the Existing Multiple Hearth Furnaces by the Theoretical
     Model

          There have been four units of  multiple-hearth  furnaces  in  service,
     about which enough data are available for  being evaluated  with  the
     theoretical model.  Of these four furnaces,  two are operated without
     auxiliary fuel, and the other two need auxiliary fuel.   Because existing
     available data were used, some of them might not fully be  satisfactory
     in accuracy.
          Table 12 shows the actual operating conditions of these four
     multiple-hearth furnaces.  The data of treatment plant A are considered
     to have high accuracy.  The furnace of this  plant has  been incinerating
     sludge without auxiliary fuel.  The data of  treatment  plant  B were
     obtained during the test run of the furnace,  and therefore,  only a
     single set of data was available as to element  compositions  and heating
     values.   The furnace,  however, was  maintained at the state of autogenous
     combustion.   The data of treatment  plant C were obtained as  the results
     of investigations to grasp the heat balance  of  the  furnace,  and are
     considered to have a higher accuracy.   The furnace  was using some
     auxiliary fuel.   The data treatment plant  D  were obtained  during a test
     run.   The heat balance calculated directly from these  data showed that
     the heat output was greater than the input.   The data  was  not so
     satisfactory from the viewpoint of  accuracy.
                                      49

-------
       Table  12   The  results  of  survey on  the actual operating conditions of the multiple-hearth furnaces
Name of sewage treatment plant
Run
Rate of cake feed (kg/hour)
Loading ratio (%)
Dewatered cake
"W+J
WflJ c
Classification (%)
Moisture conent (%)
Ignition loss (%)
Element
composition
Carbon (%)
Hydrogen (%)
Nitrogen (%)
Sulphur (%)
Oxygen (%)
Higher heating value per
ignition loss (kcal/kg-VS)
Higher heating value per
dry solids (kcal/kg-DS)
Lower heating value per wet
cake (kcal/kg-cake)
Temperature (°C)
Dry gas flow (NmVhour)
Wet gas flow (NmVhour)
Air ratio (-)
Auxiliary
Unburned
fuel consumption .
(kg/hour)
loss in the ash (dry »)
Remarks
Sewage treatment plant A
(30 ton/day furnace)
1
1,692
135
Polymer ,
press
72.2
70.5
53.9
7.7
7.7
0.9
29.8
5,730
4,040
608
450
5,610
4,017
1.89
0
0.66

2
1.429
114


74.9
69.9
53.4
6.6
7.6
0.9
31.5
5,708
3,990
490
398
3,871
2,714
1.30
0
0.15

3
1.521
122


75.7
69.2
52.2
6.8
7.1
0.9
33.0
5,621
3,890
429
362
3,701
2,365
1.45
0
0.5

4
1.088
87


74.7
68.8
52.1
7.0
6.7
0.9
33.3
5,654
3,890
470
359
3,359
2,371
1.78
0
0.33

5
1.021
82


77.2
68.2
52.6
7.0
6.7
0.9
32.9
5,689
3,880
363
284
2,889
1,916
1.36
0
0.1

6
1.038
83


83.6
69.8
54.6
6.4
9.9
0.9
28.6
5,873
4,100
131
264
3,830
2,627
Un-
clear
Heavy
oil A
25.9
1.24

B-l
4.030
64.5
SSSJd.
Filter
press
58.5
47.2
48.40
8.25
7.17
0.38
35.80
5,617
2,651
662
418
13,131
3,891
3.12
0
Un-
clear

Sewage treatment plant B
(150 ton/day furnace)
B-2
3.110
49.8


64.1
•>
•4-
-
-
492
298
9,798
3,140
3.49
0
Un-
clear

B-3
3.230
51.7


61.5
-
-
-
-
571
294
11,471
3,213
3.67
0
Un-


4
4,960
79.4


65.0
-
-
*
-
464
318
12,508
4,991
2.86
0
Un-


5
4,590
73.4


61.5
-
-
-
-
571
381
13,484
4,520
3.03
0
Un-


6
4,660
74.6


64.7
-
-
-
-
474
270
16.3D4
4,763
4.11
0
Un-


Sewage treatment plant C
(200 ton/day furnace)
1
4,638
55.7
Polymer
Euge
78.2
70.2
52.0
8.0
6.0
1.5
32.5
5,670
3,980
332
280
ft , 690
12,341
1.34
Kero-
sene
79.8
6.98
convarMd to h«vy oil
A, Bl } (ka/houz)
1.7S kq hMvy oil par
ton of caka
2
4,163
50.0


81.0
68.0
52.0
8.0
6.0
1.5
32.5
5,284
4,280
271
290
8,280
15,271
2.16
110.3
6.26
117. 4 (kg/hour)
28. 2 (kg heavy
[ oil/ton)
3
8,333
100


78.0
66.7
52.0
8.0
6.0
l.b
32.5
5,039
3,930
333
340
11,310
22,780
1.45
132.7
6.87
135. 2 (kg/hour)
16. 2 (kg heavy
oil/ton)
4
8,410
101


75.2
61.6
52.0
8.0
6.0
1.5
32.5
4,934
3,710
403
372
13,520
25,744
1.82
101.9
6.67
103. 8 (kg/hour
12. 3 (kg heavy
oil/ton)
Sewage treatment
plant D (150 ton/
day furnace)
1
6,200
100
2
Lime and vacuum filter:
1
80
45
50.9
6.9
6.0
0.3
35.9
4,667
2,100
-93.6
330
9,700
16,000
1.68
Heavy oil A 986
(kg/hour) , Diges-
tion gas 184 kg/hour
Unclear
Converted | to heavy oil
A; 194 (kg/hour) ,
31.3 kg heavy oil per
ton of cake
cn
o

-------
       Because all four furnaces are the Model II type, the data are
  plotted on the characteristic diagram of Model II of Pig. 11 putting the
  air ratio # equal to 1.6, which is shown in Fig. 15.  Similarly, data
  were plotted on the diagram of Fig. 12, and the result is shown in
  Fig. 16.
       The Run (A-l) in Fig. 15 corresponds to Run 1 of treatment
  plant A.  As shown in Table 12, the moisture content of the Run 1 is
  72.2%, and the higher heating value is 4,040 (Kcal/kg), and the
  consumption of auxiliary fuel is zero.  On the other hand, when the
  auxiliary fuel requirement is sought on Fig. 15 using the diagram with
  the higher heating value of 3,850 Kcal/kg-DS, it is found to be
  -17 kg/t-cake, which means that incineration is not only autogenous
  combustion but also energy producing.
Fig. 15  Comparison between the fuel requirement calculated on Model II
         at 0 = 1.6 and actual value
                                     51

-------
               ~  4,950
                  4,400 -
                  3,850 -
                  3, 300
                  2,750 -
                  2,200 -
                   1,650 -
                   1 ,100
[Autogenous com
 bustion area]
                                       requiring juxiliaiy I in-1 I
                      40    50     60    70    80    ')()

                            Moisture contunt s  (t)
Fig. 16  Comparison between the theoretical  boundary for  autogenous
         combustion for Model II  and  the  actual  state
     In the case of Run  (C-l), auxiliary  fuel  type was being used.  With
moisture content of 78.2 and  the higher heating value of 3,980
(Kcal/kg-DS), the amount of auxiliary fuel  consumption was 17.5
(kg/t-cake).  On the other hand, the auxiliary fuel consumption
estimated from Fig. 13 under  these condition is 11 (kg/t-cake)  of heavy
oil A using the values of j6 = 1.6 and the higher heating value of 3,850
(Kcal/kg-DS), thereby indicating the possibility of saving more fuel.
     In the both figures (Figs. 15 and 16), data from the sewage
treatment plants A and B that are performing the autogenous combustion,
fell on the autogenous combustion region  with  a few exceptions, showing
the efficient operation of the plants.
     Especially, the dewatered cake of treatment plant B has a greater
reserve in energy, exceeding  the lime of  autogenous combustion, and is
of substantial value as fuel.  At treatment plant B, the air ratio is
being raised to 3.1 - 4.1 to  meet the large heat input by making the
sensible heat of exhaust gas  greater.  A  furnace of this kind, however,
can produce energy by recovering surplus  heat  to use it for other
purposes.
     The dewatered cake of treatment plant  A has a characteristics
around the limit of autogenous combustion.  It should be noted that
although the calculation on Run A-5 shows a fuel requirement of 6
(kg/t-cake) of heavy oil, in  reality, the furnace remained in a state of
autogenous combustion.  These data were obtained during experiments to
clarify the critical moisture content for autogenous combustion, and the
operation of the furnace might not be so  stable.  Nevertheless, the
furnace has a high burning efficiency.  The air ratio 0 at that time
was 1.36, and the exhaust gas temperature was  284°C.  Therefore, the
                                    52

-------
exhaust gas sensible heat output was small.
     Both furnaces of treatment plants C and D are operated with the
auxiliary fuel addition.  Plant C was found to use a slightly larger
amount of auxiliary fuel than that expected by the calculation on the
Model II.  This was because the total heat loss including unburned loss,
shaft-cooling loss, and radiation loss was considerably large with the
maximum loss of 25%, which was much greater than the heat loss of 18%
used in the computation.  In addition, the exhaust gas temperature,
340eC and 372°C for Run C-3 and C-4, respectively, was higher than 300*C
assumed in the computation, resulting in a greater heat output.
     The heat balance computed by using treatment D's data reveal that
the input was 4,680,000 (Real/hour), whereas the amount of heat output
was 5,180,000 (Real/hour), indicating a problem in the reliability of
data.
     Based on these studies using the models and observations on the
actual statuses, the possibility of energy saving in incineration by
focusing on the input and output of heat can be summarized as follows.

(a)  The heating value of the cake:  It is important to make the heating
     value of the cake as high as possible which means to decrease the
     moisture content and to increase the organic content.  An effort
     should be made to use the dehydrating system capable of producing
     such cake.  Fig. 13 could be a reference to determine the target
     property of the cake.

(b)  Exhaust gas sensible heat:  The exhaust gas sensible heat of a
     multiple-sheath furnace is normally 20% to 40% of the heat input.
     To reduce the sensible heat, it is important that the exhaust gas
     outlet temperature be lowered.  If the heat exchange efficiency
     increase during sludge drying at the upper part of the furnace, the
     exhaust gas temperature can be lowered.  Another effective method
     is to lower the wet gas sensible heat in the exhaust gas.  Decrease
     in the air ratio to minimize the amount of exhaust gas may greatly
     affect the reduction of the sensible heat.

(c)  Sensible heat of water:  The water in the exhaust gas consists of
     water contained in the cake and water produced during the
     incineration by the reaction of hydrogen in organics with oxygen.
     Although the sensible heat of water vary greatly depending on the
     moisture content of the cake, it is usually equivalent to 40% - 70%
     of the heat input.  Because the heat output due to sensible heat of
     water cannot be controlled by manipulating the furnace, attaining a
     low moisture content by the dehydrating process is necessary.

(d)  Sensible heat of incinerated ash:  The sensible heat of ash
     accounts for only about 0.1% of the total sensible heat loss.
     Therefore, there is very little possibility of recovering a
     substantial amount of energy from the ash that may greatly affect
     total energy recovery.

(e)  Sensible heat of the shaft cooling air:  It is difficult to control
     this sensible heat because the air flow is fixed at the time of

                                   53

-------
     design,  and the temperature at outlet  is  also fixed  at  a  constant
     level.   The heat recovery,  however,  is possible by circulating  the
     heated air  into the furnace.   The  sensible  heat of the  shaft
     cooling  air is  normally  equivalent to  1%  -  5% of  the total heat
     input.

(f)   Heat loss:   The heat loss mainly consists of  the  radiation heat
     loss from the furnace  wall  and the heat loss  due  to  unburned
     combustible material.  The  former  can  be  reduced  by  enhancing the
     heat-insulating efficiency  of  the  furnace's wall  structure.  The
     heat radiation  is equivalent to about  2%  -  7% of  the total heat
     input.   The heat loss  due to the unburned combustible materials is
     unavoidable to  some extent  when incinerating  such a  highly
     inflammable material with high volatile solids.   Therefore, a
     technique capable of burning the heated wind  containing unburned
     fuel to  recover energy at the  upper  hearth  of the furnace may
     become necessary.   The amount  of unburned material depends on the
     property of cake (content of volatile  solids  with low boiling point
     and so forth),  and the heat loss ranges from  1% to 20% of the total
     heat input.
                                  54

-------
5.    EVALUATION OF  THE PLUIDIZED BED FURNACE  FOR ENERGY SAVING
        R-l:  Conventional system
Exhc
j
'--__



Exhaust gas
treatment
facility
. L

ust
1
qas
                Fuel Air for    Blower for mist
                    burner    prevention
        R-2- High-temperature heat recovery system
                                                                         Exhaust qas
(e

Furnace


t I
Heat ex-
changer
fo,r pre-
liminary
air
heating
"•uel Air for (B)
burner Blower for
f luidiEation

Blo\
pre
/


t
tfer for mist
/ention

Exhaust qa&
treatment
facility
L

0,
Stac)
        R-3: Direct drying sybLeji.
                1     T
                Fuel  Air for
                    burner
        R-4 :  Indirect drying system
                                             R-5;  Preliminary heating dring system
                                             Heat exchange
                                             for preliminary.
                                                      &
                                                  Blower for
                                                  jjAiidizatio
                                                     •.^,
                                                    ---!--
                                                           ZH3--
mi st preven-
                                                      >-© ?£*£,-
        Fig.  17  Flow chart of  each model of  the fluidized  bed furnace
           For  the five models shown in Fig. 17,  equations with respect to
     material  and heat balances were formulated,  and  the methods for  saving
     energy were reviewed in the same manner as  described in Chapter  4 for
     the multiple-hearth furnace.
                                           55

-------
          The models illustrated in Fig.  17 are:

      R-l ;   Conventional system
      R-2 ;   High-temperature heat recovery system
      R-3 ;   Direct drying system
      R-4 ;   Indirect drying system
      R-5 ;   Drying with preliminary air  heating  system

5.1  Features of the Material and Heat Balance

          In consideration of input and output of materials  and  heat,  the
     essential parameters that affect energy-efficiency are  described  below.
     The examination were made under the  conditions  of  the cake  moisture
     content of 80% and the organic content of 70% with the  capacity of  the
     furnace of 50 (ton/day).

     (1)  Heat recovery of each model

               To reduce the amount of auxiliary  fuel consumption,  each  model
          is designed to recover the heat contained  in  the exhaust  gas.  An
          index for this heat recovery efficiency was defined as being:
          Heat-recovery
Amount of heat recovered*
Total amount of heat out-
put from furnace main body
x 100(%)   ...  Equation 37
          * For  R-l and R-2,  it represents  the heat  retained  in  the  supplied
            air  for incineration.
            For  R-3, R-4,  and R-5,  it is  a  sum of  the  heat  retained  in  the
            supplied air,  the sensible heat of the cake,  and  the latent and
            sensible heats of the vaporized water  in the  dryer.

              Fig. 18 shows  the results  of computation on  each  model's heat
          recovery efficiency by using Equation  37.

1

1

1

1

1
1 1 1
321
(106kcal/H)
Total heat output
R- 1
R-2
R-~
R-4
R-5
Model

1

1

1

1 '

1
1 1 1
10 20 30
Heat recovery efficiency (%)
               Fig.  18  Heat recovery efficiency of  each model

                                      56

-------
               As seen from this diagram,  models with a higher  heat recovery
          efficiency are those provided with an indirect dryer.   In both R-4
          and R-5,  their heat recovery efficiency was the same,  32%,  followed
          by 27%  of R-3, 22% of R-2,  and 18% of R-l.
               The  total heat output  of each model is also shown in Fig. 18,
          and its ratio, based on R-l, is  shown in Table 13-(1).
               The  R-4 has the least  amount of  heat output followed by the
          R-5, R-3, R-2, and R-l.  The total heat output of R-4  is
          substantially reduced to 61% of  that  of R-l.

     (2)   Auxiliary fuel consumption

               The  auxiliary fuel consumption of each model is  shown in
          Fig. 19.   Model R-4 has the least auxiliary fuel consumption,  about
          16 (kg/H), followed by 19 (kg/H)  of R-5, 36 (kg/H)  of  R-3,  63
          (kg/H)  of R-2, and 83 (kg/H)  of  R-l.   The ratio of  the fuel
          consumption of each model based  on R-l is shown in Table  13-(2).
Table 13-(1)  Comparison of the total heat output of each model based on R-l
Model
Total heat output
Total heat output of R-l K
R-l
100.0
R-2
96.4
R-3
81.1
R-4
61.1
R-5
72.1
            Table  13-(2)   Ratio of  the  auxiliary  fuel  requirement
                          of  each model based on  R-l
Model
Auxiliary fuel requirement
of each model
Auxiliary fuel requirement ~ ""
of R-l
R-l
100.0
R-2
75.9
R-3
43.4
R-4
19.3
R-5
22.9
               The table clearly indicates  that R-4  is capable  of  saving an
          amount of fuel consumption as high as 81%  of the fuel consumption
          of  R-l.

     (3)   Exhaust gas

               The exhaust gas can be divided into dry gas and  water.   The
          quantity of  dry gas varies depending on the amount of auxiliary
          fuel  consumption when the air ratio,  and the property and quantity
          of  the cake  input are the same.   Therefore, the less  the auxiliary
          fuel  consumption, the smaller the amount of dry gas.   The greater
          part  of the  water in the cake.
                                     57

-------
100
=c 80
tr>
M x.
»w -p
&1 40
a a
•H M
"* 'H ->n
x 0*
3 0)
* * n
-



	 1















-



                   R-l    R-2    3-:   R-i    R-5

      Fig.  19   Auxiliary fuel  requirement of each model
       The amounts of  dry gas  and water  in  the exhaust gas  of  each
  model are shown in Fig. 20.

1

1


III!
4321
x 103 (kg/H)
Quantity of dry gas
R-4
3-5

	 , . ' 1
1234
x 103 (kg/H)
Quantity of water
 Fig.  20   Quantities  of  dry gas  and water  in the exhaust gas
       The  ratio of  the  dry  gas  and water  in  the  exhaust  gas  of  each
 model is  shown in  Table  14.
Table 14  Comparisons of the quantities of dry gas and water
          in exhaust gas, and the cake moisture content
Model
Dry gas of each model „„„
Dry gas of R-l * 10°
Water in exhaust gas of each model
Water in exhaust gas of R-l *
Cake moisture content of each model iOQ
Cake moisture content of R-l
R-l
100.0
100.0
100.0
R-2
91.4
98.6
100.0
R-3
80.4
81.3
81.5
R-4
72.1
55.4
52.7
R-5
73.0
71.4
71.2
       In R-l  and R-2,  the  quantities  of  dry gas and water  in the
  exhaust gas  were determined by the auxiliary fuel  consumption
  because the  cake is put into the furnace without being dried.
  Therefore,  the improvement made by R-2  is not so significant, a
  reduction of 19% of the quantity of  dry gas and a  reduction of only
  1%  of the water content.   Conversely,  in R-3, R-4, and R-5, the
                                  58

-------
     cakes were put into the furnaces after drying process.
          The moisture contents of  the cakes supplied to the  furnaces
     were reduced from 80% to 76.5% in R-3, to 67.5% in R-4,  and to 74.0
     in R-5.   As shown in Fig.  21,  the amount of  water brought  into the
     furnaces also decreased.   The  amount of water brought into the
     furnace  in R-4 was smaller by  47% than that  in R-l.
1 1 1 1
1

1

1

1

1
1 1 < 1
80 60 40 20
(%)
Cake moisture content

R-l

R-2
R-3
R-4
R-5


" 1 I 1 1 1
1

1

1

1
l, 1 I I 1
" 800 1200 1600
(kg/H)
Water in feed cake
       Pig.  21 Water  in feed cake and cake moisture  content
          Consequently,  the latent heat and sensible  heat corresponding
     to the amount of water evaporated by drying process becomes
     unnecessary,  thereby greatly reducing the  auxiliary fuel
     consumption.   This  also reduces the quantity of  dry gas and  water
     in the exhaust gas.   Table 14 shows the ratios of  reduction  in  the
     amounts of dry gas  and water in the R-3, R-4, and  R-5.  Model R-4
     showed the highest  reduction.

(4)   Cake volume

          The changes in  the moisture content of the  cake and water
     brought into  the furnace by means of drying are  shown in Fig. 21.
     Because R-3,  R-4, and R-5 perform the drying, the  volume of  cake
     fed into the  furnaces decreased.   The ratios of  reduction of cake
     volume based  on R-l  are shown in Table 15.   The  greatest reduction
     was attained  by R-4  which was 62% of R-l.
          The changes in  the heating values based on  wet cake are shown
     in Table 15.   The cake of R-4 showed the highest usable heating
     value of 762  (Kcal/kg-cake).   The heating  value  of the cake  of  R-4
     was about three times greater than that of R-l.
          As typical examples of the material and heat  balances,  the
     case of Run-1 is shown in Fig.  22 and that of Run-2 in Fig.  23.
                                  59

-------
CTl
O
(Heat balance)
(Material balance)
Drier

Heat from
cake combu-
tion
1620 (52.9%)



901 (29.4%) \

Dried
cake
2083
IJxi.lt) f
L-f S~
Fuel 83 /
,,„/ (
V

Furnace
Loss from
furnace ^
11 <8-°
JJ %>


^
Heat
3064 the
(100%)
Heat output
arising from
stituents of
^






6486
(100%)






output by water in
cake
ly the burned gas
the inflammable con-
fuel and cake

Heat output by ash


Dry gas 3392
(52.3%)
Dry air 987 (15.2%)
loisture 1982 (30.6%
X
Ash 125 (1.9%)


Heating ex-
changer for
preliminary
air heating
Heat exchange
loss A
If5"
(1.8%)
—
1610
(52.5%)
1189
(38.8%)

20
(0.7%)








^\ » \> a b t
J ) S43 (17.7%l
J



Air for combus-
tion
	 4^?0 CSf» fi%)

Heat exchanger
for drying or
waste heat
boiler




\J"o exhaust
/gas treat-
/ ment
	 ,/2221 (72.5%)
\ To exhaust
\ gas
/ treatment
/ 6486 (100%)
	 /
                      Fig. 22  Material and heat balance of R-l  (Cake moisture content of  80%
                               and organic content of 70%; incinerator capacity of  50 ton/day)

-------
a*>
(Heat balance)
Heat from cake
combustion
1620 (87.3%)
(Material balance)
Dewatered
cake
2083
(47.6%)
Air
<3ryi


X
' /^
\ \
V



(f
Eor
19
^
(
^

Drier
Drying loss
j/.345%)
^/









V





Heat loss evapora-
tion and heat loss
through heat media
A 587 (31.6%)
— *is

(
Heat from
bustion
175 (9.4%)
^
.(
f ue 1 com-




/^
Lr
Fuel 16
(0.4%
Evaporated
water 789
(18%)
JD


1294
(29.6%)

^
Lf
Air for
combus-
tion
/




Combustor
Combuster
l°SS f)
150
JJ8.»,
Heat oui
1855 rakp
(100%) Heat om
COJl£tJ^£]




4373
(100%)

(70%)






put by water in the
put by burned gas
from rn flammable
eata_D£_fLuaL and cak<
Heat output by ash



Dry gas 2449
Dry air 701
Water content 1098
^ Ash 125 (2.9%)




Heat exchanger
for preliminary
air heating.

848 (45.7%)
837 (45.1%)
20 (1.1%)



(56%)
(16%)
(25.1%)

















Heat exchanger
(or drying Or
^«aste near boiler
er
Waste heatboil-
er loss . ^
1 m.8%)
s











	 '"'V To exhaust
\ gas treat-
/ ment faci-
^=S~V llty
Recovered heat
for drying
711 (38.3%)
} I
^


\ gas treat-
\ment facl-
\llty
/ 4373
/ (100%)
/

"\
) JHeat midium for
./drier

                       Pig. 23  Materials and heat balance  (Cake moisture content of 80% and
                                organic content of 70%; incinerator capacity of 50 ton/day)

-------
     Table 15  Comparisons of cake  volume and heating value based on R-l
Model
Cake moisture content ...
Cake volume of each model
Cake volume of R-l
Heating value of the cake x 10° (4)
Heating value of the cake (Kcal/kg)
Heating value of the
cake of each model
Heating value of the K 10°
cake of R-l
R-l
80.0
100.0
246
100
R-2
80.0
100.0
246
100
R-3
76.5
85.2
394
160
R-4
67.8
62.1
762
310
R-5
74.0
76.9
500
203
5.2  Cake Moisture Content and Auxiliary Fuel  Requirement

          The auxiliary fuel requirement of  each model is shown in Fig. 24
     under the condition that the furnace capacity is 50 (ton/day) and the
     cake organic content is 70%.  As  seen from this diagram, as the cake
     moisture content of each model decreases,  the auxiliary fuel requirement
     decreases.
                       u 50
                         40
                         30
                         20
                         10 -
	1	:	1—
Ignition loss: 70% - OS
Incinerator capacity:
          50 ton/day

  ©
  ©

  ©
  ®
                                70
                                      75
                                            80
                                                85
         Fig. 24  Relationship between the cake moisture content and
                  auxiliary fuel requirement
          As shown in Table 16, the reduction in auxiliary fuel requirement
     in each model when the moisture content is reduced by 1% is almost the
     same providing that the organic content of the cake in each model is the
     same.
                                     62

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      Table 16  Reduction in auxiliary fuel requirement by 1% reduction
                 in  the cake moisture  content
\, Model
Organic content \
60%
70%
80%
R-l
4.2
4.7
5.3
R-2
4.1
4.7
5.2
R-3
4.0
4.6
5.1
R-4
4.0
4.5
5.1
R-5
4.0
4.5
4.9
          There is a tendency that when the organic content is high, the
     reduction in the auxiliary fuel requirement is large.  The reduction in
     auxiliary fuel requirement when the organic content was 60% was about
     4.0 (kg/ton), whereas the reduction was 5.1 (kg/ton) when the organic
     content was 80%.  R-4 exhibits the least auxiliary fuel requirement when
     the water content is the same.

5.3  Cake Organic Content and Auxiliary Fuel Requirement

          The auxiliary fuel requirement of each model, when the moisture
     content of the cake is 80% and the furnace capacity is 50 (ton/day), is
     shown in Fig. 25.  As the organic content increases, the auxiliary fuel
     requirement of each model decreases.
                         30
                         20
                         10 -
                               60   65 ,70   75   5
                                Cake organic content (%)
            Fig.  25  Relationship between the organic content and
                     auxiliary fuel requirement
          As shown in Table 17,  the reduction in auxiliary fuel requirement
     of  each model by the increase in the organic content is the same
     providing that the moisture contents are the same.  If the cake moisture
                                      63

-------
     content is at a low level,  the reduction in the auxiliary fuel
     requirement becomes greater.   The effect of the organic content  on the
     auxiliary fuel requirement  is smaller than that of the cake moisture
     content.  Namely,  a reduction in the auxiliary fuel requirement  when the
     moisture content is reduced by 1% may correspond to the increase of the
     organic content by 4%  to 5%.
          Table 17  Reduction  in  auxiliary fuel requirement by 1.0%
                    increase in  the organic content

                                                       (Kg/t)
\ Model
Cake moisture content\
85%
80%
75%
R-l
0.84
1.1
1.4
R-2
0.83
1.1
1.4
R-3
0.83
1.1
-
R-4
0.82
1.1
-
R-5
0.83
1.1
-
5.4  Capacity of Furnace and Auxiliary Fuel Requirement

          The auxiliary fuel requirement of each model, when the cake
     moisture content is 80% and  the  organic content is 70%, is shown  in
     Fig. 26.  As the capacity of the furnace increases, the auxiliary fuel
     requirement of each model decreases.
                           50
                           40
                           10
                               Moisture content 80%
                               Organic content 70%
                            20    40    60    30   100

                              Incinerator capacity (ton/day)
      Fig. 26  Relationship between incinerator capacity and auxiliary
               fuel  requirement
                                       64

-------
          This is because the energy loss from the incinerator's main body in
     the heat balance computation is assumed to decrease in accordance with
     the total heat input as shown in Table 18.
   Table 18  Heat loss ratio used for the calculation of the heat balance
Incinerator capacity (ton/day)
Heat loss ratio (%)
30
9.5
SO
7.9
100
6.2
          The reduction in the auxiliary fuel requirement of each model based
     on an incinerator with a capacity of 30 (ton/day)  is shown in Table 19.
Table 19  Reduction in auxiliary fuel requirement by increasing the capacity
          of incinerator, based on the incinerator with a capacity of
          30 (ton/day) (Cake with the moisture content of 80% and the
          organic content of 70%)
\ Model
Incinerator capacity \
50 (t/day)
100 (t/day)
R-l
2.1
6.1
R-2
1.9
5.4
R-3
1.7
4.8
R-4
1.2
3.5
R-5
1.5
4.2
5.5  Condition for Autogenous Combustion

          The result of the computation to seek for the moisture content that
     gives the limit for autogenous combustion is shown in Table 20.
        Table 20  Critical moisture content for autogenous combustion
                  (Incinerator capacity 50 ton/day)
                                                      (*)
\ Model
Organic content (%) \
60
70
80
R-l
67.9
71.6
74.6
R-2
70.0
73.6
76.3
R-3
72.9
76.2
78.7
R-4
75.2
78.3
80.6
R-5
74.9
78.0
80.3
          The heating values based on wet cake corresponding to the cake
     moisture contents shown in Table 20, are shown in Table 21.
                                     65

-------
    Table  21  Critical heating value for autogenous combustion
               corresponding to moisture content shown in
               Table 20  (Incinerator capacity 50 ton/day)
                                       (Kcal/kg-wet cake)
\ Model
Organic content (%) \
60
70
80
K-l
580
600
620
R-2
510
520
530
R-3
400
410
420
R-4
310
320
330
R-5
330
330
340
     The minimum heating  value that permits autogenous combustion is
about 310  (Kcal/kg-wet cake),  applicable to the case of R-4.
     The boundary for  autogeneous combustion each model is  shown in
Fig. 27.
                    30 -
                    75 -
                  =  70 -
                    65 -
                    60
                                          ixi 1
requiring
 ary fuel
                         1
                                           i
                         65    70    75    80

                      Cake moisture content (%)
     Fig. 27  Boundary  of  autogenous combustion for each model
     To clarify  the adaptability of each model with respect to the
fluidized bed furnace,  surveys are currently made to  investigate the
actual operating status of  several fluidized bed reactors  in service.
                                    66

-------
                         Tenth United States/Japan Conference
                            on Sewage Treatment Technology
  THE PERFORMANCE OF THE CARVER-GREENFIELD PROCESS
    The work described in this paper was
    not funded by the U.S. Environmental
    Protection Agency.  The contents do
    not necessarily reflect the views of
    the Agency and no official endorsement
    should be inferred.
   Kenichi OSAKO, Nagaharu OKUNO, Hitoshi DAIDO

Sewerage Bureau,  Tokyo Metropolitan  Government,  Japan
                      67

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                                 CONTENTS






1.  INTRODUCTION	    69




2.  PRESENT SITUATION OF SLUDGE TREATMENT AND DISPOSAL  	    69




3.  TRIAL OF EFFECTIVE REUSE OF SLUDGE  	    69




    (1)  Compost	    69




    (2)  Artificial light-weight aggregates 	    70




    (3)  Sludge fuel	    70




    (4)   Smelting  slag    	    70




4.  OUTLINE OF SLUDGE FUEL SYSTEM   	    71




    (1)  The intention of the project   	    71




    (2)  An outline of the pilot plant	    72




    (3)  Results of studies   	    73




5.  FULL-SCALE MODEL PLANT    	    76
                                     68

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                             1.  INTRODUCTION
     The ward areas are divided into ten drainage areas owing to the topo-
graphical features such as rivers and ground elevations.

     Under the present master plan for sewerage in the ward areas, 10.4
million people will be provided with a sewerage system over a projected
area of 53,827 ha when completed.  General facts and figures for sewerage
planning in the ward area are shown in Table - 1 and Fig. - 1 shows the
location of treatment plants and drainage areas.

     The ratio of sewered population in the ward areas rose to 80% by the
end of fiscal 1983.
          2.  PRESENT CONDITION OF SLUDGE TREATMENT AND DISPOSAL
     The average volume of daily sewage accepted by the nine plants in the
23 wards was about 4.4 million cubic meters in fiscal 1983.

     And the average volume of daily raw sludge was about 95,600 cubic
meters.

     Table - 2 shows the statistics of sewage and sludge treatment in
Tokyo's Ward Area in fiscal 1983.

     In future, Central sludge handling stations for the processing of
sludge collected by pressure conduit, are planned to be built around
reclaimed land in Tokyo Bay in order to meet the demand for sludge treatment.
The Nanbu sludge treatment plant is already in operation.

     Mechanically dewatered sludge cake is now mainly disposed to Sanitary
landfill in Tokyo Bay. But the sites available for landfill will be limitted,
so about 70% of cake is incinerated to reduce its volume.  In fiscal 1983.
                          o                                              y
the average volume of 908m  of dewatered sludge, 133t incinerated ash, and
7t of Alumina cement were kneaded for stable landfill.  On the other hand,
development of new technology for reuse of sludge Is in under way.
                  3.  TRIAL OF EFFECTIVE REUSE OF SLUDGE
     (1)  Compost
     Municipal sludge contains essential plant nutrients and useful trace
elements and therefore has potential use as a fertilizer or soil conditioner.
Liquid sludge will be available if the cropland were far from residential
area, but in Tokyo, those are close together so the dewatered cake is
fermented by aerobic bacteria.  The composted sludge is rather stable,
free of pathogenic problem and odor and is easy to handle.
                                    69

-------
     The composting plant in operation from 1978 at Minamitama treatment
plant produces two or three tons of composted sludge from the seven tons of
dewatered sludge cake daily.  The product is sold to farmers for a ferti-
lizer in vegetable fields or as a soil conditioner.  Fig.-2 is the flow
diagram for the process.
                                                     i
     (2)  Artificial lightweight aggregates

     One way  to utilize  inorganic matter  in sludge is  to make artificial
light-weight  aggregates  from sludge ash.

     The basic technology for this process has already been successfully
developed and manufacturing plant was constructed at the Odai treatment
plant in 1983.

     This plant has a daily production of 12 metrictons.

     The quality of artificical lightweight aggregate is sufficient to
replace natural lightweight aggregates and some of the uses for flower pots
and building materials,  etc. were investigated.

     Fig.-3 shows the flow diagram of this process.

     (3)  Sludge fuel

     A large pilot plant was installed at the Sunamachi treatment center for
the purpose of applying  the multiple-effects evaporation process (CG process)
for the extraction of water from the dewatered sludge  cake in 1983.

     The water extraction capacity is  about 200kg per hour.

     Dried sludge has many practical uses and one of them is as a fuel to
produce steam for power  generation.

     (4)  Smelting slag

     Techniques for utilization of the energy  in dried sludge have also been
studied.   If the dried sludge  is heated over its melting point (about 1400 to
1500°C),  and then cooled, its  volume can be reduced considerably.   And the
waste heat can be effectively  used for the drying of sludge  cake.


      In  1984, a pilot plant with  a daily  processing of 50kg  of  dried sludge,
was built at  the Sunamachi  treatment  center for performing experiments for
 drying, melting and  crystallization process technology,  and  for  the
 durability of the facilities.


      In  order to develope effective technology in the reuse  of  sewage
 sludge, many  efforts have been done in Tokyo.   Among them, some information
 about  sludge  fuel system are  as follows.

                                     70

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                    4.  OUTLINE OF SLUDGE FUEL SYSTEM
      (1)  The intention of the project

      Sewage treatment is the separation process of solid and water and
 also  such is the same in sludge treatment processes.

      So improvement in techniques in removing water from solids is the
 key point.  In this point of view, at first, the nature of raw sludge should
 be investigated carefully, and the unit processes that fit for the raw
 sludge, must be carefully adopted.

      Owing to the changes of life style of citizens in Tokyo, the ratio of
 organic materials in raw sludge has gradually increased.

      At present, about 70% of solid in sludge, is organic matter.

      So the activated sludge derived from final sedimentation tanks, is
 very  difficult in gravity thickening.

      Improving in sludge thickening process is one point.
 Research for improving gravity thicknor, dissolved air floatation, and
 centrifuge are now undergoing.

      The next is mechanical dewatering process.  Performance of vacuum
 filter, press filter, centrifuge and belt press filter are investigated.

      Now, belt press filter, with the aid of polymer dosage, is becoming
 popular.

      Third point is the process of incineration Multi-staged incinerator,
 and fluidized sand bed incinerator, equipped with anti-air pollution
 devices, are in use.

      The aim of improving incineration process is autogenous combustion
without addition of supplement fuel.
 For the treatment of special sewage sludge, reasonable combination of unit
 processes should be applied.

      In this way, the most economical sludge treatment process will be
 established in reducing the volume of sludge disposal.

     Even if the volume of disposal would be small, the sites for landfill
will be needed forever.

     On the other hand, organic substances in the sludge solids will have
nutrients for plant and also calorific values to some extent.

      So development of technology in reusing sewage sludge is very import-
ant.
                                     71

-------
     Research for effective reuse of sewage sludge will be divided into
three types owing to the nature of sludge.

     First is to use nutrient as fertilizer.  Because of the urbanization
of Tokyo area, the constant need for compost will be limitted.

     Second is to use the solids of sludge  as a construction materials
such as artificial light-weight aggregates  and artificial slags.

     Third is to use calorific substances in the solids as fuels.

     Anaerobic digestion of thickened sludge has been emploied  in many
sewage treatment plant in Tokyo.  And methane gas produced in digester
is now used for heating boiler.  But about  the half of organic  materials
remain in digested sludge for next treatment.

     Recovering the all organic substances  in sludge as fuels is  sludge
fuel system.
In sludge fuel system, the most effective and economical removing of water
from solids is expected.

     Multi-effect evaporation processes have been successfully  applied in
many food and chemical industries with less energy consumptions.

     However, this process is not applicable to slurries such as  sludge,
because of its scaling and plugging in heat exchangers.

     The carver-Greenfield process, using carrier oil for preventing scaling,
is the one that is expected efficient evaporation of water from a slurry
like sewage sludge.

     In Japan three-staged multiple-effect  evaporation system was introduced
at city of Fukuchiyama in Kyoto prefecture  in 1976.

     Therefore,  Tokyo installed experimental plant in 1982,  in  order to
investigate the  performance of multiple-effect evaporation process with
the dewatered sludge instead of the thickened sludge.

     And also studies for using sludge fuels produced as a fuel and a raw
materials in cement manufacturing industry  and for fuels in power generation
plant are now implementing.

      (2)  Outline  of  the pilot plant

     The key to energy recovery from high-moisture organics such as sewage
sludge, without use of supplemental fuels,  is the energy-efficient removal
of water prior to  combustion.

     A number of processes for industry have been developed to  separate
water from solids with less energy input than conventional heat drying
systems.
                                     72

-------
     In Japan Fukuchiyama city is now operating the three-staged multiple-
effect evaporation facilities for drying the thickened activated sludge
before combustion.

     Fig.-4 shows the flow diagram of sludge fuel system.

     Table-3 shows an outline of the pilot plant implemented in the field
demonstrations and engineering studies.

     Flow sheet, layout, sections of the plant are expressed in Fig.-5.6.7.

     (3)  Results of studies

          a)  Supplied dewatered sludge

              Thickened the composite of raw and activated sludge is
              dewatered by belt press dehydrator.
              The natures of sludge cake are shown in Table-4.

          b)  Fluidizing oil

              Dewatered sludge is first  mixed with oil.
              The carrying oil assures the maintenance of  fluidity in all
              phases of evaporation cycle and prevention of scaling,
              plugging of the heat exchangers.
              The characteristics of carrying oil should be easy in mixing
              with sludge, and maintaining fluidity in all phases.
              Also the mixture must be pumped out easily.

              For this purpose, the viscosity of oil and fiber  component in
              sludge are very important.  Heavy oil is selected and con-
              firmed the effect.
              Fig.-8 shows the viscosity of various oil correspond to tem-
              perature .
              In summer, being fiber-component in sludge 2 or 3 percent (dry
              base), 6 times of oil against the weight of  solids in sludge is
              needed.
              Meanwhile in winter, 8 times of oil is needed owing to the 10%
              of fiber in sludge.

          c)  Multiple-effect evaporator

              Sludge-oil slurry is then  pumped to four-staged multiple-
              effect evaporator where vapor from the previous effect
              vaporizes the water in the sludge.
              Fig.-9 and Fig.-10 show the performance of four-staged multi-
              ple-effect evaporator in temperature and pressure.
              In order to evaluate the performance of the  evaporator, over-
              all heat transfer coefficient, efficiency of evaporation, and
              multiple of evaporation are expressed.
                                    73

-------
    For the ability of evaporator, the rate of heat transfer q
    [Kcal/hr] is expressed as follows.

                 q = A, u, At

         where   A:  Areas of heat transfer (m2)
                 u:  Overall heat transfer coefficient
                                            (Kcal/m2.hr.°C)
                At:  Difference in temperature between vapor
                     and liquid             (°C)

    The overall heat transfer coefficient means the quantity of
    heat transfered per unit area.  Therefore it plays a important
    role in scaling-up the facilities.

    Table-5 shows the coefficient observed in this pilot plant.
    On the other hand Table-6 shows that of Fukuchiyama.
    Depending on the fluidity of slurry the coefficient of the
    fourth-stage of Tokyo is equivalent to that of Fukuchiyama.
    The economical aspect of the evaporator is referred to
    efficiency of evaporation and multiple of evaporation.
    The efficiency of evaporation 7(%), and multiple of evapor-
    ation  f water-kg/1  are expressed as follows.
          a  i	-sl i
                             x 100
           i  *— —.-  ,aa
           [/steam-kg


                        W
                      N x S

                      w     N.n
                      S     100

         where   W:  Quantity of evaporated water (Kg/hr)
                 N:  Number of evaporation effect
                 S:  Quantity of steam supplied   (Kg/hr)

    According to this pilot plant study,  2.6kg of water is expected
    to be evaporated for each kg of steam supplied.
    The efficiency of evaporation for this plant is  65%.
    Meanwhile, that of Fukuchiyama is reported 75%.
    As shown in Fig.-10, energy efficiency for vaporizing unit
    weight of water will be declining owing to the quantity of
    oil in slurry supplied.

d)  Distillate

    The vaporized water is condensed and  discharged.   The quality
    of distillate is shown in Table-7.
    It contains steam distillable and water soluble  substances
    which can be readily biodegraded by an activated sludge
    process.
    The increase in quality and quantity  of inflow sewage at the
    treatment plant by mixing the distillate will be reached few
    percent.
                           74

-------
e)  Solids and oil separation

    The remaining solid-oil mixture from the fourth-stage effect
    contains about 80 percent of oil.
    The carrying oil is separated from solids using screw-press,
    and will be recycled for reuse in the evaporative cycle.
    Table-8 shows the results of operation of screw-press.
    Oil and grease content of the dried sludge products is about
    15 or 20 percent (dry base).  While, the average content  of n-
    hexane extractables in original sludge cake is about 11 percent.
    So residual fluidizing oil in dried sludge products will  be under
    10 percent.

    City of Los Angels is now introducing thermal process in
    sludge treatment of Hyperion sewerage plant.
    Digested centrifuged sludge cake is mixed with light solvent
    oil such as AMSC0140 and then pumped to four-staged multiple-
    effect evaporator, where water is  vaporized.   The remaining
    solid-oil mixture is then centrifuged and hydroextracted  to
    separate earring oil from solids.

f)  Combustion test

    An extensive fluidized bed incineration test  for sludge fuel
    was conducted.  The objectives of  the test program were to
    develop detailed criteria for design and air  emission factors
    for subsequent air permit applications.
    Major conclusion and recommendations from the test program
    are summarized as follows.
    Sludge fuel can be combusted effectively and  organic content
    of incinerated ash is below 0.5 percent.
    The effectiveness of incineration will improve with the in-
    crease of the fluidizing air, but  significant differences in
    combustion characteristics were not observed.
    With the increase in feeding load  of sludge fuel, the
    effectiveness of incineration will be decline, and the tem-
    perature will go up.
    In this test, feeding load of 800  x 103Kcal/m2.h is optimum.
    NOX emission is related to exhaust gas O2 content, and can
    be controlled by regulating the O2 content.
    About 3% of fuel bound nitrogen will be converted to NOX,
    under the air supply of 100 percent.
    About, 80 percent of fuel bound sulfur will be converted  to
    SOX.
    As far as HCN and colour, no problem is observed in this  test.
                          75

-------
                        5.   FULL-SCALE MODEL PLANT
     Full-scale pilot plant with the capacity of 50t-DS/day will be installed
at Nanbu sludge treatment site.

     In this plant, further experiments for the  performance of multiple-
effect evaporation system, screw press, and power generator will be studied.


Table 1.  General Facts and Figures on Planning  for Tokyo's Sewerage System
                             (for the ward area)
                                            (City  plan at  end  of  March 1984)
Name of
drainage
area
Total
Shibaura
Mikawashima
Sunamachi
Odai
Ochiai
Morigasaki
Kosuge
Kasai
Shingashi
Nakagawa
Projected
sewered
population
10,358,000
883,000
974,000
957,000
371,000
678,000
2,324,000
323,000
993,000
1,980,000
875,000
Projected
sewered
area (ha)
53,827
6,420
3,936
4,309
1,687
3,506
12,882
1,633
4,540
10,474
4,440
Trunk
sewers
(m)
1,099,910
149,350
106,440
95,000
23,250
52,090
265,860
28,740
83,250
186,390
109,490
No. of
pumping
stations
68
13
10
16
4
-
9
3
8
1
4
Treal
No.
15
1
3
1
2
2
1
1
1
2
1
:ment plant
Capacity
(mVday)
9,970,000
1,590,000
950,000
1,220,000
420,000
590,000
1,810,000
450,000
940,000
1,390,000
610,000
                                    76

-------
                 Shingashi Treatment Plant
                                                            O.NakaWjM'reatment Plant
                                                                      inage Area
                                                          asai Treatment Plant
                                                   |	1 Sewered araa
                                   Mpriga*kl^Ueatment Center
                                          'vtX
Figure 1.   Total Planning for the  Ward  Areas'  (At  end  of March 1984)
             Sewerage  System
                                        77

-------
                Table 2.  Statistics of Sewage and Sludge Treatment in Tokyo's Ward Area
                          (At end of March 1984)
Treatment
Plant
Shibaura
Sunamachi
Morigasaki
Mikawashima
Odai
Ochiai
Shingashi
Kosuge
Kasai
Total
Volume of Sewage
Treatment (m3)
Annual
274,320,080
182,011,370
410,017,830
222,425,480
107,181,550
165,890,250
153,823,820
56,123,700
33,412,280
1,605,209,350
Daily
749,520
497,300
1,120,270
607,720
292,850
453,250
420,280
153,340
91,290
4,385,820
Volume of Sludge
Treatment (m3)
Annual
2,624,780
7,660,250
9,994,640
Daily
7,170
20,930
27,310
Volume of
Dewatered(t)
Annual
92,801
311,622
312,840
Daily
250
850
860
Volume of
Incineration( t)
Annual

311,622
112,117
Daily

851
306
Pumped to the Sunamachi
treatment center
8,829,470
24,120
235,096
640
204,637
559
Pumped to the Odai
treatment plant
4,306,390
847,010
733,270
34,995,810
11,770
2,320
2,000
95,620
77,633
17,151
15,330
1,062,473
210
50
40
2,900
71,568
17,151
14,202
731,297
196
47
39
1,998
CO

-------
                                   Fermemer
Sludge cake
Rlncv
rH

— *| 1 - 1 ! — i
1 	 ' . -
1 	 H ' 1 	
^\ 1 * 1 * Iseparater



	 ».
|
Scrubh
                                                           Primary compost
                                                           storage
      Storage
Recycle compost
storage
Weighing   Bagging
    Figure  2.   Flow  Diagram of Composting Process at  Minamitama
                             | Sludge ash
                              Pulverization
                           Humidification. mixing  |—
                           |  Making o( grains

                                  I
                               I DryingJ
                                Burning
                        (Multi-stage jet stream furnace)
                                Cooling  |

                                  I
                                Product  |
         Figure  3.  Flow Diagram of  the  Artificial Lightweight
                      Aggregate  Manufacturing Process
                                       79

-------
                  Thickening
                  Dewatering
                Dewatered  sludge  cake
  Recycle oil
             *j  Fluidizing  tank
 I
 I  ^^	
Low
pressure
steam
                  Multi-effect  evaporator
                Solids/oil  separator
                              Screw press
Dried cake

               Boiler |—••
                Smelting  furnace
                                  Heat
                                  recovery
                                  aoiler
Fuel
                                          For other
                                          system
                                          for ex.
                                          cement
                                          manufacture
                        Figure 4.  SF-system Diagram
                                  80

-------
                   Table 3.  An Outline of The Pilot Plant
1.  Process Design Specifications
      Dewatered sludge cake input (moisture content 80%)
      Dry solids input
      Condensed vapors output
2.  Major Equipment Specifications

    (1)  Multiple effect evaporator

         1)  Heat exchanger
             o Heating surface area
             o Dimensions

         2)  Evaporator
             o Dimensions

         3)  Condenser
             o Heating surface area
             o Dimensions

    (2)  Solids/oil separator
           Type
           Capacity
           Dimensions
    (3)   Boiler
           Type
           Fuel
           Steam capacity
           Steam pressure

    (4)   Mixed slurry feeder
         1)  Fluidizing tank
             o Dimensions

             o Capacity
             o Retention time
             o Power required

         2)  Mixed slurry feed tank
             o Dimensions

             o Capacity
                     250 kg/h
                      50 kg/h
                     195 kg/h
x 4
6.25 m2/set x
Diameter
Height

x 4
Diameter
Height
x 1
6.25 m2
Diameter
Height
x 1
Screw press
50 kg-DS/h
Diameter
Length
4 sets = 25.0 m2
  320 mm
4,200 mm

  270 mm
4,000 mm
  320 mm
4,000 mm
  300 ran
3,000 mm
x 1
Package boiler
Heavy oil
Max. 200 kg/h
Max.  10 kgf/cm2
   gage
x 1
Diameter
Height
x 2
Diameter
Height
  970 mm
2,000 mm
1,000 kg
   20 minutes
  3.7 kW

1,940 mm
3,000 mm
5,000 kg
                                    81

-------
                                       Multi-effect evaporatpc
                          Cooling
                          water
1st
stage
Condenser
rr 	 .
2nd
7) stage
i Heat
! [exchanger
3rd
fjl "-
4th
,4 stage
• '
1'
1
1
	 9, Stream
                                                                                    Deodorizing
                                                                                    system vacuum
                                                                                    pump
00
ro
                                                                                                    Solids/oil separator
                                                                                                               s)
Mixed slurry
feed tank
                                                                                                 Heavy oil -storage tank
                 195 kg/h ou/water
                         separation
                         tank
                                          Figure  5.   Pilot Plant  Flow Sheet

-------
(l)   Fluidizing tank
(T)   Mixed slurry feed tanks
(5)   Multi-effect evaporators
     3A  Condenser
     3B  Heat exchangers
(7)   Dried slurry tanks
(J)   Solids/oil separator
(6)   Dried cake conveyor
(7J   Dried cake hopper
(8)  Recycle oil tanks
(?)  Deodorizing system
W)   Heavy oil storage tank
U)   Boiler
••—'
L2)   Boiler make-up water tank
-—v
13)   Cooling water storage tank
*—*k
\A)   Gravity thickener
L5)   Sludge storage tank
                       Figure 6.  Pilot Plant  Layout
                                      83

-------
oo
                                          /
V 5F FL+13500


 Vacuun drain
 pot


V 4F FT.tlQSQC
        ^7 3F FLt7500
                                     4-
                                   ./-heat
                                     exchangers
                                             4-
                                           ,/ ~ evaporators
        V_2F_EL±425fi.
        V^2F FL-i-2500

        Oil/wati
        separator
                                                                                                   Solids/oil

                                                                                                   separator
                                  - Separated
                                   oil tank
                                                    Fluidtzing
                                      \  Separated   tank
                                      ''oil
                                                                               I
                                                                              4-
                                                                              circulation
                                                                              punps
                                                                                                  —  —    /
                                                                                               Separated
                                                                                               oil tank
                             A-A veiw
                                                                                     B-B viey
                                                                                                         2-slurry tanks
                                              Figure  7.  Pilot Plant  Section

-------
                       Table  4.  Nature of Sludge Cake

3/10
3/17
3/18
3/23
3/28
3/29
5/11
5/30
8/ 2
8/ 8
8/23
97 1
97 6
9/13
9/21
9/26
9/27
10/ 6
10/13
10/18
117 2
11/11
11/15
11/24
11/28
12/14
1/17
2/21
3/23
PH
(-)
7.4
7.9
7.6
7.2
6.2
6.1
6.8
-
-
-
-
-
5.5
-
-
-
-
-
-
-
5.7
5.6
5.2


5.5
5.8
-
6.0
Mois-
ture
content
(%)
74.9
72.8
71.1
74.5
73.6
72.7
74.5
78.7
80.6
79.7
78.4
79.0
79.3
79.0
76.3
76.9
75.6
76.8
79.8
76.9
76.9
80.7
76.8
77.0
79.3
79.1
80.6
77.3
78.1
Furnace
reduct-
ion
(%-DS)
77.6
74.5
74.6
75.0
77.3
77.6
78.0
-
-
-
74.1
-
73.2
-
71.2


64.3
70.4
75.9
76.3
78.0
79.2
77.6

77.8
77.8
74.1
65.7
N-hexane
extracts
(mg/g-DS)
(36.4)
(30.5)
(25.8)
(31.9)
(31.4)
(40.1)
(30.4)
-
(20.4)
(27.4)
97.8
91.8

92.0
-
-
107.0
119.0
-
126.0

91.9
88.1
96.7
-
14.4
-
10.5

NH3-N
(mg/g-DS)
17.3
12.5
11.0
12.2
9.1
9.2
3.4
-
-
-
12.3
-
6.8
-
-
6.1

-
3.7
-
3.6
3.8
-
-
5.4
5.9
6.5

4.5
Volatile
organic
acid
(mg/g-DS)
52.9
50.2
58.1
54.9
64.5
33.1
93.5
-
-
-
89.8
-
66.9
-
-
65.8

-
71.7
-
56.4
63.1
-
-
86.2
51.8
83.3

60.9
Metal
soap
(%-DS)
-
-
-
-
0.79
-
0.74
1.49
3.94
2.41
-
2.97
-
1.45
-
-
-
2.01
-
1.97
-
1.45
-
1.63
-
1.42
-
3.12
2.21
Coarse
sus-
pended
solid
(%-DS)










6.5

6.6


9.4

16.0


16.8
14.2

23.2

18.7
14.5
16.5
13.9
1983
1984
                                      85

-------
       500



       400





       300







       200
       100

        90

        N



        ™
        60
        «
        X
    (CP)
        20
                     •2ot- 7. OOOCP
                              C heavy oil
                    B heavy oil
                                          ++S" A heavy oil









                                          •*\.special A heavy oil





                                             ^- kerosene
                  20       40       «o       so      too


                                          temperature(°C)
Figure 8.   The Viscocity of Heavy Oils Correspond to  Temperature
                                    86

-------
  fourth effect
                                140-
                                 120
                                100
  third effect
  second  effect
                                 80
feeded slurry
                                 60-•
 first  effect
  16
                                 40-
                                 20
                                    C C )
IS
                  14
                           13
                                   12
                                           II
10       9
    hour
           Figure 9.  The Temperature of Evaporator
                                               hour
          Figure 10.  The  pressure  of Evaporator

                                87

-------
     Table 5.  Overall  Heat Transfer  Coefficient  of  Pilot Plant
Fourth effect U value
Third effect U value
Second effect U value
First effect U value
- Average
290 Kcal/m2.h.eC
260 Kcal/m2.h.°C
240 Kcal/m2.h.°C
170 Kcal/m2.h.°C
240 Kcal/m2.h.°C
Table  6.   Overall Heat  Transfer Coefficient of Fukuchiyama Plant
Third effect U value
Second effect U value
First effect U value
290 Kcal/m2.h.°C
280 Kcal/m2.h.°C
280 Kcal/m2.h.°C
                 Chickened sludge
               (moisture content 96%)
           77.4*
  dewatered sludge
(moisture content 80%)
                                   water
                                   oil •
                                  solid
                                                          36.4*
                 54.5*
                                                           9.0*
    Figure 10.  Component of Slurry  (6 times of oil for solids)
                                    88

-------
Table 7.  Quality of Distillate
PH
SS
TS
CODMn
BOD5
NH,, - N
Volatile organic acid
9.4
11.5
123
mg/£ -
mg/fc
1,740 mg/& -
11,890 rag/Si .•
2,940
mg/Jl
6,080 mg/£
            89

-------
Table 8.   Results of Operation of Screw-Press
Operation
date
1983 Nov. 25
Nov. 30
Dec. 2
Dec. 7
Dec. 9
1984 Jan. 18
Jan. 24
Jan. 27
Feb. 1
Feb. 6
Feb. 9
Feb . 13
Feb . 16
Feb . 20
Feb. 22
Feb . 24
Mar. 6
Mar. 8
Mar. 13
Mar. 15
Mar. 21
Mar. 23
Apr. 2
Apr. 10
Apr. 12
Operational condition
Number
of
rotation
rpm
0.5
0.5
0.5
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
0.8
Taper
corn
mm
39^42
36
36
40
35
40
36
36
38
38
40
36
38
36
38
40
40
39
37
40
40^43
44
39-W.2
40
38^42
Slurry feed
Slurry
q'ty
kg/h
437
460
460
381
409
349
388
355
470
491
434
494
481
407
478
427
437
391
464
387
465
419
365
606
646
Solid
kg/h
49
53
51
40
44
41
44
41
55
52
49
58
56
44
53
50
51
46
53
49
57
56
46
77
81.6
Rates
of oil
for
solids
7.9
7.7
8.0
8.5
8.3
7.5
7.9
7.7
7.5
8.4
7.8
7.5
7.6
8.2
8.0
7.6
7.5
7.5
7.8
6.9
7.2
6.5
7.0
6.9
6.5
Temper-
ature
°C
120
120
120
120
120
115
117
115
115
114
115
114
113
114
114
115
116
116
114
115
115
114
115
115
115
Quantity
kg/h
45.6
48.5
47.5
39.5
40.4
37.1
43.9
34.8
46.2
48.6
47.7
52.2
48.4
37.8
55.3
47.4
47.6
41.3
47.2
45.6
43.0
48.2
45.9
72.9
78.3
kg-
DS/h
37.8
39.6
38.1
29.9
32.5
30.4
35.1
27.9
37.1
39.7
39.0
41.0
39.1
31.2
44.5
38.6
38.7
34.4
38.5
37.6
34.5
40.1
38.1
57.9
62.2
Dried cake
Solids
*
83.0
81.7
80.2
75.6
80.5
82.0
80.0
80.1
80.2
81.6
81.7
78.5
80.8
82.5
80.5
81.5
81.4
83.3
81.6
82.5
80.2
83.2
83.1
75.2
79.4
Moisture
content
»
2.5
3.0
3.8
4.1
4.7
3.4
2.5
3.5
3.6
3.2
3.3
2.5
3.0
3.2
4.0
4.0
3.0
3.5
4.1
3.3
3.0
3.4
3.2
3.9
4.2
%-DB
3.0
3.7
4.7
5.4
5.8
4.2
3.1
4.4
4.5
3.9
4.0
3.2
3.7
3.9
5.0
4.9
3.7
4.2
5.0
4.0
3.7
4.1
3.9
4.9
5.3
Oil
content
'
14.5
15.3
16.0
20.3
14.8
14.6
17.5
16.4
16.2
15.2
15.0
19.0
16.2
14.3
15.5
14.5
15.6
13.2
14.3
14.2
16.8
13. .4
13.7
16.7
16.4
%-DB
17.5
18.7
20.0
26.9
18.4
17.8
21.9
20.5
20.2
18.6
18.4
24.2
20.0
17.3
19.3
17.8
19.2
15.8
17.5
17.2
20.9
16.1
16.5
21.0
20.7
Recovered oil
Mois-
ture
content
0.4
0.5
0.9
0.7
0.5
0.5

0.4
0.6
0.5
0.4
0.5
0.4
0.5
0.5
0.5
0.5
0.5
0.6
0.4
0.4
0.5
0.5
0.5
0.7
Solids
3.5
4.8
5.2
5.8
5.1
6.3

3.4
5.3
2.2
3.3
5.7
4.8
5.8
5.1
3.7
2.1
3.8
4.7
4.0
2.8
2.5
5.5
3.1
4.5
Vlscoclty
20 °C
33.5
28.4
23.7
26.7
26.4
38.9

39.9
25.7
33.5
33.2
30.5
32.8
30.1
27.8
31.1
31.1
27.8
23.7

29.8
27.8
36.2
14.6
15.5
40 °C
19.3
14.2
13.2
13.9
13.9
14.9

16.2
14.9
15.9
16.6
16.6
15.2
15.2
13.9
15.0
14.2
12.9
11.8

12.5
13.2
17.3
9.1
8.2
60°C
8.8
8.1
7.8
8.8
7.4
7.8

8.1
8.1
8.1
8.8
8.8
8.5
8.1
8.1
8.1
7.1
6.8
6.4

5.4
6.4
10.2
5.1
4.8
80 °C
5.8
5.8
5.1
-
5.4
4.9

5.4
5.4
5.8
5.6
5.4
5.4
5.4
5.1
5.2
4.7
4.7
4.1

3.7
4.4
6.4
3.1
3.3
Ratio of
recovered
77.1
74.8
74.7
74.8
73.9
74.2
79.8
68.0
67.4
76.3
79.5
70.7
69.8
70.9
84.0
77.3
75.9
74.8
72.7
76.8
60.5
71.6
82.8
75.2
72.2

-------
                        Tenth United States/Japan Conference
                           on Sewage Treatment Technology
    Centralized Sludge Treatment in Yokohama
         Sakuji Yoshida, Chief Engineer

Sewer Designing Division, Construction Department

     Sewage Works Bureau, City of Yokohama
     The work described in this paper was
     not funded by the U.S. Environmental
     Protection Agency.  The contents do
     not necessarily reflect the views of
     the Agency and no official endorsement
     should be inferred.

-------
                                   CONTENTS


1.  Introduction                                                    93

2.  Yokohama's Sewer System and System Planning                   93

3.  Present Sludge Treatment and Disposal                           97

4.  Centralized Sludge Treatment                                  10°
    4.1 Sludge collection systems                                  100
    4.2 Construction status                                        104

5.  Overview of Sludge Treatment Centers                          105
    5.1 Unit processes
        5.1.1 Thickening                                           105
        5.1.2 Anaerobic digestion                                   106
        5.1.3 Wet air oxidation                                     106
        5.1.* Dewatering                                          107
        5.1.5 Pelletization (as fertilizer)                            107
        5.1.6 Incineration                                          107
    5.2 Present and planned facilities                              108
        5.2.1 Hokubu Sludge Treatment Center                      108
           a. Present facilities                                     108
           b. Selection of treatment process                        109
           c. Construction plans                                   112
        5.2.2 Nanbu Sludge Treatment Center                       113
           a. Present facilities                                     113
           b. Selection of treatment process                        113
           c. Construction plans                                   116
    5.3 Energy use planning                                       117
    5.* Instrumentation                                            121
        5.4.1 Basic structure of instrument systems                  121
        5.4.2 Sludge feed and intake system instrumentation          123
           a. Overview                                            123
           b. Control                                             123
           c. Supervision                                          124
           d. Measurement                                        124
           e. Detection of pipe clogging and leakage                 124

6.  Conclusion                                                    126
                                      92

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1.    Introduction

     Eleven sewage treatment plants have come into operation according to plan over
the past two decades.  As of March  1985, the population served by the Sewer System
was 1.78 million, or 60 percent of the total population of Yokohama. Population growth
has rapidly increased the volume of sludge requiring treatment.  In the past, sludge was
treated at the sewage treatment plants where it was produced.  But  this separate
treatment method has become inadequate in view of the increasing quantities of sludge
to be  treated  and disposed  of,  and in  consideration of questions of  environmental
impact. New responses have become  necessary.

     To improve sludge treatment efficiency, we have drawn up and begun putting into
execution a plan to collect the sludge from all of the sewage treatment plants and treat
it  at special sludge treatment centers in the Nanbu (southern) and Hokubu (northern)
coastal districts.   This report  describes  the  planning  and execution  of  collective
treatment by our Bureau.


2.   Yokohama's Sewer System and System Planning

     One of Japan's foremost commercial and industrial  cities, Yokohama boasts  an
international port with Japan's largest trade volume and participation in Japan's largest
industrial region, the Keihin Industrial Zone. It also serves as a bedroom community for
nearby Tokyo,  Japan's capital and largest city.   These factors  have contributed  to
making Yokohama the second largest city in  Japan.   It has a population of about 2.9
million and covers an area of some 430 square  kilometers.

     As Figure 1  shows,  the city's  population and territory have  undergone  major
changes  over   the  years.   Although the  population has  grown  practically  without
interruption since Yokohama was officially designated a city in 1889, postwar growth
has been especially spectacular.

     In the course of  rapid urbanization, comprehensive planning and improvement of
such basic segments of the infrastructure as roads and sewers were disrupted  first  by
the  Great Kanto  Earthquake of 1923,  then  by  the bombing  in  World War II and
expropriation of land by the American occupation forces. Their presence in Yokohama
delayed the installation of sewer systems as  compared to  other major cities.  The
effects of this delay are still felt.

     Sewer construction in Yokohama began in 1870 with the laying  of  sewers in the
foreign concession, located in what is now Yamashita-cho in Naka Ward.  Sewers  were
later laid in some parts of the downtown area, but there was very little systematic
improvement and expansion of the system before the war.

     Systematic improvement began in 1950 when  a  flood control project was launched
in parts of Tsurumi  Ward  in northeast Yokohama.  Expansion of  the system and
construction of sewage treatment plants  was initiated in 1957 with improvements in the
Chubu treatment district.

     In response  to rapid urbanization, five-year  improvement plans were formulated
beginning in 1963.  From the  first five-year plan (1963-1967) to the fifth (1981-1985), a
total of  approximately ¥1,375.9 billion was  invested to expand  the sewer system

                                       93

-------
quickly.  The second five-year plan (1968-1973) was revised in 1969 to effect expansion
of the system to cover the entire city.

      Under the revised second plan, the city's 430 square kilometers were divided into
nine sewage treatment  districts according  to  topographical  and other features.  One
sewage treatment plant was constructed  in  each of  these except  the Hokubu  and
Totsuka districts where two were built.  Almost all these sewage treatment plants were
equipped to treat both sewage and  sludge.

      The city had  two types of  sewer systems.  The  coastal  areas,  which had been
intensively developed  for decades, were provided  with  combined sewer systems.   The
inland areas, on the other hand, to which rapid  urbanization had come with the period of
great economic growth in the mid-1960s, had separate systems.
    Population
   3,000,000-,
   2,500,000-
    2,000,000-
    1,500,000-
    1,000,000
     500,000
     100,000-
                                Area
Area (Km2)
    -500
                                                                                400
                                                                                -300
                                                                                •200
                                                                                -100
                               End of WWII
                  Great Kanto Earthquake
           1889 1902 12 16202530354043454750556065666768697071 72737475767778798081 828384
             '97   '07                     Year


         Figure 1. Trends in Yokohama's population and area under municipal jurisdiction
                                          94

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                                            ©
                                     Kohoku Sewage
                                     Treatment Plant
                                                                           ©
                                                                         Hokubu I Sewage
                                                                         Treatment Plant
Midori Sewage
Treatment Plant
                                        Kanagawa Sewage
                                        Treatment Plant
                                                                     Hokubu II Sewage
                                                                     Treatment Plant
                          Kanagawa District
                                                    Chubu  District
                                                  Nanbu Sewage
                                                  Treatment Plant
               Totsuka II Sewage
               Treatment Plant
                                     Kanazawa Sewage
                 ©
                   Totsuka I Sewage.
                   Treatment Plant   )
                                      Kanazawa District
Seibu Sewage
Treatment Plant
                                                                          Tokyo Bay
                 Kamakura
Figure 2. Sewage treatment  districts and plants in  Yokohama

                                95

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      Table 1 shows capacity  usage levels for Yokohama's eleven sewage  treatment
plants as of the end of fiscal 1984.  In the approximately two decades since  1962 when
the Chubu Sewage Treatment  Plant came on line, all of the eleven plants called for in
the initial plan have been constructed and put into operation.
                 Table 1.  Sewage treatment plants in Yokohama in March 1985
Plan
Sewage
treatment
plant
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
II.
Chubu
Nanbu
Hokubu 1
Totsuka II
Kohoku
Midori
Kanagawa
Kanazawa
Seibu
Hokubu II
Totsuka 1
Site
area
m2
68,300
70,620
84,520
88,450
125,360
87,000
103,000
236,070
83,470
370,000
31,260
Service
area
hectares
1,287
2,458
2,150
4,232
6,270
8,096
5,049
5,082
4,087
974
2,004
Treatment
capacity
(service
population)
m3/day
96,300
(185,000)
225,000
(433,000)
196,000
(377,000)
206,000
(396,000)
439,000
(844,000)
433,000
(833,000)
543,200
(1,074,000)
345,000
(663,000)
191,000
(367,000)
86,400
(166,000)
124,000
(238,000)
Service
Area
Service Treatment Treatment
area capacity process
hectares m3/day
781.9
2,038.5
1,993.4
1,655.2
1,245.2
1,566.8
2,641.3
2,480.2
172.4
208.5
675.7
47,000 Activated
sludge
225,000 a
196,000 a
131,000 a
67,800 n
108,300 n
272,000 »
172,500 "
31,800 a
43,200 "
31,000 "
Receiving Month
water operation
initiated
Tokyo Bay Apr. 1962
n Jul. 1968
Tsurumi River Jul. 1968
Kashio River Oct. 1972
Tsurumi River Dec. 1972
n May 1977
Tokyo Bay Mar. 1978
a Oct. 1979
Sakai River Mar. 1983
Tokyo Bay Aug. 1984
Itachi River Dec. 1984
      Table 2 gives data on Yokohama's sewage network as of the end of fiscal 1984.
                              Table 2. Sewage network data
                     Flush toilet service rate
                     Service population
                     Service area
                     Service area as percent of total
                     Plants in operation
                     Pump stations in operation
                     Length of pipe network
60%
1.78 million
15,460 ha
36%
11 (I I designed)
16 (25 designed)
5,726km
      Sewer  improvements are near completion in the  old, long-served coastal areas,
and are still  advancing in peripheral inland areas.
                                          96

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3.   Sludge Treatment and Disposal Today

     The methods of sludge treatment and disposal employed at the different sewage
treatment plants as of the end of fiscal 1984 are shown in Table 3.
                   Table 3.  Sludge treatment and disposal (March 1985)
Sludge treatment
Sewage Average Treatment process
treatment volume of sewage
plant treated
(mVday)
1.

2.


3.

4.

5.

6.

7.

8.

9.

10.

II.

Chubu

Nanbu


Hokubu 1

Totsuka II

Kohoku

Midori

Kanagawa

Kanazawa

Seibu

Hokubu

Totsuka 1

68,600

199,000


138,000

75,000

61,000

38,700

187,100

95,200

3,530

16,800

9,340

Anaerobic sludge digestion,
followed by vacuum dewatering
Anaerobic sludge digestion,
followed by centrifugal
dewatering
Pipe to Hokubu II Sewage
Treatment Plant
Thickened sludge is
dewatering directly
Anaerobic sludge digestion,
followed by pressure dewatering
Thickened sludge trucked to
Kohoku Sewage Treatment Plant
Thickened sludge is
dewatering directly
Piped to Nanbu Sludge
Treatment Center
Thickened sludge trucked to
Nanbu Sewage Treatment Plant
Piped to Hokubu Sludge
Treatment Center
Piped to Totsuka II Sewage
Treatment Plant
Method of
disposal
Incineration,
landfill
Incineration,
landfill, drying

—

Incineration,
landfill
Landfill



Incineration,
landfill
Incineration,
landfill


Incineration,
landfill


Dewatered cake
production
(metric tons/year)
5,846

26,565




21,697

8,268



42,137

3,935



31,846



      Generally  speaking,  there are  three  types of  sludge  treatment:   i) gravity
thickening followed by digestion and dewatering; ii) gravity thickening followed by wet
air oxidation and dewatering; and iii) gravity thickening followed by dewatering.

      The dewatered  cake produced by wet air oxidation is disposed of in  landfills,
whereas most  of the dewatered cake produced  by  digestion  and  dewatering and
undigested dewatered cake is incinerated before landfill disposal.

      The incinerators, as  explained  below,  are  installed  at the  sludge treatment
centers, and the dewatered cake is trucked in from  the various sewage treatment plants
where it  is produced.  Figures 3 through 6 show total volumes and volumes for  the
various types of thickened sludge over the past ten years.

      During the past decade, the flush toilet service rate  has jumped from 27 percent
to 60 percent.  Along with this rapid increase, the amounts of both thickened sludge and
dewatered cake have trebled.
                                        97

-------
1,000 cubic meters /year
 2000
 1500
 1000-
 500-
                   I  Thickened sludge for digestion
                  II  Thickened sludge for undigested sludge dewatering
                  III  Thickened sludge for wet air oxidation
                                                                      III
                u
        1975    1976    1977    1978    1979   1980   1981   1982   1983   1984
                                     Fiscal year
         Figure 3. Trends  in annual thickened sludge production
                                    98

-------
1,000 cubic meters/year
I SOn
100-
 50
              I  Dewatered cake produced by digestion
              II  Dewatered cake produced by undigested sludge dewatering,
              III  Dewatered cake produced by wet air oxidation
       1975   1976    1977   1978   1979   1980    1981    1982    1983    1984
                                    Fiscal year
         Figure 4. Trends in annual dewatered cake production
1,000 metric tons/year
lOO-i
 50-
                 I Digested dewatered cake
                 II Undigested dewatered cake
II (incinerated)
       1975    1976    1977    1978   1979   1980    1981   1982    1983    1984
                                    Fiscal year
        Figure  5.  Trends in incineration  and pelletization
                                      99

-------
             1,000 metric tons/year
             50 n
                                                         Dewatered cake
                                                         (landfill)
                       Palletized sludge (for fertilizer)
                  1975   1976  1977   1978   1979   1980   1981   1982   1983   1984
                                        Fiscal year
                          Figure 6. Sludge disposal trends
     Yokohama's  landfill sludge disposal  became  inadequate.   The sudden  growth in
sludge volume and  the difficulty of finding new landfill sites  within  the city led
Yokohama to begin incinerating sludge to reduce  disposable volumes in 1977.  Sludge
incineration permits  a reduction  in  the amount of dewatered  cake to between one-
seventh and one-tenth of its original volume.  This is  very effective in extending the
length of time disposal sites can be used.

     Sludge disposal  in  Yokohama continues to have a landfill  policy as its core, but
because sludge is also considered an important resource, steps have been taken to use it
effectively.  One method in  use  since  1977 is to turn the digested sludge  into dried
pellets and to  use the pellets as  fertilizer at such places as golf courses,  parks and
farms.

     Ash from the incinerator contains unslaked lime which hardens on  contact with
moisture and can therefore be used as a construction material in roadbed and other such
construction.   The city  is now studying the technical and economic aspects of these
uses.
*t.   Centralized Sludge Treatment

*f.l  Sludge collection systems

     Yokohama designed its sewage treatment plants to treat both waste water and
sludge.  The environment surrounding the city's sewage treatment plants has changed
markedly  in the years since land was acquired for their construction, however, because
of its intensive urbanization.

     There have been  increasingly strong calls from residents of surrounding com-
munities for measures to be taken against the malodor and the noise produced by sludge
treatment facilities.  These calls are expected to continue to increase in volume.

     Present efforts  to control  offensive odors  include covering primary sedimentation
tanks and sludge thickeners at  all  the sewage treatment  plants, as well as restricting
the hours  during which sludge treatment facilities can be operated.

                                       100

-------
     Thus, from the viewpoints of both facility maintenance and community pressure,
circumstances  increasingly  favor avoiding wherever  possible  further expansion  of
individual sludge treatment facilities at existing sewage treatment plants.

     In response to this situation, we have developed plans to build centralized sludge
treatment  centers  where increasingly  massive quantities of sludge can  be treated
without creating environmental problems.  Centralizing sludge treatment is expected to
have the following effects:

a.   Increase sludge treatment efficiency in terms of  treatment facility construction
     and maintenance.

b.   Reduce the amount of pollution control equipment required at sewage treatment
     plants.

c.   Improve the residential  environment in the area surrounding sewage  treatment
     plants and reduce the congestion and inconvenience  caused by truck transporta-
     tion of dewatered cakes  by  piping sludge from the plants to the sludge treatment
     centers.

d.   Eliminate  the need to  treat  recycled  process  water  from sludge  treatment
     equipment at sewage treatment plants, improving secondary effluent quality.

e.   Centralize and increase  efficiency  of  process water treatment at  the sludge
     treatment centers.

f.   Allow comprehensive use and recovery of energy from sludge by making greater
     volumes available through sludge collection and centralized treatment.

     With  these goals in mind, it was decided to build sludge treatment centers at the
Hokubu II and  Kanazawa  sewage treatment  plants, where sufficient land had been
acquired beforehand, and to begin centralized treatment of sludge.  The construction
plan involved dividing the eleven sewage treatment plants  into two groups as shown in
Figure  7.  Sludge from the Midori, Kohoku, Hokubu I, Hokubu II, and Kanagawa sewage
treatment plants would be piped to the Hokubu Sludge Treatment Center, while sludge
from the Chubu,  Nanbu, Kanazawa, Totsuka I, Totsuka II,  and Seibu  plants would be
piped to the Nanbu Sludge Treatment Center for centralized treatment.
                                      101

-------
                                               Kawasaki
                                                                              I. Hokubu II STP
                                                                              ^   *
                                                                                  ^^1

                                            Kanagawa STP(QY""^L = 5,030 J Hokubu Sludge Treatment Center
                                       Isogo Relay
                                     /Pumping Station


                                     Y          0450X2
                      0300         /         L=6,980
                         = 2,OIO/
                               V,      (To)  0500
                        Totsuka I STP ^^   I3<420    Nanbu Sludge
     fj    L =7,570
Seibu STP
                                                                            ©Sewage treatment plant
                                                                                   (STP)
                                                                       ®   Slud8e treatment center
                                                                       <>   Relay pumping station
                                                   Yokosuka
                    Figure  7.  Map of plrtiincil sludgr pipt'  net work
                                            102

-------
     The pipelines do not  link  the various sewage treatment plants directly to  the
sludge treatment center.  Instead sludge is sent from one plant  to  the next in  the
direction of the treatment center. Table 4 supplies details of the pipeline network.

                              Table 4.  Sludge pipeline data
Data
Route No.
1.
2.
3

4.
5.
6.
7.
8.
9.
10.
1 1.
Diameter
(mm)X
no. of pipes
450 X 1
600X1
300X1
700X1
450X2
200X1
300X1
450X2
350X1
300 X 1
500 X 1
450X2
Length(m)
6,010
7,680
4,600

5,030
5,800
2,370
6,980
7,570
2,010
13,420
9,670
Remarks
Completed
Under construction
(#300 completed
Under construction
Under construction
Completed
M
Under construction
//
Not yet began
;;
Under construction
      In  view of a  future  interchange between the two groups, a route  was planned
linking the Kanagawa Sewage Treatment Plant with the Isogo Relay Pumping Station.
Part of this line has already been completed.
      Table 5 provides data on the two sludge treatment center facilities.
                          Table 5. Sludge treatment center data
"Sludge containing 99% water
Sludge
treatment
center
Hokubu
Sewage
treatment
plants served
Midori
Kohoku
Hokubu 1
Hokubu II
Kanagawa
Volume of
sludge
received *
mYday
45,000
Sludge treatment process
Thickening (by gravity & centrifugation)
Anaerobic digestion
Dewatering (by centrifugation)
4 \
Incineration, Pelletization for fertilizer
                                             Thickening (by gravity & centrifugation)
                                                 I
Wet air oxidation
I
Dewatering
Nanbu Chubu m3/day
Nanbu
Kanazawa 31,000
Totsuka 1
Totsuka II
Seibu
Thickening (by centrifugation)
I
Anaerobic digestion
Dewatering (by pressurization)
i
Incineration
Thickening (by centrifugation)
                                                 i
                                             Wet air oxidation
                                                 4
                                             Dewatering (by pressurization)
                                         103

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     Three types of  sludge  treatment are planned for the Hokubu Sludge Treatment
Center.  These  involve combinations  of the  thickening, anaerobic digestion, wet  air
oxidation, dewatering, pelletization (into fertilizer) and incineration processes.

     Two  types  of  sludge treatment  are planned at  the Nanbu  Sludge Treatment
Center, involving combinations of  the thickening, anaerobic digestion,  wet air  oxida-
tion, dewatering, and  incineration processes.  The plurality of processes at both centers
is  intended to increase sludge treatment  flexibility and facilitate responses  to  future
technological innovations.  Construction of the centers is proceeding in stages, allowing
for maximum use of existing sludge treatment equipment at sewage treatment plants.

     The pipeline will consist  of single or double ductile cast iron pipes ranging from
200 to 700  mm  in diameter  with a total length of about 88 kilometers. To date only
single-pipe  lines  are  in place, but a  two-lane network is planned for the future to
facilitate response to any damage or trouble in the pipeline.

     Specifications for the pipeline are as follows:

a.    Piped sludge:  a mixture of raw sludge and excess sludge at a concentration of TS
     1 percent.

b.    Flow velocity:  1-1.5  m/sec.

c.    Pipe diameter:  sufficient to allow completion of  sludge piping in  20 hours of daily
     operation, in view of  the need for pipe washing and maintenance.

d.    Equipment: gate valves, air valves, blow-off valves, and others, as required.

     Facilities include sludge storage  tanks,  sludge pumps, and sludge receiving  tanks.
Existing thickening tanks and digestion tanks have been rebuilt for use  as sludge storage
tanks; new sludge receiving tanks have  been built.

     One of the main items of sludge  piping equipment is the sludge pump. A non-clog
centrifugal  pump was chosen because of  its  economical efficiency and its ability to
provide the reliability required  for transporting sludge over great distances.

     The operating organization of the feeding and  receiving  facilities was designed
with the need for a  continuous system linking the sludge treatment facilities  to the
piping facilities in mind.  Control of the sludge feed system operation  is centralized at
the sludge treatment centers, from which commands  are  sent to the  sludge feeding
equipment  at the different  sewage treatment plants.

4.2  Construction status

     The centralized sludge treatment system is still under construction. As of the end
of  fiscal 1984, construction had begun on most of the sludge pipe routes.  Sludge was
already being piped on Route 1 from the Midori to the Kohoku sewage treatment plants,
and on Route 3 from the Hokubu I to the Hokubu II plants.  Almost all  of the routes are
expected to be in operation by fiscal 1988.
                                        104

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     Table 6 shows the state of progress in construction of sludge treatment equipment
at the centers.
                    Table 6. Status of sludge treatment center facilities


Hokubu
Sludge
Treatment
Center



Nanbu
Sludge
Treatment
Center
Facility
Egg-shaped digestion tank

Thickening tank

Centrifugal dewaterer
Incinerator (fluidized bed)
Wet air oxidizer



Incinerator (vertical-multistage)
Incinerator (fluidized bed)
Capacity
6,800m3/tank

1 ,200m3/tank

50m3/riour
lOOt/day
57lmYday



1 OOt/day
I50t/day
Quantity Remarks
12 tanks Under
construction

8 tanks

3
2
2 side-by-side 20 metric tons of
pipes dry solids/day


1
1 Drier
     Construction of the incinerators was given priority over other  processing equip-
ment scheduled to be introduced at  the  siudge treatment centers.   The dewatered
sludge cakes produced at the sewage treatment plants are now brought to the center by
truck for incineration.  Incineration reduces their volume and extends landfill site use.
5.   Overview of Sludge Treatment Centers

5.1  Unit processes

     The Hokubu and Nanbu Sludge Treatment Centers employ combinations of the unit
processes that  are currently thought most likely to ensure maximum sludge treatment
efficiency.  The following explains why these processes were chosen and describes them
in simple terms.

5.1.1  Thickening

     The gravity thickening method was  used  in 3apan  in the past, but because the
organic content of sludge has risen  sharply in recent years and sludge putrefaction has
made it impossible  to obtain the desired concentrations, mechanical  thickening is now
usually employed.

     Mechanical thickening is used  to thicken only  excess sludge,  while gravity
thickening is used to thicken only raw  sludge.  For the following reasons, it is standard
procedure at both of our sludge treatment centers to mechanically thicken all sludge:

a.   In a pumped sludge system, it is difficult to separate and pipe both excess and raw
     sludge.

b.   Sludge  putrefaction is difficult  to prevent when  the sludge must be piped  over
     long distances.

                                       105

-------
     There are two main types of mechanical thickening, flotation and centrifugation.
Experience with both  has  accumulated since 1975.  Mechanical thickening  makes it
possible to maintain higher and relatively more  stable concentrations of solids in the
concentrated sludge than does gravity thickening.

     With centrifugation,  electricity  and maintenance costs  rise  as  the  scale of
operation increases, but operating procedures are simpler and less manpower is required
than with flotation.

     Flotation uses less electricity  but requires a larger site than centrifugation. In
addition,  plant construction  costs  are  higher,  the variety of  auxiliary equipment
required makes maintenance  difficult,  vastly greater quantities of tank gas must be
deodorized and environmental protection costs increase.

     After  studying  the above factors,  Yokohama decided to adopt  centrifugation
thickening.

5.1.2  Anaerobic digestion

     Sludge digestion is  a stable method of treatment which is commonly used in Japan
and which has given good results at  the Chubu, Nanbu, and  Kohoku sewage treatment
plants in Yokohama. The anaerobic  digestion  process has been adopted for Yokohama's
sludge treatment centers because it allows for energy recovery in the efficient form of
methane gas.

     Digestion tanks  can be  classified according  to  shape as Anglo-Saxon,  classic
continental, or egg-shaped tanks. Although Yokohama had used cylindrical tanks in the
past,  it  became  the  first city in  Japan  to  opt for  egg-shaped  digestion  tanks in
consideration of the following advantages with respect to other types of tank:

a.   They require less energy to stir and include little or no internal dead space.
b.   They are structurally efficient, are not subject to stress concentrations and can
     be made very large.
c.   They are not prone to sand sedimentation because of their shape or for other
     reasons.
d.   They produce less scum.
e.   They release less heat.
f.   Their shape is attractive.

5.1.3  Wet air oxidation

     Wet air oxidation of sludge is a method of combusting organic substances in sludge
in the presence of water  using oxygen from the air. It is characterized  by:

a.   Simultaneous digestion and incineration of sludge in a single process;
b.   Easy dewatering of ashes without chemical conditioning; and
c.   Compact equipment and modest space requirements.

     A wet air oxidizer with a solids  capacity  of  20 metric tons  a  day has been in
operation at  the Hokubu I  Sewage Treatment Plant since 1968.  It was the first to be
put into regular use in Japan.  A second oxidizer with the same capacity was installed in
1973.

                                       106

-------
     The performance of these two machines has proved the method's excellence. It is
technically stable and safe in terms of both process and equipment and is relatively cost
efficient. It was consequently selected as one of the treatment processes at the sludge
treatment centers.

5.1.^  Dewatering

     Types of dewatering equipment currently in use in Japan include vacuum filters,
pressure filters, centrifuges and belt press filters.  Of these, all but belt  press filters
have been used recently in Yokohama.  The dewatering devices employed at the sludge
treatment centers were chosen to meet the following requirements:

a.   A high sludge treatment capacity necessitated by the massive volumes of sludge
     collected from the different sewage treatment plants;
b.   A low manpower requirement to derive maximum benefit from the centralization
     of sludge treatment;
c.   Production of low-water-content dewatered cake to facilitate  incineration; and
d.   Maximum recovery of solids.

     It was decided on the basis  of practical  results  to employ  a  centrifuge at the
Hokubu Sludge Treatment Center  and  a high-pressure belt-press  filter at  the Nanbu
Sludge Treatment Center.

5.1.5  Pelletization  (as fertilizer)

     At the  Nanbu Sewage  Treatment Plant,  about 2,800  metric tons  a year of
dewatered cake with a polymer coagulant added after anaerobic digestion are currently
being dried and pelletized using a  rotary drier and sold as a fertilizer to golf courses
and parks.

     The utility of sanitary sludge fertilizer is  well known.   Sludge  recycling to
agricultural and park land is not only beneficial to the soil but an excellent method of
sludge disposal.  For sludge to be easily used as a fertilizer, however, its water content
must be lowered considerably. Driers serve this purpose.

     Plans  are  for about  one-third  of the sludge treated at  the  Hokubu Sludge
Treatment Center to be dried for conversion to fertilizer.

5.1.6  Incineration

     Sludge incineration in Japan began in the early  1960s as a measure to reduce
sludge  volumes.    The  various  types  of   sludge  incinerators  include  flash-drier
incinerators, vertical-multistage incinerators, rotary-drier  incinerators and fluidized-
bed  incinerators.    The  type most widely  used today is the  vertical-multistage
incinerator, followed by the fluidized-bed incinerator. It  was decided to use these two
tried-and-tested types at the Hokubu and Nanbu sludge treatment centers.

     The fluidized-bed incinerator produces  exhaust gases  with temperatures in the
area of 800 C.  An economical and energy-saving incinerator has been developed by
installing a drier at the  previous stage which uses the incinerator's hot  gases to dry
dewatered cake before incineration.
                                        107

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     This completes  our  description  of  the  unit processes now  in use in Yokohama.
Sludge treatment requires the full exploitation of the features of each process as well
as an intelligent combination of the processes themselves.

     Figure 8 is a flow sheet showing  the processes determined to be most effective at
Yokohama's sludge treatment centers.
                                    (A)  Digestion-Pelletization process
Sludge arrives from
.sewage treatment
plant
^-r^

Receiving facility







Thickening


Anaerobic
digestion


Dewatermg


Pelletiliza-
tion


Fertilizer y
(B) Digestion-incineration process


Thickening


Anaerobic
digestion


Dewatering


Incineration


Landfill ^>
(C) Wet air oxidation process


Thickening


Wet air
oxidation


Dewatering




Landfill y
                      Figure 8. Sludge flow at the sludge treatment center
5.2  Present and planned facilities

5.2.1  The Hokubu Sludge Treatment Center

a.   Present facilities

     The Hokubu Sludge Treatment Center  is Yokohama's largest, treating about 60
percent of the sludge produced in  the city.  Four sewage treatment plants—Midori,
Kohoku, Hokubu I and Kanagawa—send their sludge to the center.  This sludge combined
with that produced at the Hokubu II Sewage Treatment Plant adjacent to the center will
amount,  according  to the  master plan, to 45,600 m^/day (with  a 99 percent water
content).

     Facilities built  to  date  comprise a waste water  facility and two fluidized-bed
incinerators burning powdered coal.

     The segments of the  planned  sludge pipeline network already in  operation are
Route  1  from the Midori to the Kohoku plant and Route 3 linking the Hokubu I and
Hokobu II plants.   Other  pipelines  are now under construction.   The Kohoku and
Kanagawa plants are equipped with dewatering facilities.   Until their pipelines are
completed, they will continue to send dewatered cake to the Hokubu Sludge Treatment
Center by truck.  Sludge   piped from the  Hokubu I and  produced  at  the adjacent
Hokubu II plants is incinerated immediately following dewatering at the center.
                                       108

-------
b.    Selection of treatment process

      Table 7 shows treatment processes and volumes handled at the Hokubu Sludge
Treatment Center.

      Collected sludge is first thickened by gravity and centrifugation. Then one-third
is subjected to anaerobic digestion, dewatering, and incineration; one-third to anaerobic
digestion,  dewatering,  and drying;  and the remaining  third to wet  air oxidation and
dewatering.

      The center is  careful to recover energy from the collected sludge and to use it
effectively.  It emphasizes the anaerobic digestion-incineration process for this reason,
and is constructing facilities to generate electricity from  digestion gas and to use t^e
waste heat from incinerators.  These  methods  are  essentially  combinations  of unit
processes already in use for a long time, but they incorporate new technologies.

                 Table 7.  Process flow at Hokubu Sludge Treatment Center
Volume of
treated Thickening
Treatment
Process
A
B
C
solids
(metric Gravity
tons/day)
I5l.9t 1,256m3
X8 tanks
I5l.9t l,256m3X
8 tanks
fuges
I5l.9t l,256m3X
8 tanks
Digestion
Centrifuga-
tion
lOOmVhr
X6 centri-
fuges
IDOmVhrX
6 centri-
fuges
lOOmVhr
6 centri-
fuges
Dewatering
Anaerobic heat-
ing at 35°C for
30 days
6,800 rtrVtankX
1 2 tanks
Anaerobic heat-
ing at 35°C for
30 days
6,800ms/tank
1 2 tanks

Drying
Centrifugal
dewatering
SOnvYhrX
4 centrifuges
Centrifugal
dewatering
50m3/hrX
4 centrifuges
Filter pressing
8.5kg/m2/hrX
10 presses
Incinera-
tion
Rotary
kiln 48
metric
tons/day X
8 kilns


Wet air
oxidation
process

Fluidized-bed
incinerator
20 metric
ton/day X 1
kiln 30
metric tons/
dayX3 kilns




Wet air
oxidizer
20 metric
tons/day X
8 oxidizers
      The properties of sludge have changed in recent years, making it more difficult to
thicken.   Piped sludge is particularly  prone  to acidic fermentation.   It  becomes
anaerobic after several hours.  The  resulting  deterioration  of  its properties makes
thickening especially difficult.

      Recent poor results with gravity thickening require gravity thickened sludge to be
further thickened by centrifugation.  This lessens the amount of sludge sent to the
digestion tanks and the amount of heat needed to warm it.

      It has long been known that their shape enables the contents of egg-shaped tanks
to be stirred thoroughly and that they afford highly  efficient sludge digestion.  They
have not been used in the past, however, because of  the high cost of installation and
scaffolding and the underdeveloped state  of prestressed concrete construction  methods.
The solution of these problems led to the construction of the first  Japanese egg-shaped
digestion tank.  It has been in use at the Hokubu  Sludge Treatment Center since 1983.

                                       109

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      Design specifications for the center's egg-shaped tanks are as follows:

a.    Design requirements: low-cost construction, email surface area, seismic structure
      for safety during earthquakes
b.    Type: anaerobic two-stage digestion
c.    Water content of thickened sludge:  95 percent
d.    Water content of digested sludge: 95 percent
e.    Digestion period:  30 days
f.    Heating method: external heat exchanger, mesophilic digestion (at about 35  C)
g.    Mixing method: mechanical and digestion-gas stirring
h.    Digestion rate:  ^0 percent
i.     Dimensions:  inside diameter 21.8 m x 30.8 m deep; radius of curvature 15.55 m
      (egg-shaped)
j.     Number of tanks:  2k
k.    Material grade: fissure-resistant, high-strength, water- and air-tight prestressed
      concrete
1.     Methane gas utilization:  power generation using digestion gas;  incoming sludge
      heated by waste heat from gas engine

      Figure 9 shows  the layout of the Hokubu Sludge Treatment Center and Figure 10
the digestion and incineration flow sheet.
      Advanced waste water
      treatment area
                                                                      Existing facilities
                                                                  Rffig Under construction
                          Discharge
                             t=
                                    Tokyo Bay
                                              -ilncmerator  ~
                             Cnlormation Pretreatmet 11 gag)  II  f-ij Incinerator yard
                                        Wet air oxidation yard
                          r:
|Chamb_er^ faeries   J|
                            Secondary'
                ^^_
       Storm     DewSenng f Boiler room
       water      f acmt jgs Jfeaaa:
                                   Digestisn   Digestion-pelletization yard
                                   gas holder
                                  ML
                                                Sludge-
                                          Administration building
                          9.  Layout of the Hokiibn Slndg<> Tri>ntint>nt C.i
                                          110

-------
                                                   Heated water
                                                                            Exhaust gas


                                                                 Waste heat boiler
      Exhaust gas
r	
(Digestion gas holder
                Thickening tank
n                                                                                                                                       Exhaust  gas
                                                                                                                                            A
                                                                                                                         equipment    j       ' '
Sludge
 receiving facilities
Recycled process watar
                                                     Heated water circulation pump
                                                                                                                                                      ash
                                                                                                                                         Dewatered  cake
                                             Figure  1O. Digestion and incineration flow  sheet

-------
 c.    Construction plans

       Figure 11 shows the construction plan and trends in sludge volumes treated at the
 center. Quantitative data were obtained from the growth in sewage amounts  coming
 from  the sewage treatment plants.

       All the sludge  produced at the Hokubu I Sewage Treatment Plant has been sent to
 the center since the summer of 1983 and  treated by  gravity thickening, centrifugal
 dewatering and incineration.  In fiscal 1986 piping of sludge is to begin from the Midori,
 Kohoku, Hokubu I and Kanagawa sewage treatment plants, increasing the total  volume
 of sludge  treated to 95 metric tons of dry solids per day; sludge from these plants will
 be  treated  by  gravity  thickening,  centrifugal thickening, anaerobic  digestion  and
 incineration.

       Sludge volumes will increase  linearly as the number of flush toilets increases, but
 for the time being  priority will be given to expanding  the digestion and  pelletization
 processes.  Centrifugal thickening and  wet  air oxidation processes are scheduled for
 adoption later.

Metric tons/day
 800
       1983 1984 1985
                             1990
                                            1995
                                                            2000
                      Figure 11. Construction plan at the Hokubn Sliulgi- Treatment Center
                                          112

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5.2.2  Nanbu Sludge Treatment Center

a.    Present facilities

      The Nanbu  Sludge  Treatment Center is scheduled to receive a total  of  31,000
m^/day (with a 99 percent water content) of  sludge  produced at the Chubu, Nanbu,
Totsuka I, Totsuka II, Seibu and Kanazawa sewage treatment plants.

      Facilities completed thus far include two wet air oxidation lines with a capacity
of 20 metric tons of dry  solids  per day each, one vertical multistage incinerator with a
capacity of 100 metric tons/day and one drier-equipped fluidized-bed incinerator with a
capacity of 150  metric  tons/day.  Because sludge pipes to the center are still under
construction, dewatered cake produced at the sewage treatment plants is trucked to the
center for incineration.   The amounts involved  are 5,850  metric tons/year from the
Chubu plant, 21,750 metric tons/year from the  Nanbu plant,  9,830  metric  tons/year
from  Totsuka I and II  plants and 1,000  metric  tons/year from the Seibu  plant.  The
196,200 m^/year of sludge produced at  the adjacent Kanazawa Sewage Treatment Plant
is treated by wet  air oxidation.

      Sludge treatment facilities are in operation at the Chubu, Nanbu, Totsuka II, and
Seibu plants. Even after the sludge pipelines to the Nanbu Sludge Treatment Center
begin operation, these  plants will continue to treat their own sludge, in the interest  of
efficient use of existing  facilities, and the excess will be  piped to the Nanbu center.
Equipment at the plants will not be replaced, however, so that the  volumes they send  to
the center will gradually  increase over time.

b.    Treatment process selection

      The processes used  at large-scale collected  sludge treatment facilities must allow
for both the efficient treatment of large quantities of sludge and substantial economies
of scale.  At the  same  time, they must satisfy such requirements as adaptability to  load
fluctuations and back-up capability in the event of trouble elsewhere in the network.

      The processes used in the system must also ensure  flexibility in future  sludge
treatment.  There is  room for improvement  in current  sludge  treatment and  unit
processes, and remarkable new sludge treatment technologies are still emerging.
                                       113

-------
     Table 8 shows combinations of sludge treatment processes employed at the Nanbu
Sludge Treatment Center.

                 Table 8.  Process flow at the Nanbu Sludge Treatment Center

B
B
Volume of treated
solids (metric Thickening
tons/day)
95.0 Centnfugation:
lOOnvYhrXS
centrifuges
35.3 Gravity:
522m3 X 4
ponds
138.4 Centrifugation:
lOOmVhr
X8 centrifuges
Digestion
Anaerobic
heating at
35°C for
30 days
6,400m3/tankX
9 tanks

Wet air
oxidation
process

Moist oxidization
20 metric tons/day
X4 oxidizers
23 metric tons/day
X4 oxidizers
Dewatenng
Belt press
ISOkg/m/hrX
3m X 18 presses
Pressure
I4.5kg/m2/nr
X6 presses
Incineration
Vertical multi-
stage incinerator
100 metric tons/day X
1 incinerator
fluidized-bed incinera-
tor ISO metric tons/
days X 2 incinerators

     One-third of the expected volume  of  sewage is to be  treated  by centrifugal
thickening, anaerobic digestion, belt-press dewatering and incineration (the combination
known as the digestion-incineration process).  The remaining two-thirds is to be treated
by thickening, wet air oxidation and pressure dewatering.  A gravity thickening tank
will  be  used to  concentrate  35.3  metric tons/day of  the sludge  produced at the
Kanazawa Sewage Treatment Plant.

     Figure 12 shows the layout of the Nanbu Sludge Treatment Center.
                                       114

-------
Sludge  storage
     V-.
tank   ,\.\
Administration building
(completed section)       (Planned)
                                                                   rj
                                                     Screenings washer"
                                                       111
Transformer
station
'"1
u»
'(—
'"1
r-1
i
i
i
J
r~!
v i

j i
(Planned)
1 Wet air oxi
J
-N
Jat
J

0
r
i pro
L
_i
, r
Completed) |U
L

Completed) |_

L


.-
L

1
-
c


1
1
1

^

s
)
1s
)
                                               Thickeners
                                                                                  (completed)
                                         Sludge incinerators
                                         (completed part only)
                                                        Sludge digestion tank   ! Slud&e digestion tanks
                                                                                               Pi
                                                                                              (Completed)
                                      I
                       	i
 Sludge digestion tanks   ,	1
            "  '      i Digestion  gas-fueled
                       generator room  )
              C  Boiler L..     I  V^
                   &
                blower
                                                                                                Dewatering equipment
                                                                                                               n
                                                                                        o
                                                                                                     gas holder
                                                                              Compressor room
                                                                                                       Site boundary
                                                                                  :q
                                                                                  :n
                                                                                   cRMo
                                                   LD
                           Figure  12.  Layout of the Nanbu Sludge Treatment Center

-------
 c.    Construction plans

       Figure 13 shows the construction plan for the center and trends in sludge volumes
 treated there.  Quantitative data were obtained from the growth in amounts of sewage
 arriving from the sewage treatment plants.

       The center will begin  to receive sludge in  1988. Until this time, it is scheduled to
 treat only the  sludge  from the adjacent Kanazawa Sewage  Treatment Plant  using a
 gravity thickening, wet air  oxidation process. When  sludge piping begins, the volume of
 sludge will roughly double, and the existing  process will be combined with a centrifugal
 thickening-digestion  process not yet constructed.

       Thereafter, sludge volumes will increase linearly as the  number of flush toilets in
 the service area grows.  Initial expansion will focus on the use of digestion processes.
 Centrifugal thickening and wet air oxidation processes will be added later.
Metric tons/day
   300
                                                                                   263.7
                                                              Wet air oxidation process (C)
                                                          135.00 ^^      ( 138.4-Metnc tons/day
                                                                          (31 .7-Metric tons/day
                                           Digestion-incineration process (B)
                                                       (35.3 Metric tons'day
                                           Wet air oxidation process (C)
        1980   1982   19841985
          1981   1983
1990
              1995
                                                              2000
                                          final fiscal year
               Figure 13. i Nanbu Sliulge  Treatment Center construction plan
                                           116

-------
 5.3   Energy use planning

      One of the greatest advantages of centralized sludge treatment is that it allows
 energy to be effectively recovered.  Both of Yokohama's sludge treatment centers were
 designed for optimum utilization of the energy derived from sludge.

      The forms of energy recoverable from sludge—electric, mechanical, chemical and
 thermal—are shown in  Figure 14.   This figure  also  indicates  rough rates of energy
 conversion.  Analysis of the possible uses  of  energy recovered  at  the center revealed
 that thermal energy could be used to heat  the digestion tanks and for local heating and
 air conditioning, and that  mechanical energy could be used to drive the blowers and
 pumps at the center. The study showed  these uses to  be limited, however.  Electricity,
 on  the  other hand,  was found  to  offer a broader sphere  of  applications,  including
 lighting and driving machinery.  This suggested that the most effective system would be
 one that used digestion  gas to generate  electricity and made use of both this electric
 energy and the thermal energy derived from waste heat.

      In light of this analysis, electric  power generation using digestion gas was chosen
 as the basic method for both centers.  Results of trial calculations concerning energy
 recovery  with  the digestion gas-fueled generator  system  in use at  the  Nanbu Sludge
 Treatment Center are described below.

      The system centrifuges 95 metric tons of dry solids per day of incoming sludge to
 a concentration of 5 percent solids and subjects it  to  high-concentration digestion.
 Most  of the resulting digestion gas is burned by a  gas engine to generate electricity, and
 the waste heat from the gas engine is recaptured by an external  heat  exchanger and
 used to warm the digestion tank.

      Table 9 shows the conditions under which the  system's  energy balance  was
 calculated.

      Figure  15 shows the heat balance in the digestion gas cycle. The data are grouped
 in three rows. The top row shows data for summer and the middle row for winter.  The
 bottom  row shows the average.  On the average, 136 x 10^ kcal/day are recovered in
 the form of digestion gas from the first-stage tank.

      The heat required  to  warm the digestion tanks is the sum of the heat  released by
 the tanks (10 x 10^ kcal/day) and the  heat required to heat the incoming sludge (29 x
 106 kcal/day) or 39 x 106 kcal/day.

      To  recover enough waste  heat  from the  gas  engine-generator-heat exchanger
system to warm the digestion tanks,  it  is therefore sufficient to  supply the system with
fuel equivalent  in heat to about  89  percent of  this,  or 136  x  106 kcal/day.   The
remaining 11  percent of the digestion gas can  be used  as fuel  in  other  systems or
facilities, as  auxiliary fuel for the vertical multistage  incinerator or as fuel for the wet
air oxidation system's deodorization equipment, for example. Because the multistage
incinerator (capacity 100  metric tons/day)  requires  23 x 106  kcal/day,  the  use of
digestion gas reduces its  fuel requirement by about 76 percent.
                                       117

-------
00












Organic matter
1
T
Anaerobic digester

*

Digestion gas 	 •





















































-^ n —- r

1
Waste heat
I




__ -,- ,


Waste heat
1



	 ^


	 p...,.





T 1 '





















fc





























Electrical energy







Electrical energy


Thermal energy


Mechanical energy










































Approximately
30%



Approximately
40%


Approximately
18-24%




40%

Approximately
30%

Approximately
80%

Approximately
30%

Approximately
21%



1 — Fuel

^ — Industrial feedstocks
L- Others
1 — • Site power


' — Others

1 — Digestion tank heating
I

1— Others
1 — Site power




I — Digestion tank heating
_ 14--

' — Others
ESite power


Others
| — Digestion tank heating


•— Others
1 — Blowers


' — Others
E Blowers


Others
                                                       Figure 14.  Uses for recovered energy

-------
      Turning now to heat recovery in the digestion gas-fueled generator  system, 41 x
     kcal/day (about 30 percent of the  136 x 10^  kcal/day of heat supplied) is recovered
as electricity, and 84  x 10*> kcal/day (about  62 percent of the heat in the  waste gas
from the gas engine and the engine cooling water) is recovered as heat  energy.  Of the
latter, about  46 percent, or 39  x 10*> kcal/day, is  used by the sludge and other heat
exchangers to  warm  the digestion tanks.  Although the boiler is  not necessary  to the
heat energy balance, it was included in the system design  to  serve as a back-up during
start-ups and system  malfunctions.
      The 41 x Ifl6 kcal/day heat recovered  in the form of electricity is equivalent to
47,600 kWh/day.  This contributes  substantially to  energy  savings  by providing about
33 percent of the electricity used at the Nanbu Sludge Treatment Center.
                     Table 9. Energy balance conditions in the Nanbu Sludge
                             Treatment Center's digestion gas-fueled generator system
                          Item
                                                                Value
         Incoming sludge
         Incoming sludge
         Incoming sludge concentration
         Incoming sludge VTS
         Incoming sludge temperature
         (summer)
         Incoming sludge temperature
         (winter)
95 DST/day
I,900m3/day
 rO/
 5/0
65%
25°C

I2°C
         Digestion period

         Digestion temperature
         Digestion tank capacity
         Heating method
30 days
 I st stage ' 20 days
 2nd stage • 10 days
35 °C
6,400mYtank x 9 tanks
External heater
         Volume of digestion gas generated
0.45m3/VTS/kg of incoming sludge
         Net calorific value of digestion gas
5,500 Kcal/IMm3
         Overall heat transfer coefficient
Air    K = 0.9l9Kcal/mVhr°C
Soil-  K=l.853kcal/mVhr°C
         Ground temperature
         Air temperature (summer)
         Air temperature (winter)
I62°C
262°C
 49°C
         Gas engine type
         Gas engine output
Electric ignition
800 HP
         Generator type
         Generator output
Three-phase AC
500 KW x 4
         Conversion efficiency of
         digestion gas engine-generator system
30%
         Gas engine heat recovery
         rate  (sludge warming heat)
                                                40%
                                             119

-------
                                    Digestion gas generator heat balance
                             Heat generated by digestion tank
                                                                             Top row:   summer
                    Middle row:   winter
                                                                             Bottom row:   average
                                           ( Unit:  I06kcal/d)
                                                                                 Gas engine



46
60
54





9
12

1
J®i




71
94
84
u

Heat exchanger
                                                                                                 25
                                                                                                 34
                                                                                                 30

Number
®

Item
Total digestion tank heat requirement
Legend
| Number
(?)

Item
Heat lost by heat exchanger
       Heat used to warm incoming sludge
       Heat lost by digestion tank
'CD     Heat generated by digestion tank
(D     Heat supplied to gas engine
(6)     Gas engine exhaust heat
(D    Heat recovered from gas engine
(f)    Heat used to generate electricity
©    Heat lost by gas-fueled generator
(jj)    Heat lost by sludge heat exchanger
@    Heat supplied to digestion tank
           Figure 15.  Nnnbu Sludge Treatment Center digestion gas energy balance
                                                 120

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5.4  Instrumentation

5.4.1  Basic structure of instrument systems

     The sludge  treatment centers are equipped with large-scale  equipment—sludge
receiving,  thickening,  digesting  and  digestion  gas-fueled  units—whose  control  is
extremely complex.

     For comprehensive  integrated sludge control,  the  units must be  organically
interconnected.  This is accomplished at the centers through a centralized  supervision
and distributed control system.

     The data processing  system at the heart of the supervision and control  system
consists of two side-by-side 32-bit computers for reliability and  ease of  maintenance.
One of the computers is usually on standby.

     Distributed  local stations control the various  complex automatic functions and
perform  the  necessary computations.   The  local stations have microcontrollers and
sequence controllers with data transmission capability to the main computer.

     Fiber optic  cables are used for data transmission between local stations and the
main computer. They are linked by an N:M transmission method.

     The system  that pipes sludge from the sewage treatment plants to the center for
centralized treatment also  involves a remote data transmission link between the center
and the various plants.  The sludge piping system is an integral part of the centralized
supervision and distributed  control system.  It is treated at  the control level in the same
way as the other local stations.

     Figure 16 is a diagram representing the sludge treatment centers' instrumentation
system.
                                       121

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ro
ro
1 	 , 	 	 | 	 , Central control station computer system
Mam computer | j pp Standby computer
^nrg. ^j£
	 -* ~^}rm
T
^™ FHDrS/VHC
RSA MSTA ™OCJFHC
W \J
tRSQ RSQ RSQ RSQ ..
00 00 DO 00
CS CS CS CS CS
TQ TQ TQ TQ TQ
RP n p DP DP DP
U K l^ Ko r\u r\ u i
u 	 _J 1 	 — — 1 1 	 -J * 	 1 1— 	 — I
Sludge Sludge thickening Sludge Sludge dewatermg Sludge
receiving equipment anaerobic equipment mcinera
I/O TW
|

J^MST Optical communications dataway
w
Rsn ] r R-
ITTl!
L
LJ LJ | •• -

1 	 1_p_.igenerator ^'-Z^--'-
_ - " ^ ' C- x /
tion ^^"^ s-''''' '
equipment digestion equipment ^^^ ^^ x" /
equipment ^*-"" ^, '''_,''
1 <^e^ •'"'^ ^^'^^^ /
\|s^'?ei^'' ^^^' xx Slue
^-'°'" .-"''
Transmission device Transmission device Transmission device
f-^ i Pipeline J ^..^ [ Pipeline ^ Pipeline
[ r*-i i r~"~
L J L —i u -i
Midori Sewage Kohoku Sewage Hokubu 1 Sewage
Treatment Plant Treatment Plant Treatment Plant
l /
ge receiving tanks ,
i /

Transmission device Tra
i
Pipeline ^ ] Pipeline
i

b" "
^^ Remote data
tran<;mk<;ion rievir.e


J"l (jonlrol device
j 	
' ^ j^~ Transmission
"l device
>
i
\
\
\
\
\
\
\
\
\
\
\
\
1 Local control
nsmission device
1 I
i l
i i
L J
Hokubu II Sewage Kanagawa Sewage
Treatment Plant Treatment Plant
                                                                                                                                          FD  Floppy disk drive
                                                                                                                                          LP  Line printer
                                                                                                                                          TW  Output typewriter
                                                                                                                                          SYC  System console
                                                                                                                                          FHD  Fixed head disk
                                                                                                                                          MST  Master station
                                                                                                                                          RS  Remote station
                                                                                                                                          l/OTW  Input/output
                                                                                                                                            typewriter
                                                                                                                                          CRT  Cathode ray
                                                                                                                                            tube display
                                                                                                                                          CB   Control board
                                                                                                                                          IB  Instrument board
                                                                                                                                          CTR  Microcontroller
                                                                                                                                          SQC  Sequence
                                                                                                                                            controller
                                                         Figure  16. Sludge  treatment center instrumentation

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5.4.2  Sludge feed and intake system instrumentation

      The sludge  piping instrumentation at the completed Hokubu Sludge Treatment
Center will now be described in greater detail.

a.    Overview

      Sludge  produced at sewage treatment plants is  pumped  to  the Hokubu Sludge
Treatment Center through pipelines.  To facilitate  planned, efficient treatment of the
sludge collected from these plants, the sludge pumps are remotely  controlled from the
sludge treatment center.

      Thus the  center also acts as the central control station for the system, with the
various sewage treatment plants acting as local or site piping control stations.

      The local facilities  are equipped with microcontrollers  and sequence controllers
which receive operating instructions  from the central control station and control the
equipment according to fixed control  procedures. The central and local control stations
are linked by remote data transmission equipment using telephone lines.

      Instructions concerning volumes of sludge  to be sent  and methods of transporting
it are sent from the central control  station to  the local station via this remote data
transmission  equipment.  The local microcontrollers take the instructions and convert
them  into specific control procedures for the sequence controllers which activate the
pumps and valves.

      Information concerning  such things as  the  operating status  of the pumps  and
valves at the local station, volumes of sludge being piped, amounts  of solid matter and
equipment problems is transmitted from  the local  station back to the central control
station. It is received here in batches by input/output control equipment and relayed to
the central computer system via the center's internal dataways.

      At the center, the central computer system batch-treats data received  from the
local  stations and displays them  in diagrammatic, numeric and character form on the
CRT displays which function as the man-machine interface.

b.    Control

      Sludge feed pumps can be controlled in three modes:  monitoring sludge storage
tank levels,  presetting and timer setting.  These modes determine the values at  which
control functions are activated from the central  control station.

      i.    Level control

      Tank levels can be controlled  to achieve a balance  between the  sending  and
receiving side.

      The sending pumps begin operation when storage tank levels on the receiving side
fall below a predetermined value. Pumping continues  until either there is no more
sludge on the sending side or  tank levels  at the receiving side have reached  a
predetermined maximum level.
                                       123

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     ii.    Preset control

     In this control method, total daily quantities and the overall frequency of sludge
piping at a given sewage treatment plant are set in advance. Based on this setting, the
microcontroller  calculates quantities  for  a single sludge piping session  and a piping
schedule,  then begins  regular consecutive piping according  to the program  it  has
established.

     Since the quantity of sludge piped in one day is determined according to its solid
content, solid concentrations are  measured  and converted into  equivalent  sludge
volumes.   This preset control method is extremely effective in keeping track of the
amounts of sludge piped daily.

     iii.   Timer control

     The timer sets the  frequency  of sludge piping and the number of hours that the
pipes are in operation for each piping session,  then  carries out piping consecutively.
This method is a very effective in keeping track of piping time.

     Once a piping session is over, secondary effluent  is piped through the pipeline to
flush it clean.

     Piping  operations can  also  be  controlled  from  the central control station  by
manually starting and stopping the pumps.

c.   Supervision

     Information concerning the state of sludge piping equipment operation  is sent by
the remote data transmission instruments to the central control station.

     At the  central control station  this  information is  input to  the computer for
observation on CRT displays and instrument  boards.   It  is also recorded  on output
typewriters and recording instruments.

     Table 10 shows the main items observed.

 d.    Measurement

      Data readings at  the sending facilities on piped sludge volumes, sludge concentra-
 tions, sludge  storage tank levels and so forth are sent  by the remote data transmission
 instruments to the central control station.

      At  the central contml station, this information is  input to the  computer and
 displayed  on the  CRT  display,  as well as  continuously recorded  by   recording
 instruments.

 e.    Detection of pipe clogging and leakage

      Obstructions  in  the  sludge pipes are detected by  logic circuits as shown  in
 Figure 17.   These conclude a pipe is blocked  if  a  pump's outlet pressure  exceeds a
 certain value and sludge  flow either reaches a certain minimum  value or drops suddenly.
 When  an  obstruction  is detected,  the feed  pump is immediately shut off  and an
 obstruction warning buzzer sounded.

                                        124

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                                Table 10.  Supervision items
Equipment
1.
Feed pump
2. Outlet valve
3
4,
5.
6.
7.
Draw valve
Sludge storage tank
Control mode
Electric failure
Other
Item
1. Automatic/manual
2. Preparations complete
3. Start/stop/trouble
Closed/open/trouble
Closed/open/trouble
High/low
1. Level control
2. Timer control
3. Preset control
Ground fault, overvoltage,
voltage, temperature rise,
power failure, sequence
controller trouble
under-
control
1. Fire
2. Pipeline abnormality
3. Transmission
                                                 abnormality
                                                Building or ancillary
                                                 facility trouble
               High pump outlet pressure

                            Low flow

                    Sudden drop in flow
Obstruction
                        Figure  17. Obstruction logic circuit
      Sludge pipe leakage is also detected by logic circuits as shown in Figure 18.  They
conclude a pipe is leaking  if its outlet pressure  falls below a certain level and sludge
flow either exceeds a certain normal value or registers a sudden increase.  On detection
of a leak, the feed pump is immediately shut off and a leakage warning buzzer sounded.
                Low pump outlet pressure

                            High flow

                    Sudden rise in flow
Leakage
                           Figure 18.  Leakage logic circuit
                                            125

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6.   Conclusion

     In  the  past,  sludge  treatment  in  Yokohama  was  performed at  the sewage
treatment plants where  the  sludge was produced.   A  plan  is being implemented in
stages,  however, to centralize sludge treatment  at  two sludge treatment centers
located on the coast.  Centralized treatment is considered necessary in  view of the
growing quantities of sewage and sludge requiring treatment, the impact of treatment
on the environment surrounding sewage treatment plants, and the need to  increase the
efficiency of sludge treatment and disposal.

     There are, however, disadvantages as well as advantages to centralized sludge
treatment. Problems requiring solution include the following:

a.   Transport of sludge over long distances

     Linking the eleven  sewage treatment plants requires 88 kilometers of  pipe.  The
magnitude of  this network makes detection of leaks and other problems  extremely
difficult.

b.   Stability and safety of the sludge pipe network

     The network is currently designed for single-lane pipelines.  This leaves much to
be desired in terms of  system stability and safety in the event of earthquakes or other
disruptions.   One  possible  remedy is  to  lay double piping  between all  the sewage
treatment plants and to  develop the system  into a  network of two-way links between
plants.  Ways must also be found to use all the facilities at all of the plants in the event
of earthquakes or other emergencies.

c.   Recycling of process water from sludge treatment centers

     Recycling of process water was not a problem in the past when sludge was treated
at individual sewage treatment plants.   However, at the sludge treatment centers, the
enormity of the recycling load is expected  to cause problems.  In response, experiments
have been performed in search of methods to  treat and recycle process water, including
pressurized aeration, deep shaft aeration,  and other biological processes.   The results
showed that these  methods yielded an unsatisfactory 50 percent reduction in chemical
oxygen demand (COD(^n).

     These are the problems  we face.  Several years will be required before the sludge
treatment centers  are  completed, and  we hope that in the meantime new sludge and
recycled process water treatment technologies will be  developed and put to use.  We
wish to be able to adapt flexibly to such new technologies and thereby establish a more
efficient sewage and sludge treatment system.


                                      //##
                                      126

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                                    Tenth  United States/Japan Conference
                                       on  Sewage Treatment Technology
ODOR CONTROL IN MUNICIPAL WASTEWATER TREATMENT PLANT
              The work described in this paper was
              not funded by the U.S. Environmental
              Protection Agency.  The contents do
              not necessarily reflect the views of
              the Agency and no official endorsement
              should be inferred.
                           Masahiro Takahashi,

                  Research Engineer, Sewage Works Section,

            Public Works Research Institute, Ministry of Construction


                             Shigeru Ando,

                   Director, Water Quality Control Division,

            Public Works Research Institute, Ministry of Construction
                               127

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                              TABLE OF CONTENTS
                                                                          Page
1.   PRESENT STATUS OF ODOR PROBLEMS IN JAPAN	      129
2.   PURPOSES AND OBJECTIVES OF RESEARCH AND STUDY 	      131
3.   ODOROUS SUBSTANCES AND THEIR SOURCES IN THE PLANT 	      131
 3.1   Odor Measurement 	      131
 3.2   Odorous Substances 	      133
4.   MECHANISM OF ODOR DEVELOPMENT	      137
 4.1   Study on Ventilation Rate	      137
 4.2   Overall Mass Transfer Coefficient at the Channel
       and Weir 	      140
5.   DEODORIZATION TECHNOLOGIES 	      143
 5.1   Odor Collection 	      143
 5.2   Deodorization 	      145
6.   EXAMPLES OF DEORODIZATION MEASURES 	      151
                                     128

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1.   PRESENT STATUS OF ODOR PROBLEMS IN JAPAN

          It dates back to the 1950s when offensive odors started to be a
     social problem in Japan.  In the 1960s when Japan achieved a miraculous
     economic growth, odor problems took on a pandemic phase.  In 1966,
     statistical survey was initiated about the odor complaint cases; the
     number of cases filed with the public bodies in 1966 was 3,500.
24000
21000
18000


9000
3000
0






f-j_
TTl f






*"














r-j











































-
- ;















—















TT»























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"































F~I



H*
















                      1966 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 32

                                    Fiscal Year

         Fig. 1  Annual changes of complaints about offensive odors
          Fig.  1 shows the transition of odor complaint cases from 1966 to
     1982.   As  demonstrated,  the number of cases rose six times in the first
     six years  from 1966 till 1972.  Concerned about the situation, the
     Government put into effect the Offensive Odor Control Law in 1972 to
     authorize  the local municipalities to control odor concentrations.  From
     1973 afterward, the number of complaint cases had been on the decline;
     in 1982, it fell to about 13,000.
          At present, local municipalities are empowered by the offensive
     Odor Control Law to control eight odorous substances at the metes and
     bounds of  every odor source, as shown in Table 1.
          According to the Law, the prefectural governor is authorized to
     determine  the regulated  areas and standard odor concentrations after
     hearing out the opinion  of local municipalities.  As of 1982, 1,256
     municipalities or 39% of all, have regulations by the Offensive Odor
     Control Law.
          Ever  since the enforcement of the Law, the complaint cases have
     been decreasing.  According to the statistics for FY 1982, livestock
     farming and service industry led the list of odor complaints with 28.1%
     and 19.8%, respectively  as seen in Fig. 2.
                                      129

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  Table 1  Odorous substance limits according to Offensive Odor Control  Law
Odorous substances
Ammonia
Methyl mercaptan
Hydrogen sulfide
Dimethyl sulfide
Tr ime thy lami ne
Dimethyl disulfide
Ace toaldehyde
Styrene
Limits (air-borne concentration
at plant boundary (ppm) )
1 to 5
0.002-0.1
0.02-0.2
0.01-0.2
0.005-0.07
0.009-0.1
0.05-0.5
0.03-20
              Food prai-e-sing plants
                                           Construction sites, 1.8%
                                                                Drainage channels
  National
  total
(12,741 cases)
Feeds tufi and fertilizer
olants, 3.0%

Livestock farming
28.1*









5 7%


cj. i°
Moving odor sources , 0.3%
\
Othrr
manufacturing
pi ants
13. 2*
Service industry,
etc.
19. Ht.
1 f hemji d 1 plants




6.


1%
Residential houses , 0.6%

Garbage
col Lee ticn
yards ,
8.6*
Un-
known ,
7. IS


Waste water treatment
plants, 0. 4%
   Fig. 2  Percentage  distribution of  sources blamed for offensive odors
         The number  of  complaint cases against the wastewater treatment
    plants was 49, or 0.4%.
         While the siting  conditions  are important for the prevention of
    odor problems, there are many wastewater treatment plants adjacent to
    residential quarters that have obviated odor problems with proper
    measures.  One of the  most viable measures is to cover up the odor
    source.  In Japan,  70% of sludge  thickners and 75% of grit chambers are
    installed indoors or covered.  Thirty percent of rather larger
    facilities such  as  aeration tanks and primary settling tanks are also
    covered with  covers made of FRP and other plastic materials.  At
    present, the  open yard drying beds have been replaced almost totally by
    mechanical sludge dewatering processes installed indoors.  Some 13% of
    dewatering machines are  covered.   Sixty-nine percent of sludge cake
    hoppers are totally sealed.
         The wastewater treatment facilities equipped with deodorizing
    equipment are 38% for  grit chambers, 43% for sludge thickners, and 58%
    for sludge dewatering  machines.
         About a  decade back, it was  a common practice to scrub odors simply
    with a sodium hydroxide  solution  or water.  Today, many wastewater
    treatment plants use absorbents such as activated carbon and ion
    exchange resin or sodium hypochlolide to remove odors.
                                      130

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          Soil absorbability and biological decomposing activities are used
     to remove odors, as well as a process in which foul air is blown into
     activated sludge reactor for deodorization.
          With the progress of deodorization technology, there are few odor
     problems with the existing wastewater treatment plants, except for some
     special cases.


2.   PURPOSES AND OBJECTIVES OF RESEARCH AND STUDY

          In Japan, the deodorization measures have been working well.  Many
     of technologies applied in deodorization are originated from paper and
     pulp industry and night soil treatment plants.  In the municipal
     wastewater treatment plants, malodorous substances are lean in
     concentration as compared with those in paper and pulp mills or night
     soil treatment plants, but the volume of air to be handled is quite
     large.
          The study was prompted to review deodorization measures for the
     wastewater treatment plants according to the following topics.

     1)   To determine characteristics and volume of odor substances from
          each of the processes, including grit chamber, aeration tank,
          sludge thickner, and sludge incinerator, and to make clear their
          organoleptic relationships quantitatively.

     2)   To study the method of predicting the volume of odorous substances
          and predicting the dispersion into the atmospheric environment.

     3)   To identify the covering and ventilation methods suitable for each
          of the processes.

     4)   To study the optimum deodorizing methods.
3.   ODOROUS SUBSTANCES AND THEIR SOURCES IN THE PLANT

3.1  Odor Measurement

          The data of odor measurement here were obtained by following
     methods.

     (1)   Odor concentration

               The concentration of an odor was measured on an following
          organoleptic test.  First, two scent bags are purged with the room
          air cleaned through activated charcoal, and another bag is prepared
          purged with an odor which is diluted with clean air.  These bags
          are then numbered 1 through 3 at random, and are sniffed at by the
          members of a test panel, all having a sound sense of smell, through
          a nose cone.  They are asked to take down the number of the bag
          that stank most.  If the panel answered correct, the dilution ratio
          is increased a notch.


                                     131

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          The  test  closes when  the dilution ratio has begun to confound
     the panelists.

(2)   Odor strength

          This is also measured by an organoleptic method, and the odor
     strength  is expressed  in six grades  as shown in Table 2.
                Table  2   Six-grade of odor strength
Odor strength
0
1
2
3
4
5
Description
No odor
Barely detectable (detection threshold level)
Barely identifiable level of odor (identification threshold
level)
Easily identifiable
Strong odor
Very strong odor
(3)   Ammonia

          Several milliliters  to  several hundred liters of  ammonia  gas
     is blown into  20 milliliters of  0.5%  aqueous  solution  of  boric acid
     as an absorbent at a rate of 1 to  2 liters a  minute, the  volume of
     ammonia gas to be supplied being dependent on the concentration of
     ammonia gas.   The odor  strength  is then measured according  to  the
     indophenol  method.

(4)   Sulfur compounds (hydrogen sulfide, methyl mercaptan,  methyl
     sulfide, methyl disulfide)

          The odor  collected in a gas collecting bag is passed through a
     sample concentrating tube which  is refrigerated with liquefied
     nitrogen.   In  this way, sulfur compounds  are  concentrated and
     subjected to gas chromatography  for fractionation.

(5)   Lower fatty acids

          An odor is passed  through a column filled up with glass beads
     coated with strontium hydroxide  for trapping  lower fatty  acids by
     reaction.
          Formic acid is then  added to  the column, and the  eluate
     containing  lower fatty  acids is  fractionated  through a gas
     chromatograph  equipped  with  a flame ionization detector.

(6)   Aldehydes

          Aldehydes are trapped in a  solution  of 2,4-dinitro-diphenyl
     hydrazine,  and are extracted with  carbon  tertachloride.   The
     extract is  then concentrated 20  times and gas-chromatographed.
                                132

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3.2  Odorous Substances

           A wide spectrum of malodorous  substances which have been identified
     by  the survey  since 1976  to be present at a level higher than the
     olfactory threshold value are as listed in Table 3.
           Table 3   Substances  associated  with odors  from wastewater
Classification

Mercaptans

-------
   respective threshold values are correlated for each wastewater treatment
   facility  as shown in Figs.  3 through 9.
                    10' -
                    101 /
                                         O :  H2S

                                         • :  Methyl mercaptan
                                     io3
                                                    io
    Fig   3   Observed vs.  estimated odor  concentrations  (grit chamber)
                                         O :  H2S

                                         • :  Methyl mercaptan
                    io1
                      IO1        10:        IO3        101*

                            Estimated concentration (Y)
Fig. 4  Observed vs. estimated odor concentrations  (primary setting  tank)
                                      134

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                     10
                       10"
                                               H2S
                                               Methyl mercaptan
                                               Methyl sulfide
                                               n-cutync  acid
 101      1C;      103      10"
Estimated corc-ntration (10
 Pig.  5  Observed vs.  estimated odor concentrations  (aeration tank)
                     10"
                     10"
                     10J
                 0   102
                     101
             0  :  H2S
             •  :  Methyl mercaptan
                                                        _l
                       1C1     10:     103    10"     10s    10"
                               Estimated concentration (Y)
Fig.  6  Observed  vs. estimated odor  concentrations  (sludge  thickner)
                                       135

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                        10J r
                        10'  -
                                              O :  H2S
                                              • :  Methyl mercaptan

                                              	1
                           10'              10:              103
                                  Estimated concentration (Y)
Fig.  7  Observed vs.  estimated odor concentrations (sludge elutriation tank)
                        10 r
                        10* -
                                               • :   Methyl raercaptan
                                               O :   H2S
                                               o :   Triraethylamine
                        10"
                                                     1
                                                           j
                          10°     101    102     103    10*     105
                                  Estimated concentration (Y3
  Pig.  8   Observed vs.  estimated odor  concentrations (dewatering  equipment)
                                         136

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                                               Nitrogen dioxide
                                               Trimethylamine
                                               Acetoaldenyde

                                               Isovaleric aldehyde

                                           A :  n-butyric acid
                               Estimated concentration (Y)
      Fig.  9  Observed vs.  estimated odor concentrations  (incinerator)
          As grit chamber, primary  settling  tank,  sludge elutriation tank and
     sludge thickner are in an anaerobic  condition,  hydrogen sulfide and
     methyl mercaptan are major odor  substances common to them.   The above
     two substances are also ascribable to the  odor  from the sludge
     dewatering machines.  When digested  sludge is dewatered with lime,
     alkaline odors like trimethyl  amine  are produced which, together with
     the irritating odor of ammonia,  produce a  peculiar odor.
          In the aeration tank, methyl mercaptan is  most blamable, and its
     observed concentration often exceeds the estimated one; this suggests
     that there may be some odor-contributing substances other than
     chemically analyzed.
          The sludge incinerator is found to give  off nitrogen dioxide and
     aldehydes, and requires odor-preventive measures different in nature
     from those for other facilities.
4.   MECHANISM OP ODOR DEVELOPLMENT

          The propagation of smell from  the  sewage  or  sludge into air can be
     explained as a phenomenon of mass transfer  between gas and liquid.  The
     open channels of grit chambers, weirs of  primary  settling tank, aerated
     channels of aeration tank, etc. offer chances  of  transfer.  Usually,
     odors ar cut off at source by cover-up, and the concentrations of
     malodorous substances in the open air are governed by the rate at which
     the freeboard space of the covered  odor source is ventilated.

4.1  Study on Ventilation Rate

          For a covered aeration tank, for example, experience shows that the
     ventilation is satisfactory if  it is  20%  to 30% greater than the
     aeration rate.
                                      137

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      The leakage from  the primary settling tank,  sludge  thickner,  etc.,
can  be prevented by keeping their freeboard space in a vacuum.  When
there is a  temperature difference between the freeboard  and the open
air,  the thermal convection effect asserts itself,  and the  ventilation
rate required to prevent odor  release  should naturally be controlled.
Fig.  10 shows a system used for  a series  of ventilation  tests.
        (l)  Water circulation pump
        (3)  Cooling pipe
        (5)  Water suction port
        (jj  DO sensor
        (?)  vacuum pipe (covered space)
        (y)  Plow control valve
            (covered space)
        @  Cooling unit  (covered space)
        @  Vacuum pipe (upper space)
        (y)  Flow control valve
            (upper space)
        ©  Cooling unit  (upper space)
(T)  Water flow regulating value
(t)  Flowmeter
(
-------
                 o.io i-
              « 3
              T


              _ >-
                 0.05 -
                 0.00
                                  TO- - Tow
      Fig. 11  Relationship between critical air velocity and
               temperature difference
     Indicating that, when Tw gets lower than Ts, the critical air
velocity to prevent leakage get higher.  As in the sludge thickner,
dewatering machine, and other machines can be covered by the opening
area ratio of less than 1%, ventilation rate can be held practically
small enough at the value as 0.3 m/sec.  At the grit chamber and primary
settling tank, the inlet and outlet are exposed, and the ventilation
rate needs to be considerably large.  However, this ventilation rate can
be reduced successfully by covering such exposed parts with a canvas
sheet to minimize the opening.
     Using the test system illustrated in Fig. 10, we studied the
overall mass transfer coefficient of oxygen and carbon disulfide from
the water into or to the air.
     Fig. 12 shows the relationship between the ventilation frequency
and the overall mass transfer coefficient (K^y) obtained by the test
at the range of ventilation frequency between 4 and 57 times/hr.  While
the Kj^y value of carbon disulfide remained constant, that of oxygen
tended to go down a little with increase in the ventilation frequency,
it looked almost constant.  It is estimated from above result that the
overall mass transfer coefficient of odor substance assumes a
characteristic value of the channel under normal conditions.
                                139

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                     0.01 _
                                          o :  Oxygen

                                          A :  Carbon disulfide
                  l     0   10   20   30  40  50  60   70
                  >
                  3
                       Covered space ventilation frequency (times/hr.)

             Fig. 12  Relationship between ventilation frequency
                      and overall mass transfer coefficient
4.2  Overall Mass Transfer Coefficient at the Channel and Weir

          Kyosail) proposed a method of estimating the overall mass
     transfer coefficients of odorous substances from the mass  transfer
     coefficient of oxygen for which volumes of field data  at channels, weirs
     and aerated channels are available.  The overall mass  transfer
     coefficient of a volatile substance not dissolved in the water  is
     expressed by Eq. (1) as a function of  the overall mass transfer
     coefficient of oxygen under the following conditions.

     i)   The transfer coefficient of the volatile substance at the  gas layer
          film is negligible as compared with that at the liquid layer film.

     ii)  The volatile substance liberated  into the  air  is  dissipated
          immediately, and its partial pressure in the air  is negligibly
          small.
     iii) The liquor is a complete mix situation.
          KLY/KLZ '  (VCZ/VCY>
                             0.3144
                             Y,Z
                                             (1)
          K
           LZ'
     where KLY:  overall mass  transfer  coefficient,  Y (m/hr.);
      overall mass transfer coefficient of reference substance, Z
(oxygen here)  (m/hr.); Vcz:  critical volume of  substance,  Z
(m3/h-mol); Vcy:  critical volume of substance,  Y (m3/9-mol);
By z:  a constant relating to  Y and z.
     The system shown in Fig.  10 was used as a channel model.
     Tap water laced with 0.5  mg-Co/£ in the form of cobalt
chloride was added with sodium sulfite  to reduce the dissolved
oxygen concentration to about  2 mg/£.   This water was then added
                                     140

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     with, carbon  disulfide,  hydrogen sulfide, methyl mercaptan, methyl
     sulfide and methyl  disulfide,  at a concentration of 10 mg/S, to
     obtain a test sample.
          The test sample was circulated at a rate of mainly 11 cm/sec.
     or 23 cm/sec,  while the  ventilation was made at a rate of 4 times
     an hour.  Dissolved oxygen was measured with a DO meter, and the
     decline of the test subject  was  measured by a gas-chromatograph by
     real-time sampling.  The substances other than carbon disulfide and
     methyl sulfide inhibited the oxidation of sodium sulfite, and the
     mass transfer  coefficient of oxygen measured with such
     oxidation-inhibiting substances  was discarded, and the transfer
     coefficient obtained in  the  measurement of carbon disulfide alone
     was accepted.
          Table 4  shows  the mass  transfer coefficients of various
     substances measured.  The value  of By QO obtained from KLY and

     KLO? was 82 to 116% of the value calculated based on the critical
     volume proving that Kyosai's method is good for practical use.
   Table 4   3
             Y,Z
determined from the measurement of mass  transfer
            coefficients of sulfur compounds and oxygen, and
            theoretically determined 3Y z
Substance

Carbon
disulfide
Hydrogen
sulfide
Methyl
meroaptan
Methyl
sulfide
Methyl
disulfide
Oxygen
Circula-
ting
velocity
cm/sec.
3.3 - 23
23
11
23
11
23
11
23
-
Critical
volume
cm/mol
170
98.5
145
201
260
73.4
Mass transfer
coefficient
KLY
(m/hr.)
0.0390*
0.0666
0.0133
0.0453
0.0272
0.0483
0.0209
0.0307
-
KL,20
(m/hr.)
0.0519*
0.0630**
0.0377**
0.0630*
0.0377**
0.0630
0.0355
0.0557
-
Ratio of mass
transfer coeffi-
cients, BY z
Mea-
sured
0.0751
1.06
0.803
0.719
0.721
0.767
0.589
0.551
-
Calcu-
lated
0.76
0.912
0.807
0.728
0.672
-
Measured/
calculated
%
98
116
109
89
99
105
88
82
-
      * Average value of 17 cases with different velocities
      ** Measured value for carbon disulfide
     The same test was conducted on a weir model.
outlined in Fig. 13.
                                   The model used is
                                 141

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                                                   ventilation
                                                   blower
          Fig. 13  A schematic view of mass transfer coefficient
                   measuring system with weir
         The weir  was rectangular with a crest width of 150 mm and the head
    on the crest was set in the range of 75 to 350 mm.  The overflow loading
    was changed over a range of 58 to 285 mVm.day.  The depth of the
    waterfall was  fixed at 50 mm.
         This system was covered with an acrylic resin covering, and
    ventilated 7.6 times an hour.  According to the same procedure as with
    the channel, carbon disulfide test was conducted.  6Y,Oo was determined

    as the ratio of the mass transfer coefficient per weir of oxygen, K2 Q

    (I/day)  to that of test substance, Y-2 y (I/day) .  The relationship
    between the mass transfer coefficient of oxygen and 3Y Q  *s given in

    Fig. 14.
Fig. 14  Mass transfer coefficient of oxygen, and 6Yf0   (carbon disulfide)
                                   142

-------
          It was found that the larger the mass  transfer coefficient of oxygen
               the  smaller the value of B; and  that the value of B levels off

     when K2 QO is 50  (V^ay)  or greater.  At  the  weir, mass transfer is

     considered to take place at the gas-liquid  contact layers as offered by
     bubbles at the waterfall basin.  The change of 6 may be explained by the
     fact that the hypothesis ii) above does not hold good for the bubbles.
          Hydrogen sulfide and other substances  were also measured with
     K2,02 set at  37'3 and 60'8  (V<3ay) , to determine Sy^c^.  Table 5 shows
     the calculated values of 3 and the measured values of 6.  Observed
     values are close  to the calculated values.  On the other hand, the
     observed  values are 30 to 70% of the calculated values.  We compared a
     grit chamber  as a typical open channel with a primary settling tank
     offering  a typical weir with respect to the mass transfer rate of
     hydrogen  sulfide, and found that the mass transfer rate was far and away
     greater at the weir than the channel, with  the ratio of 1 to 330.
         Table  5   Comparison of channel and weir  in terms of B value
N.
\X
Substance N~x
Carbon disulfide
Hydrogen sulfide
Methyl mercaptan
Methyl sulfide
Methyl disulfide
Calculated
value
*c.o2
BY,02 Vcy
0.764
0.912
0.807
0.728
0.672
Channel
Measured
value
P KLY/KL,02
0.750
1.06
0.883
0.719
0.721
0.767
0.589
0.551
test
Measured/
calculated

0.982
1.16
1.09
0.891
0.990
1.05
0.876
0.820
Weir
Measured
value
(j ' cR /K

0.563
0.493
0.375
0.439
0.465
0.397
0.432
0.229
0.207
test
Measured/
calculated

0.737
0.645
0.411
0.544
0.576
0.545
0.593
0.341
0.308
           Note:  Two values appear in a box.  For the channel test, the upper and lower
                values correspond to 0.0377 m/hr. and 0.063 m/hr. of Kj^,
                respectively.  For the weir test, the upper and lower values correspond
                to 37.3 U/day) and 60.8 (t/iay) of K2,o2' respectively.
          Even in  the  open channel, bubbles offer  a  major liquid-gas
     interface, and  are considered to cause the  same condition as with the
     weir.
5.   DEODORIZATION TECHNOLOGIES

5.1  Odor Collection

          An example  of  odor collection method  is  illustrated in Fig. 15.
     To collect  and deodorize the room air as in Fig.  15-(T), the volume of
     air to be collected becomes bulky, but the concentration of odors in the
                                       143

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exhaust becomes lean.
      A solution to this  problem is naturally to cover the  odor source
for  facilitating local forced ventilation.   If accommodation quarters
such as administration office are present in the same building that has
an odor source, it may be necessary  to  ventilate the accommodation space
as well as the covered odor source as illustrated in Fig.  15- (f).
                                           to deodarizer
                                           ()drge f1ow o1
                                           lean odors)
                (T) Collection of odors from a bpacioub room
                                            to deodorizer
                                            {t,mal ] flow of
                                            rich odors)
               (2) Col lee t ion of odors by 1 oca 1  forced vent j 1 at ion
                                          Exhaust
                                          Venting to the open air
                                          after deodorization
                  Where rice ommudu 11 on space and odor bouice are
                  present in the same bui1dinq

                  Pig.  15  Odor collecting methods
      Several forms of covers for odor sources are shown in Fig.  16.
A simple  cover is suitable for outdoor plants such as sludge  thickners,
Where odors are to be collected from sources in a building, a double
cover  (double decked cover)  is preferrable.
                                   144

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                          Pig. 16  Covering methods
          The lifting equipment for grit chamber,  screens,  dewatering
     machines, etc.  may defy covering depending on their  types as the
     workability may be impaired by the covering.   Thus,  the types of
     covering and the feasibility of covering should be studied with care.
          As the test results in Chapter 4 suggest, the forced ventilation
     for the covered freeboard will be enough if the air  velocity at the
     opening is about 0.3 m/sec.  For those facilities like sludge thickner,
     it will be advisable to install a draft tube  of about  50 mm in diameter
     in order to check excessive depressurization within the cover.

5.2  Deodorization

          There are  four major deodorization methods available for the
     wastewater treatment plants.
          They are:   a wet chemical method using an aqueous solution of
     sodium hydroxide or sodium hypochlorite; an absorption method using
     activated carbon or ion exchange resin;  an incineration to burn out
     odors;  and a biological method using soil microorganisms or activated
     sludge.   Table  6 is a classification of  the methods  recommended for
     applications.  While the wet chemical method  can be  applied at a large
     ventilation rate,  chemicals to be used must be selected properly.
                                     145

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Table 6  Deodorizing systems proposed for wastewater treatment facilities



High-concentration
odors
(concentration:
10,000 up)
Medium-concentra-
tion odors
(concentration:
1,000 to 10,000)








Low-concentration
odors
(concentration:
up to 1,000)

Odors from wastewater and sludge
3
100 m /min.up
o Wet chemical
scrubbing +
Adsorption

o Wet chemical
scrubbing +
Adsorption
o Adsorption
(combined use of
chemical and phy-
sical adsorbents)
o Odor removal by
soil
o Oxidation by
aeration

3
up to 100 m /min.
o Direct burning
o Wet chemical
scrubbing +
Adsorption
o Direct burning
o Wet chemical
scrubbing -f
Adsorption
o Adsorption
(combined use of
chemical and phy-
sical adsorbents)
o Odor removal by
soil
o Oxidation by
aeration
o Wet chemical scrubbing
o Wet chemical scrubbing + Adsorption
o Absorption
o Odor removal by soil
o Oxidation by aeration
Odors from sludge
drying and incinera-
tion processes
o Direct burning
o Wet chemical
scrubbing
o Contact reduction
by ammonia











o Wet chemical
ai;rul)l)ing
o Contact reduction
by ammonia

        Table 7 summarizes empirical data obtained with respect to
   scrubbing efficiency.  There are a wide variety of absorbents for the
   adsorption method,  in the wastewater treatment plant, however,
   activated carbon and chemical absorbents lead the others.  Activated
   carbon is available in two types.
                                   146

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Table 7   Recommendations on scrubbing methods to  follow for successful
          deodorization of various  odor substances (empirical  data)
Chemicals
Compounds
Ammonia
Trimethylamine
Hydrogen sulfide
Methyl mercaptan
Methyl sulfide
Methyl disulfide
Acetoaldehyde
Styrene
Clhoride
Oxygen dichlorlde
Water
scrubbing
o
A
A
X
X
X
X
X
X
A
Acid
scrubbing
©
®
X
X
X
X
X
X
X
X
Alkali
scrubbing
X
X
o
X
X
X
X
X
©
©
Alkaline
sodium
hypochlo-
rite
scrubbing
o
A
©
®
®
A
X
X
X
X
Neutral
sodium
hypochlo—
rite
scrubbing
X
X
o
©
©
©
X
X
X
X
Wet
reduction
scrubbing
X
X
X
X
X
X
o
X
®
&
         * Conditions:  Space velocity:  1 m/sec.; contact time:  1 sec.; gas/liquid
          ratio:  2 l/m3

          ®: Removal  efficiency, 90 to 100%
          o: Removal  efficiency, 70 to 90%
          A: Removal  efficiency, 30 to 37%
          x: Removal  efficiency, 0 to 30%
       One for  physical adsorption, the  other coated  by acid, alkali  or
  oxidizing  agent to meet the type of  odor substance  to be removed.
  Table 8 shows the adsorption capacity  of the various  types of activated
  carbon.
           Table 8   Adsorption capacity of activated charcoal
Activated
charcoal
Malodorous
substance
Ammonia
Trimethylamine
Hydrogen sulfide
Methyl mercaptan
Methyl sulfide
Methyl disulfide
Acetoaldehyde
Styrene
Plain charcoal
for physical
adsorption
Neutral


o
o
o
o
©
©
Special activated charcoal for chemically
enhanced selective adsorption
A (acid)
©
©






B (alkaline)


©
©
o
o


C (oxidative)

o
o
©
©
©


           Excellent
           Good
       Three  different  types of activated carbon - one for acid odors
  (hydrogen sulfide and methyl mercaptan), one for alkali odors  (ammonia,
                                      147

-------
 trimethylamine),  and  one for  neutral odors (methyl sulfide, methyl
 disulfide) - are  used in multiple  layers.
      Incineration is  effective  in  burning  out high-concentration odors
 of small ventilation  rate,  and  is  not so common in the wastewater
 treatment plant.   The biological method using soil microorganisms has
 come to stay mainly in the  livestock rearing industry for deodorizing
 animal wastes.  In recent years, it has become increasingly appealing
 for wastewater  treatment plants, though it has some problems that a wide
 tract of land is  required and that preliminary tests are necessary
 because the optimum gas feed  rate  varies depending on the type of soil.
 If these problems were solved,  the method  will spread for its simple
 operation and maintenance and high deodorizing efficiency.  Table 9
 shows the design  particulars  and operating conditions of a subterraneous
 deodorizing system at the Tarumi Wastewater Treatment Plant, Kobe.  The
 land area required for the  processing of odors at a rate of 1 Nm/min. is
 3.7 m2.
      Fig. 17 shows the structure of this system.   The deodorizing
 performance of  Tarumi's system  is  quite impressing as demonstrated in
 Table 10.
        Table 9  Design example of soil deodorization facility
               Facility to be deodorized!  Sludge thickening facility

               Deodorized air flow:  200 Nm /rain.
               Soil bed:  735 m2

               Void velocity:  4.5 mm/sec.
      Table 10  Deodorization  effect of  soil odorization effect

                                              Unitt  ppra
^~~\^ Sample
Name ^^^
of matter ^^-\
Ammonia
Trimethylamine
Hydrogen sulf ide
Methyl mercaptan
Methyl sulfide
In let air
0.3
tr.
0.44
0.05
0.01
After nniL deodorization
(average at 4 places)
tr.
tr.
o.ooon
tr.
Ir.
     The  biological  method can use composted sludge instead of soil, and
its deodorizing peformance is  as good as soil.

     Another biological method is a simple one  in which odors are blown
into an aeration  tank.  Fig. 18 shows a flowchart of this simple method
employed at the Fusekogawa Wastewater Treatment Plant,  Sapporo.
     There, foul  air from  the  sludge processing systems such as sludge
thickners is used as an air source for the aeration tank.  The system
shows a very high efficiency in removing malodorous substances, and the
odors generated from the aeration  tank are almost on a  level with the
system using fresh open air for aeration.
                                  148

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                                       JLL
                                                                      r
                                                                             , Outlet pipe
Main pipe
(air pipe)
                                                                             Auxiliary
                                                                             pipe
              Crushed stune Ulwn
              (small)
                                    S.jnd 20^
                                    Comport tor grow] IKJ niiu.lii«- -m !i) i,
                                    Grdiu te eaith 40%
                                    C.uth  lot
                                         rcivel l"or bearing
Pig.  17  Construction  of  soil  deodorization equipment
                                 149

-------
bludqo thickner,
1 , UO in Vn (4.8)
                              Cake hopper  freeboard,
                   bludge cake  3,600 m^/ll (10);
                   hopper       Cake unloading chute,
                              900 mVll (5)
SJudge teservoir,
H'10 in '/H (4)
                                               AJ r for Deration
                                  Foul cu r SIK tion
                                  blowet
                                                                Bloweil—
                                                         open an
                                                         (in case ot
                  e I ui n L,l udge wel 1 ,
                  40 m
                     Blower capacity:  ]9,800 mj/ll

                     The values in mVll denote Hie toul alt collecting rate",.
                     The valuer in parentheses denote  the number of
                     vent t I a ti on;, pL'i Ix-uj .

      fig.  18   Flowchart  of deodorization  system using aeration tank

                 (Fusekogawa Wastewater Treatment Plant, Sapporo)
     Table  11   Deodorization  effect of  aeration  by  activated  sludge
Point of sampling
Entrance to
wet filter
room
Entrance to
dry filter
room
Entrance to
aeration tank
Mid-part of
aeration tank
Exit from
aeration tank
Entrance to
aeration tank
Mid-part of
aeration tank
Exit from
aeration tank
Normal
de-
odori-
zation
Aera-
tion
by the
open
air
only
Threshold
odor
5,500
1,700
55
130
170
730
73
73
Strength
of odor
5
4
3
4
3
4
3
3

Odor type
Ammonia,
ami no
Rotten smell,
ammonia
Fusty smell
Fusty smell
Fusty smell
Kitchen
drainage smell
Sewer smell
Fusty smell
Ammonia
66
55
0.15
0.32
0.11
0.097
0.18
0.12
Tr imol hyl-
aml lie
0.651
0.195
N.D.
(<0. 00005)
N.D.
(< 0.00005)
N.D.
(•,0.00005)
N.D.
(-.0.00005)
N.D.
(<0.00005)
N.D.
('0.00005)
Unit: ppm
Hydrogen
sulf ide
0.53
0.46
<0.0005
< 0.0003
<0.0002
< 0.0003
< 0.0002
< 0.0002
Metbyl-
mer-
captan
0.54
0.48
0.0064
0.0009
0.0006
0.016
0.001
0.0011
Methyl
sulf ide
0.24
0.19
0.018
0.003
0.0012
0.033
0.0012
0.0011
Carbon
methyl
0.170
0.120
0.0088
0.002
0.0011
0.016
0.0028
0.0014
                                           150

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     The blower which had handled corrosive gases such as hydrogen
sulfide for five years and six montns was taken down for inspection,  but
neither pitting nor wear was noticed.  The odor gas pipe needs drain
wherever water is likely to be condensed because the odor gas contains
much water.  The metal fittings of the dry filter, gas flowmeter, etc.
must be of stainless steel of protection from corrosion.
     The replacement of dry filter element usually is once every five
years, but its frequency must be increased to once every several months
when handling odorous gases.
 EXAMPLES OF DEORODIZATION MEASURES

      Examples  of  6  kinds of  deodorization methods  that have recently
 been  used  at the  sewage treatment plant are explained here.
             Table  12   Example  of  deodorization facility
Deodorization
process






Facility to be
deodorized



Capacity of
facility
(Nm3/m)
Deodorization
effect
Construction cost
(thousand yen)

Maintenance and
administrative
cost (thousand
yen/year)
Construction cost
per 1 Nm
(thousand yen)
Maintenance and
administrative
cost per 1 Nm
(thousand yen)
Active
carbon
absorp-
tion




Aeration
tank



1,000


85% or
more
210,000
(cost in
1978)
44,000



210


44



Acid
cleaning
+ alkali
hypochlc—
rous acid
cleaning
+ active
carbon
Sludge
thickner
dewater-
ing
equipment
350


99%

206,000


107,300



589


30.7



Special
active
carbon
(neutral
•f acidic
+ alkali)


Sludge
dewater-
ing
equipment

395


96%

-


22,600



-


57.2



Catalytic
reduction
using
ammonia




filudge
incinera-
tion


1,800


98% or
more
410,000
(cost in
1903)
83,000



228


46.1



Soil
deodori-
zation





Sludge
thickner



1,978


92% or
more
30,600
(cost in
1977)
14,800



15.5


7.48



Oxidation
using
activated
sludge




Sludge
thickner
dewater-
ing

265


96% or
more
-


_



_


-



                                 151

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          Table  12  is  the  summary of  the object for deodorization,  the
     capacity of facility,  effect of  deorodization, construction  cost and
     operation and  maintenance costs.  Activated carbon is  used for
     deodorization  of  the  aeration  tank, and.the odor  has characteristics
     that  it  has a  large air  flow but has low odor concentration.   Therefore,
     it is possible to absorb the odor only  by making  the air  pass  through
     the absorption tower,  and life of the activated carbon is long.
          The catalytic reduction process is the method that removes nitrogen
     monoxide and nitrogen dioxide  in the discharge gas from sludge
     incinerator.
          Acid cleaning +  alkali hypochlorous acid cleaning +  active carbon
     has a good  results of deodorization of  the high concentration  odor  from
     the sewage  treatment  plant, but  construction cost and  maintenance and
     administrative costs  in  this method are very high.  In the operation  and
     maintenance costs, power consumption and chemical costs are  56% and 36%
     respectively and  the  rest is for regeneration of  the activated carbon
     and water charges.
          Operation and maintenance cost for special activated carbon  is high
     and 90%  of  the cost  is for  regeneration of  the  special activated
     carbon.   In this  case, the  activated carbon  is regenerated once a year,
     but since it is possible to operate for almost  2  years without
     regeneration,  the cost could be  reduced to half of the cost  shown.
          In  the case  of  soil deodorization, construction cost and  operation
     and maintenance costs are rather low although it  is effective. In  this
     facility, aeration tank is  installed in the  building and  the roof  is
     used  for deodorization,  so  land  cost and building cost are not included
     in the cost shown in  the Table.  For  instance,  the  site area is
     3750  m3  and if it is  possible  to secure the  site, the  construction
     cost  would be  less than other  methods.
          The aeration process by activated  sludge is  to modify the
     ventilation of the ordinary sewage  treatment plant, so accurate
     construction cost and operation  and maintenance cost are  not obtained.
     But it is certain that this method  is  less  expensive compared  with  other
     methods.

                                 Reference

1)   S. Kyosai, "Study  on Desorption of Volatile Compounds Dissolved in
    Water", Japan Journal  of  Water  Pollution Research, Vol. 4, No.  4,  1981
    (in Japanese)
                                     152

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                   Tenth United States/Japan Conference
                     on Sewage Treatment Technology
SLUDGE DISPOSAL BY  COMPOSTING

            IN  FUKUOKA
         Yukio Hirayama
  Director of Planning Division
       Sewage Works Bureau
         City of Fukuoka

              153

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                                 CONTENTS





1.  Introduction	155



2.  Outline of Sewarage Service 	  157



3.  Outline of Sludge Treatment 	  160



4.  Composting of Sewage Sludge 	  163



    4.1   Move Toward Agricultural  Use	163



    4.2   Sludge Control Center	165



    4.3   Distribution and Diffusion Promotion Measures	181



    4.4   Regulations Concerning Heavy Metal  Content 	  185



    4.5   Researches into The Effects of Compost on Soil  and Crops  .  .  .  190



5.  Summary	196
                                    154

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1  INTRODUCTION
     As more and more areas are  served by  sewer systems, the  amount  of sewage
sludge  produced  in Japan is increasing year by year.   However,  during the
past several years sludge to be  carried  off for ultimate disposal has remained
at almost the  same level.  This  is due to  the introduction  of high-performance
dehydrators capable of  removing  far more moisture  than ever,  the progress made
in composting, and more dependance on incineration for sludge disposal.
           3,000
     JE
     o
           2,000
           1,000



1,820

-







2,219
^§^5
6£








2,383
lHH
yyvy
&S&C








2,397
HH
vyvv
OOOC








2,387
mm.

-------
     Up until recently, most sludge in Japan was landfilled.   However,  over
the past several years it has become increasingly difficult  to find  sites for
landfill.  At the same time, voices calling for effective  use  of  resources
have been mounting.  These two factors have prompted  local authorities  to
study various ways of turning sludge into something reusable - building
material, compost, etc.  When the results of the studies showed that pro-
duction of compost required less energy than that of  building  material,
emphasis has been placed on the development of composting  technology.   The
progress made in this field has now brought the number  of  municipalities
which embarked on composting to approximately 40.
     Fukuoka City took a lead in this move when it decided in  1967  to launch
a "Sewage for Agricultural Use Project" - a project aimed  at recycling  sewage
waste.  In 1981, the City completed the construction  of the  "Sludge  Control
Center," a composting facility, which has enabled a systematic implementation
of this recycling project.  At present, all sludge produced  in the  City is
recycled into compost.
                        1970
                                   1975
                                               1980
1984 (fiscal \ ear)
                       Figure 3. Sludge disposal in Fukuoka City.


     In  the  following pages  are  reported the  details of the "Sewage for
Agricultural Use Project," general information on the Sludge Control Center
including  operational data and the quality  of compost produced in this
Center,  and  future  problems  of composting.
                                      156

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2  OUTLINE OF SEWERAGE SERVICE


2.1  GENERAL VIEW OF FUKUOKA CITY

     Fukuoka City is situated in the southwestern part cf the Japanese
Archipelago, some 1100km west of the nation's capital of Tokyo.  The City,
bounded by Hakata Bay on the north and mountains on the other sides, is full
of scenic places.  Being close to the Chinese Continent, Fukuoka has been a
gateway to foreign politics, economies, and cultures since 2,000 years ago.
     Fukuoka became a city in 1889 with a population of 50,000.  Now it has
developed into the 8th largest city of Japan with 1.15 million inhabitants,
playing an important role both in the economy and in the politics of Japan.
It has a total area of 335.6km2, 60% of which is covered with plains.  The
population density in the urban areas is 80 persons per hectare.
     To promote internationalization of the City, Fukuoka went into a sister-
city-relationship with Oakland, U.S.A. in 1962.  It is now affiliated with
two more major cities of the world - Kuangchou in China and Bordeaux in
France.  These affiliations have been greatly helping the citizens living in
different countries to exchange ideas and information in wide-ranging fields.

2.2  SEWER SYSTEM OF FUKUOKA CITY

     Fukuoka City launched its first sewerage project in 1930.  The project
in those days dealt only with domestic sewage water and rainwater.  It was
in 1963 when the first 5-years sewerage improvement project started that the
construction of a treatment plant came to be included in the sewerage
planning.  Since then, efficiently coping with the expansion of urbanized
areas, the City has been carrying out well-planned projects to improve its
sewer system.  With approximately 40 billion yen allocated annually for
building related facilities and equipments, sewerage improvement project is
now one of the three major public works undertaken by the City.

     Fukuoka City has planned to expand sewer-system-service areas to
14,504 ha.  As of March, 1985, 7,682 ha. or approximately 680,000 inhabitants
which account for 59% of the total population have received the benefit of
this sewer system.  (See TABLE 1, 2 and Figure  4)
                                     157

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                       TABLE 1.  Sewerage service plane of Fukuoka City
• — 	 __^ Sanitation disctict
Categon 	 	 	 	 SS^_
T\ pe of svsrem
Start of operation
As of March 19B5
c
c_
H
Service area
Population in sen-ice area
Treatment capacm
(m3 da\ at maximum)
Service area
Population in service area
Sewage
(m3/dav at maximum)
Remarks
Saito-
zak,
Separate,
Combined
1962
120
4,900
6,500
153
10,000
n.ooo

Wajiro
Separate
1975
482
30,600
20,000
1.270
93,000
64,000

Tobu
Separate,
Combined
1975
1,736
111,600
83.000
3,935
234,000
200,000

Chubu
Separate.
Combined
1966
3.177
337,200
350.000
2,697
276.000
350.000

Nagao
Separate
1965
76
11,700
5,500
227
24,000
5.500
	
Nanbu
Separate
1975
1.569
135.500
(80.000)
.3.320
279.000
(429.376)
1)
Seibu
Separate.
Combined
1980
474
40500
3-.500
54P
491.000
300000

Nokata
Separate
1975
48
8,400
4.600



2)
Total
—
—
7.682
680.400
507.100
17.019
1,407.000
9.32.500

l)Sewerage area controlled b\ Fukuoka prefei
2)Will be included m seibu treatment plant
                TABLE 2. Sewerage service of Fukuoka City (As of Marchi 985)
  Total area of the city
  Total area of urbanized districts
  Total population
  Total sewerage service area
  Sewerage-service area m urbanized districts
  Population sewerage-servise  area
  Percentage of population sewetage-service area to total population
  Sewers length
  Treatment capacities(of seven plants in total)
   33,564ha
   14.500ha
1,152,}00
    7.682ha
     53.0"0
 680,400
     59.0°0
   2.194km
 •>07.100m3'dav
                                                158

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                                                                        Sanitation
                                                                         district  Future Present
                                                                         Saitozaki  E3  Bg&
                                                                anbu plant \jf^(ro   V7~^\  VZZ%
                                                                         Tobu    t -1  E^SI
                                                                         Chubu       CD
                                                                         Seibu    rm  ircimn
                                                                         Nagao   FCTT1  PB
                                                                         Nokata       FT~1
                                                                         Nanbu   ES3  E3
               Nokata plant -
              Will be included m
              Seibu sanitation district.
                                                        Nagao plant
                 Figure 4. Location map of treatment plants and sewerage districts.
The  long-term plan calls on  the  City  to extend  this  service  to all of  the
urbanized areas by 1995.  When this is realized, the system  will  serve 97%
of the  City's total population.
                                             159

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3  OUTLINE OF SLUDGE TREATMENT
     At present, there are seven sewage treatment plants in Fukuoka City.
These plants, when combined together, are capable of treating approximately
507,000m3 of sewage per day (at maximum daily capacities), serving 680,000
persons.  All sewage water is given conventional activated sludge process,
secondary treatment.  The effluent is all discharged directly, or through
rivers, into Hakata Bay.  Five of the seven sewage treatment plants -
Saitozaki, Wajiro, Tobu, Chubu, and Seibu Treatment Plants - are equipped
with sludge treating facilities.  Sludge produced at Nagao and Nokata Plants
which are smaller in size than the other plants are sent to Chubu or Seibu
Plants for treatment.
     The basic process for treating sludge consists of gravity thickening,
anaerobic digestion and mechanical dewatering.  Direct dewatering process is
also applied to some extent.  Dehydrators used at each plant now are all of
pressure type.  Vacuum filters were once used at the Chubu Sewage Treatment
Plant.  But because of its improved dewatering capability brought by recent
technological development, pressure filters replaced vacuum filters and are
now in use at all of the five plants mentioned above.  The pressure filters
have reduced sludge moisture content from 56 to 65% - figures which fall
within the City's target range.
     Sludge produced in fiscal 1984 was approximately 51,400 tons in volume
with average moisture content of 64%.  This figure is expected to double in
1995 to about 103,300 as the sewerage-service areas expand from year to year.
                        1980    1985   1990    1995   2000 (fiscal vear)

                        Figure 5. Forecast of sludge to be produced.
     The following paragraphs explain the problems facing  the Chubu  and Tobu
Treatment Plants.  They are the major treatment plants of  Fukuoka  City, the
Chubu Plant having maximum daily capacity of 350,000m  (main system,
combined system) and the Tobu Plant 83,000m3 (main system,  separate  system).
     During the past decade ignition loss content of sludge at  the Chubu
Treatment Plant and the Tobu Treatment Plant has risen by  27% and  37%
respectively.  This increase is attributable to people's diversified diet and
                                     160

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expansion of separate system areas, which in turn  have brought a change in
substrate that flows off  to  the plants in sewers.   In addition, solids
content has  decreased from 4% to 3% at the Chubu Plant and from 4%  to  2.5%
at the Tobu  Plant.
        Tobu treatment
	Solids content
	Ignition loss content-
        1975
                    1980
                                  70
                                  60 X
                                  50
                                  40 S
                                  30
           1984 (fiscal year)
1975
1980
1984 (fiscal year)
            Figure 6. Solids content and ignition loss of thickened sludge 1975~1984-
     This  has resulted in decline of sludge thickening,  and has been
affecting  treatment process  at various stages:  the gravity system  thickening
tanks now  work only as storage tanks; increase  in the amount of sludge
carried  into the digestion tanks causes insufficient digestion due to the
shortage of stay; degrading  of digestion supernatant liquor has increased
return water load.  More water in sludge has also increased the use of
dewatering auxiliaries.  During the past five years at the Chubu Treatment
Plant, for example, 30 to 50%  more dewatering auxiliaries had to be added
to the sludge to obtain a given moisture content.
                        TABLE 3.Information on dewatered sludge
                                                                 (1984 fiscal year)
"~ • 	 _____^ Treatment plant
Category • 	 -_^^_^
Slndge treatment process
Dehydrator
Coagulant
Moisture content
(%)
Ignition loss content
(%)
Range
Average
Range
Average
Saitozaki
Thickening -f
Anaetodic digestion
Filter press
Lime +
Feme chloride
57 1-662
61 1
40-52
46
wajiro
Thickening +
Anaerobic digestion
Filter press
Lime +
Feme chloride
526-686
648
33-55
44
Tobu
Thickening +
Anaetodic digestion
Filter press
Lime 4-
Feme chloride
584-66.1
616
37-50
42
Chubu
Thickening +
Anaerodic digestion
Vacuum filter
Lime +
Ferric chloride
69.1-750
72 1
29-38
34
Thickening
Filter press
Lime +
Ferric chloride
481-629
561
28-46
35
Seibu
Thickening
Beit press
Lime +
Ferric chloride
61 1-74.7
703
37-57
47
                                       161

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     Increase of inorganic matter in dehydrated sludge may cause another
problem in sewage disposal, as it raises pH value.
     To cope with these problems, Fukuoka City set up picket fences in the
thickening tanks and installed vacuum protection devices (an equipment to
improve dehydration rate by covering the top of the drum with a vinyl sheet)
to the vacuum filters.  However, more important than anything else is higher
thickness of sludge.  Therefore, discussions on the introduction of
mechanical concentration or pressure floatation concentration of excess
sludge are now under way.
                                     162

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4  COMPOSTING OF SEWAGE SLUDGE


4.1  MOVE  TOWARD AGRICULTURAL USE

4.1.1  DECISION MAKING

     In  regards to disposal of sludge,  since the time  the  Chubu sewage  dis-
posal plant commenced operation adopting the conventional  activated sludge
method in  1966, we have been consistently restoring it for the creation of
green zones and agricultural areas.
     In  starting sludge disposal, Fukuoka City discussed such ways of disposing
the most of dewatered sludge as landfill or agricultural use.

The results of discussion are as below:

(1)  Utility of sludge as resources
     Consisting of nitrogen, phosphorus, organic substances,  and minerals  of
     various kinds, sludge can make good fertilizer.

(2)  Nontoxicity
     Heavy metal content  in sludge proved to be considerably  low.  The  reason
     for this is that Fukuoka is a commercial city with most  citizens engaged
     in  tertiary industry and that consequently the City's sewage is primarily
     domestic waste water.  Also, waste water from industrial operations
     mainly comes from food processing  industry.
                       TABLE 4. Heavy metal content in sewage sludge
Heavy metal
Zn
Cu
Ni
Cr
Cd
Pb
Fukuoka
City
720
170
22
20
1.5
26
Japan
1.760
350
80
—
3 7
62
UK
1,820
613
188
744
29
550
US.A
1,700
800
80
500
10
500
W Germany
2,000
400
—
—
10
400
Sweden
1,567
560
51
86
67
180
       1) Average values in 26 different sludges produced in September, 1979,Japan Soil Association
       2) Average values in sludges disposed of on land in 1977
       3) Medium values in typical sludges by R L Chany
       4) Heavy metal in sludges handled by Fedaral Water Bureau Lowest limits of interim guide values by U Mallen
       5) Beggren and Oden report(1972), Medium values shown in data at 93 treatment plants
 (3)  Availability of  land to fertilize
     There still remained a large area  of land fertilize in and around  the
     central part of  the City.

(4)  Future outlook for  sludge disposal
     If  the City was  to  continue to dispose of sludge into  landfills, the
     problem about the availability of  land to fill was  expected to arise.
                                        163

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     Since the start of the project, with the improvement made in the
composting technology (a shift from sludge drying process to high-rate
composting process), the products have gained better qualities and become
easier to handle.  This has boosted the demand for the products to the extent
that all dewatered sludge produced in the City can be used at fields.
     However, the way to composting was not without any obstacle, because
people complained about odors emitted from compost manufacturing factories.
In the wake of this public nuisance a project to discuss future measures for
sludge treatment was launched in 1975.

This project deals with:

(1)  Making an estimate of future increase of sludge

(2)  Making an estimate of agricultural area which needs to be supplied with
     compost

(3)  Discussing systematic way of sludge recycling

(4)  Making research on composting technology

(5)  Making plans on experimental use of compost to test its effects on soil
     and crops

     In addition to this project, the construction of the Sludge Control
Center, a composting facility, was started in 1979 and completed in 1981.  The
completion of this facility has precipitated the implementation of the
"Sewage for Agricultural Use Project".

4.1.2  RECYCLING SYSTEM

     Compost made from sludge must meet the requirements below to ensure
effective recycling.

(1)  Must be of good quality.

(2)  Stable supply and proper prices must be maintained.

(3)  Voices of the users must be reflected in the products.

(4)  Proper instructions must be given as to the use of compost according to
     soil and crops to grow.

(5)  Inspection on the quality of compost and on the soil after the supply of
     compost must be carried out in an efficient way.

(6)  Effort must be made to tap the market for compost by expanding its sales
     network.
                                      164

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     Fukuoka City deliberated on these requirements and concluded that joint
efforts by both the municipality and citizens were indispensable for the
promotion of this recycling project.  Figure 7 shows how the project works  in
collaboration with the private sector.

	 ]
Sewage treatment plant Sewage works bureau
Municipality Sludge Con
Manufact
Processor
Distnbu
1
urers &
> \
Secondary fe
Powdering,
rrol Center 1

T i j Sludge
Unnpened , °
compost testing
rmentation.
Sorting, Bagging
Storage
N
1 Delivery
neseacn on toxicity, ettects
on crops and soil, and use
[Universities,
Agricultural stations

ers Sales network of Trading companies
and retailers Agricultural producers
association such as agricultural
cooperative
                             Users
                   Figure 7. Recycling system for agricultural use.


4.2  SLUDGE CONTROL CENTER

4.2.1  CONSTRUCTION PLANNING

Basic requirements of the composting facility were set as follows:

(1)  Preparatory step:                     "Non-Adding Method"

(2)  Sludge to be handled:
Pressure dewatered sludge & vacuum
dewatered sludge
(3)  Moisture content after fermentation:  Less than 35%

The reasons for setting the above were:

1.  Preparatory step before fermentation includes moisture and pH adjustment,
    improvement of permeability, and addition of seed microbe.  In general,
    there are two different ways of preparation.  One is "Adding Method
    Preparation" in which organic materials are added to the sludge; the
    other is "Non-Adding Method Preparation" which returns fermented sludge
    to circulate.  Organic materials such as rice husks, straw, sawdusts,
    or wood chips to be added to the sludge are difficult to obtain in suffi-
    cient quantities.  Preservation also causes a problem.  In addition, high
    transportation costs and longer ripening period gave way to the
    "Non-Adding Method Preparation".
                                      165

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2.   Sludge dewatered with polymer coagulant was not taken for experiments
    because of its lower permeability.   Instead, sludge treated with lime of
    ferric chloride as dewatering aid (pressure dewatered sludge and vacuum
    dewatered sludge) was selected.

3.   Ultimate moisture content of 30  to 35% does not allow compost to refer-
    ment,  putting it in a stable condition.  Compost with this much moisture
    content is easy to handle.
                            TABLE 5. Composting process
Process
Purpose
Operation
Remarks
Dewacered sludge— T*Prepararor

To creat a better environment
for microorganism to gron
* Improvement of permeability
# Adjustment of moisture content
# Adjustment of pH
* Adjustment of nourishment
* Addition of seed microbe
Mixing of dewarered sludge
and return compost
sfc m some cases, bulking
agent replace return
compost
^ In some cases, neither
bulking agent nor return
compost is added
	 p r
;
; P

(Ripening) , 6' *

; To perform aerobic fermentatmn To perform aerobic fermenta- ' 70 i($d more \alue to the
'^Decomposition and stabiliza- tion • product
; tion of easily decomposable * Decomposition and stabili ; (T/0 make the product
'• organic matter zation of decomposable oream easier to hanhle)
;# Destruction of germs and matter
i parasites
; # Inactivation of weed seeds * Production of humic substance
' # Lowering of moisture content
; # An supply bv bJowers * Turning -j- Sie\int;
; * Turning * Air supph * Graining
I * production of return ' # Biding
; compost
; # In some cases, composr # In some cases air is not
! is not returned supplied
; # In some cases priman
! and secondary process
1 are performed in the
; same tdnk
     The experiments based on the above conditions showed the following
results:

(1)  Ratio of dewatered sludge to compost
     When using vacuum dewatered sludge, the moisture content of the feed
     mixture (a mixture of vacuum dewatered sludge and return compost) should
     not exceed 50%; turning operation for permeability would otherwise be
     affected.   If the moisture content rises above 55%, sludge becomes
     anaerobic resulting in unstable fermentation.
     If more return compost is added to the feed mixture, it can reduce the
     moisture content, but will also reduce the amount of easily decomposable
     organic matter in the mixture shortening the high-heat lasting hours.
     To keep fermentation in process, moisture content of 45% or more is
     necessary.  The results of the experiments reveal that the optimum
     moisture content of the feed mixture is 47 to 48%.  (for a mixture in
     which pressure dewatered sludge and vacuum dewatered sludge are mixed at
     the ratio of 1 : 1 in terms of wet weight.)
     The weight ratios of sludge to compost should be 1 : 2.0 to 3.0 for
     vacuum dewatered sludge and 1 : 1 for pressure dewatered sludge for
     stable fermentation.
                                     166

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(2)  pH  conditioning

     pH  is closely  related  to the number of days  required  for fermentation.
     To  facilitate  fermentation, pH of  10 or below is desired.   Sludge
     dewatered with the aid of lime shows pH value of about  12.  Adding return
     compost to this sludge can reduce  the pH value of the mixture  to 11.  In
     addition, carbon dioxide in the  gas generated during  fermentation works
     as  a neutrilizer when  this gas is  circulated for air  supply after being
     dehumidified.   As a result pH value is further decreased to 9.5,  the
     optimum pH for fermentation.  The  pH value after fermentation  is com-
     pleted will be less than 8.
       80
       70
       60
   P  50
      40
      30
      20
      10
-A	temperature

--A	pH value
                       Amount of air flow
                       5oP/m3/min
                       (to be circulated)
                                      11
                                     10
                                  12'


                                  11
                                             £10
                                     5  days
       Figure 8. Variation of fermentation tank
              temperature and pH value.
Start of fermentation
            •Circulation of gas emitted
             during fermenranon
             •50 P /m3/min
      \\     OFresh air supply
       \      50('/m3/min
  \^   \    (pressure dewatered sludge)
                                        Starr of fermenranon
                                       1   23456  davs


                                       Figure 9. Variation of pH value.
                                         167

-------
(3)  Amount of air flow  and  turning operation

     The optimum amount  of air flow varies depending on environmental  condi-
     tions such as atmospheric heat or humidity, and on the condition  of
     sludge.  Until the  fermentation temperature rises high enough,  60-100
     litters of air per  minute per cubic meter of the mixture, and  during and
     after the water sprinkling period that follows, 150 litters of  air per
     minute per cubic meter  of the mixture is required to expedite  fermenta-
     tion.
                    hours
                     100

                      80

                      60
                      40

                      20

                      0
                             50
                                  100
                                         150
	1  Air supply
 200  («/ms/mm)
                     Figure 10. Amount of air supply and hours during
                             which temperature of 65 C or above
                             is maintained.
(4)  The number of days  required for fermentation

     Fermentation process  is  controlled with attention paid to  the  fermenta-
     tion temperature, heu, odors,  and density of the gas produced.   Seven
     to ten days is  required  before the moisture content decreases  to less than
     40%, and 10-14  days to less than 35%.   If the room temperature lowers to
     15°C or below,  two more  days or so should be added.
                       0  2  4  6  8  10 12 14 16 18 day}

                         Figure 11. Variation of moisture content.
a)  Selection of Fermentation Tank
    The fermentation  tank must be designed as to meet the needs below:

(1)  How far the fermentation has proceeded in the tank must be checked easily.

(2)  Structure must be  simple and flexible to handle different qualities and
     quantities of sludge.

(3)  Construction costs  should be low.
                                       168

-------
(4)  Deordorization must be simple  and  easy.

(5)  Turning  must be carried out to the full  extent.

(6)  Adjustment  of air flow in accordance  with the progress of  fermentation
     must be  made easily.

     Based  on these needs, study on the designs of various types  of  fermenta-
tion tanks  was made.  The results of  the study revealed that, although the
"plane fermentation type" took up more  space  and was more difficult  to cope
with odors, it had more merits in the other points.  Return compost,  on the
other hand, can  easily ferment if primary  fermentation proceeds in good
condition.  Thus, we concluded to adopt "plane fermentation type" with verti-
cal silo type which is efficient in heat insulation and therefore facilitate
secondary fermentation.  As for a tool  for turning, shovel loaders were chosen.
                               Off gas
                                I   I
                                                    In put
                                                  "Out put
                             (Front vjew)
                                        Air
(Side view)
                         Figure 12. Plane type fermentation tanks.
                                In put
                                       Primary fermentation tanks
                                         Air
                                        -O-
                                            Out put
                        Figure 13. Vertical type fermentation tanks.
                                       169

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4.2.2
THE OUTLINE OF THE FACILITIES
     The construction of the Sludge Control  Center  scheduled to  have a com-
posting capacity of 206 tons/day started  in  1979.   The  construction cost was
about 2.2 billion yen.  The center was  completed  in 1981 and operation began
in January, 1982.

a)  Facilities
    TABLE 6, Figure 14 and TABLE 7 show the  outline of  the facilities, the
    flow chart and the main equipment respectively.   The facilities consist
    of (1) pre-adjustment equipment,  (2)  primary  fermentation equipment,
    (3) return-compost production equipment,  (4)  deodorization equipment and
    others such as vehicle washing and  waste-water  treatment equipment.
    (See TABLE 6, 7 and Figure  14)
                TABLE 6. General Information on the Sludge Control Center
Site area
Floor area
Design volume of sludge for treatment
Design production capacity
Type of fermentation
Fermentation tank capacities
Construction
Construction period
Site
Cost Gvilengineering and construction
(2247 million yen) Mechanical and electric equipment
Sue preparation
Designing and reasearches
Start of operation
16,000m2
7,800m2
206t/day
Vacuum dewatered sludge lOOt/day (Moisture content 75%)
Pressure dewatered sludge 106t/day(Moisture content 60%)
110t/day
Primary fermentation sluge(Moisture content 40%)
"Non-Adding method" Plane fermentation
Vertical fermentation tank 117m3 8 units
Plane fermentation tank 792m3 13 units
1979-1981
156 million yen
879 million yen
1110 million yen
65 million yen
37 million yen
January, 1982
                                       170

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                                TABLE 7. Specifications of main facilities
Facility
Material
reservoir
Return compost
production
Primary
fermenranon
Deodonzation
Ventilation

ewa er tea en
Name
Plane type tank
Material sludge hopper
Conveyor
Steel plant vertical type tank
Sludge hopper for teturn compost
Conveyor
Blender
Blower
Plane type tank
Return compost hopper
Conveyor
Blender shredder
Blower
Acid cleaning -Alkali cleaning
+ Activated carbon absorption
Blower
R 1 1
0 6
Specification
733m3(9X22X4m)
12m3
450X36 Om
83m3(6 5X5 0X3 8m)
4m^
600 — 750X27 Om
50m3/h
0400X 103mVminX75KW
733m3(9X22X4m)
4m3
450— 1.100X 30 Om
50mVh
0500X 175m3/mmX90rCW
570m3/mm
01,050 X 780mVmmX 37KW
3/

Unit
2
2
8
1
7
1
1
11
1
19
2
2
1
1


fT,                                    ^    Kecu™
* Sludge hopper for return composr Refurn cornpOSf   h«PP"
                                            Return compost
                            fermentation tank       ^ ^ Primary compost fermentation tankQCj  \    ^rx,
                              KM   J-N    i-^  (I   ^V~-x ,, 	'~   r ^v    ^    ^    ^ T^    \\  C^--XA   i—,
                                                 Deodorizing blower
   Primary fermented       Secondary         Secondary fermented Shredder  Weighing
   sludge reservoir         fermentation tank   sludge hopper      sorter     machine
                                                                                                   (private operation)
                                                                       Automatic
                                                                       bagging machine
                                                                               ]         ^?    ^> shipraent
              	      —  —  —	135,000       -   -----

                           Figure 14. Compost production flow chart.
                                                       171

-------
b)  Operation Method

    Dewatered sludge brought in from treatment plants is conveyed to the
    material reservoir where it is blended by tyre shovel to acquire uniform-
    quality.  While it is stored, the material is aired with the waste gas
    from fermentation tanks to lower its pH value.  Then the material is
    transferred into the blender-shredder to be blended-shredded with return
    compost.  When this is completed, the mixture is conveyed to a fermenta-
    tion tanks.  This mixture is aerobic-fermented by being compulsively
    aired (50 - 100£/misture m3. minute) with the demoisturised waste gas
    supplied from the vertical-type fermentation tanks through three
    gas-discharge pipes equipped at the bottom of the tanks.  The temperature
    of the mixture rises to its peak about one to three days after the
    mixture has been transferred to the fermentation tank.  After the peak
    temperature (75° to 80°C in ordinary cases) is maintained for a certain
    time period (more than 24 hours), a large amount of air (100 to
    150£/mixture m3.minute) is supplied so that the moisture of the mixture
    is discharged into the atmosphere and the temperature declines.  When the
    temperature of the compost is lowered to 50° - 60°C, a tyre shovel turns
    this compost.  The temperature rises again.  Then, a part of the
    fermented material is conveyed into the vertical-type fermentation tank
    for the production of return compost.  All remaining material is aired
    and turned twice or three times to be secondary-fermented.  When all
    these processes are completed, the product is sorted and bagged.  After
    the first transferal of the mixture, it takes seven to ten days to
    complete the primary fermentation and 14 to 16 days to complete all
    processes to obtain finished product.
                                    172

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4.2.3  THE STATE OF OPERATION

     Since its start of  the operation  in  January 1982,  the facility has  been
operating  successfully and treating all of the dewatered sludge produced in
municipal  treatment plants as originally  scheduled.  TABLES 8 and 9 show the
results  and the indicators of the operation.
                             TABLE 8. Operation results
                                                                  (Unit tons)
^"""""-- ~^_^ Item
Fiscal year ""—--^^
1983
1984
Dewarered sludge
49,298
51,369
Primary fermentation sludge
24,522
25,685
Product compost
14,488
16,393
                                           Note Product compost does not include shipment in bulk
                           TABLE 9. Operation indicators
Item
Deodorizing
Resolving of organic substance
easy to be resolved.
Killing of parhogenic bacteria
and parasite eggs. Deacrivatmg
weed seeds
Moisture content of the deliver-
ed primary fermented material
Hue
pH after fermenration
Indicator
Little ammoniac odor. No putrid smell.
BOD less than solid substance 30 mg/g
Fermentation temperature : over 65°C for 48 hours.
40?^ and less
Reddish brown as a result of ferric chloride in the
sewage sludge being oxidized
8.5 and less
                                         173

-------
a)  Property Changes of Sludge
    Property changes of sludge  in  May 1985 were as follows.
                     TABLE 10. Property analysis in each process
                                                        (1985 5 1-5 15)
\
Dewatered
sludge
(Five rreatmenr
plants)
Return
compost
Feed
mixture
Primary
fermentation
sludge
Product
compost
Analysis
item
Unit
Average
(max — mm)
Average
(max — mm)
Average
(max — mm)
Average
(max — min)
Average
(max — mm)
Moisture
Content
%
65.4
508-71.8
34.0
30.8-34.8
45.6
45.2-45.9
39.0
37.0-42.4
308
23.6-31.5
Ignition
loss
%
37.3
28 1-54.9
24 9
24 1-26.2
28.8
28 2 — 29.4
25.2
24.9-25.3
24.1
229-24.3
pH
(H20)
124
11 5 — 12.6
8.2
8 1- 8.3
109
104—11.1
8.3
82-84
80
80—81
T-C
%
20 5
15 9-26 3
166
14.2-17 6
186
179-192
17.3
169-17.6
16.5
14 6—17.3
T-N
%
2 4
1.6-3 5
1 3
1 2-1.3
1.7
16—17
1.3
1.2-1.4
1.3
1.2-1.3
BODs
mg/g
144
73-215
10
9- 12
58
52- 63
13
12— 14
12
11— 13
                                                Notes Ignition loss, T-C, and T-N refer to dry
(Temperature)

     As Figure 15 shows, the  temperature reaches its peak of over 80°C, 60  to
70 hours  after the first transfer  of the mixture and remains at 65 °C for  75
hours.  When the temperature  is maintained at over 65°C  for 48 hours and
more, almost all pahtogenic bacteria die and weed seeds  are deactivated.
(See Figure  15)
                                       174

-------
       80
       70
   P   60
i   5°
4J
cP   40
s
0,
J   3°,
       20
       10
                                   Turning
                                                          Primary fermentation completed
            'Temperature    Water scattering   Temperature
             rising period    pend          rising again period
                                                          Amount of air per feed mixture
         0123456789    10  (days)

                    Figure 15.Change in composting temperature with time.
(Airing)
        •
Amount  of air for airing when the  temparature is  rising...
      40 - 80£/mixture  m .minute
Amount  of air for airing after the peak temperature  is achieved...
      100  - 150£/mixture m3.minute
Amount  of air for airing of the vertical-type fermentation tank...
      158  - 1735,/amount of the material put into the  fermentation  tank m3.
      minute

(Moisture Content)

      The  moisture content is reduced  to 47% after  the dewatered  sludge of
the water content of 65% and the return compost of 37% are mixed.   After the
primary fermentation,  it is further reduced to 39% and the ultimate product
contains  31% moisture  which shows  favorable drying and fermentation conduc-
ted.
                                        175

-------
(Ignition Loss)

     The ignition loss which is 28% on average at the stage of feed mixture
declines to 25% after the primary fermentation.  The figure of the finished
product compost is similar to that and 24%.

(BOD5)

     BODs is used as an indicator of organic matter easy to resolve.  Solid
material has BODs of 144mg/g on average which reduces to 13mg/g after the
primary fermentation and to 12mg/g at the stage of the finished product.
BOD removal rate is 89%, which shows favorable fermentation.

(PH)

     The pH of the dewatered sludge is about 12 which declines to about 11
at the feed mixture stage which has been mixed with return compost.  After
the, completion of the primary fermentation, this figure goes down to 8.3 and
to 8.0 at the finished product stage.

(Weight Changes)

     Figure 16 shows weight changes.  About 60% or 40tons of the moisture
contained in material sludge (65tons per lOOtons material sludge) is volati-
lized during primary fermentation and about 10% or 5tons during the process
of producing return compost.  The moisture content of the sludge to be sent
to secondary fermentation is about 30% or 20tons of the original 65tons.
During secondary fermentation, 7tons of moisture is further volatilized.
This means that composting helps volatilization of 80% of the material
sludge.  Fifty percent of ignition loss is also observed.
     As a result, the x^eight of material sludge is reduced to 50% after the
primary fermentation and to about 42% after the secondary fermentation.
(See Figure 16)
                                      176

-------
                                 Amount of volatilization 44 cons
                                                         Amount of volatilization Stons
aterial sludge
(ewatered sludge) 100 tons
^^^^
ffl
®
®
X
63
37
65
ton
22
13
65
eturn compost 180 tons
^^^
®
®
®

%
75
25
37
ton
85
28
67




Fe

ed mixture 280tons
^-^^
®
®
®
X
72
28
47
ton
107
41
132


(
\
~~-~-~^
®
®
^ ferme
Primary fermentation





~~~~~~-^
®
®
®
(
Produc
ton
4
40

^ — ^^ ton
® 1
® 7
Primary fermentation sludge 50tons Product compost 42tons
nary
nation ^
^
)


sludge 186to
%
75
25
39
ton
85
29
72
"~ — --^^ % ton ~""--^^^ % ton
® 75 22 /- Secondary A ® 76 22
® 25 8 V fermentation J ® 24 7
® 39 20 ® 31 13
ns
on of ^
      (7) Amount of non organic matter
      (£) Ignition loss
      (3) Moistute content
Amo
ant of
vo
"~~-\^
®
®
anlizat
ton
1
5
on 6tons
b)  Fertilizing Elements
                            Figure 16. Daily mean mass balance.
                             (per 100 tons of material sludge)
    Concerning quality  control of the product, property analysis is conducted
    twice  a month to ascertain the fertilizing elements of  the compost.
    Table  11 shows the  result of property  analysis in 1984.   The compost  is
    a slow-effect fertilizer and is abundant  in nitrogen  and phosphate even
    though potassium content is low.  The  product is favorably evaluated  as
    being  able:  (1) to bring about harvest  increase, (2) to have a restric-
    ting effect on growth  retardation by continuous cropping and on soil
    pathogenic bacteria,  (3) to improve quality and (4) to  have soil amelio-
    lation.   (See TABLE 11)
                                        177

-------
                         TABLE 11. Constitution of sludge compost
c)  Odors
Item
Moisture content( % )
T-N (%)
T-P205(%)
T-K20(%)
T-C (%)
C/N
Ignition loss(% )
pH(H20)
Constituent
amount
30.8
1.3
2.8
0.2
16.5
12.7
24 1
8.0
                       Notes. T-N, T-P2O5, T-KZO, T-C, and Ignition loss refer to dry
                          compost
    Odors in fermentation  tanks have a high percentage of  ammonium and other
    sulfides such as methyl mercaptan, methyl sulfide and  methyl bisulfide.
    The ammonium density declines as fermentation progresses  but when the
    amount of air for  airing increases or turning takes  place it increases
    again.  In this facility's  case, the odor is removed by sucking blowers
    from the fermentation  tanks, then acid cleaning and  alkali cleaning is
    conducted.  After  the  odor  level is thus reduced, the  activated-carbon
    absorption treatment is applied to acquire favorable conditions regarding
    odor treatment.   (See  TABLE 12)
                                       178

-------
                           TABLE 12. Odor matter density.
\
Odor
density
mg/1
Methyl
mercaptan
0 34
0.01
Hydrogen
sulphide
ND
ND
Methyl
sulphide
0.18
001
Methyl
bi-sujphide
060
0.03
Tnmethyl
amme
ND
ND
Acetaldehyde
ND
ND
Styrene
ND
ND
Research
date
Winter
18 January
Spring
18 Match
Day passed
    after
fermentation
      1


      2


      3


      4


      5


      6


      7

    days
Airing
    amount
Wintet, Spring
 60   55


 59   72


 84   96


 84   95


 71   94


 71   90


 84   88

I /mixture -m3
      • mm



    (mg/1)

      100



 >,
 •a
 S   10.0
                 1.0
                 0.1
                   Ammonium density

20   40   60    80  100  120  140  160  180  200   ppm
    o	
                ~-	___             oSp
I     i      I     i

      Wintet research

     O Spring research
                                   -o
                                    G
                                                        a,
                                                        8
                                                        -a
                                           179

-------
4.2.4  UTILITIES COSTS

     TABLE 13 shows the results  of  calculation of utilities costs per one  ton
of dewatered-sludge dry material treated at the facility.  Calculation  factors
are the amount of dewatered  sludge,  required electricity and chemicals  used.
The utilities cost per one ton is about 4,200 yen.  The electric power  cost
for as much as about  87%  of  the  cost.   When th^ personnel cost needed for
the operation of the  center  is taken into consideration, the cost is about
7,100 yen per one ton of  dewatered-sludge dry material.  On the other hand,
the calculation result of the  costs  when sludge is incinerated is about
11,300 yen.  Compared with this, the utilities cost of the Sludge Control
Center is lower.  (See TABLE 13, 14)
     TABLE 13. Utilities cost (Sludge Control Center) per one ton of dewatered sludge material
— 	 _^^
Electricity
"w
£
u
rt
£s
Chemicals
(Deodorizer)
|sjs
^se
>~t
QJ
•5
O
High voltage equipment (400V)
Low voltage equipment (200V)
Lighting
A heavy oil
Water supply
Hydrochlonde(35%)
Sodium hydroxide (20%)
Activated carbon
Sludge treatment
Tablet of chlorine
Chart sheets
Amount
1346
21.9
10.1
3.3
0.7
2.1
07
0.05
0.006
0.002
0.002
Unit
KWh
I!
II
i
m3
kg
/;
//
ms
kg
Bundles
Unit (yen)
21.7
21 7
21.7
64.0
303.7
27 7
18.3
620.0
2,390.0
5400
1,000.0
Total
Personnel cost
Equipment mentenance
Shovel operation
Person on night duty
Cleaner
0 14
0.05
0 02
0.07
person
/;
//
//
12,300
12,100
8,900
6,500
Total
Grand total
Per one ton of dewatered sludge (Moisture content 65%)
Cost (yen)
2,921
475
219
211
213
58
13
31
14
1
2
4,158
1,722
605
178
455
2,960
7,118
(2,491)
                                      180

-------
          TABLE 14. Utilities cost required for incinerating one ton of solid sludge material
\
Fuel
A heavy oil
Fuel
Kerosine
Electricity
Chemicals
water
(Treatment water)
Others
Silica sand
Personnel cost
Grand total
Unit price
I
64yen/ i
I
67yen/(,
KWH
21 7yen/KWH
kg
4lyen/kg
m3
30yen/m3
kg
25yen/kg
person
12,300yen
/person

Standard flow
Vertical
multistage
incinerator
—
—
—
—
300
6,510
10
410
90
2,700
—
—
0.14
1,722
11,342
fluidized-bed
incinerator
120
7,680
—
—
330
7,161
20
820
95
2,850
30
750
0 14
1,722
20,983
Rotary
drying oven
80
5,120
—
—
320
6,944
20
820
145
4,350
—
—
0.14
1,722
18,956
Standard flow with incineration
deodorize
Vertical
multistage
incinerator
—
—
285
19,095
300
6,510
10
410
90
2,700
—
—
0 14
1,722
30,437
fluidized-bed
incinerator
120
7,680
—
—
330
7,161
20
820
95
2,850
30
750
0.14
1,722
20,983
Rotary
drying oven
80
5,120
240
16,080
320
6,944
20
820
145
4,350
—
—
0.14
1,722
35,036
                                                                   en = ldollar
4.3  DISTRIBUTION AND DIFFUSION PROMOTION MEASURES

4.3.1.   IMPROVEMENT  IN  THE  DISTRIBUTION SYSTEM

     All sludge produced  in the City that has been composted since 1972 has
been restored to green  zones and agricultural areas.  The factors which have
enabled  this to be possible are as follows.

a)  Demand Increase

    The  amount of organic matter used in agricultural lands in Japan has been
    drastically reduced due to  the tendancy of high dependency on chemical
    fertilizer and agricultural chemicals and to the difficulty in obtaining
    organic matter as a result  of the lack of labor to produce farm manure.
    This has resulted in  the deterioration of the soil.  Under these circum-
    stances, the merits of  organic matter has started to draw attention and
    it has lead to the  increase in demand for compost.

b)  Distribution System

    In the case of compost, distribution range is limited due to high
    transportation cost.  Improvement in the distribution system, however,
                                      181

-------
to sell  compost in  large quantities by private corporations has  contri-
buted  greatly to the promotion  of compost  diffusion.   Figure 17  shows
the distribution system which is  similar to  the case  of  chemical
fertilizers, i.e.,  production-storage-sales-use.  The shipped amount of
compost  in 1984 is  shown in Figure 18 which  indicated that consumption of
compost  is nationwide.
    Treatment plants (Average moisture content 65%)—> Sludge Control Center (Primary fermentation, Moisture
    content 40%) —> Private  consignment (Secondary fermentation, Moisture content 30*) —> Pulverization—*
    Sorting —> Bagging —> Warehouse storage —> Shipment —> Wholesaler —> Primary store —» Retailer —>
    Consumer


                              Figure 17. Distribution system.
Uses  of compost  are:   vegetables (30%),  fruits (20%),  golf courses (15%),
pasturage (10%),  paddy rice  (6%),  public green zones  (4%) and others
(10%) .
The final consumer price differs according to transportation distances.
In the  case of  20kg-bagged compost transported within  100km (inside
Fukuoka Prefecture),  it is 500 yen.  The price increases as the  distance
increases.
                                    182

-------
       Fukuoka
    169,200 "'
        151,100
                                                             Unit. bags
                                                    Note Sipment in bulk is not included
        Figure 18.Shipment distribution of product compost. (May 1 984~March 1985}

4.3.2  DIFFUSION  PROMOTION MEASURES

     It has been  only some ten years since the compost  produced in the City
was first put  on  the  market.   It is thought to be needed not only to improve
the quality of compost but also to stabilize the use  of it for the continued
composting of  sludge.   To promote diffusion of compost, measures such as the
follows are being implemented.

a)  Compost Variety
    Products of as many as fourteen varieties  in particle size and moisture
    content according to their use such as paddy rice,  vegetables, golf
    cources and hortculture or to sprinkling methods  such as machine
    sprinkling and hand sprinkling are produced to  meet each demand specifi-
    cally.  It is considered, however, to be necessary  to further expand the
    variety in the future to meet demands in better ways.  Sales in bulk is
    also conducted in suburban areas.
                                      183

-------
b)  Public Relations and Education

    For the promotion of the use of compost, efforts as follows are being
    made.

(1)  Lectures on needs for compost and its effects

     Lectures on usage and management of compost and its constituents or
     consultation meetings on heavy-metal issues are conducted.  Usage  leaf-
     lets are distributed.

(2)  Presentation of the users' experiences to learn their views and ideas
     and agricultural fairs of the users are held.

(3)  Exhibition lands by agricultural-education organizations are set up.

(4)  Compost for home gardening is distributed free at events on sewage and
     agriculture.

c)  Use in Urban Public Green Zones

    As an organic fertilizer, the compost produced in the facility is used in
    all afforestation projects of parks and roads conducted by the City.

4.3.3  USAGE GUIDANCE

     Usage guidance is given to the users of the compost with the coopera-
tion of agricultural-education organizations and distributors of the compost.
     The compost usage research conducted by the City has proved the effects
as follows.

(1)  It brings about increase in activated soil microorganism and restrain
     soil pathogenic bacteria.

(2)  It helps increase yield of green vegetables which require high ratio of
     nitrogen.

(3)  It improves qualities of fruits and fruit vegetables by enhancing
     sweetness in them.

(4)  It darkens the color (green)  of lawns in proportion to the amount used.

(5)  Its effect is enhanced by being used with potassic fertilizer.

(6)  Lime contained in the compost prevents acidification of soil, increases
     the gaseous phase,  forms aggregated structure, improves physical and
     chemical properties of soil.

     The compost, however, raises the pH of soil when used in great amount
and it requires appropriate amounts to be used as shown in Table 15.
     It is recommended not to use the compost, though, for soil of over 6.5
pH since it is necessary to sprinkle and mix the compost thoroughly with the
soil before planting or sowing. (See TABLE 15)
                                     184

-------
                   TABLE 15. Standard amount of compost to be used
Farm products
General products
Rice, Wheat, Soybean
Fruit trees
Tea trees
Mulberry trees
Potted plants
Lawn
Newly cultivated field
Yearly amount used
per 10 are
400kg
250kg
300kg
250kg
600kg
10% of soil
or 300kg
300kg
2000kg
Use
Do not use for soil of over 6.5 pH
Mix thoroughly with soil.
II
;;
//
;;
/;

This amount should be wed only for three years. After
initial three years, follow the above amount for use.
4.4  REGULATIONS CONCERNING HEAVY METAL CONTENT

     In Japan there are two kinds of regulations concerning heavy metal:
the heavy metal concentration regulations in compost prescribed by  the
Fertilizer Control Act and the regulations controlling  total quantity of
heavy metals in soil based upon the Soil Control Act.

4.4.1  HEAVY METAL CONCENTRATION IN COMPOST

     The Fertilizer Control Act classifies fertilizer made from sewage  sludge
as special fertilizer and it is subject to the heavy metal concentration
regulations.  (See TABLE 16)
                                      185

-------
                    TABLE 16. Heavy metal content in compost
~~~~- — ^_^^
~ — — — __^_^^
^~^^~~^-__


II
Is
S "°
0. C

S "g



be
~ 9"
si
3 i
S g
)< !„
o y
J5 ~
« a

As
Hg
Cd
Pb
Cr

Cu

Zn
Ni
Arsenic or its compounds
Cyanides
Mercury or its compounds
Cadmium or its compounds
Lead or its compounds

Sexivalent chromium compounds
PCB
Organic phosphorous compounds
Mercury alkylides
Compost in Fukuoka City(1984 year)


Average
1.3
0.69
1.5
26
20

170

720
22
ND
ND
0.0014
ND
ND

ND
ND
ND
ND

Maximum
29
091
2.6
47
30

200

990
10
ND
ND
00023
ND
ND

ND
ND
ND
ND

Minimum
0.5
0.4
0.94
19
16

160

390
28
ND
ND
0.0008
ND
ND

ND
ND
ND
ND

Standards

Not to exceed 50
// 2
II 5







Not to exceed 1.5
II 1.0
// 0.005
n 0.3
// 3.0

// 1.5
n 0.03
w 1.0
Should not be detected
                                                          ND Not detected


     The regulations provide that the content of As(arsenic),  Hg(mercury),
and Cd(cadmium) in dried fertilizer should not exceed  50 rag/kilogram,
2 rag/kilogram, and 5 rag/kilogram respectively; furthermore  the solution
extraction regulations protect soil from the solution  extraction of heavy
metals.
     All compost produced in Fukuoka City is tested  twice a month to ensure
safety.  From this test, positive results were obtained as  Figure 19 suggests:
heavy metal contents were constantly lower than the  limit required by the
regulations and it remained stable throughout the year.   (See  Figure 19)
                                     186

-------
                  50.0


                   6.0


                   5.0


                   4.0


                   3.0


                   2.0


                   1.0
  Limit of arsenic
   Limit of cadmium
Limit of total mercury
                                                  Total mercury
                       1976  1977  1978  1979  1980  1981  1982  1983  1984 (fiscal year)
                        Figure 19. Change of heavy metal content in compost.
4.4.2  REGULATIONS CONCERNING HEAVY METAL CONTENT  IN SOIL

      The permissible limit level of Zn(zinc)  in soil was established in  1984:
the  content  of Zn  in dried soil  should not exceed  120 mg/kg-DS.   This regula-
tion ensures the safety  of compost, and thus  prevents soil  contamination
caused by  the accumulation of Zn.
                         TABLE 17. Guide lines for  level of Zn, Cu, and Ni
                                                           (Unit mg/dned soil kg)
\
\
Zn
Cu
Ni
Permissible limit level
in soil
Japan
120


West
Germany
300
100
50
Maximum permissible level to soil (See the note)
o^c^r' Canada U.K. Holland
223 162 560 81
112 75 280 20
112 16 128 20
                                 Note Calculated based upon the guide lines regarding the permissible limit level
                                           187

-------
     The following formula shows how many times it is possible to harvest out
of 400 kilograms of compost.

Assuming that

1)  The content of Zn in compost is 720 mg/kg«DS.

2)  The amount of compost used in soil is 400 kg per 10 ares (compost con-
    tains 30% of moisture.)

3)  The content of Zn in soil is 60 mg/kg of dried soil.

4)  The permissible limit of Zn in soil is 120 mg/kg of dried soil.

5)  The depth of soil is 15 cm.

6)  The volume weight of soil is 0.9.

7)  The accumulation percentage of Zn is 100%.

Thereby

X(harvests) x 0.4(tons/harvest) x (1-0.3) x 720(g/ton) =
                0.15m x 1,000m* x 0.9
X=40

     This formula suggests that it is possible to harvest at least 40 times
out of 400 kg of compost per 10 ares.
     However, it could be possible to harvest more than that because some
amount of Zn can drain out or might be absorbed by crops.
     There have been no reports claiming that soil contamination was caused
by compost.
     The behavior of heavy metals in soil depend upon a number of  factors:
the amount of compost, the pH value of compost, the content of organic  sub-
stance, soil property, and the category of crops.  These complex factors make
it necessary to conduct further detailed surveys.
     In view of the fact that compost produced in the City is shipped to
almost every part of Japan, Fukuoka is planning to establish the nationwide
network to research the soil condition in farmland where compost is used.
                                      188

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4.4.3  MEASURES TO REDUCE HEAVY METAL CONTENT IN SUJDGE

     Simply satisfying the regulations will not protect farmland from soil
pollution; there is no doubt that the less heavy metal content in compost is
the better both for safety of soil and for sales promotion of compost.  In
this respect the City set up the following measures to assure the safety of
compost and to promote the recycling of sludge:

a)  Control over Facilities Discharging Waste Water Containing Heavy Metals
    The most effective way to reduce heavy metals in sewage is to check the
    discharge of heavy metals into the sewers at their resources.
    In Fukuoka City, facilities letting out large amount of waste water are
    designated as Special Facilities.  There are about 670 such facilities.
    Out of these Special Facilities, the facilities which are under the
    application of the standards described in Table 18 are required to submit
    a report on their water analysis and maintenance data.  To further enhance
    the control of heavy metal discharge, the City conducts water sampling
    inspections at these facilities.  Moreover, at such facilities as research
    institutions, hospitals, and metal plating plants, which discharge large
    amount of heavy metals, the City carry out on-the-spot inspections and
    water sampling inspections; beside that, these facilities are required to
    use professional waste water and sludge collectors.
                       TABLE 18. Effluent standards into sewerage
Chemical substance
Cadmium or its compounds
Cyanides
Organic phosphorous compounds
Lead or its compounds
Sexi-valent chromium compounds
Arsenic or its compounds
Mercury or its compounds
Mercury alkylides
PCB
Unit
mg/<
n
II
II
II
n
II
n
n
Specially designated facilities
Other facilities
Amount of drainage discharge
50m3 or more
per day
0 1
1
1
1
0.5
0.5
0.005
Not detectable
0.003
Less than 50m3
per day
0.1
1
1
1
0.5
0 5
0.005
Not detectable
0.003
50m3 or more
per day
0.1
1
1
1
05
0.5
0005
Not detectable
0.003
Less than 50m3
per day
0.1
1
1
1
0.5
0.5
O.O05
Not detectable
0003
                                     189

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b)  Prevention  of Heavy Metal Mixture in Dehydration Process

    Lime  and  ferric chloride are applied as dehydration auxiliaries  in  the
    dehydration process.   Fukuoka has the standards for these two  auxiliaries
    in  compost  to assure safety; only the auxiliaries that passed  the standard
    tests  conducted by such a public agency as the Pollution Analysis Center
    can be used in the dehydration process.
             TABLE 19. Content standards of heavy metal in Dehydration Auxiliaries
                     Lime
"\
Cd
As
T-Hg
Content standards
Not to exceed
2.5mg/kg
/;
2.5mg/kg
n
0.04mg/kg
Actual content
1.88
(2.3-087)
0.92
(1.3-0.5)
Less than 0.01
      Figures m the parenthesis indicate the range.
                                                     Ferric chloride
\
Cd
As
T-Hg
Pb
Cu
Zn
T-Cr
Content standards
Not to exceed
0.3mg/kg
//
15mg/kg
/;
0.005mg/kg
/;
3 Omg/kg
//
JOmg/kg
/;
50mg/kg
//
20mg/kg
Actual content
0.2
(less than 0 3-003)
0.6
(less than 1 3 — 05)
0.002
(less than 0.05 — 0 001)
09
(less than 2 0 — 0.3)
1.5
(less than 2 — 1)
297
(44-18)
9.0
(13-2)
c)  Others

    Fukuoka City is working  on  the development of heavy metal separation
    methods in cooperation with the Hydolic and Sanitary Engineering Research
    Laboratory (headed by Dr. Hanajima)  at Fukuoka University.
    A new kind of heavy metal separation technique using floatation machines
    is under experiments.  Promising results have been obtained so far.  These
    results prove that it is possible to separate considerable amount of heavy
    metals from used water.  Further detailed researches are being carried  on
    aiming at the practical  adaption of  this technique.

4.5  RESEARCHES INTO THE EFFECTS OF COMPOST ON SOIL AND CROPS

4.5.1  THE RESULTS OF RESEARCHES

     Since 1977 the City has been  conducting extensive researches into effects
of compost used in fields and paddies in cooperation with agricultural re-
search organizations and university research laboratories.

The main research subjects are  as  follows:

(1)  The effects on the yield and  soil improvement
                                       190

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(2)  The examination of  adequate applying technique for compost and of
     applying limit of compost

(3)  The accumulation of heavy  metals in soil

(4)  The absorption of heavy  metals by crops

(5)  The effects on growth  of crops

     The followings are  the reports on the effects of compost used in paddy
fields and newly developed  agricultural fields.

a)  Tests in Paddy Fields

(1)  Research Method

     The compost section and  the control section were set up in 1977:   in  the
     former section 240  kilograms of compost is used per 10 ares and in 18.3
     ares of the latter  section only chemical fertilizer is used.  Since then,
     the long-term comparative  study has been made in these two sections.

(2)  Results

     As TABLE 20 indicates, the stalk diameter of rice in the compost section
     was 6% bigger than  that  in the control section in 1984; the subterranean
     portion in the compost section grew by 68%, which means that the fall-
     resistancy of rice  in  this section improved a great deal.
     The yield in the compost section has become stable recently, and has
     exceeded that in the control section by 10%, which indicates that  the use
     of compost is effective.

                 TABLE 20. Study of growth condition of paddy rice 1980-1984
\
1980
1981
1982
1983
1984
Weight
of
terrestrial
portion
95
88
104
104
105
Weight
of
sudterra-
-nean
portion
86
90
108
120
168
Number
of rice
seeds
per nee
stubble
104
93
109
104
114
Total
weight
of rice
seeds
per nee
stubble
104
98
110
104
109
Length
of
head
101
98
101
101
99
Length
of
stalk
97
99
104
101
107
Number
of
heads
per rice
stubble
99
97
114
97
106
Total
weight
of
1,000
rice
seeds
100
103
101
100
96
Number
of
seeds
per
head
—
—
108
108
108
Diameter
of
stalk
—
—
102
108
106
Unhulled
nee
/straw
112
108
105
104
104
                                   Note The base figure of 100 is the figure of each item in the control section
                                      191

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(3)   Behavior of Heavy Metals

     Among heavy metals, Zn(sinc) can be absorbed most easily by  plants.   In
     the compost section, the amount of Zn in the edible portion  of  rice
     increased by 20% in these eight years.  However, such harmful heavy
     metals as As(arsenic), Hg(mercury), and Cd(cadmium) were absorbed only
     by the subterranean portion; these heavy metals were not detected in the
     edible portion.
     Though it is eight years since this test started, no distinct difference
     in heavy metal content was found between in the compost section and  in
     the control section.  One reason for this could be that the  amount of
     compost was limited to 240 kilograms per 10 ares (which is well within
     the adequate limit for paddy fields.)  For another reason, the  water in
     paddies may have some influence on the behavior of heavy metals.
                        TABLE 21.  Heavy metal content in crops
                                                             (mg/kg: dried)
~- — _
As
Hg
Cd
Cr
Pb
Cu
Mn
Fe

Zn

Ni

^^_
Control
section
Compost
section
Conttol
section
Compost
section
Conttol
section
Compost
section
Control
section
Compost
section
Conttol
section
Compost
section
Conttol
section
Compost
section
Conttol
section
Compost
section
Control
section
Compost
section
Control
section
Compost
section
Control
section
Compost
section
Polished rice
Not detected
Not detected
Not detected
Not detected
Not detected
Not detected
Not detected
Not detected
Not detected
Not detected
3.9
4.2
21
20
17
17
25
25
Not detected
Not detected
Brown rice
//
;/
/;
/;
//
H
II
n
n
II
4.1
4.5
26
27
23
24
24
27
;;
//
Unhulled rice
//
//
;/
/;
n
II
II
II
n
II
3.9
4.0
58
55
42
41
23
19
/;
//
Leaf and stalk
;/
//
//
//
//
;/
1.7
1.6
;;
;;
67
6.8
500
440
240
330
20
20
/;
II
Subterranean
portion
12
9.8
n
n
061
0.23
49
40
10
10
69
55
340
440
57,000
66,000
82
84
26
26
                                                           Note • ten point average
                                       192

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 (4)  Another Test

     A large amount of  compost was given  to  soil  in  bench  scale  test  every
     year and the effects were studied.   From this test, the  following results
     were obtained:

 1)  The productivity of soil improved.

 2)  The alkalinization  in soil advanced.

 3)  The growth of rice  was restrained at  early stage, but  it  recovered later.

 4)  Heavy metal density in crops didn't increase.
                  TABLE 22. Analysis of brown rice grown and soil after harvest

I
>s
rt
D
T3
c
rt
W5
>-,
j
kg/ 10 are
0
400
800
1,600
0
400
800
1,600
Soil after harvest
Base
pH T-N T-C saturation
percentage
% % *
5.3 0.19 1.64 84
6.6 0.19 1.58 148
7.0 0.18 1.62 177
7.6 020 1.73 253
5.9 0.12 096 63
6.7 0.14 1.12 109
7.3 0.15 1.30 155
7.9 0.13 1.55 330
Brown rice
N P K Cd Zn Cu
% % % mg/kg mg/kg mg/kg
1.38 0.37 1.11 <0.01 19.10 2.84
1.34 0.35 1.01 0.03 1875 297
1.37 0.35 1.03 0.02 17.95 2.78
1.33 0.35 1.08 <0.01 23.90 4.07
.1.25 0.37 1.08 0.03 18.76 2 94
1.29 033 1.03 002 18.38 2.67
1.26 0.36 1.00 0.04 19.07 3.47
1.31 0.36 101 0.02 18.32 303
b)  Tests in Newly Developed Fields

(1)  Research Method

     Newly developed fields were divided into three sections:  1.8 ares of  the
     control section in which chemical fertilizer was applied, the compost
     section in which 2tons of compost were used per 10 ares for the  first
     and the second year (lime in compost was reduced and calcium carbonate
     was added instead), and the farm manure section.  In each section, taros
     were planted in the first year, turnips in the second year, and  potatoes
     in the third year.

(2)  Results
     Crops in the compost section grew more thrivingly than those in  the
     control section.  The yield in the compost section was 15% better than
     that in the control section.  Though the total yield of potatoes in the
     compost section was less than that in the farm manure section, the yield
     of large- and medium-sized potatoes surpassed that in the farm manure
     section.
                                     193

-------
(3)
The quality of potatoes is measured by the starch value.  Potatoes  grown
in the compost section showed the highest starch value.  This  suggests
that compost has effects on improvement of the quality of potatoes.
In the compost section, nitrogen content in crops increased; however
phosphorus and potassium content was smaller than that in the  control
section.  (See TABLE 23, 24)
The pH value and the base saturation percentage in soil  of  the compost
section went up slightly by the effect of lime contained in compost.  The
total nitrogen and carbon rose in the first and the second  year.   In the
third year, the total nitrogen went down to the same  level  of  that  in the
control section.
In soil of the compost section, the true density became  smaller,  the air
phase became amplified, and the porosity and the coefficient of perme-
ability went up.  These results indicate that compost upgraded the  soil
condition.

Behavior of Heavy Metal
In the compost section, heavy metal content in stems  and leaves rose
slightly, but the edible portion had less heavy metals than that  in the
control section.
The heavy metal content in soil of the compost section did  not show any
increase after three years.  There was little difference between  heavy
metal content in compost section and that in the other two  sections.
(See TABLE 24, 25)

                  TABLE 23. Growth condition and yield of potatoes
\,
^\


Item



Control section
Farm manure section
Compost section
Growth
May 8
Length
of
stem



cm
10.0
12.0
11.1
Number
of
stems




1.90
1.95
1.75
June 18
Length
of
stem



cm
61.2
64.7
55.4
Number
of
stems




1.85
2.30
2.10
ViplH

Weight
of
stem
(dried)


kg/are
19.34
16.28
20 25
Large
-sized
potato
(120gr
and
more)
kg/are
346 3
371.7
364 0

Medium
-sized
potato
(60-
120gr)

kg/are
118.0
168 3
180.0

Small
-sized
potato
(less
than
60gr)
kg A re
60 8
106.9
63 3

Total
weight
of
potatoes


kg/are
525 1
646.8
607 3

Total
weight
of
dried
potatoes

kg /are
93.7
109.7
113.7

Starch
value
(%)




11.7
109
13.1
                              TABLE 24. Analysis of potatoes
                                                                 (96 dried)
^\^^
^^~\^
rt
J
u
C/J
O
O
CL,
Control section
Farm manure section
Compost section
Control section
Farm manure section
Compost section
Water
(*)
89.7
90.8
89.5
82.2
83.0
81.3
N

3.41
3.77
348
1.25
1.28
1.45
P

0.37
0.38
0.33
0.19
0.21
0.20
K

4.83
4.83
4.14
1.65
1.65
1.57
Ca

2.06
1.32
2 28
004
0.03
0.04
Mg

0.89
0.92
1.09
0.07
0.07
0.07
Heavy metals (mg/kg)

Cd
1.39
1.76
1.38
0.19
0.14
0.17

Zn
45.8
59 8
49.6
31.8
22.2
18.7

Cu
8.28
1467
8.91
3.37
4.07
3.18
                                       194

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                        TABLE 25. Analysis of soil after harvest
\^
Control section
Farm manure section
Compost section
PH T-C T-N **•
% « me/100g
77 0.38 006 114
7.0 0.35 0.04 7 3
7.9 0 32 0.04 13 1
Perchloric acid
decomposition
Cd Zn Cu
mg/kg mg/kg mg/kg
0.12 100.8 30.2
0.11 108.5 324
0.17 113 1 33 8
True
density
2.64
2.60
2.62
Three phases
Solid Liquid Air
phase phase phase
% % %
51.6 17 5 30.9
48.8 16.6 34.6
43.1 15.9 410
Coeffici-
Available m o!
water watcr
permeability
121 1 IX 10~3
13 9 1 5X 10~3
12.2 3.2X10-'
4.5.2  FUTURE RESEARCHES

     Researches carried out so far proved that compost improves soil  condition
and productivity.  It is being planned to conduct the following researches
regarding heavy metal behavior.

(1)  Researches to find out the appropriate amount of compost  to be used  in
     farmland, how the accumulation rate of heavy metals varies by the nature
     of soil, and how the accumulation rate in crops changes by the category
     of crops

(2)  Researches concerning activity of heavy metals and absorption of heavy
     metals by crops in the acid soil.  No tests as yet have found heavy
     metals in the edible portion of crops in the compost section.  However
     it is suspected that this is because the alkalinization of soil  might be
     preventing crops from absorbing heavy metals.  Consequently it is neces-
     sary to observe heavy metal behavior in soil when soil turns into acid
     soil.

(3)  Researches into multiplex effects of compost
                                     195

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5  SUMMARY


     As stated in 1  INTRODUCTION, Fukuoka City believes that turning sludge
into compost is the most adequate sewage disposal method because

1)  sludge contains useful organic and inorganic substances;

2)  sludge in the city is safe to use as compost;

3)  there still remains farmland in many parts of the city;

4)  this method is appropriate from a long-term viewpoint.

     The City has made efforts to improve compost quality and to expand
distribution network with the cooperation of SANKYO YUKI CO., LTD. to which
the City entrusted treatment of sludge.  Fukuoka City has been also trying
to reduce heavy metal content in sewage.
     These efforts have now come to bear fruit:  100% of sludge in the City
has been made into compost since 1972, and compost produced in the City is
shipped to various parts of Japan.
     Fukuoka City holds that Japan, being scarce in natural resources, should
make use of sludge to improve soil productivity.
     Varied researches have been conducted past eight years with the purpose
of estimating the effects of compost and grasping heavy metal activities in
soil.  The City is projecting to carry out further detailed researches
working together with such administration agencies as the Ministry of
Construction and the Ministry of Agriculture, Forestry and Fishery, as well
as with research institutions at universities.
                                      196

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                                       Tenth  United States/Japan Conference
                                          on  Sewage Treatment Technology
TECHNICAL EVALUATION OF "ENERGY-SAVING" AERATION DEVICES
                The work  described  in this paper was
                not funded  by  the U.S. Environmental
                Protection  Agency.   The contents do
                not necessarily  reflect the views of
                the Agency  and no official endorsement
                should be inferred.
                              Tokuji Annaka,

                                  Chief,

              Water Quality Section, Water Quality Control Division,

             Public Works Research Institute, Ministry of Construction


                            Masahiro Takahashi,

                             Research Engineer,

              Sewage Works Section, Water Quality Control Division,

             Public Works Research Institute, Ministry of Construction


                                  197

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                              TABLE OP CONTENTS
1.   PRESENT SITUATION OF AERATION DEVICES IN JAPAN 	     199
2.   BACKGROUND TO DEVELOP ENERGY-EFFICIENT AERATION DEVICES 	     201
3.   AN INTRODUCTION TO THE AERATION DEVICE EVALUATION SYSTEM	     203
 3.1   Construction Technology Assessment System 	     203
 3.2   Goals of Development	     203
 3.3   Evaluation Procedure 	     203
4.'   RESULTS OF EVALUATION	     204
 4.1   Evaluated Devices 	     204
 4.2   Test Procedure 	     206
 4.3   Test Results 	     208
 4.4   Conclusion 	     213
5.   TAP WATER TEST	     213
 5.1   Experimental Equipment and Method 	     213
 5.2   Results of the Experiment	     216
 5.3   Conclusion 	     218
6.   PERFORMANCE AT THE ACTUAL PLANTS 	     218
                                     198

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1.   PRESENT SITUATION OF AERATION DEVICES IN JAPAN

          As of the end of FY 1982, there are 529 publicly owned wastewater
     treatment plants in service in Japan.  Table 1 shows their
     classification by treatment processes.
     Table 1  Classification of wastewater treatment plants by processes
                                                            (FY 1982)
Process
Conventional activated
sludge
Step aeration
Extended aeration
Contact stabilization
Oxygen aeration
Rotating biological
contactor
Oxidation ditch
High-rate trickling filter
High-rate activated sludge
Chemical coagulation
Plain sedimentation
Total
Public
sewerage
331
70
10
1
5
4
5
13
19
2
7
467
Basin-wide
sewerage
35
6
-
-
-
-
-
-
-
-
-
41
Designated
public
sewerage
3
1
-
-
-
1
-
-
-
-
3
8
Designated
environ-
mental
sewerage
1
-
3
-
-
7
2
-
-
-
-
13
Total
370
77
13
1
5
12
7
13
19
2
10
529
          As shown, 491 plants,  or 93% of all,  adopt activated sludge
     process, including modified processes.
          Sewerage construction in Japan has so far been pushed forward in
     densely populated areas through the construction of comparatively large
     plants, and the activated sludge process has taken a leading role to
     cope with a limited availability of land.
          Of the 491 wastewater treatment plants with activated sludge
     process, those using the mechanical aeration devices number only 46, and
     the remaining 445 are with diffused aeration devices.
          The specifications of the diffused aeration devices employed in
     Japan are described in the "Guidelines for Sewers and Wastewater
     Treatment plants,^" as summarized in Table 2.
          Most of diffused aeration devices used in Japan are plate or pipe
     diffusers capable of generating fine bubbles.  The maximum pore size of
     the plate diffuser is about 400y°, and the standard air flow rate is 80
     to 100 £/min per plate.  The larger air flow rate increases the bubble
     sizes, reducing the oxygen transfer efficiency.  This in turn is likely
     to increase air flow resistance due to clogging.  The maximum pore size
     of the pipe diffuser is about 450y°, and the standard air flow rate is
     120 to 150 H/min per pipe.  In most cases, these diffusers are installed
     on a sidewall along the bulk flow direction for a spiral flow
     configuration in the aeration tank.
                                     199

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                Table 2  Specifications  for  diffusers
\~ ' — 	 — _Jype_
^\ Material
Item ^\
Standard air flow rate
U/min)
Pore size (um)
Dimensions (mm)
Weight (kg/unit)
Fine bubble
Porous ceramics
Plate
diffuser
80 to
100/sheet
Max. 400
H 300 x
300 x
30 t
4
Pipe
diffuser
120 to
ISO/
piece
Max. 450
75 o.d. x
50 i.d. x
500 L
2
Disk
diffuser
30 to 40/
piece
avg. 150
178 o.d.
x 38 H
x 19 t
1.3
Unplasticized
plastics
Plate
diffuser
80 to
120/sheet
200 to
500
E300 x
300 x
30 t
1.8
Pipe
diffuser
100 to
ISO/
piece
200 to
500
75 o.d. x
50 i.d. x
500 L
0.8
Coarse bubble
Stainless
steel
(SUS304)
Perforated
pipe
300/piece
dia.
4.0 nun
25 o.d. x
650 L x
15 holes
1.7
Cast
iron,
ABS
resin
Sparger
250/
piece
6.3 mm

0.2
(ABS)
Ductile
cast
iron and
PVC
Disk
diffuser
200/
piece
Max.
gap,
4.0 mm
100 o.d.
0.6
      Those fine-bubble aeration devices  have been in use since 1928.
 But there is little information available about service life of plate
 diffusers concerning replacement frequency.   Figure 1 shows annual
 changes in air flow resistance of  the plate  diffusers measured by the
 Public Works Research Institute, Ministry of Construction, for 14 years
 at the Ochiai Wastewater Treatment Plant, Tokyo.
      While abrupt changes in air flow resistance were noticed during a
 total period of 10 intervening years, they would have been not so
 serious a problem.
           800
           700
           600
                                         \!
Permeability of plate
(dry air condition),
cc/cm2.min.
  	 1200

  	1800
  	240C

  	3000
                   '63
                        '70
                               '72
                                     '74
                                           '76
                                                 '78
                                                       '80
                                                             '82
Fig. 1  Yearly changes  in  head loss of four different plate diffusers
                                  200

-------
          The clogging degree of plate diffusers is dependent on the
     characteristics of influent wastewater and the operating conditions of
     aeration tank (blower shutdown frequency, concentration of dissolved
     oxygen (DO), air flow rate etc.)/ and their service life varies from
     plant to plant.   As the wastewater treatment plants constructed in the
     past ten years account for more than 50% of all the plants, the renewal
     of diffused aeration devices will grow in future.
2.   BACKGROUND TO DEVELOP ENERGY-EFFICIENT AERATION DEVICES

          The total electric energy generated in Japan in FY 1982 was 581 x
     10^ kWh, of which 2.9 x 10^ kWh, or 0.5%, was consumed by sewerage
     works.  At present, public sewer-covered population in Japan is as low
     as 33% of the total.  With increase in the sewer coverage,  the power
     consumption by sewerage works will increase.
          Table 3 shows the breakdown of operation and maintenance costs for
     sewerage works all over Japan in FY 1982.  As shown, the electric bills
     are the largest of all the cost items, registering 24.1%.  This
     indicates that the reduction of power consumption has a significant
     effect on the reduction of overall expenditure.
          Table 4 is a summary of the survey of the power consumption of at
     six wastewater treatment plants which employ either conventional
     activated sludge process or step aeration process, both being typical
     processes in Japan.  At the plants sludge treatment processes consist of
     gravity thickening, anaerobic digestion, elutriation, and mechanical
     dewatering.  As shown in Table 4, power to operate aeration blowers are
     found to account for an average 45% of total plant power consumption,
     suggesting that the improvement of energy efficiency of aeration devices
     will be directly effective for the reduction of plant operating costs.
                                     201

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Table 3  Breakdown of  operation and maintenance costs  of  sewerage works
         (FY 1982)
                                                 (in thousand yen)
"\^Facility
Item ^^^^
Electricity
Labor
Commission
Cleaning
Repairs
Chemicals
Fuel
Others
Subtotal
Administration
Total
Sewer
-
-
-
-
7,374,389
(29.6)
2,019,404
(8.1)
6,682,654
(26.8)
-
-
-
-
-
-
16,076,447
(64. S)
8,857,531
(35.5)
24,933,978
(100.0)
Pump
station
10,046,348
(28.9)
-
-
4,142,551
(11.9)
-
-
3,687,709
(10.6)
-
-
276,937
(0.8)
-
-
18,153,545
(52.2)
16,607,756
(47.8)
34,761,301
(100.0)
Treatment
plant
49,099,672
(26.4)
40,009,193
(21.5)
34,259,157
(18.4)
-
-
15,138,212
(8.1)
13,925,793
(7.5)
8,998,550
(4.8)
10,874,455
(5.9)
172,305,032
(92.7)
13,559,717
(7.3)
185,864,749
(100.0)
Total
59,146,020
(24.1)
40,009,193
(16.3)
45,776,097
(18.6)
2,019,404
(0.8)
25,508,575
(10.4)
13,925,793
(5.7)
9,275,487
(3.8)
10,874,455
(4.4)
206,535,024
(84.1)
39,025,004
(15.9)
245,560,028
(100.0)
                Table 4  Breakdown of  power consumption
Treatment plant
1
2
3
4
5
6
Average
Pumping
-
21.9
22.5
16.7
25.1
24.8
22.2
Wastewater
treatment
-
-
55.5
70.2
60.4
53.9
60.0
Sludge
treatment
17.2
-
9.9
10.4
12.9
17.2
13.5
Others
-
-
12.1
2.7
1.6
4.0
5.1
Blower
44.8
43.3
40.3
61.3
-
34.7
44.9
                                   202

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3.   AN INTRODUCTION TO THE AERATION DEVICE EVALUATION SYSTEM

3.1  Construction Technology Assessment System

          In 1978, the Ministry of Construction introduced the Construction
     Technology Assessment System for implementation of advanced technologies
     for public works.  The underlying purpose of this system is to assess
     new technologies and to reflect the findings in the public works.  The
     details of the system and the technologies evaluated under the system by
     FY 1983 were already reported by Nakamoto at the 9th U.S.-Japan
     Conference on Sewage Treatment Technology.
          On agenda for FY 1984 and FY 1985 in relation to sewage works are
     the following projects.

     FY 1984:  "Development of solid-liquid separation devices by screening
               method"
     FY 1985:  "Development of dissolved oxygen sensors for automation of
               aerator control"

          The evaluation of energy-efficient aeration devices was conducted
     in FY 1982 under this evaluation system.

3.2  Goals of Development

          The development of energy-efficient aeration devices was promoted
     to achieve the following four major goals.

     (1)   Reduction of power consumption by 20% as compared with the
          "conventional" diffusers (plate and pipe diffusers).

     (2)   Reduction of biochemical oxygen demand (BOD5)  and suspended
          solids (SS)  in the effluent to less than 20 mg/a and 70 mg/&,
          respectively, when the diffusers are installed in the activated
          sludge reactor for the secondary treatment of domestic wastewater.

     (3)   Easy adaptation to the existing aeration tanks.

     (4)   Improved operation, and easier inspection, repair and parts
          replacement.

3.3  Evaluation Procedure

          The evaluation was made based on the test results submitted by the
     applicants,  and the Construction Minister accorded a certificate of
     approval to  the accepted products.
          Prior to the invitation of  manufacturers to the assessment,  a
     technology evaluation committee  consisting of the engineers and
     researchers  representing the Ministry of Construction and local
     municipalities and academic authorities from  the universities formulated
     guidelines for the evaluation procedures of testing and data analysis.
     The guidelines for the testing methods are summarized below.
                                     203

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     (1)   To demonstrate performances of  the  new  devices  by  treating  actual
          wastewater either  at the actual facility or  pilot  plant  of  a
          comparable scale,  by making a comparison between these and
          conventional  plate or pipe diffusers.

     (2)   To conduct above tests for at least one month each including both
          summer and winter  time operation.

     (3)   To collect data, including power consumption by aeration device,
          wastewater flow, oxygen transfer efficiency, distribution of DO and
          MLSS concentrations in the aeration tank, characteristics of
          influent,  mixed liquor and effluent.
4.   RESULTS OF EVALUATION

4.1  Evaluated Devices

          The evaluation was made on five types  of  "new"  diffusers.   Fig.  2
     illustrates the operating principles, structural  designs and
     installation methods of these devices.
          The evaluated devices can be classified into two groups as to
     operating principles.
          "Bayer Injector" of Mitsui Shipbuilding & Engineering,  "Hanshin
     Aquarator" of Hanshin Power Machinery,  and  "Jet Aerator" of  Nishihara
     Environmental Sanitation Research Corporation, are of a type designed to
     inject air into turbulent wastewater for fining the bubbles, and the
     resultant high velocity jet of water is used to mix wastewater  in the
     tank.  Bayer Injector and Jet Aerator also  use a  pump to circulate mixed
     liquor; the former has a liquid nozzle of 8.2 mm, which is a little
     smaller than enough, and requires a kind of strainer in its  water
     delivery line.  Hanshin Aquarator has a submerged impeller dubbed the
     diffused aeration rotor, which is driven by a submerged motor to
     generate a circulating water flow.
          Aeration device of NGK Insulators and  the dome type diffuser of
     Mitsui-Miike are for the whole floor distributed  aeration, designed to
     generate ultrafine bubbles.  Both types are submerged parts, such as
     riser pipes, made of synthetic resins, and  are fitted with a water drain
     pipe, in order to prevent pipe scale from blocking up diffusers.  In
     case of 260 m° plate diffusers, the air filter is a combination of wet
     and dry filter elements as it is in wide use currently.  In  the dome
     type diffuser, a special filter is used to  prevent airborne  dust from
     clogging up the diffuser pores.
                                      204

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                                                         902
(D

NJ
o
c
rt
h-J
H-
3
(D

O
Hi

CD
ft
(D
 (D
 <
 H-
 O
 (D
 CO
o d i— ><: QJ
                                                 Existing air pipe
                                                                                      Moisture blower

-------
4.2  Test procedure

          The testing conditions applied to the newly developed devices are
     summarized in Table 5.
          With the exception of the facility used for Bayer injector, all the
     evaluated devices were operated in the aeration tanks in service.
     Accordingly, the test conditions could not necessarily be standardized
     for all the evaluated devices.  The power consumption was directly
     measured with a watthourmeter or calculated from air delivery rate,
     delivery air pressure, etc. to meet specific site conditions.
          For the determination of oxygen transfer efficiency, the aeration
     tank was divided into several compartments, and the respiration rate and
     DO content in the mixed liquor were measured in each compartment in
     order to figure out the oxygen demand of the entire aeration tank.
          The analytical data were taken at an interval of 2 hours on an
     around-the-clock basis to obtain total oxygen demand of a day which was
     divided by the total amount of oxygen supply to determine oxygen
     transfer efficiency.
                                      206

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                                                    Table 5   Test  conditions

Wastewater inflow

4.2
D - 4.5
H o 6
L - 165
-
Manual centre
at 'the outlet
tion tanks of
ties becomes
Control
facility
same as test-
ed facility
same as test-
ed facility
same as test-
ed facility

same as test-
ed facility
Plate
diffuser
1 so that DO
both facili-
the same.
Same plant
Jet aerator
Tested
facility
73,700 to
75,400
0.37 to 0.68
4.8 to 4.9
4.6
D - 10
W - 10
L • 152
-
Manual control
a required qui
of effluent it
Aeration tank
outlet: DO, 1
to 2 mq/l
Control
facility
77,800 to
80,800
0.32 to 0.55
5.6 to 6.0
4.5
D - 4.5
W - 7.4
L - 152
Plate
diffuser
to minimize
the extent
11 ty level
maintained.
Aeration tank
outlet: DO, 3
to 4 mg/l
Same plant
Plain plate diffuser
Tested
facility
4,000
0.34
7.0
3.55
D > 4
W - 6
L - 52
-
Control
facility
same as test-
ed facility
same as test-
ed facility
same as test-
ed facility
3.75
same as test-
ed facility
Plate
diffuser
Manual control so that the
aeration tank outlets of
both facilities show the
same DO value.
Same plant
Dome diffuser
Tested
facility
6,600 to
7,000
0.24 to 0.40
6.1 to 6.8
5.77
D - 6
W - 8
L - 38
-
Automatic
control to
keep DO at
1 or 1.5 rag/I
in the center
of the aera-
tion tank.
Control
facility
5,800 to
5,900
0.25 to 0.34
7.5 to 7.6
5.5
same as test-
ed facility
Pipe diffuser
Automatic
control to
keep DO at 1
or 2 mg/l
in the center
of aeration
tank.
Same plant
ro
o
        * Same as specified for the ceramic diffusers in Table 2.

-------
4.3  Test Results

     (1)   Power consumption
               The evaluated devices were compared in terms of power
          consumption per m^ of effluent or kg of 6005 removed.
          Performance of each device is summarized in Table 6.
                    Table 6  Summary of power consumption

Power consumption per m
of effluent (kwh/m3)
Power reduction xatio, %
Power consumption per kg
of BODj removed (kwh/kg)
Power reduction ratio, %
Bayer injector
Tested
facility
0.0729
facility
0.0973
25.1
0.703
0.949
26.0
Hanshin aquarator
facility
0.0732
facility
0.1045
29.9
1.19
1.66
28.3
Jet aerator
facility
0.0653
facility
0.0994
34.4
1.002
1.474
32.0
Plain plate diffuser
Tested
facility
0.0694
Control
facility
0.1098
36.8
0.889
1.422
37.5
Dome diffuser
Tested
facility
0.068
Control
facility
0.098
30.6
0.82
1.25
34.4
               The power consumption per m^ of effluent was 0*065 to
          0.073 kWh for the tested devices as against 0.097 to 0.11 kWh for
          the conventional devices, indicating to achieve 20% power
          reduction.  On the other hand, the power consumption per kg of
          BOD5 removed was 0.7 to 1.2 kWh for the tested devices as against
          0.95 to 1.66 kWh for the conventional devices, also achieving the
          20% power reduction.

     (2)  Oxygen transfer efficiency

               As tested devices were operated by a lower air flow rate than
          for the conventional devices, it was difficult to make direct
          comparison between these in terms of oxygen transfer efficiency.
          Table 7 shows relationship between oxygen transfer efficiency and
          air supply rate  (amount of air supplied into a unit volume of
          aeration  tank per hour).
           Table 7  Air supply rate vs. oxygen transfer efficiency

Air supply rate (m /m .h)
Oxygen transfer
efficiency («>
Bayer injector
Tested
facility
0.436
20.5
Control
facility
0.656
8.9
Hanshin aquarator
Tested
facility
0.229
21.1
Control
facility
0.775
6.7
Jet aerator
Tested
facility
0.35
27.0
	
Control
facility
1.11
10.7
Plain plate diffuser
Tested
facility
0.69
10.2
Control
facility
1.12
5.5
Dome diffuser
Tested
facility
0.51
23.3
Control
facility
1.05
10.4
               Air supply rates for  the  tested devices were  30  to  66%  of  that
           for  the conventional device.   Every new device was proved to have
           more than  twice as high an oxygen  transfer  efficiency as the
                                      208

-------
          conventional ones.   However, as they require a power-consuming
          device other than  blower or have a high  air flow resistance,  the
          overall power reduction was not as high  as the rate expressed by
          oxygen transfer  rate,  which was indicated in Table 6 listed earlier,

     (3)   Mixing performance  in  the aeration tank

               Degree of mixing  was studied by the measurement of  the
          distribution of  MLSS in the tank.  The results of survey are  as
          shown in Figs. 3 through 7.  As shown  in these figures,  every
          device seems to  have a sufficient mixing capability.
         Running conditions

         Blower capacity:   175 Nm3/hr
         Drive water flow:   39 m /hr

         Air supply rate:  0.7 m /m ,h
(Unit:  mg/l)
Final
settling
tank
B0()




, 2800 .

kA d
)E (

„ 2800 .

5B ^
5F (

, 2800 r
Raw
sewage
\
kc c
SG (

fioq

D
)»



o
o
in
o
o
0
CN
8
in
,-t
                      Return sludge

            Measuring points
"~\^^ Water
^--Jepth
Measur-^^f
ing point ^^~\.
A
B
C
D
E
F
G
H
0.5 m
1770
-
-
-
-
1800
1800
-
2.5 m
1770
1770
1735
1700
1770
1870
1720
1735
4.5 ro
1690
-
-
-
-
1800
1740
-
          Fig. 3  Distribution of MLSS  in  the aeration tank during
                  operation of Bayer  Injector
                                       209

-------
                           Running conditions
    Inflow
                                  Air supply rate: 0.23 ma /m1 .h
1
*
0
o
lo
o
2°
o
o
3°
6
O
O
o
5
0
O
o
4
0°
o
o
o
°7
o
8o°
o
o
0Q
2
->• Outflow

Measur-
ing
point
1
2
3
4
5
6
7
8
9
Average
MLSS
Upstream
1,520 mg/e.
1,370
1,370
1,240
1,140
1,060
1,090
1,050
1,110
] ,216
Down bt roam
1,540 mg/S.
1,330
1 ,340
1,180
1,160
1,090
1,030
1,100
1,100
1,207

     Measuring point

Fig.  4  Distribution  of MLSS  in the  aeration tank  during
         operation of  Hanshin  Aquarator
                                     Running conditions

                                         Air supply rate:  C.39 mVm'.h
\











r



L






\

S43
663




671








I


646
648
i



.669



641


653
652




660



669 j


663
674




694



660 690

	 ^l










. y







Max. 694 mg/5.

Min. 643 mg/i
Standard
deviation: 15.4 mq/i


    Cross-sectional view of aeration tank
Fig.  5  Distribution of MLSS in  the aeration tank during
         operation of Jet  Aerator
                               210

-------
                       Baffle
Outflow i
          52m
                    32m    20m   Urn   I)
o
-

O 0
                                          Inflow
     Measuring points in the bulk flow direct Jon
1
l.ficn
^_ \ 	
J.5m ].!jrn

1.5m
                                               MeasutJnq points on
                                               t he cross section
\
1
2
3
4
5
A
1570
1630
1680
1580
1580
B
1620
1650
1650
J660
1660
C
1710
1590
1740
1660
1610
D
1640
1580
1640
1540
1520
  Fig.  6   Distribution  of MLSS in  the aeration  tank
            during operation of plate diffuser
                             211

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-1st staqe -


<

•
,2-1 2-2 .
- 2nd stage ~
•2-3 2-4*
.3-1 3-2.
-3rd stage -
•3-3 3-4 •
.4-1 4-2.
~4th staqe "


                                                           Outflow
      Dome diffuser

      location
ro
t—»
r>o
                             Sampling position
MLSS distribution measuring conditions

1st
stage
2nd
stage
3rd
stage
4th
stage
Total
Air flow rate
(NmVhr)
138
110
88
64
400
Aeration rate
(Nm'/hr.m3)
0.31
0.25
0.20
0.15
^-""^
^^^^ Sampling
SampT::^^--^depth
ing position ^^
1st
stage
2nd
stage
3rd
stage
4th
stage
1-1
1-2
1-3
1-4
Average
2-1
2-2
2-3
2-4
Average
3-1
3-2
3-3
3-4
Average
4-1
4-2
4-3
4-4
Average
Surface
1,802
1,900
1,914
1,874
1,873
1,892
1,854
1,932
1,854
1,883
1,812
2,008
1,806
1,876
1,876
1,886
1,928
1,796
1,910
1,880
1 m
1,948
1,826 ,
1,824
1,880
1,870
1,926
1,874
1,886
1,854
1,885
1,830
1,920
1,766
1,840
1,839
1,910
1,852
1,888
1,906
1,889
2 m
1,816
1,900
1,900
1,900
1,879
1,904
1,926
1,882
1,876
1,897
1,848
1,928
1,806
1,886
1,867
1,924
1,868
1,850
1,926
1,892
3 m
1,850
1,824
1,860
1,824
1,840
1,934
1,926
1,850
1,836
1,887
1,876
2,008
1,818
1,934
1,909
1,870
1,906
1,840
1,914
1,883
4 m
1,848
1,912
1,908
1,876
1,886
1,894
1,942
1,928
1,896
1,915
1,858
1,938
1,794
1,866
1,864
1,894
1,896
1,880
1,914
1,896
Average
1,853
1,872
1,881
1,871
1,870
1,910
1,904
1,896
1,863
1,893
1,845
1,960
1,798
1,880
1,871
1,897
1,890
1,851
1,914
1,888
                                                                     Note:  Average MLSS in the aeration tank:  1,881 mg/Jl
                              Figure  7.   Distribution  of  MLSS in  the aeration  tank

-------
     (4)   Effluent quality

               There was little difference in the removal efficiency between
          two facilities one with new diffusers, the other with conventional
          devices as far as effluent quality was concerned.  No significant
          difference was also noticed in the settleability of activated
          sludge between them.

4.4  Conclusion

          Prom the results of above mentioned field tests, five devices
     tested were approved by the committee to satisfy these qualifications
     mentioned earlier.
5.   TAP WATER TEST

          To verify performance of the aeration devices, particular types of
     devices were tested using tap water.  Those tested were the conventional
     type plate diffuser (maximum pore size 400 °), jet aerator, and
     Hanshin-Aquarator.  The experiments were done to manifest oxygen
     transfer efficiency for two kinds:  Tap water only and tap water with
     added surfactant.

5.1  Experimental Equipment and Method

          The experimental aeration tank at the Public Waters Research
     institute was used for the experiment (see Fig. 8).  The capacity of the
     tank is 200 m3, and the depth of the water is 5.5 m.  The sides and
     bottom of the tank are made of glass, which allows visual observation
     through the glass.
                                     213

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«-




Sliding 	 ^
base
Movable
platform
	 2000 -




1

— *


i 	 1
i i
i i
i i
i i
i 	 i

• 	 2000 	 »

*




« 	 2000 	 p.



c
c
^





3
3
3



           O




           500
Fig. 8  Outline of the experimental tank
                   214

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               Table 8  Amount of chemical additions
Sodium sulfite (Anhyd.)
Sodium sulfite (Anhyd.)
Cobalt chloride
Surfactant
5 mg/a as MBAS
100 mg/£
0.5 mg-Co/£
5 mg/£ as MBAS
     Sodium sulfite as oxygen remover, cobalt chloride as catalyzer, and
detergent  (sold on the market) as surfactant were added to tap water for
the experiment.  Table 8 shows the amount of each that was added.  The
experiment was performed to measure dissolved oxygen  (DO) within the
tank (continuous measurement by DO sensor), air flow rate, air pressure,
air temperature, and water temperature using a non-steady state method.
As for the jet aerator, injected water flow and injected water pressure
were measured to estimate the motive power required for water
circulation.  Concerning the Hanshin-Aquarator, the motive power
consumed by the mixing motor was directly measured,  photo. 1 shows a
view of the tap water test.  Table 9 describes specification of the
device used for the experiment.
                  Photo.  1  View of  tap water  test
     From continuous records of DO, the overall oxygen transfer
coefficient (Kla) was obtained.  Calculation was done using the observed
DO saturation method.
     Conditions which bring out oxygenation capacity (OC) of 20, 40, 80,
and 100 mg/O2/^«h were obtained in a preparatory experiment.  The
experiment was done under each condition obtained in the preparatory
experiment.
                                 215

-------
                                   Table 9
Plate dlffuser
Jet aerator
Hanshin-aquarator
Maximum pore sise) 400 M
Permeability (dcy air condition) r 3,000 cc/min. on2
Area rate ol diffusers; ot
Depth of plat«; 4.5 m, spiral Clow type
Diameter of liquid nozzle; 28 nun
Diameter of air-liquid nozzle) 50 mm, 7 nozzles
Depth of plate; 4.5 m, spiral flow type
Diameter; 1.15 m
Draft tube height; 0.65 m
Weight; 575 kg
Number of installations) 1 unit (installed at the
center)
          Kla is converted to 20°C using the expression (1)  below.

          Kla (20)  » Kla (T)  x 1.024
-------
       30-
       20-
       10.
       0
                                            O =   Plate diffus
                                            a
               Jet aerator

               Hanshin-Aquarator


                Tap water test

                     th surfactant added
              o-
                 	O—•
                   20
                                                 80
                                                            100
                                                                      120
                             40         60

                           Oxygen supply capacity (

Fig.  9  Comparison of oxygen transfer  rates among aeration devices
     Fig.  10 shows the comparison of power efficiencies.  The tap water
test with  the three methods mentioned  above shows hardly any difference
in efficiencies.   When surfactant is added, however, the performance  of
the jet  aerator and that of the Hanshin-Aquarator exceed that of the
conventional type plate diffuser.
       6-
     n 2-
     
-------
5.3  Conclusion

          Fig.  9 and Fig.  10 show that the aeration devices employing forced
     mixing by external force such as the jet aerator and Hanshin-Aquarator
     have high oxygen transfer rates and almost the same power efficiencies
     as conventional type plate diffusers in the experiment using tap water.
     When surfactant is added, however, the oxygen supply capacity of either
     of them does not deteriorate, or it deteriorates by a smaller rate
     compared to deterioration with the conventional type plate diffuser.  As
     a result,  the jet aerator and Hanshin-Aquarator are advantageous in
     comparison to the conventional type plate diffuser.  Such
     characteristics are also found in mechanical aeration devices employing
     surface mixing.  Accordingly, it can be said that the main effect of the
     jet aerator and/or Hanshin-Aquarator is the oxygen transfer function
     such as surface film renewal.
6.   PERFORMANCE AT THE ACTUAL PLANTS

          Those tested aeration devices have been applied practically to
     twenty-eight (28) publicly owned wastewater treatment plants.  Newly
     established treatment plants tend to adopt these aeration devices.
     Table 10 lists typical treatment plants employing each device.
              Table 10  Examples of operating aeration devices
Device name
Jet Aerator
Hanshln
Aquarator
Bayer Injector
Full-surface
Aeration by
Plate Diffuser
Dome Diffuser
Installation
Hirano Treatment
Plant, Osaka-city
Nakahama Treatment
Plant, Osaka-city
Kawanakaj ima Treatment
Plant, Mobara-city
Central Treatment
Plant, Hamamatsu-city
Central Treatment
Plant, Nagasaki-city
Treating
capacity
(m3/day)
29,600
53,000
12,000
246,000
50,000
Starting
date of
operation
March,
1983
November
1978
April,
1982
February
1981
June, 1981
Energy saving effects
Power efficiency in the
aeration tank is
2.5 kg-02/kWh.
Power consumption per
1 m of treating water
is 0.084 kWh/m3.
Results indicate! by
technical evaluation.
Power consumption was
cut by 20%.
Results indicated in
technical evaluation.
Oxygen transfer rate in
the aeration tank was
increased by 56%.
Power consumption was
cut by 20%.
Remarks
Other treatment plants
employing the jet aera-
tor have been operating
without problems since
1975.
Often used as a
denitrif ication mixer.
Clogging of the nozzle
can be avoided by
cleaning the circulat-
ing water strainer once
a week.

Slime is generated
partially on the sur-
face of the diff user.
          Photo.  2 shows the jet aerator setting.   Jet aerators are mostly
     set in a deep aeration tank (about 10 m deep).  During the operating
     period of a jet aerator of eight years, no maintenance has been
                                     218

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 performed on the aeration device itself.
      Photo. 3 shows the Hanshin-Aquarator setting and Photo. 4 the
 operating aeration tank.  This device is easy to install because the air
 pipe and frame are of unitary design.  This allows installation  (with
 the help of a wrecker) even while the tank is running.  Employment of a
 draft tube enables setting the aquarator in a deep aeration tank.  These
 days the number of treatment plants that employ biological nitrification
 and denitrification are increasing, and Hanshin-Aquarators are being
 adopted for them.  This is because the Hanshin-Aquarator can be
 effectively utilized as a mixer.
      Photo. 5 shows an example of the Bayer injector.  At this treatment
 plant, this device is used for denitrification.  The device has a small
 diameter nozzle with a simple strainer.  The strainer needs to be
 cleaned once about a week.  No other operations are required for
 maintenance.
      Photo. 6 shows the setting of the full-surface aeration process by
 the conventional type plate diffuser.  This method has been operating
 without any problems since it was set up in 1981.
      Photo. 7 indicates the setting of the dome diffuser.  Not only in
 the dome diffuser but also in the conventional type plate diffuser and
 tube diffuser, the surface of the plate or tube becomes covered with
 sludge when used in a mixture of activated sludge.  It has not been
 clarified to what extent the oxygen supply capacity is deteriorated
 under such conditions.
Photo. 2  Jet aerator setting
Photo. 3  Hanshin aerator setting
                                  219

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                                  r
Photo. 4  Aeration tank with Hanshin
          aerator
Photo. 5  Bayer aerator setting
Photo. 6  Plate diffusers of full
          surface setting
Photo. 7  Dome diffuser setting
REFERENCE

1)  "Design Guidance for Sewer and Wastewater Treatment Plants" (in Japanese),
    Japan Sewage Works Association, 1981

2)  "Reflection on Seven Decades of Activated Sludge History" by Alleman,
    prakasam, JWPCP, Vol. 55, 1983 May

3)  "Asahi Nenkan (Yearbook)" (in Japanese), by Asahi Shinbunsha, 1982

4)  "Statistics of Sewages"  (in Japanese), by Japan Sewage Works Association,
    1982
                                     220

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5)  "Annual Research Report, 1977", P.163, by Public Works Research Institute,
    the Ministry of Construction

6)  "Construction Technology Assessment System and Development of Mechanical
    Aerators for the Oxidation Ditch Process", by I. Nakamoto, Ninth US/Japan
    Conference on Sewage Treatment Technology, USEPA, 1983

7)  "Effect of Water Temperature on Stream Reaeration", by Pro. ASCE SAD,
    P.59, 1961 Nov.
                                      221

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                             Tenth United States/Japan  Conference
                                on'Sewage Treatment  Technology
              FULL SCALE EVALUATION
                         OF
BIOLOGICAL PHOSPHORUS AND NITROGEN REMOVAL
        The work described in this  paper was
        not funded by the U.S. Environmental
        Protection Agency.  The contents do
        not necessarily reflect the views of
        the Agency and no official  endorsement
        should be inferred.
                      K. Tanaka,
                 Senior Research Engineer
                       T. Ishida,
                   Research Engineer
                     T. Murakami,
                   Research Engineer
        Research and Technology Development Division
               Japan Sewage Works Agency

                         223

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                              TABLE OF CONTENTS


                                                                          Page
     FULL-SCALE EVALUATION OF BIOLOGICAL PHOSPHORUS AND NITROGEN REMOVAL

1.   INTRODUCTION	   225
2.   DEVELOPMENT OF ADVANCED TREATMENT TECHNOLOGIES IN JAPAN, AND
     ITS BACKGROUND 	   226
3.   IMPLEMENTATION EXAMPLES OF BIOLOGICAL ADVANCED WASTEWATER
     TREATMENT PROCESSES 	   227
 3.1   Introduction 	   227
 3.2   implementation Examples 	   228
4.   RECENT TRENDS IN RESEARCH AND DEVELOPMENT	   250
 4.1   Introduction 	   250
 4.2   Step Inflow Biological Nitrogen and phosphorus
       Removal Process 	   250
 4.3   Improvement of Nitrification Rate by Pelletization
       of Microbes	   259
                                     224

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     FULL-SCALE EVALUATION OF BIOLOGICAL  PHOSPHORUS AND NITROGEN REMOVAL
1.   INTRODUCTION

          In Japan, eutrophication of  lakes  or  coastal seas has been known
     for long.  But it was not  until 1979 that  the first definite step
     against it was taken.
          In 1979, the Environment Agency set up guidelines for the reduction
     of phosphorus discharge  into the  Seto Inland Sea.  Then, effluent
     standards concerning nitrogen and phosphorus for the Lake Biwa and the
     Lake Kasumigaura were formulated  by the corresponding prefectural
     governments to administer  water quality control with a full commitment.
          Later, in December  1982, the Environment Agency promulgated
     environmental standards  concerning nitrogen and phosphorus in lakes.
         Table  1  Environmental water quality standards on nitrogen
                  and  phosphorus in lakes and reservoirs
Category
I
II
III
IV
V
purpose of water use
Conservation of natural environment, and uses
listed in II-V
Water supply classes 1, 1 and 3 (excluding
special types); Fishery type 1, bathing; and
uses listed in III-v
Water supply class 3 (special types) , and uses
listed in IV-V
Fishery type 2, and uses listed in V
Fishery type 3; industrial water; agricultural
water; conservation of the living environment
Standard values
Total
nitrogen
0.1 rng/H
or less
0.2 rag/*
or less
0.4 mg/je
or less
0.6 mg/je
or less
1 mg/je
or less
Total
phosphorus
0.005 mg/t
or less
0.01 mg/jj
or less
0.03 mg/X
or less
0.05 mg/£
or less
0.1 mg/£
or less
              Notes: 1. The standards are measured in terms of annual averages.
                   2. The standards for total phosphorus are not applicable to
                      agricultural water uses.
          At present, the designation of  lakes  to the categories of the
     environmental standards are being formulated by the hand of the Central
     Council for Control of Environmental Pollution.
          In addition, the Law concerning Special Measures for Conservation
     of Lake Water Quality was put  into effect  in March 1985.
          According to this new law, which is based on the Water Pollution
     Control Law, it is provided for that such  lakes that need special
     regulations and overall control measures on  account of serious water
     pollution be designated, and that water quality preservation plans be
     formulated for such designated lakes in order to:  (1)  control the
     pollution loadings from new or expanded sources, (2)  control effluents
     from designated sources, (3) and control the equipment and its use at
     specified and constructive specified sources.
                                      225

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          Of the lakes to be designated,  about 40 will  have both nitrogen and
     phosphorus discharge regulation,  and for  about  1,000  phosphorus
     discharges will be limited.
          Pursuant to the amendment  of the Ordinance for the Enforcement  of
     the Water pollution Control  Law,  nitrogen and phosphorus  effluent
     standards for facilities discharging 50 mV<3ay  or  more will be put
     into effect in mid-July, 1985,  to limit total nitrogen to less than
     120 mg/£.  (daily average,  60 mg/£)  and total phosphorus, to less than
     16 mg/£ (daily average, 8 mg/£).
          Backed by these recent  legislative measures,  the administration for
     water quality preservation  has  made  a major  step toward the prevention
     of not only organic pollution but also eutrophication.
2.   DEVELOPMENT OP ADVANCED TREATMENT TECHNOLOGIES IN JAPAN,  AND ITS
     BACKGROUND

          In 1972,  the Public Works  Research  Institute of  the  Ministry of
     Construction installed a 250 nr/day pilot plant in the Shitamachi
     Wastewater Treatment Plant,  Yokosuka,  in order to start the  research  on
     the phosphorus removal of  the secondary  effluent by the
     coagulation precipitation  process,  marking the first  step in the
     development of advanced treatment technologies in Japan.   To follow
     suit,  the Japan Sewage Works Agency, and major cities including  Sapporo,
     Tokyo, Yokohama, Yokosuka, Kawasaki, Osaka,  Kyoto, Kobe,  Kita-Kyushu
     Fukuoka launched their research and development projects  for advanced
     treatment technologies.
          These R & D efforts were concentrated on  physicochemical processes
     as represented by filtration, coagulation/precipitation,  break-point
     chlorination,  adsorption of  ammonia by zeolite,  and ammonia  stripping.
          The achievements of these  projects  have been presented  at the
     Inter-Government Cooperation Conference  on the Advanced Wastewater
     Treatment Technology sponsored  by the  Ministry of Construction for
     lively discussions and information  exchange.   The information about the
     advanced wastewater treatment technology from  the United  states
     contributed greatly to technology development  in this field  in Japan,
     particulary the information  brought through the US/Japan  conference on
     Sewage Treatment Technology, which  started in  1971.
          With the outbreak of  Oil Crisis in  mid-1971 as a turning point,
     saving energy and resources  has become a social imperative,  and  has
     become even more important at energy-guzzling  wastewater  treatment
     plants.
          japan's R & D efforts for  advanced  wastewater treatment technology
     have naturally been shifted  away from  energy and resource intensive
     physicochemical processes  toward the implementation of biological
     nitrogen and phosphorus removal processes.
          The Public Works Research  Institute of the Ministry  of  Construction
     has achieved substantive results in the  field  study of single-stage
     nitrified liquor recycled  nitrogen  removal process, development  of a
     nitrogen and phosphorus removal process  in which the  nitrified liquor
     recycled nitrogen removal  process and  simultaneous coagulation process
     are combined,  and in many  other R & D  projects.


                                      226

-------
          The Japan Sewage Works Agency has completed a demonstration test of
     nitrified liquor recycled nitrogen removal process after pilot plant
     study, and is currently pushing forward a field test on an
     anaerobic-aerobic process for simultaneous removal of nitrogen and
     phosphorus.
          In recent years, interest has been growing in the development of
     biological technologies for removal of nutrients, and pilot plant study
     or full-scale field investigations are under way by many municipalities,
     including Ibaraki, Nagano, Tokyo, Kawasaki, Yokosuka, Nagoya, Fukuoka
     and Kyoto.  The research and development in this field has also been
     promoted vigorously by private research institutions.
          Triggered by the enforcement of effluent standards for lakes and by
     the needs of times for the saving of energy and resources, the
     development and implementation of advanced wastewater treatment
     technology in Japan have been pushed forward with emphasis on biological
     processes.
          For example, the improvement of the performance of biological
     secondary treatment process and simple modification of the existing
     secondary treatment system are actively pursued.
3.   IMPLEMENTATION EXAMPLES OF BIOLOGICAL ADVANCED WASTEWATER TREATMENT
     PROCESSES

3.1  Introduction

          In Ibaraki and Shiga Prefectures, the regulations for the control
     of eutrophication are enforced to protect the water environment of Lake
     Kasumigaura and Lake Biwa, respectively,  and nitrogen and phosphorus
     removal are carried out at the wastewater treatment plants discharging
     effluents into these lakes.
          As regards nitrogen removal, the single-stage nitrified liquor
     recycled nitrogen removal process is implemented at the wastewater
     treatment plants located within the catchment areas of the lakes.
          In the small-scale wastewater treatment plants, the endogenous
     denitrification process is employed when  a long retention time in  the
     reactor can be assured.  As regards phosphorus removal, the simultaneous
     precipitation  process using alum, poly-aluminum-chloride or other
     metallic salt  as a coagulant in the aeration tank is employed as a
     practical answer.   However, Phosphorus removal by chemical coagulation
     has drawbacks  including high chemical cost and additional production of
     sludge.  As a  viable alternative, biological phosphorus removal
     processes have been the focus of research and development in recent
     years.
          The most  stringent effluent standards are enforced in Shiga and
     Ibaraki, where the T-P concentration in the effluent from sewage
     treatment plant is limited to less than 0.5 mg/S,.  This value is
     considered a target to be achieved by the biological phosphorus removal
     processes.
          Table 2 shows wastewater treatment plants where advanced treatment
     for nitrogen and phosphorus removal was already in practice as of  the
     end of  FY 1984.   Their tooling and performance will be discussed in
                                     227

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3.2.  The biological phosphorus removal processes are still in the stage
of field experimentation by the Public Works Research Institute
(Hamamatsu, Kyoto), the Japan Sewage Works Agency (Saitama, Shiga,
Itako), Kawasaki Municipal Government and Fukuoka Municipal Government.
     In Japan raw sewage is generally weak; the total phosphorus
concentration of the effluent of PS usually is in the range of 2 to
6 mg/Ji.
     The phosphorus load of domestic wastewater is taken as
1.8 g-P/capita/day.  Assuming that the basic domestic wastewater flow is
300 A/capita/day, the T-P concentration in domestic wastewater is
calculated at 6 mg/Z.
     What posed a serious problem in the experimentation was the
influence of rainfalls on the wastewater treatment conditions.  In
Japan, the Baiu front and typhoons bring heavy rainfalls in summer.
Stormwater dilutes the concentration of substrate represented by BOD,
etc., while increasing the concentrations of DO and nitrate nitrogen.
This  is highly detrimental for keeping anaerobic condition in the
anaerobic compartment.  The role of the anaerobic zone is to feed
readily biodegradable substances such as acetic acid to the phosphorus
accumulating bacteria through acid fermentation and to help the
phosphorus accumulating bacteria to preempt such substances.  If
Stormwater destroys the anaerobic condition, acid fermentation is
impaired, and the phosphorus removal performance is degraded.
     The biological phosphorus removal process can reduce the phosphorus
concentration in the secondary effluent (effluent from the secondary
settling tank) to less than 0.1 mg/Ji in orthophosphate and less than
0.3 mg/Z in T-P if the biological phosphorus removal reaction is
perfectly controlled by the injection of methanol or by other means.  It
is generally recognized that, for the ordinary municipal wastewater, the
T-P concentration in the secondary effluent can be reduced below 0.5 or
1 mg/l.
Table 2  Wastewater treatment plants practicing advanced treatment
         for nitrogen  and phosphorus removal
Receiving
waters
Kasumigaura

Lake Ilamana

Lake Blwa


Name of wastewater
treatment plant
Kasumigaura Sewage
Treatment plant
Itako Sewage
Treatment Plant
Hltomlgaoka Sewage
Treatment Plant
Kotoh Sewage
Treatment Plant
Konan Chubu Sewage
Treatment plant
Oklnoshlma Sewage
Treatment Plant
Kosel Sewage
Treatment plant
Design
capacity
(mVday)
55,400
4,200
1,620
1,980
14,000
210
5,000
process
Recycled process, simultaneous
precipitation process
Recycled process + simultaneous
precipitation process, modified
Phoredox process
Biological phosphorus removal
process + Wuhrmann process

Recycled process + simltaneous
precipitation process, modified
Phoredox process
Sequential oxidation ditch process
+ simultaneous precipitation
process
Bardenpho process + simultaneous
precipitation process
                                 228

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3.2  Implementation Examples

     (1)   Hitomigaoka Sewage Treatment Plant and Kotoh Sewage Treatment Plant
          (Lake Hamana)

               Both the Hitomigaoka and Kotoh Sewage Treatment Plants stand
          on Lake Hamana.
               The final effluent from the Hitomigaoka and Koto Sewage
          Treatment Plants must satisfy the strict water quality standard
          shown in Table 3 in order to prevent the pollution and
          eutrophication of Shonai Bay and Lake Hamana.  Both plants have
          advanced treatment facilities such as nitrification,
          denitrification and coagulating sedimentation equipment,  rapid
          filters, and activated carbon absorption towers, in addition to
          secondary treatment facilities.  To cut down the operational and
          maintenance costs, both plants are also equipped with extended
          aeration tanks designed to provide a longer retention time for the
          energy- and resources-saving type biological
          nitrification-denitrification using the endogenous denitrification
          reaction, as well as for the phosphorus removing process.
                     Table 3  Water quality standard in
                              Shonai Bay and Lake Hamana
               Fig. 1 shows the process flow diagrams,  (a)  is the flow sheet
          for the non-circulating type treatment process newly developed on
          the basis of the recent discovery that when nitrogen is removed
          efficiently by the endogenous denitrification reaction, the
          phosphorus release takes place in the second stage of the oxic
          section and its uptake phenomenon is observed in the aerobic
          section,  (b)  is the flow sheet for the anaerobic-aerobic
          non-circulating treatment process developed to improve the
          phosphorus removal rate by accelerating its release in the presence
          of organic subtances in the influent wastewater.  This process is
          also based on the endogenous denitrification reaction.
               Table 4 shows the wastewater treatment results of these two
          processes.  The greatest misgiving concerning these processes was
          in the possible decline in the nitrogen removal rate due to the
          endogenous denitrification.
                                     229

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      (a)





ftO

RS
"ft




\
/-
      (b)



AA



0


AO
RS


0

— ^
          A^: Ar.aer'jbic section
          AQ: Anoxi<- n^ction
          O : Aerobic section
          3 : Settling tank
          Rg: Rpturn sludge
Fig. 1  Flow diagram of Hitomigaoka and Kotoh sewage  treatment  plant
          The phosphorus  removal  rate  is  notably  different for these two
     processes.  For  flow sheet  (a), the  removal  rate is not as high as
     shown in Table 4 for two  reasons:  the  phosphorus-releasing
     anaerobic Section  is installed after the BOD oxidation and
     denitrification processes, which makes it difficult to maintain the
     anaerobic state  if the denitrification performance in the preceding
     line is poor, and  the quantity of  organic substances is not
     sufficient  to accelerate  the phosphorus release.  For flow sheet
     (b), the anaerobic section  is installed at the influent inlet,
     which makes it possible to attain  a  high removal rate of about 90%.
          From the experience  gained at these plants, the endogenous
     denitrification  method can be evaluated as a highly useful process
     of  simultaneous  nitrogen  and phosphorus removal, if the retention
     time in  the aeration tank can be  sufficiently extended.

 (2)  AraKawa  Sewage Treatment  Plant  (Saitama Pref.)

          The Arakawa Sewage Treatment Plant is located on the left
     basin of the Arakawa River which  divides Tokyo and Saitama from
     each other.  Its planned  design daily  maximum flow is
     1,380,000 m^.  At  present,  the facilities with a treatment
     capacity of 356,000  m^/day have been completed.  The served area
     is  to be convered  mostly  with a separate sewer system.  For the
     area where  sewers  have already been installed, however, the
     combined and separate sewer  systems divide almost equally.
          The wastewater  treatment is  carried out according to the
     conventional activated sludge process.
          The sludge  treatment flow is  as follows.
           Sludge  thickening tanks
           Centrifugal  thickeners
Filter presses
Vacuum filters
Multiple hearth
furnaces
          Using one  train  of  the Plant,  the Japan Sewage Works Agency
     conducted an  experiment  with the nitrified liquor recycled
     nitrification denitrification process during the 1980 - 81 period
     and with the  biological  phosphorus  removal process and biological
     nitrogen and  phosphorus  removal process during the 1982 - 83 period.
                                 230

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       Table 4  Wastewater  treatment results by Hitomigaoka  and Kotoh sewage  treatment plant, Hamamatsu City
Processes
(a)
(b)
Operating conditions

-------
     The Arakawa Sewage Treatment Plant is the first plant in Japan
that has implemented these processes.
     Table 5 shows design factors of the experiment facilities.
When operated as a conventional activated sludge process, the
experiment facilities have a daily maximum design flow capacity of
17,600 m3/day.
     Table 5  Design factors of the experiment train

primary
settling tank
Aeration tank
Secondary
settling tank
Width
(m)
4.3
9.0
4.3
Length
(m)
50.0
85.0
56.0
Effective
water depth
(m)
4.0
5.0
4.45
Number
of tanks
2
1
2
Volume

-------
effluent
of PS
                                                  where,
                                                  A =  anaerobic zone
                                                  O =  aerobic zone
                                                  PS = primary sedi-
                                                      mentation tank
                                                  FS = final sedimen-
                                                      tation tank
                   (a)   Operation mode I
                     ML
etriuent 	
of PS




,
A

1
r
DN


0


0





RS


FS
^^
ML =
DN -
                                      ML = mixed liquor circulation
                                      DN = denltrification zone
                   (b)   Operation mode II
                      ML
eiriuent 	
of PS









" ft

A


DN

O

°
-------
                          Table 6   Operation  conditions
Operation
mode
I



II







III



RUN

F-l
F-2
F-3
F-4
F-5
F-6
F-7
F-8
F-9
F-10
F-ll
F-12
F-13

F-14

Period

•82 6/7 - 6/28
6/29 - 7/14
7/15 - 7/30
'83 1/24 - 2/9
'82 8/27 - 10/25
11/8 - 11/24
11/25 - 1/19
'83 6/22 - 7/8
7/13 - 8/12
•84 1/25 - 3/5
3/9 - 3/23
3/26 - 4/13
'83 8/19 - 10/7

11/2 - 12/14

Qin
(m3/day)
22,600
25,300
16,900
18,400
13,900
15,700
12,600
12,700
12,800
9,100
10,200
10,300
17,200

12,500

r

0.15
0.17
0.14
0.16
0.18
0.20
0.22
0.19
0.19
0.36
0.27
0.34
0.14

0.19

R

-
-
-
-
0.59
0.50
0.68
0.64
0.64
1.25
0.51
0.90
0.48

0.65

T

4.1
3.6
5.4
5.0
6.6
5.8
7.3
7.2
7.2
10.1
9.0
8.9
5.3

7.3

MLSS

2,040
2,330
1,940
2,540
1,970
3,740
4,050
3,670
2,720
3,020
2,760
2,530
2,360
(3,400)
2,660
(3,460)
VSS

72.1
74.4
72.7
76.1
68.7
71.1
72.3
68.4
67.3
78.7
77.5
76.9
72.1

76.0

SVI

76
72
74
82
81
98
92
126
85
223
157
147
90

138

t

21.6
22.1
22.8
14.4
22.4
19.2
16.2
21.4
24.4
12.3
13.3
14.9
23.5

17.6

          Where, T - Nominal retention time of reaction  tank (h)
                VSS - Organic content of MLSS (%)
                SVI - Sludge volume index after 30 minutes (mjt/g)
                and the value of ( ) is MLSS concentration of anaerobic tank
                t - Water  temperature (*C)
               The performance of each  run  is shown in  Tables  7  through  9.
              Table 7   Summary of  operation mode  I performance
                                                                                      (Unit: mg/jj)

Temperature
("0
T-P
Soluble PO -P
T-N
imJ-N
BOD
Soluble BOD
SS
M- Alkalinity
P/MLSS (%)
F-l
Influent
21.6
(20.5 - 22.1)
3.43
(1.75 - 4.8)
1.57
(0.83 - 2.58)
21.6
(14.5 - 26.8)
15.0
(10.0 - 17.2)
87
(53 - 113)
30.6
(14.6 - 47.5)
71
(40 - 120)
127
(102 - 144)
Effluent
-
0.44
(0.14 - 0.94)
0.30
(0.05 - 0.70)
13.2
(9.9 - 16.1)
5.5
(3.7 - 8.0)
6.0
(4.1 - 7.5)
1.6
(0.8 - 4.3)
4.5
(1.8 - 11.4)
72
(58 - 90)
4.09
(3.69 - 4.49)
F-2
Influent
22.1
(21.2 - 23.3)
4.78
(2.28 - 10.3)
2.05
(0.92 - 4.25)
29.1
(17.9 - 43.4)
13.9
(10.7 - 16.7)
106
(72 - 162)
32.9
(19.2 - 45.1)
109
(30 - 260)
139
(115 - 154)
Effluent
-
0.41
(0.14 - 0.85)
0.23
(0.02 - 0.76)
14.6
(12.8 - 16.6)
10.9
(5.4 - 13.0)
5.3
(4.3 - 7.3)
1.0
(0.8 - 1.2)
3.1
(1.5 - 4.6)
125
(103 - 148)
3.91
(3.60 - 4.25)
F-3
Influent
22.8
(21.8 - 23.2)
3.30
(1.58 - 4.13)
1.71
(0.74 - 2.57)
19.5
(17.9 - 20.7)
(4.1 - 12.8)
74
(67 - 79)
24.5
(23.1 - 27.2)
62
(24 - 130)
131
(91 - 146)
Effluent
-
0.80
(0.17 - 1.24)
0.63
(0.05 - 1.06)
11.3
(10.2 - 12.2)
1.4
(1.0 - 2.2)
4.2
(2.1 - 5.0)
4.2
(0.4 - 7.4)
2.0
(0.7 - 3.7)
66
(49 - 95)
3.98
(2.75 - 5.08)
F-4
Influent
14.4
(14.0 - 14.9)
4.16
(3.32 - 5.07)
2.13
(1.78 - 2.43)
31.8
(30.5 - 34.6)
20.8
(19.8 - 22.3)
116
(101 - 131)
57.2
(51.3 - 64.2)
83
(48 - 114)
151
(146 - 156)
Effluent
-
0.80
(0.61 - 1.18)
0.46
(0.27 - 1.0)
20.7
(19.1 - 22.6)
17.4
(14.2 - 20.3)
6.7
(5.8 - 7.5)
3.7
(1.8 - 8.7)
9.2
(4.6 - 13.8)
145
(134 - 153)
3.82
(3.65 - 4.10)
Notes: 1. Upper line shows the average and lower line shows (minimum - maximum)
      2. P/MLSS was measured with the sample taken at the end of nitrification zone.
                                            234

-------
            Table  8  (a)   Summary  of  Operation mode  II  performance
                                                                                          (Onit:

Temperature
CO
T-P
Soluble PO.-P
T-N
unJ-N
NOT-N
BOD
Soluble BOD
SS
M- Alkalinity
P/MLSS (%)
F-5
Influent
22.4
(18.6 - 25.1)
2.16
(1.11 - 4.93)
0.79
(0.33 - 1.59)
16.5
(8.0 - 22.9)
10.0
(3.0 - 14.6)
0.5
(0.0 - 1.9)
60
(28 - 112)
16.1
(6.8 - 35.3)
55
(20 - 144)
123
(58 - 147)
Effluent
-
O.S2
(0.09 - 1.13)
0.37
(0.01 - 0.95)
8.3
(4.8 - 10.7)
0.2
(0.0 - 2.0)
7.2
(3.5 - 9.6)
2.7
(1.4 - 10.3)
0.9
(0.2 - 1.7)
3.5
(0.5 - 19)
66
(37 - 76)
3.52
(2.88 - 4.75)
F-6
Influent
19.2
(19.0 - 19.5)
J.57
(1.85 - 3.67)
0.94
(0.45 - 1.41)
22.1
(16.1 - 29.7)
14.4
(9.6 - 19.6)
0.2
(0.02 - 1.1)
71
(53 - 95)
31.7
(17.5 - 41.9)
60
(36 - 72)
146
(129 - 157)
Effluent
™*
0.19
(0.14 - 0.23)
0.05
(0.03 - 0.07)
10.6
(7.7 - 13.6)
5.6
(0.0 - 10.1)
4.0
(2.3 - 6.9)
4.5
(1.1 - 6.6)
0.9
(0.3 - 1.2)
3.0
(0.3 - 4.4)
101
(62 - 121)
3.62
(3.42 - 3.77)
F-7
Influent
16.2
(14.3 - 17.8)
4.35
(2.50 - 6.71)
2.13
(0.82 - 3.66)
28.1
(17.2 - 34.8)
17.7
(9.5 - 20.9)
0.5
(0.02 - 1.7)
100
(45 - 130)
40.5
(22.1 - 53.0)
W
(42 - MO)
147
(105 - 158)
Effluent
"
0.28
(0.21 - 0.53)
0.11
(0.05 - 0.24)
11.8
(7.8 - 17.1)
4.9
(0.0 - 8.2)
5.6
(3.5 - 7.3)
4.0
(1.6 - 6.4)
0.9
(0.4 - 1.7)
3.7
(0.1 - 13)
93
(72 - 110)
4.04
(3.60 - 4.70)
F-8
Influent
21.4
(19.9 - 22.8)
5.18
(4.20 - 7.50)
2.47
(1.48 - 3.38)
24.1
(17.5 - 31.8)
14.3
(7.2 - 18.3)
0.3
(0.02 - 1.0)
63
(26 - 96)
19.6
(12.7 - 26.7)
61
(26 - 90)
131
(55 - 154)
Effluent
'
1.39
(0.00 - 2.39)
1.01
(0.00 - 1.61)
10.2
(5.9 - 15.5)
0.9
(0.0 - 3.6)
6.7
(4.9 - 9.3)
3.5
(2.2 - 5.4)
1.5
(0.8 - 2.3)
2.3
(0.4 - 5.6)
71
(60 - 86)
4.40
(3.81 - 4.68)
Notes: 1,
      2.
Dpper line shows the average and lower line shows (minimum - maximum)
P/MLSS was measured with the sample taken at the end of nitrification zone.
            Table  8  (b)   Summary  of  Operation mode  II  performance
                                                                                          (Unit: rag/*)
Temperature
CC)
T-P
Soluble PO -P
T-N
NH*-N
1W~-N
BOD
Soluble BOD
SS
M- Alkalinity
P/MLSS (%)
F-9
Influent
24.4
(22.0 - 27.2)
5.07
(3.06 - 9. 45)
2.03
(1.59 - 3.68)
20.3
(15.9 - 24.7)
14.3
(10.9 - 16.6)
0.1
(0.02 - 0.2)
99
(36 - 211)
40.3
(10.7 - 55.2)
56
(26 - 124)
141
(115 - 155)
Effluent
—
1.29
(0.57 - 2.06)
0.65
(0.27 - 1.13)
9.7
(7.8 - 11.0)
0.1
(0.0 - 0.3)
8.5
(6.9 - 9.8)
2.0
(1.5 - 3.1)
1.0
(0.7 - 2.0)
1.3
(0.2 - 3.6)
67
(55 - 75)
4.22
(2.81 - 5.34)
P-10
Influent
12.3
(10.5 - 13.0)
3.02
(1.43 - 3.67)
0.98
(0.71 - 1.32)
29.1
(24.6 - 35.6)
16.5
(12.6 - 20.6)
0.8
(0.09 - 2.1)
118
(86 - 176)
47.5
(29.8 - 66.4)
76
(61 - 122)
143
(127 - 151)
Effluent
-
0.21
(0.09 - 0.39)
0.05
(0.01 - 0.21)
10.8
(7.7 - 13.6)
7.5
(3.7 - 10.9)
1.5
(0.5 - 3.0)
3.8
(1.5 - 6.7)
0.9
(0.4 - 2.0)
3.2
(1.8 - 4.9)
117
(85 - 136)
2.87
(2.35 - 3.33)
F-ll
Influent
13.3
(12.7 - 13.9)
2.95
(1.99 - 3.69)
0.99
(0.76 - 1.36)
33.2
(23.4 - 45.3)
17.2
(13.4 - 20.9)
1.1
(0.3 - 1.9)
133
(105 - 182)
45.9
(28.6 - 65.6)
74
(41 - 102)
140
(123 - 158)
Effluent
*
0.20
(0.11 - 0.27)
0.03
(0.02 - 0.04)
l't.7
(11. S - 17.4)
10.4
(7.0 - 15.0)
1.9
(0.7 - 3.4)
5.6
(2.9 - 8.9)
1.2
(0.6 - 2.3)
3.6
(1.5 - 6.0)
123
(100 - 135)
2.56
(2.39 - 2.86)
P-12
Influent
14.9
(13.8 - 16.0)
2.66
(2.32 - 3.12)
0.83
(0.49 - 0.94)
27.8
(21.5 - 32.6)
17.0
(12.4 - 20.3)
0.4
(0.1 - 0.8)
88
(22 - 114)
44.5
(31.8 - 58.5)
77
(58 - 90)
136
(108 - 149)
Effluent
-
0.16
(0.13 - 0.22)
0.02
(0.01 - 0.03)
11.8
(8.7 - 13.8)
7.8
(2.4 - 10.5)
2.8
(1.7 - 4.4)
5.3
(3.0 - 6.9)
0.7
(0.5 - 0.9)
3.7
(2.6 - 6.0)
115
(93 - 132)
2.50
(2.35 - 2.90)
Notes: 1,
      2,
Upper line shows the average and lower line shows (minimum - maximum)
P/MLSS was measured with the sample taken at the end of nitrification zone.
                                             235

-------
   Table  9   Summary of operation mode ill performance

                                              (Unit:

Temperature
CO
T-P
Soluble PO.-P
T-N
NH*-N
NOT-N
BOD
Soluble BOD
SS
M- Alkalinity
P/MLSS (%)
F-13
Influent
23.5
(19.2 - 26.0)
2.02
(1.09 - 4.07)
0.63
(0.29 - 1.40)
15.7
(6.5 - 21.8)
10.0
(2.9 - 14.9)
0.5
(0.05 - 4.2)
82
(20 - 231)
27.2
(9.2 - 56.9)
42
(14 - 89)
131
(76 - 162)
Effluent
—
0.25
(0.16 - 0.56)
0.10
(0.04 - 0.28)
8.7
(6.4 - 10.4)
1.7
(0.0 - 5.3)
6.1
(3.1 - 9.3)
3.3
(1.5 - 5.4)
1.0
(0.5 - 2.5)
1.8
(0.0 - 3.2)
90
(67 - 115)
3.32
(2.21 - 5.42)
P-14
Influent
17.6
(16.0 - 19.0)
3.08
(1.69 - 4.47)
1.10
(0.65 - 2.08)
26.9
(17.9 - 34.5)
14.1
(5.1 - 21.3)
0.2
(0.09 - 1.3)
103
(66 - 130)
44.3
(22.7 - 62.3)
59
(22 - 79)
136
(103 - 194)
Effluent
-
0.24
(0.10 - 0.71)
0.05
(0.01 - 0.20)
7.9
(5.0 - 10.1)
1.3
(0.0 - 2.9)
5.9
(2.7 - 7.9)
3.7
(1.7 - 6.4)
0.8
(0.5 - 1.5)
1.5
(0.2 - 2.5)
76
(49 - 104)
3.58
(2.46 - 6.69)
        Notes: 1. Upper line shows the average and lower line shows
               (minimum - maximum)
             2. P/MLSS was measured with the sample taken at the end
               of nitrification tanks.
     In Japan, while  the DO concentration and the NOT-N
concentration of  inflow rise under the effect of heavy rainfalls
during the rainy  and  typhoon seasons, the substrate concentration
and the oxygen consumption rate of activated sludge fall  due to an
increase in flow  rate.   As a result, it becomes difficult to
maintain anaerobic  conditions in anaerobic zone.
     F-5 without  step inflow and F-13 with step inflow were
performed almost  in the same period of heavy rainy searson though
in different years, with regard to phosphorus and nitrogen removal
efficiency.  Their  nitrogen removal efficiency is almost  the same,
considering the larger  inflow rate of F-13.  Although the T-P
concentration of  inflow seems the same as shown in Fig. 3, the
phosphorous removal efficiency of F-13 with step inflow operation,
is much more stable as  shown Fig. 4.  In F-13 the average T-P
concentration of  effluent and the average T-P removal efficiency
reached 0.25 mg/Z and 88%, respectively, while they were  0.52 mg/Z
and 76% in F-5.
                            236

-------
                      100

                      90

                      80

                      70


                      60

                      50

                      40

                      30

                      20

                      10 -
F-13
                        01   2  34   567

                      T-P concentration of influent (mg/£)
Fig.  3  Cumulative frequency curve of influent T-P concentration
                     100

                     90

                     80

                     70

                     60

                     50

                     40

                     30

                     20

                     10
                       0       0.5     1.0      1.5

                      T-P concentration of effluent (mg/4)
Fig. 4  Cumulative frequency curve of  effluent T-P concentration
         COD of influent  and the T-P concentration  of effluent in both
    F-5 and F-13 are  also shown in Fig. 5.  The  effect of rainfall
    appears as a drop in  COD of influent.  While in F-5 the T-P
    concentration of  effluent increased in many  days when the substrate
    concentration was low,  the T-P concentration of effluent in F-13
    was kept in a low level and all the measurements were below
    0.5 mg/S, except for a few days after the experiment started.
                                237

-------
M
E-i (U
       ,  , , I I  I I I I  I , , I  I I I I ,  . I I ,  I , I . ,  , I I ,  . , , I ,  , , , I  , , , ,  I . , .  , I , ,
           20     25
                       30 
-------
                                       Return sludge
                                                              Secondary settl-
                                                              ing tank
                                                              (double-decked)
                                                                            (Anaerobic-aerobic process)
                                                                                      Lftluent to
                                                                                      Tokyo Bay
Fig. 6   Flow sheet of the east train  of iriezaki  sewage Treatment  Plant
              Table 10   Design  particulars of the test facility
Process
Anaerobic-
aerobic
process
15°C
up
below
15'C
^-^^ Item
Name o?\.
facility ^\^
Anaerobic tank
Aerobic tank
Anaerobic tank
Aerobic tank
Secondary settling tank
Conventional
activated sludge
process
Aeration tank
Secondary
settling tank
Width
On)
9.0
9.0
9.0
9.0
8.6
9.0
8.6
Length
(m)
53.2
83.7
32.95
103.95
71.5
136.9
71.5
Effective
water
depth (m)
6.5
6.5
6.5
6.5
3.0
6.5
3.0
Number of
tanks
1 tank
3 (compart-
ment)
1 tank
3 (compart-
ment)
1 tank
2 (compart-
ment)
1 tank
4 (compart-
ment)
3 tanks
1 tank
3 tanks
Volume

-------
     An anaerobic-aerobic facility for biological phosphorus
removal and another facility for conventional activated sludgs
process were run in parallel for comparison.  As stated in
Table 11, the experiment was divided into several runs depending on
the operating conditions.  In Table 11, two figures are shown in
each column; the upper refers to the anaerobic-aerobic process, and
the lower to the conventional activated sludge process.
     Table 12 shows the phosphorus removal performance achieved in
each run.
     Figs. 7 and 8 show the T-P and orthophosphate concentration
cumulative frequency curves for the influent and effluent,
respectively.
     The cumulative percentage of the T-P concentrations of up to
0.5 mg/je in the effluent from the biological phosphorus removal
process  (anaerobic-aerobic process)  was 96%, bearing out a high
stability of the phosphorus removal performance.  It was when the
MLSS concentration in the reactor fell below 2,000 mg/j£ and when
the DO concentration in the mixed liquor of the aerobic tank fell
that the phosphorus removal efficiency went down.  The
characteristics of generated sludge were compared with respect to
thickenability and dewaterability.  There was no significant
difference in thickenability between the anaerobic-aerobic
phosphorus removal process and the conventional activated sludge
process.
     As regards the dewaterability, the sludge from the
anaerobic-aerobic process was found 1.5 to 2% lower in cake water
content than that from the conventional activated sludge process.
                            240

-------
                        Table  11   Test conditions
^---^Test period
Item \^^
Influent flow

2.95
214
141
3 , f .i 0
1,360
8,910
3,770
12.3
12.2
6.5
2.9
4.9
2.9
Note:  The upper values in the boxs refer to the anaerobic-aerobic process a'ftd the  lower
      values to the  conventional activated sludge process.
                                       241

-------
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-------
     100
   >.
   g
   2
   3
                                              100
          1.0 2.0 3.0 4.0 5.0 6.0 7.08.09.010


                  Influent 0-P (mg/i)
                                        .0
                                                            o Conventional

                                                              activated
                                                              sludge process
0.4    0.3    1.2    1.6


  Effluent 0-P (mg/2.)
     Pig. 8   Orthophosphate P  (0-P) concentration  cumulative curve
                          Methanol
           Effluent from

           primary settl-

           ing tank
                                           ML
                                  (DN)
                                     DN
                                          RS



                                 (a)   Test  train


                                         ML
Methanol


Effluent- from



primary settl-
ing t-.ank


Coagulant
injection

7

DN DN DN DN 0


|
T

0
— .







7

FS
^-^
                                                                               2.0
                               (b)   Control train


Fig.  9  Flow diagram of Konan  Chubu Sewage Treatment  Plant  (Lake Biwa)
                                         243

-------
(4)   Konan Chubu  Sewage  Treatment  Plant  (Lake Biwa)

         The Konan Chubu Sewage Treatment Plant was put into operation
     in April 1982 as Japan's first plant operating on the single-stage
     nitrified liquor recycled nitrification denitrification process.
     It serves the southeastern part of shiga, including the capital of
     the prefecture, and covers a  planned area of 25,500 ha.
         The collection system is the separate sewer.  While its
     ultimate daily maximum design flow is 1,020,000 m3, the Plant has
     now been operated on a limited scale with a daily flow of
     21,000 m3.   The plant uses a  nitrified liquor recycled
     nitrification denitrification process for nitrogen removal, and the
     phosphorus removal  is carried out by injecting
     poly-aluminum-chloride  (PAC)  into the end of the reactor.
         The plant has  a rapid sand filter for the final cleaning of
     the effluent.
         On the  other hand, the sludge treatment system used is
     composed of  gravity thickeners for thickening process and filter
     presses for  dewatering process.
         At the  Konan Chubu Sewage Treatment Plant, one train of
     facilities has been used for  experiment with a biological nitrogen
     and phosphorus removal process since June 1984.  Fig. 9 shows a
     process flow of the test train and control train.
         Bach train has a reactor with a volumetric capacity of
     2,250 m3.  The reactor is divided into four compartments.  In the
     test train,  the first two compartments of the reactor are
     subdivided into two each in order to make either one eighth or a
     quarter of the reactor anaerobic and also to measure the
     denitrification rate in the denitrification chamber with a passable
     accuracy.  The baffles in the reactor for the test trains are
     constructed  to protect surface flow for the purpose of determining
     the nitrification and denitrification rates accurately.  In the
     control train, however, the top ends of baffles are set about 30 cm
     below the overflow  surface, and a considerable secondary
     circulation  is noticed across the baffle between the
     denitrification and nitrification compartments.  The test train is
     designed to  allow step inflow of raw sewage for the purpose of
     stabilizing  biological phosphorus removal against stormwater inflow.
         For accurate determination of influent flow, a self-priming
     pump is used to pump up the settled sewage from the primary
     settling tank and feed it through a flowmeter at a constant rate.
         At the  Konan Chubu Sewage Treatment Plant, the primary
     settling tank is operated to  provide a residence time of 0.5 to
     1 hour for the purpose of increasing the BOD source to the
     reactor.  Since the start of  test, methanol has been injected to
     make up for  a shortage of BOD source.  As BOD of the raw sewage has
     been increasing annually, the methanol injection rate has been on a
     steady decline.  The running  conditions and phosphorus removal
     performance  of the  test train are as shown in Figs. 10 and 11.
                                    244

-------
                                                      9172
                                                                        T-P concentration (mg/£)
O

*~\
(a
H
PJ
rt
H-

§

O

§
&
H-
rt
H-
O
3
tn
8"
n
c
CO
3
•n
 n>
 M
 Ml
 o
 o
 (D
 (0

 ff
 o
 o
 cr
 n>
                                                                       BOD concentration

-------
                                             T-P concentration  (mg/Jl)
L/i 00
-* o
08
^ o
                                  *3 W  » 13  H-0
                                  t ft  Q H  1 >1
                                  13 O  g H  T3I
                                    I        -
                                   2    g    g
                                            BOD concentration  (mg/J.)

-------
O
•H
(1)
O
c
o
o
en
                                                                                u
                                                                                o
                                                                               ft
                                                                               0)
                                                                               -P
                                                                               S-i
                                                                               0)
                                                                               -P
                                                                               ri
               Pig. 11 (a)   Daily changes of water temperature and
                            MLSS concentration (June to October)
<^
e
 §
 •H
 -P

 OJ
 U

 O
 o

 CO
                                                                               U
                                                                               o
                                                                               (L)
                                                                               M

                                                                               4J
                                                                               0)
                                                                               4-1
               Fig.  11 (b)   Daily changes of water temperature and
                            MLSS concentration (November to March)
                 As the target level of phosphorus in the effluent is set at
            0.3 mg/jK,  the injection of methanol is unavoidable for the moment.
            It is found from Pig. 8 that the concentration of total phosphorus
            in the effluent from the secondary settling tank can be held below
            0.3 mg/Z as far as there is an sufficient supply of BOD.  In the
            early stages of test, sludge from the control train was used as
            seed  sludge, and the effluent quality was very satisfactory owing
            to the effect of residual coagulant.  In about two weeks after
            start, however, the effluent quality plunged as the residual
            coagulant  was spent.   In order to accelerate the growth of
                                       247

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biological phosphorus removal sludge and replacement of
coagulant-added sludge, heavy injection of methanol and he?vy
withdrawal of sludge were carried out.  As a result, the phosphorus
removal performance was improved gradually,  in the meantime, the
influent flow was increased while the methanol injection rate was
decremented.  When the methanol injection rate was reduced down to
9 mg/£, the phosphorus concentration in the effluent began to
fluctuate.  In early September, the phosphorus concentration in the
effluent started to rise again.  This was due to the overhaul
inspection of the self-priming pump for step feed of inflow, which
prevented MLSS in the anaerobic zone from being kept at a
sufficiently high level as shown in Fig. 8.  To overcome the
situation, the methanol injection rate was increased, and the
phosphorus concentration in the effluent improved gradually.  But
the plant administrator wanted to keep the phosphorus level below
the monthly average target value of 0.3 mg/£, and a coagulant was
thus injected for a quick recovery.  The coagulant injection
continued for two weeks.  Transition from chemical removal to
biological removal was made without any trouble.  From the end of
November, phosphorus removal got unstable again, and coagulant
injection was restarted, which continued about three weeks.
      Following this, biological phosphorus removal was resumed
steadily.  For the operation of the biological phosphorus removal
process which is sensitive to various factors because it is
dependent on microbial activities, the coagulant injection was
proved to be a useful and effective backup as explained above.  As
for the biological phosphorus removal process in the Konan Chubu
Sewage Treatment Plant, the orthophosphate concentration in the
effluent can be stably held below 0.1 mg/£ if the methanol
injection rate is set at about 20 mg/SL in summer and about 30 mg/S.
in winter.  The difference in methanol injection requirement
between summer and winter will probably be due to the fact that the
reaction rate for the organic acid fermentation in the anaerobic
chamber falls when the water temperature is low.
     In the Konan Chubu Sewage Treatment Plant, the retention time
in the primary settling tank is short, and the BOD/P ratio in the
influent into the reactor is relatively high at about 40.
Nevertheless, methanol injection is required for the stabilization
of biological phosphorus removal process.  The volatile fatty acids
as a source of readily biodegradable BOD are considered to play an
important role in the biological phosphorus removal process.  In
the Konan Chubu Sewage Treatment Plant, however, about two-thirds
of generated sludge is coagulant-injected activated sludge which is
fairly stable against biodegradation, and the return load of
volatile fatty acids from the sludge treatment system is low.  In
addition, the retention time in the primary settling tank is
short.  This makes relatively high apparent BOD due to SS-form BOD
which is considered not to work much for the biological phosphorus
removal reaction.  This reasoning may explain out the high methanol
injection requirement even with high BOD/P ratio.
                            248

-------
     Fig. 12 shows the nitrogen removal performance of the test
train and control trains.  The target effluent quality is
10 mg«TN/£.  In winter when the nitrogen concentration in the
influent exceeds 30 mg/S., the methanol injection rate is increased
to about 40 mg/i.  The total-nitrogen removal efficiency of the
nitrified liquor recycled nitrification denitrification process is
estimated at 60 to 70% for ordinary municipal wastewater.
Pri
* 	 ^ (te
(co
mary effluent
rnmon to test and
trol trains)
ondary effluent
st train)
ntrol train)
          Fig. 12  Nitrogen removal performance
     In order to keep the total-nitrogen concentration in the
effluent below 10 mg/SL even when the nitrogen concentration in the
influent exceeds 30 mg/H, it is required to inject methanol to
increase the sludge production for the purpose of removing nitrogen
in the form of sludge.
     The nitrogen concentration in the effluent of the control
train was about 2 mg/S, lower on the average than that of the test
train.  This may have been caused by the secondary circulation of
nitrified liquor in the control train created by loose partition
between the nitrification and denitrification compartments.
                           249

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4.   RECENT TRENDS  IN  RESEARCH AND DEVELOPMENT

4.1  Introduction

          Research  and development have been pushed forward through pilot
     scale plant experiments or bench scale tests in  search of the measures
     to overcome several  problems identified as standing  in the
     implementation of advanced biological sewage treatment processes.
          Among these,  this chapter deals with a step inflow type biological
     nitrogen and phosphorus removal process designed for stabilized
     phosphorus removal against stormwater and a process  using nitrifying
     bacteria encapsuled  in high polymer gel for improved nitrification
     efficiency.

4.2  Step Inflow Biological Nitrogen and Phosphorus Removal Process

     (1)  Operating principles of step inflow process

               The  biological nitrogen and phosphorus removal efficiency can
          be improved  by  feeding influent into the anaerobic zone and
          denitrification zone in steps as illustrated in Fig. 13.
    effluent -
    of PS
                            (ML)
             (a)
                      (1-a)
                     Oi
where,

A -  anaeroln c zone

DN - dc'iu t.r i t i fat i on
    zone

Oi = t-lit- NrbL
    n 111j t i CM I ion
    zone


    n i t i i t i il I i ijiior

    it'ci i cul tit ion

US -- ruLurn i. ludcju
     Pig.  13  proposed biological nitrogen  and phosphorus removal process
              with step inflow
               In  the  step inflow process, the flow of  solids brought in by
          return sludge remains unchanged, but the wastewater inflow into the
          first chamber of a reaction tank decreases.   Therefore, the MLSS
          concentration in the former part of the reaction tank increases.
          This feature does good for nitrogen and phosphorus removal as
          detailed below.
                                       250

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(a)   The step inflow process can increase the MLSS concentration in
     the anaerobic zone without increasing the return sludge ratio,
     and therefore the inflow of nitrate nitrogen into the
     anaerobic zone can be minimized.   The increase of the MLSS
     concentration increases the oxygen consumption rate and
     denitrification rate, eliminating the unfavorable influences
     of dissolved oxygen and nitrate nitrogen in raw sewage, which
     pose serious problems during rainy season.

(b)   The step inflow process illustrated in Fig. 13 can increase
     the MLSS concentration in the first nitrification zone.  As a
     result,  the total amount of solids that can be held within the
     entire reactor can be increased considerably.   This is
     particularly useful in winter when the SRT must be extended to
     make up for the decrease in the growth rate of nitrifying
     bacteria.  If the SRT is to be held constant,  the return
     sludge ratio can be reduced, reducing the evil effect of
     nitrate nitrogen in the return sludge upon the biological
     phosphorus removal performance.

(c)   In the step inflow process in which the influent is divided
     into the first chamber,  i.e.,  the anaerobic zone,  and the
     third chamber, viz.,  the denitrification zone, nitrogen
     entrained into the first chamber  which is nitrified at  the
     second chamber can be removed in the denitrification zone
     without circulation.   In the step inflow process,  a
     considerably high T-N removal can be expected  depending on the
     step inflow ratio.

     In the ordinary nitrified liquor  recycled nitrification
     denitrification process, for example, part of  nitrogen  is
     removed  in the form of sludge,  and the ratio of conversion
     from influent T-N into nitrate nitrogen remains at a level of
     60 to 80%.   If 20% of T-N in the  influent is to be removed in
     the form of sludge, if the remaining 80% is completely
     nitrified,  and also if nitrate nitrogen returned into the
     denitrification zone is completely removed, the T-N removal of
     the nitrified liquor  recycled nitrification denitrification
     process can be expressed by Eq.  (1).
     where R = recirculation ratio

        Return sludge flow + Nitrified liquor  recirculation  flow
     (=                         Influent flow                    '

     In  case of the step inflow process,  on the other  hand,  under
     the same assumptions as before,  the  T-N removal can be
     expressed by  Eq.  (2)  on condition that the step inflow  ratio
     is  2:1.
                           251

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x 100
                                                                     (2)
          These two processes  are  compared in Fig.  14 with respect to
          the T-N removal efficiency  as  a  function  of the recirculation
          ratio, R.  Compared  with the ordinary nitrified liquor
          recycled nitrification denitrification process, the step
          inflow process provides  a greater T-N removal at a smaller
          recirculation ratio.  This  suggests that  the nitrified liquor
          recirculation pump may be dispensed with  if the conditions are
          favorable.  Since the step  inflow process can increase the T-N
          removal above 80%, it will  be  useful, particularly when the
          effluent standard is tightened or when the nitrogen
          concentration in the influent  rises.
                 100
                 50
                             Proposed step inflow
                             process
                                Nitrified liquor recycled
                                process
                          Recirculation ratio, R

        Pig.  14  Relationship between removal efficiency of
                 total nitrogen  and recirculatiion ratio R
     (d)   in the step inflow process, the MLSS concentration  in  the
          succeeding chambers remains the same as when  the  step  inflow
          is not applied.  Accordingly, it is possible  to improve the
          nitrogen and phosphorus performance without increasing the
          hydraulic loading and SS loading in the secondary settling
          tank.

(2)   An outline  of the experiment

          The step inflow process was experimented with using pilot
     plant (A) where a 9.5 m3 reactor wad divided into  four equal
     compartments and pilot plant (B) where a 51 m3 reactor was
                                 252

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divided into six equal compartments.  The  operating modes were as
shown in Fig. 15.
of PS








1
A

O.



DN

O-


•>
\fj
RS



FS
^-^
          (a)   Operation mode IV (pilot plant A)
       effluent
       of PS
                     O]
                         DN
                       RS
           (b)  Operation mode V (pilot plant A)
   raw sewage
                                02
                                         FS
          (c)  Operation mode VI  (pilot plant B)

        Fig.  15  Operation modes of pilot plants
     The raw sewage was pumped from the adjacent sewage  treatment
plant to the pilot plants.  For pilot plant  (A), the raw sewage  was
first run through a primary settling tank.  For pilot plant  (B),
the raw sewage was directly fed into the  reactor because of
limiting restraints of testing facilities,  influent and effluent
were analyzed by making use of 24 hours composite  samples.
     As regards the water quality in the  reactor,  spot samples were
analyzed at 10:30 a.m.  In principle, measurements were  carried  out
three times a week - Monday, Wednesday and Friday.
                            253

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          The process was also  tried at a actual sewage treatment plant
    under the operating conditions specified in Table 6.   The operating
    conditions of pilot plants (A)  and (B) are as  shown in Tables 13
    and 14.   The operating period was divided into several runs
    depending on the operating conditions.  The values on the tables
    are the  average values of  each run.  The influent flow, return
    sludge flow and nitrified  liquor recirculation flow were regulated
    to be nearly constant in each run.
          Table  13   Operation condition of  pilot plant A
Operation
mode
IV
V
Run
A-l
A-2
A-3
A- 4
A- 5
A-6
A-7
A-8
A-9
Period
'84 6/16 - 7/6
7/7 - 8/2
8/3 - 9/3
9/4 - 10/1
•84 10/2 - 10/24
11/14 - 12/7
12/8 - 1/9
•85 1/10 - 2/1
2/2 - 3/1
Qin
24
24
24
24
24
19.2
15.4
15.4
15.4
r
0.3
0.4
0.4
0.4
0.4
0.5
0.5
0.63
0.63
R
0.8
0.9
0.9
0.9
0.4
0.5
0.5
0.63
0.63
T
9.5
9.5
9.5
9.5
9.5
11.9
14.8
14.8
14.8
MLSS
AT2
3350
4010
3670
3600
3220
3780
3420
4080
3690
AT4
2320
2880
2700
2790
2510
2990
2940
3440
3240
VSS
71.2
68.4
66.2
69.5
71.9
73.0
73.1
75.8
73.2
SVI
112
121
119
132
161
256
291
279
291
t
23.1
25.5
27.4
25.2
22.9
17.7
14.8
14.1
13.7
         where
             Qin
             r
             R
             T
             VSS
             SVI
             t
Influent flow rate (m3/<3ay)
Return sludge ratio
Recirculation ratio
Nominal retention time (h)
Organic contents of MLSS (%)
Sludge volume index (m£/g)
Hater temperature (°C)
          Table 14  Operation condition of pilot plant B
Operation
mode
VI
Run
B-l
B-2
B-3
Period
'84 12/8 - 1/9
'85 1/10 - 2/1
2/2 - 2/22
Qin
79.2
79.2
79.2
r
0.5
0.64
0.64
T
15.5
15.5
15.5
MLS
AT3
4620
4830
4490
S
AT6
3700
3930
3650
VSS
75.9
76.3
75.3
SVI
165
189
202
t
14.4
13.4
13.2
(3)   Test results and  discussions

     (T)  phosphorus removal

               Let  us  express the phosphorus  removal performance (Yp)  by
          Eg.  (3).  Then,  its relation  to  the BOD-SS loading  (Xp)  in the
          anaerobic zone which is defined  by  Eg.  (4) is represented by
          Fig. 16.
                                  254

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      1.0
T
OF-1 -
AF-5 -
AF-13,
'•A-l -
»B-1 -
4
12
14
9
3 .
with sLc>£>
inflow

                                             without step inflow
                                         o    Yp = O.OJ7bXp - 0.087
                              with step inflow (a = 0.67)
                              Yp = 0.0403Xp + 0.054
                          I
                                   I
                                                    I
Fig. 16
       10       20       30       40       50       60
       BDD-SS loading in anaerobic zone, Xp (mg BOD/gss.h)

Relationship  between phosphorus removal  ability and
BOD-SS loading  in anaerobic zone
            Yp
         (Pin - Pout) x Qin
          MLSSp x Vp x 24
                                    (3)
            where Yp = phosphorus removal ability  (mg AT-P/gSS'h);
                  Pin = T-P concentration in influent  (mg/£);
                  Pout = T-P  concentration in effluent  (mg/£);
                  Qin = influent flow (mV<3ay);
                  MLSSp = mixed liquor SS concentration  in  the
                          anaerobic zone (g/£);
                  Vp = volume of anaerobic zone  (m^).
            Xp
                             (4)
            ax Qin x BODin
          MLSSp x Vp x 24 '
     where  Xp = BOD-SS loading in  anaerobic zone
      (mg-BOD/gSS-h);
           a = ratio of inflow to the first compartment.

     Eq.  (5)  representing the line of  regression in the figure
was determined from the results of the biological phosphorus
removal process and modified phoredox  process tried at the
actual sewage treatment plant.  The result of the step inflow
process is  given by Eq. (6).
                              255

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     o Without step inflow:
       Yp = 0.0375 Xp - 0.087 ... (5)
       (correlation coefficient = 0.937, n = 12)

     o With step inflow:
       Yp = 0.0403 Xp + 0.054 ... (6)
       (correlation coefficient = 0.858, n = 14)

     Assuming the form of the function Yp = a«Xp + b, AT-P is
expressed by Eq. (7)  using Eqs.  (3)  and (4).

     AT-P = a x a x BODin + b x MLSSp x Tp ...  (7)

     where AT-P = Pin - Pout (mg/j2);
           Tp = retention time in anaerobic zone
           .  Vp x 24.   ...
           (=   Qln—}   (h)'

     By substituting Eqs. (5)  and (6) into Eq.  (7), we can
express AT-P by Eqs.  (8) and (9), provided that Tp = 3 (h),
and MLSS for non-step inflow,  MLSSp = 3 (g/£).  MLSS for step
inflow was assumed to be MLSSp = 4 (g/£), with  ex = 0.67 and r
= 0.3.

     o Without step inflow:
       AT-P = 0.0375BODin - 0.78 ... (8)

     o With step inflow:
       AT-P = 0.0270BODin + 0.65 ... (9)

     As shown above,  the concentration of total phosphorus
removed can be expressed as a function of influent BOD.  As
shown in Fig. 17, the step inflow process is effective
particularly when influent BOD is low.
     At influent BOD of 50 mg/jK, for example, the step inflow
process removes twice as much T-P concentration as non-step
inflow process does.   It is therefore evident that the step
inflow process performs better during summer season when the
influent BOD concentration becomes generally low on account of
rainfalls, etc.  It should be borne mind here that the
situation is reversed when the influent BOD concentration
exceeds 150 mg/£.
     The reason why the step inflow process is better when the
BOD concentration is low may be explained as follows.

a.   A high MLSS concentration in the anaerobic zone increases
     the oxygen utilization rate and denitrification rate,
     which in turn reduces the consumption of BOD necessary
     for keeping the anaerobic condition.
                       256

-------
         I
         10
         I   2
         a
         4-1 ^
         o °t
         •23  1
         >
         0 tt.
         S I
         tu E-t
         « O
                              without step inflow
                      I
                               I
                                       I
                      50       100      150       200

                InHui-iit BOD concentration, BOD in (mg/i)
 Fig. 17  Relationship between  removed total phosphorus
          concentration and influent BOD  concentration
     b.    The actual residence time in the anaerobic zone  is  also
          increased, and the output of readily biodegradable
          substrate used as culture ground of phosphorus removal
          bacteria is increased.

(2)   Notrogen removal

     a.    Increase of SRT

               In Run A-6, for example, where step inflow  was
          applied with a = 0.67 and r = 0.5, the SRT is increased
          14% over the non-step inflow process.  To maintain  the
          same level of SRT without step Inflow, it is necessary  to
          increase the return sludge ratio, r, to 0.61.  Although
          it is supposed for the computation here that the return
          sludge SS concentration remains unchanged, the fact is
          that the return sludge SS concentration decreases with
          increase in the return sludge ratio; namely, that the
          return sludge ratio must be increased further.

     b.    Increase of T-N removal efficiency
          and
 The nitrogen removal performance of pilot plants  (A)
(B)  is shown in Table 15.
                           257

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Table 15  Nitrogen removal efficiency of proposed step inflow process
Operation
mode
IV
V
VI
Run
A-l
A- 2
A-3
A-4
A-5
A-6
A- 7
A-8
A-9
B-l
B-2
B-3
Influent
(mg/Jt)
T-N
23.2
25.7
24.0
25.7
28.2
29.3
30. B
35.6
29.5
38.0
53.9
47.6
NH*-N
13.0
11.8
14.1
14.2
14.3
15.8
16.7
20.6
17.3
16.1
20.8
19.1
Effluent
(mg/je)
T-N
7.9
6.2
7.3
7.7
7.8
10.2
12.8
12.1
11.2
5.1
6.1
6.4
%-N
6.4
4.5
4.6
5.0
6.0
6.0
10.2
5.9
8.9
1.5
1.4
4.1
NH*-N
0.1
0.2
1.1
0.7
0.4
1.9
1.5
4.6
1.4
2.0
2.6
0.9
Denltrlfica-
tion zone
(mg/*)
NO~-N
3.5
2.1
2.2
2.7
1.6
2.2
4.8
0.6
4.4
0.1
0.3
2.1
BOD/N
3.7
4.6
3.7
5.1
6.9
4.8
4.4
9.2
3.5
11.0
16.4
11.1
Removal
efficiency of
T-N (»)
65.9
75.9
69.6
70.0
72.3
65.2
58.4
66.0
62.0
86.6
88.7
86.6
                     In the operating mode IV,  nitrate nitrogen always
                stayed on in the denitrification zone.  For this reason,
                the operation of nitrified liquor recirculation pump was
                cut off in the test thereafter.  Assuming that all of
                nitrate nitrogen running into the denitrification zone is
                removed, the test conditions dictate that the T-N removal
                efficiency rate ought to be more than 80% as calculated
                by Eq. (2).  In pilot plant (A), however, the T-N removal
                rate efficiency 10 to 20% lower than calculated because
                the BOD/N ratio was generally low as shown in Table 15 to
                make the denitrification capacity insufficient.  Runs A-7
                thru A-9 and Runs B-l thru B-3 were conducted almost
                concurrently; in pilot plant (B), the raw sewage was
                directly used, and the T-N removal efficiency became
                higher than the value calculated from Eq. (2)  because the
                BOD/N ratio got higher.
                     This is also explained by the fact that,  in the
                primary settling tank, the BOD removal efficiency larger
                than T-N removal efficiency, and therefore that the BOD/N
                ratio of influent becomes larger than that of primary
                effluent.
                     To sum up, the step inflow process can achieve a T-N
                removal efficiency of more than 80% without recirculation
                of nitrified liquor if the BOD/N ratio is high enough to
                keep a required level of denitrification capacity.
                                 258

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                    Alkalinity in the first nitrification zone
                         Even though a denitrif ication zone follows  the first
                    nitrification zone, it is almost unlikely that the
                    alkalinity will run short in the first nitrification zone
                    if the step inflow retio is kept at 2:1.  During test,
                    the alkalinity of the influent was in the range  of 136 to
                    175 mg/H, and the alkalinity in the first nitrification
                    zone was from 72 to 101
4.3  Improvement of Nitrification Rate by Pelletization of Microbes

          One of the recent technological developments is the encapusulation
     of nitrifying bacteria in high molecular gel such as polyacrylamide.
     The fixation of nitrifying bacteria in this way prevents the washout of
     nitrifying bacteria due to shortage of SRT during the low-temperature
     season, and thus increases the nitrifying efficiency.  There are a wide
     variety of binders available for the fixation of nitrifying bacteria.
          The Japan Sewage Works Agency conducted a test for improving the
     nitrifying efficiency using nitrifying bacteria pelletized with
     polyacrylamide as binder which has been in wide use for the purpose.
     The characteristics of the pellets used are shown in Table 16.
       Table 16  Initial characteristics of pellets  used for  the  test
" " 	 	
pelletized sludge seed
Sludge concentration (%)
Material of binder
Binder concentration (%)
Pellet size (mm)
Pellet strength (kg/cm )
Initial activity*
(mg-cy.e-gel)
Pellet 1
Activated sludge from
recycled process

Polyacrylamide
18
30 x 1.3 - 1.5
1.4

Pellet 2
Ammoniaassimllated
activated sludge

polyacrylamide
18
20 x 2
1.4

               * Respiration rate at 20°C, NH4-N 20 mg/Jt, and more than DO 4 mg/jj.
          Fixed microbes of pellet 1 was obtained by directly thickening of
     activated  sludge from the sewage treatment plant operating on the
     nitrified  liquor recycled nitrogen removal process, and that of pellet 2
     was  obtained  by assimilating the same sludge for 2 months using ammonia
     nitrogen and  nutrients alone.
          Pig.  18  shows the test arrangement.   Two trains of the same test
     arrangement were used.  For one train, pellets of nitrifying bacteria
     were filled.   The other train was not filled with pellets, and was used
     as a control.   The capacity of the reactor was 9 Si for pellet 1 and 4 S.
     for  pellet 2.
                                      259

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        Aeration tank mixed liquor
	 (E




H


	 ^y-

W !
°o/T^ cV~N\o!

o

-------
than in  train  B where suspended sludge alone was used,  in the test
using  Pellet 2,  the same tendency was observed.
     In  the  encapusulation of nitrifying bacteria, DO and HN|-N are
fed through  high-molecular gel.  Accordingly, the dispersion stage in
the gel was  suspected to govern the nitrification rate in the low
concentration  range.   This matter was studied, and the results were as
shown  in Figs. 19  and 20.
                                              Water temperalurej  20"C
                               Suspended solids MLSS approx. 3.UOO rog/8.
                            2             3

                           DO concentration lug/8.)
                                                                     1	
           Fig.  19  DO concentration vs. respiration rate
     Fig. 19 shows  the DO concentration vs. respiration rate,
relationship with respect to Pellet 1,  Pellet 2 and control activated
sludge.  The control  activated sludge was assimilated for about 2 months
with NH4C1 as a major substrate.   Its MLSS was about 3,000 mg/£.
Fig. 20 shows the relationship between  DO concentration and respiration
rate ratio with the respiration rate at DO » 4 mg/£ taken as 100.  As
shown in Fig. 20 when the nitrifying bacteria were pelletized, the
effect of DO on the respiration rate started with a higher concentration
range than the activated  sludge.   This  tendency was more conspicuous
with Pellet 2 which was larger in size  than Pellet 1.
                                 261

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loo -
                                     w

                                  o-€c
                                   «  /
                               e      /
                                     Pellet, 30 * 1.3 to 1.5 mm
                                         Respiration rate at DO 4 nig/?.:  lOO't
                             1 - 1
                             234

                             DO concentration (mg/&)

         Fig. 20  DO concentration  vs.  respiration rate ratio
       In Fig.  19, Pellet 1 and Pellet 2 .show a large difference  in
  respriation rate despite the assimilation under the same conditions.
  This difference may have come from the difference in the number of
  bacteria between Pellet 1 and pellet 2.  If the number of pelletized
  bacteria is small, the activity will not be enhanced sufficiently even
  after a long period of assimilation.  It is therefore important to
  pelletize high-density sludge of a high activity.  The effect of
  NHj-N concentration was also studied; as compared with the
  activated sludge, there was found no significant -Influence of NflJ-N
  dispersion in the gel used for pelletization on the NH^-N removal
  rate.  The findings of the test are summarized as follows.

  (1)   It is expected that, by using nitrifying bacteria pelletized with
       polyacrylamide and activated sludge in combination, the nitrifying
       bacteria can be held at a high concentration level even during a
       low-temperature for a high-rate nitrification in a short time.

  (2)   If the initial activity of pellets is low, a required level of
       nitrification rate may not be achieved for a long period.  Microbes
       may be encrusted upon the surfaces of th pellets depending on  the
       surface property of the pellets.  It is therefore highly desirable
       to establish the palletizing technology that will ensure a high
       nitrification efficiency stably for an extended period.
                                  262

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(3)   As regards the dispersion of DO and NH^-N through pellets,
     there is no practical problem.   However,  the pellets should
     preferably be as small as possible without detriment to the ease of
     their handling.

(4)   For the implementation of the process,  studies must be made on the
     pellet fluidity conditions,  reduction pellet specific gravity, mass
     production technology of  pellet,  durability,  production cost,
     operation and maintenance costs,  etc.
                                263

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                     Tenth United States/Japan Conference
                        on Sewage Treatment Technology
   PERFORMANCE EVALUATION

                OF

   OXIDATION DITCH PROCESS
The work described in this  paper was
not funded by the U.S. Environmental
Protection Agency.  The contents do
not necessarily reflect the views of
the Agency and no official  endorsement
should be inferred.
              K. Matsui,

           Research Engineer

              T. Kimata,

           Research Engineer

Research and Technology Development Division

       Japan Sewage Works Agency



                 265

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                              TABLE OF CONTENTS


                                                                          page
                  ENGINEERING EVALUATION OF OXIDATION DITCH

1.   CURRENT STATUS OF THE OXIDATION DITCH PROCESS IN JAPAN 	     267
 1.1   Definition 	     267
 1.2   History	     267
 1.3   prospect for the Oxidation Ditch Process in Japan 	     269
2.   SURVEYS ON THE OXIDATION DITCH PROCESS .v	     270
 2.1   Pilot Plant Study 	     271
 2.2   On-site Survey 	     274
 2.3   Assessment of the Mechanical Aerators 	     281
3.   PROCESS PERFORMANCE	     282
 3.1   BOD Removal 	     282
 3.2   Suspended Solid Removal 	     284
 3.3   pH	     285
 3.4   Nitrogen Removal 	     286
4.   OTHER PROPERTIES 	     295
 4.1   sludge Settleability	     295
 4.2   Sludge Production 	     297
 4.3   Oxygen Consumption Rate 	     298
5.   CONSIDERATIONS ON DESIGN 	     299
 5.1   Recovery and supply of Alkalinity 	     299
 5.2   Nitrification and Denitrification Rate 	     300
 5.3   Oxygen Supply 	     300
 5.4   Control and Adjustment of Aerator 	     301
6.   CONCLUSION 	     301
                                     266

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                  ENGINEERING EVALUATION OF OXIDATION DITCH


1.   CURRENT STATUS OF THE OXIDATION DITCH PROCESS IN JAPAN

1.1  Definition

          The oxidation ditch process is one of the variations of the
     activated sludge treatment process and is generally defined as follows;

     (1)  An endless channel (called ditch)  with a mechanical aerator is used
          as a reactor.

     (2)  The mechanical aerator supplies oxygen required for the biological
          treatment.  In addition, the aerator mixes the activated sludge and
          the wastewater, and provides the flow of the mixed liquid in the
          ditch, so that the activated sludge is kept in a suspended
          condition.

     (3)  The range of BOD-SS loadings is 0.03 to 0.05 kg-BOD/kg-SS/day, the
          MLSS concentration in the ditch is 3,000 to 5,000 mg/£, and the
          ditch depth is about 1 to 3 m.

     (4)  The oxidation ditch process can be operated by two different flow
          patterns; one is the continuous flow system, and the other is the
          batch system which uses the ditch as a settling tank as well as a
          reactor.

1.2  History

          The publicly owned wastewater treatment plant employing the
     oxidation ditch process for the first time in Japan is Yumoto Treatment
     Plant,  in Nikko City.  It was put into operation in 1966.  Nikko City is
     very famous for Shogun's shrines, spa and beautiful lakes located in the
     National Park, and many tourists visit there every year,  in early
     1960s,  the deterioration of the water quality in Lake Unoko brought
     Nikko City consider treating the wastewater discharged from the hot
     spring  recreation area into the lake.  The city made investigation into
     wastewater treatment systems in various countries considering the
     climate of Nikko City, where the ambient temperature sometimes falls
     below -20°C in winter.  As a result,  the city decided to employ an
     oxidation ditch process capable of treating wastewater efficiently even
     in the  cold area.
          Because the oxidation ditch process was adopted at Nikko City,
     people  become  increasingly interested in this process, which resulted in
     the construction of two wastewater treatment plants employing this
     process, one in Ogata Village in Akita Prefecture and the other in
     Toyohashi City.   The former was put into operations in 1969 and the
     latter  in 1977.   These two plants are located in rural communities.
     Takane  Wastewater  Treatment Plant in  Toyohashi City treats the
     wastewater with especially high nitrogen content compared with general
     domestic wastewater because it includes livestock waste.  This
                                     267

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characteristics of the wastewater resulted in an operational problem,
which was a deficiency of alkalinity due to consumption by
nitrification.  The mechanical aeration system was replaced in 1981,
then nitrogen removal by nitrification and denitrification was intended
in the oxidation ditch.  As a result, this problem was solved, and the
plant continued satisfactory operations since then.
     In 1979, the Yufutsu wastewater treatment plant in Tomakomai City
was put into operation.  The plant adopted the
nitrification-denitrification process for the oxidation ditch process
first in Japan.  At Omihachiman City a batch system for their oxidation
ditch was adopted, and started the operation of this plant in 1982.  The
locations of these plants are shown in Fig. 1, and each treatment
capacity is shown in Table 1.  The largest plant has a capacity of about
3000 m3/day.

                          Long. 135=E
            Fig. 1  Locations of oxidation ditch plants
                                 268

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                    Table 1  Oxidation  ditches in service

Nikko City
Ogata village
Toyohashi City
Tomakomai City
Ohmi Hachiman City
Teiai Cho Town
Hikami Cho Town
Treatment capacity
(m3/aay)
3,084
1,536
650
2,140
210
900
3,560
Mechanical aeration
device
Horizontal axis type
Horizontal axis type
Axial Clow pump
Horizontal axis type
Vertical axis type
Axial flow pump
Vertical axis type
Fiscal year,
in service
1966
1969
1977
1979
1982
1982
1983
1.3  Prospect for the Oxidation Ditch process  in  Japan

          As of the end of fiscal 1984,  about  35% of  total population was
     served by sewarage system in Japan, while that in ten large cities, i.e.
     Tokyo, Yokohama, Osaka, Nagoya and  so  on, was about 80% of their
     populations.  Therefore, it is expected that the central point of
     constructions of sewer systems is gradually  shifting from large cities
     to local medium-sized or small communities.   Table 2 shows the numbers
     of the wastewater treatment plants, classified by treatment processes,
     with a treatment capacity of less than 5,000 m3/clay, which were
     planned for construction during the five  years from fiscal 1979 to
     fiscal 1983.
     Table 2  Number of newly projected wastewater  treatment plants with
              a design wastewater capacity  of  less  than 5,000 m3/c3ay,
              and changes in the treatment  method

                                          (Investigated by the
                                          Ministry of Construction)
• — ____^^ Fiscal year
Treatment process"""- — 	 	
Oxidation ditch process
Extended aeration process
Conventional activated
sludge process
Others*
Total
1979
1
2
5
5
13
1980
5
3
4
6
18
1981
8
5
2
2
17
1982
10
0
6
4
20
1983
9
0
8
6
19
                     Notes Others includes the RBC process


          According to Table  2, about 20 plants have been planned annually,
     and about 50% of them were to employ  the oxidation ditch process.   This
     may clearly indicate that people place great  expectations on the
     oxidation ditch process for small communities in spite of that only four
     oxidation ditch plants were in service in  1970s.
          Generally, the municipalities planning to build a small sewage
     system have the following common features:
                                      269

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     a.  The population is small.
     b.  The budget is small.
     c.  Price of land is less expensive than that in large cities.
     d.  It is difficult to employ skillful personnel.

          Therefore, the treatment plants in small communities are required
     following characteristics.

     (1)  To treat the wastewater with large fluctuation stably.
     (2)  To provide easy equipments to maintain.
     (3)  To meet the water quality standards without skillful personnel.
     (4)  To be constructed much cheaper than the conventional system.
     (5)  To be operated and maintained much cheaper than the conventional
          system.

          The oxidation ditch process is designed as a low loading process;
     the BOD-SS loading ranges from 0.03 to 0.05 kg-BOD/kg-SS/day.  The
     primary settling tank and blower are not usually provided.  This system
     therefore, has a certain potential to meet the requirements of (1), (2),
     and (3)  noted above,  which are the requirements for a small wastewater
     treatment plant.  In addition, because its ditch depth is designed to be
     less than 3 m deep.  It is possible to construct the ditch wall surface
     and floor simply with asphalt or block in order to reduce the
     construction cost described in (4).
          The Japan Sewage Works Agency has been employing the oxidation
     ditch processes for small wastewater treatment plants of which capacity
     are less than 5,000 mVday (1-32 MGD) .
2.   SURVEYS ON THE OXIDATION DITCH PROCESS

          The oxidation ditch process has become increasingly noticeable as a
     secondary treatment process for small communities, as its ability to
     remove nitrogen by providing an aerobic and anoxic portion in a ditch.
     For this reason, extensive research and investigations have been
     conducted by various institutions to evaluate the process performance
     including BOD and suspended solids removal, sludge settlability and
     sludge production and so on, as well as to evaluate the denitrification
     characteristics and the aeration devices.  Major research projects that
     have been carried out so far as follows:

     fl)  Pilot plant studies by the Public Works Research Institute,
          Ministry of Construction.

     (2)  Investigations of the actual treatment facilities in service by the
          Japan sewage Works Agency.

     (3)  Performance evaluation of the mechanical aerator for the oxidation
          ditch process by the Ministry of Construction.

          This paper describes the contents and results of these
          investigations.


                                     270

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2.1  Pilot Plant Study

2.1.1  Outline

          The Public Works Research Institute, Ministry of Construction has
     conducted investigations by using a pilot plant of oxidation ditch for
     more than three years.  The purpose of the investigations were to obtain
     useful informations for design and maintenance such as treatment
     characteristics, sludge production and the current distribution in the
     ditch under various operating conditions.  (They have also been doing
     research on the difference of the treatment characteristics between the
     continuous flow system and batch system.)  The outline of pilot plant
     facilities is shown in Table 3, and the facility layout is shown in
     Fig. 2.
          The average BOD, soluble BOD and suspended solids in influent were
     120, 40, 90 mg/jZ, respectively, on the average during the investigation.
            Table 3  Outline of main facilities of a pilot plant
Ditch capacity
Hydraulic retention time
Ditch width
Length of circumference
Depth of water
Rotor revolutions
Ditch surface area
160 - 224 m3
48 hours
2 m
36.2 m
2.0 - 2.0 m
36, 48, 72 rpm
80 m
               I    B    ^^	
                   I I Level      Floating weir
               Fig.  2   A sketch for pilot plant (batch system)
                                      271

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2.1.2  Pilot plant study of the continuous flow system

     (1)   Operating conditions

               The experiments were carried out after the activated sludge
          had been acclimated for about three months.  The operating
          conditions during the experiments were as shown in Table 4.  The
          MLSS concentration during the experiments was 5,200 mg/Ji on the
          average and a little higher than that of the design standards.
        Table  4  Operational  conditions  at  ditch process pilot plant
                  (continuous  system)
Areation time period
BOD - SS loadings
BOD volumetric loadings
MLSS
SRT
Return sludge ratio
Retention time in final
settling tank
Overflow rate of final
settling tank
24 hours
0.028 kg-BOD/kg MLSS/day
0.147 kg-BOD/m3/day
Average 5,200 mg/je (2330 - 8620)
56 days or no drawing
100%, partially 150%
3.5 hours
13.8 m3/m2/day
      (2)  Contents of survey

               The major items of the survey were as follows:

          (l)  process performance

                    To study the process stability of wastewater regarding
               the removal of BOD, suspended solids and nitrogen under  the
               large daily fluctuations of loadings.

          (2)  Sludge production

                    To clarify the amount of sludge production when  the
               sludge retention time is fixed as a certain value  (56 days are
               used for the experiment) during both summer and winter.

          (3)  Oxygen consumption rate

                    To clarify the relations between the oxygen consumption
               rate and the daily fluctuations of loadings,  water
               temperature, and MLSS concentration.
                                      272

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2.1.3  Experiment of batch system

     (1)   Operating conditions

               As for batch system, the experiments were carried out under
          the three different operating conditions as shown in Pig.  3.
s

s
I








81.4.23
)
81.7.13
81.7.13
81.10.26
81.10.26
j
82.2.10
Cycle

Time (hr)
6

Aeration \!??~!i wlth- '. Filling
'*Uns\ drawing ,
\ '-,
t 1
1 1
1 1 I

Rotor
revolu-

(rpm)


48



Rotor ' s
immersion

(cm)
Tank
capacity;
tank
depth ; 2 m
15
156 m3
1.95 m
15
156 m3
1.95 m
Q

(mVcycle)


36



SRT

(day)


No sludge
drawing
No sludge
drawing
                 Aeration


                 Settling


                 Drawing
              Fig. 3  Operating conditions of  the batch  process


               These three conditions were:

          (Series I)

                    The purpose of series I was to clarify  the effects of a
               complete nitrification.  An operating  cycle  of series I
               consists of the aeration period for 6  hours,  the  settling
               period for 1 hour, and withdrawing of  supernatant and filling
               of wastewater for 5 hours.  The sludge retention  time on this
               series was set as being 56 days.
                                     273

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          (Series II)
                    The purpose of series II was to clarify the influences
               given by an extremely long sludge retention time to the
               process performance and the amount of sludge production, and
               the effects of aerobic-and-anaerobic operation on the process
               performance.
                    An operating cycle of series II consists of three cycles
               of aeration period for 15 minutes and idle period for
               30 minutes, followed by the second aeration period for
               4.5 hours, the settling period for 1 hour, and withdrawing of
               supernatant and feeding of wastewater for 4.25 hours.  Excess
               sludge was not withdrawn during this series.

          (Series III)

                    The purpose of series III was to clarify the effects of
               aerobic-and-anaerobic operation on nitrogen removal.   An
               operating cycle of series III consists of 10 times repetitions
               of 15 minute aeration and 30 minute idle periods, followed by
               the settling time for 1 hour and the withdrawing of
               supernatant water and filling of wastewater for 4.5 hours.
               Excess sludge was not withdrawn during this series.

     (2)   Contents of survey

               The major items of the survey were as follows:

               Process performance
               Sludge production
               Oxygen consumption rate
               Velocity distribution in the ditch

2.2  On-site Survey

2.2.1  Outline

          The Japan Sewage Works Agency made an investigation into the
     problems of oxidation ditch in service in connection with the removal of
     BOD, suspended solids and nitrogen, and maintenance.  The Agency has
     been making a technical evaluation of the oxidation ditch process based
     on the results of the investigation.  The periods of investigation were
     three years from April 1982 to March 1985, and generally, the period for
     one treatment plant was one year.
                                      274

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2.2.2  Outline and the operating conditions of  the surveyed treatraenc plants

      (1)   Yufutsu wastewater treatment plant
                The Yufutsu wastewater treatment plant  is connected to a
           separate sewer  system and its influent is basically a  domestic
           wastewater.  The outline  of the facilities is shown in Table 5,
           treatment flow  diagram  is shown in  Pig. 4, and the operating
           conditions are  shown in Table 6.
the
           Table  5  Outline of major  facilities of the  Yufutsu plant
^^^System
Facility^.
Main pump
Oxidation
. ditch
Final
settling
tank
Main rotor ~
I
Main rotor
11
Sub-rotor
Thickener
First system
Second system
Submerged motor pump (4100 x 2 units, Q = 1.6 m3/min per unit
Submerged motor pump 0450 x 2 units, Q • 4.0 m /rain per unit
6.0 m (width) x 154 m (length)
x 1.2 n (water-depth)
" 1,100 m3 (capacity)
Aeration time;
24.7 hours* (11.5)**
BOD-SS loading;
0.085 kg/SSkg/day***
BOD volumetric loading;
0.20 kg/m3/day*
4.0 m (width) x 41.0 (length)
x 1.2 m (depth) x 2 (ponds)
Capacity; 392 m3.
Length of weir; 36.9 m
Detention time;
4.4 hours* (2.0)**
Overflow rate;
6.5 m3/m2/day (14.0)**
Discharge per unit length;
29.0 ra3/m/day (62.4)**
Cage type;
^820 mm, L = 5720 mm
immersion depth;
160 mm, 10 - 80 rpra, 37 kW
Bursh type;
01000 mm, L = 4500 m
Immersion depth;
175 mm, 40 - 80 rpm
6.0 m (width) x 154 m (length)
x 1.4 m (water-depth)
= 1.283 m3 (capacity)
Aeration time;
28.8 hours* (13.4)**
4.0 m (width) x 41.0 m (length)
x 1.4 m (water-depth) x 2 (ponds)
Capacity; 456 m3,
Length of weir; 36.9 m
Detention time;
5.1 hours* (2.4)**
Overflow rate;
6.5 m3/m2/day* (14.0)**
Discharge per unit length;
29.0 m3/m/day* (62.4)**
Cage type;
/5820 mm, L = 5720 mm
Immersion depth;
160 mm, 30, 45, 60 rpm, 22 kW
Cage type; 0820 mm, L * 3720 mm,
Immersion depth; 175 mm, 60 rpm, 11 kW
03.8 m x (water-depth) 2.0 m
x 2 (units)
03.8 m x 2.0 m (water-depth)
x 2 (units)
                Notess   * A value corresponding to the schematic daily maximum flow,
                        1,070 m3/day.
                      ** The numerical value in the parentheses expresses a value
                        corresponding to the capacity of main pump  (1.6 x 24 x 60 »
                        2,304 m3/day).
                     *** The measured value of BOD-SS loadings in fiscal 1981 and 1982
                        were 0.01 to 0.09 kg-BOD/kg-SS/day.
                                         275

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  Pig.  4  Flow diagram of the Yufutsu wastewater treatment plant
      Table 6  Operation condition (Yufutsu  treatment  plant)
Research period
1982.9.1
- 10.29
1982.10.30
- 12.24
1982.12.25
- 1983.2.16
1983.5.26
- 7.14
Series
number
1
2
1
2
1
2
1
2
Aeration unit operation condition
Main rotor I
(number of
rotations)
Continuous (45)
Continuous (60)
Intermittent:
10 hrs/day (60)
-
Intermittent:
10 hrs/day (60)
Continuous (60)
-
Intermittent!
10 hrs/day (60)
Main rotor II
(number of
rotations)
-
-
Continuous (45)
Continuous (60)
Continuous (45)
Continuous (60)
Continuous (60)
Continuous (60)
Oxygen
supply
rate
kg-02/day
-
140
230
170
230
310
210
240
Average
inflow rate
(minimum -
maximum)
m3/day
-
• 609
(467 - 892)
614
(548 - 686)
594
(520 - 748)
518
(471 - 599)
519
(477 - 570)
706
(516 - 1025)
661
(416 - 1183)
BOD-SS loadings
kg-BOD/kg-ss/day
-
0.026 - 0.045
0.018 - 0.037
0.017 - 0.034
0.016 - 0.039
0.013 - 0.036
0.023 - 0.073
0.018 - 0.068
water
temperature
in ditch
°C
-
14 - 19
9.0 - 12.8
9.0 - 12.7
4.2 - 7.5
4.2 - 6.9
12.1 - 15.8
12.0 - 15.3
MLSS
concentration
mg/je
-
2810 - 3610
3900 - 5320
3900 - 4500
3800 - 5400
3700 - 4900
3170 - 4010
3380 - 4520
  1. The main rotor I stops during operation of the final settling tank mechanical aeration unit (sub-rotor).
  2. The number of main rotor rotations is shown by rpfn.
  3. The oxygen supply rate refers to the estimate (calculated value) by KLa2Q measured in the mixed liquor.
(2)   Takane  wastewater  treatment plant

          The  Takane wastewater treatment plant is connected to a
     separate  sewer system in a rural area.  Because its  influent
     consists  of domestic wastewater  and livestock waste,  the wastewater
     is characterized by its greater  concentration of BOD  and nitrogen
     compared  with general wastewater.  The outline of the facilities is
     shown in  Table 7,  the treatment  flow diagram is shown in Fig.  5,
     and the operating  conditions  are shown in Table 8.
                                  276

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          Table 7   Outline of  major  facilities  of the Takane plant
Facility
Main pump
imhoff tank
Oxidation ditch
Final settling tank
Mechanical aerator
Sludge drying beds
Structure and specification
Submerged pump 0.5 m3/min. x 11 m x 4.5 kw x 1 (unit)
6.0 m (width) x 6.0 m (length) x 7.5 m (Depth)
Capacity ; 238 m3
Water area; 36 m^
6.0 m (width) x 200 m (length) x 1.1 in (water-depth)
Capacity ; 1,320 m3
Aeration time ; 48 hours*
BOD-SS loadings ; 0.05 kg-BOD/kg-SS/day*
BOD volumetric loadings; 0.08 kg-BOD/m'/day*
6.0 m (width) x 6.0 m (length) x 3.0 m (water-depth)
Capacity ; 100 m3
Hater area ; 36 m3
Overflow rate ; 18 m3/m2*
Detention timer 3.7 hours*
Axial flow pump 01200 x 11 kw x 2 (units)
Roots type blower;
4.0 mVmin. x 0.22 kg/cm2 x 3.7 kw x 1 (unit)
Total sand bed area; 245 m2
               Note: Those with the asterisk mark are the values at design.
                                                Excess sludge
Influent
    Wet well
                           OxidaLion ditch
                                                          Final settling
                                                          tank
                                                        Digested s]udg>
                                                               Sludge drying
                                                               bed
       Fig. 5   Flow  diagram of  the Takane wastewater treatment plant
                                         277

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       Table  8  Operation  condition  (Takane  treatment plant)
Research
period
1983.7.25
- 8.19
1983.10.17
- 11.25
1983.12.2
- 12.22
1984.2.27
- 3.23
Air-flow
rate
m /min.
1.9
0.8
0.7
1.6
Average
inflow rate
(minimum -
maximum)
m3/day
318
(274 - 386)
309
(264 - 399)
270
(251 - 280)
291
(249 - 424)
BOD-SS
loadings
kg-BOD/
kg-SS/day
0.010 - 0.022
0.010 - 0.018
0.011 - 0.016
0.015 - 0.019
Water
temperature
in ditch
°C
27.2 - 31.8
12.5 - 21.2
7.8 - 10.4
6.5 - 9.0
MLSS
concentration
mg/je
2820 - 3540
3480 - 3900
3590 - 4160
3150 - 3780
          To clarify the effects  of  the  increase  or  decrease  of  the
     aerobic zone in the ditch on the nitrogen removal,  this  treatment
     plant is operated by changing air flow rate  from blowers into two
     stages.  Aerator mounted in  Takane  plant consists of  an  axial flow
     pump for mixing and a blower for oxygen supply  into mixed liquor.
     Therefore,  it is possible to control oxygen  supply  easily.   One
     operating mode (called the full nitrification mode) is intended to
     facilitate  the complete nitrification as much as possible with the
     air flow rate from 1.6 to 1.9 m3/roin. (7.5 to 9.0 m3  per 1  m3
     of wastewater).   The other is an operating mode (called  the
     nitrification control mode)  that controls the nitrification to the
     extent whereby the effluent  quality (mainly  T-BOD)  is not adversely
     affected, with the air flow  rate from 0.6 to 1.0 rn^/min.  (2.9 -
     4.8 m3 per  1 m3 of wastewater.)   The DO distribution  in  the
     ditch in each mode is shown  in  Fig. 6.
          The effluent qualities  of  the  Yufutsu plant and  the Takane
     plant were  analyzed by taking composite samples.

(3)   Okinoshima  wastewater treatment plant

          The Okinoshima wastewater  treatment plant  was  constructed on
     an island in the Lake Biwa and  its  wastewater is mainly  general
     domestic wastewater.  To prevent the lake water from
     eutrophication, this plant was  planned to employ a  nitrification
     and denitrification system with a batch operation mode at the time
     of design.   The outline of facilities is shown  in Table  9,  and the
     treatment flow diagram is shown in  Fig. 7.  The plant is presently
     operated with two cycles per day and its time sequence is shown in
     Fig. 8, and operating conditions in Table 10.
                                278

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    0.8

    0.6

    0.4
    0.2
      0

    0.8

    0.6

    0.4
      0
     0.6
August 5, 1953
Air flow rarer 1.3 mVmin.
November 14, 1983
Air flow rate;  0.8 m'/min.
December 15,  1983
Air flow rate;  0.7 n"/mm.
                                                         200
                                 March 9,  1984
                                 Air flow rate; 0.6
                  Distance from i-.e aechanical
                                       29 m
Fig. 6   DO distribution in  each operating mode
                            279

-------
  Table 9  Outline of major facilities of the Okinoshima sewage
           treatment plant
Facility
Wet well
Oxidation ditch
Supernatant water
reservoir
Sand filter
Sludge reservoir
Sludge drying bed
Mechanical aerator
Main pump
Structure and specification
8 m (width) x 9 ra (length) x 1.5 m (water-depth)
Capacity; 108 m3
2.5 m (width) x 68 m (length) x 2.5 m (water-depth)
Capacity ; 425 m3
Detention time ; 48 hours
BOD-SS loadings ; 0.05 kg/-BOD/kg-SS/day
MLSS ; 3000 mg/£
Sludge detention time; 30 days
Capacity; 50 m3
1.8 m (diameter) x 4.5 m (height) x 2 (units)
Filtering speed; 200 m/day
Capacity; 82 m3
Sand floor total area; 64.3 m2
Vertical axis type rotor; 7.5 kW x 1 (unit)
Submerged pump; ftlSO
1.8 m3/m x 10 m x 7.5 kW x 2 (units)
              Coagulant
              injecting device
Drying sand
bed
Fig. 7   Flow diagram of  the Okinoshima wastewater treatment  plant
                                 280

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Cycle
1) Filling
Initial hiqh-speed mixing
*' operation
3) Denitrif i cat] on
4) Nitrificat ion
5) Adding of PAC
6) Settle
7) Draw
8) Drawing sludge
gi Retention in the treated
water storage tank
Return oE the settled sludge
in storage tank
11) Water supply of the tiller
Operating hours
20 rain.
20 mm.
3 hours
5 hours 15 mm.
3 mm .
2 hours
30 mJn.
4 mln.
4 hours 30 min.
25 mJn.
24 mV'ir
03 6 (hr) 9 U
SI
D
f^^S^N^\^\l

l^^^^;^^N^^^^^N^^^^
i
D !
b
s\\\X\\\\\\\\\\\\\^1
1
fc^£££-._S3
             Fig. 8  Operating schedule of the Okinoshima plant
     Table 10  Operation condition  (Okinoshima sewage treatment center)
Research
period
1984.7.1
- 9.30
1984.10.1
- 12.31
1985.1.1
- 3.31
Number of
aeration unit
rotations
rpm
21
(Denitrification)
39
(Nitrification)
21
(Denitrification)
39
(Nitrification)
21
(Denitrification)
39
(Nitrification)
Average
inflow rate
(minimum -
maximum)
m^/day
94.3 (85.1
- 102.7)
89.9 (73.6
- 97.1)
94.4 (83.9
- 137.7)
BOD-SS
loadings
kg-BOD/
kg-ss/day
0.012 - 0.021
0.012 - 0.023
0.011 - 0.018
Hater
temperature
in ditch
•c
22.8 - 29.7
10.3 - 24.5
7.7 - 11.3
MLSS
concentra-
tion mg/l
3500 - 4960
3450 - 5200
4100 - 5210
2.3  Assessment of the Mechanical Aerators

2.3.1  Construction technology assessment system

          This system is to assess the functions and performances of new
     technology developed by manufactures.  First, the Minister of
     Construction announces the technical subjects to be assessed in an
     official publication, inviting the manufacture to submit their
     proposal.  The Minister of Construction issues a certificate of its
     performance after the assessment by the Technology Assessment Committee
     organized by the Ministry of Construction.   This system contribute to
     promote the application of new technology as well as technology
     development.
                                     281

-------
          One of the subjects for assessment in fiscal 1981 was "Development
     of a mechanical aerator for the oxidation ditch process".  Eight
     manufactures submitted applications.  Because the submission of
     applications continued even after this assessment, the Technology Center
     for National Land Development, one of the public corporation under the
     control of the Ministry of Construction assessed applications from
     manufacture.

2.3.2  Goals of development

          The predetermined goals for the development of the aerator on the
     official publication were as follows:

     (1)   To assure sufficient velocity in a ditch to keep solids in
          suspension; the minimum velocity must be more than 10 cm/sec.

     (2)   To supply oxygen efficiently; the efficiency must be more than
          1.8 kg-02/kWh.

     (3)   To provide a sufficient mixing; the deviation of MLSS within any
          cross section must be less than 10%.

     (4)   To assure easy maintenance.

     (5)   To be in structure that measures can be easily taken for protection
          of surrounding environment.

2.3.3  Results of assessment

          The 13 applications, of which; 7 in the horizontal axis type, 3 in
     the vertical axis type and 3 in the others, were submitted in fiscal
     1981 to 1982.  All aerators were assessed as being capable of satisfying
     the goals of development.
          More detail information is in the proceeding of the 9th US/Japan
     Conference on Sewage Treatment Technology entitled "Construction
     technology assessment system and the development of a mechnaical
     aerators for oxidation ditch process".
3.   PROCESS PERFORMANCE

3.1  BOD Removal

          The sludge retention time of this process is long so that the
     nitrification is progressed easily.  Therefore, effluent BOD consists of
     the carbonaceous oxygen demand and oxygen demand by nitrification.  As
     the carbonaceous oxygen demand was measured as nitrification inhibited
     BOD by addition of allylthiourea (called ATU-BOD), BOD by nitrification
     (called N-BOD)  was calculated by subtracting ATU-BOD from ordinary BOD
     (called T-BOD).
          Fig.  9 shows cumulative frequency distribution curves of effluent
     BOD.  The data shown in the figure are of T-BOD of the three plants


                                     282

-------
selected for  the  field survey, and soluble BOD  (called  S-BOD)  and
ATU-BOD of the Yufutsu plant.   According to Pig. 9,  in  the continuous
flow system effluent T-BOD occasionally exceeded 20  mg/i  (effluent T-BOD
with the oxidation  ditch process is regulated to be  less  than  20 mg/£ by
the effluent  standards in Japan), whereas effluent ATU-BOD was generally
less than 10  mg/j? during investigations.  Thus, it is important to
decrease N-BOD in order to meet the effluent standards.
                                        o  Yufutsu plant    T-BOD

                                        •  Yufutsu plant    ATU-BOD

                                        3  Yufutsu plant    S-BOD

                                           Takane plant     T-BOD

                                           Qkinoshima olant  T-BOD
             02  4  6  8  10 12 14 16 18 20 22 24 26 23 30 32 34 36 38 40
                          Effluent BOD (mg/i)

     Fig. 9  Cumulative frequency distribution curve of T-BOD,
             ATU-BOD  and S-BOD of the effluent
     Fig. 10 shows  the cumulative frequency distributions  of T-BOD of
effluent samples  with Kjeldahl nitrogen more  than  2  mg/K, and less than
2 mg/£ at the Yufutsu plant.
     It is clear  from the figure that nitrification  greatly affects
effluent T-BOD.   That is, the value of T-BOD  are always smaller than
20 rag/Z in case of  the well nitrified effluent.  On  the other hand, the
frequency exceeding the effluent T-BOD 20 mg/£ was about 50% in case of
the partial nitrification.   Therefore, one solution  would  be to
accomplish the nitrification completely in order to  meet the effluent
standards.
                                 283

-------
             100
              90  -
              80  -
                                                     Idanl nitrogen; ~|
                                                     of less tnan   i


                                                     Idahl nitroaen; !
                                                     of more tr.an   I
                                                     -11.-. -a, 1)
                   02  4  6  8 10 12 14 16 1820 22 24 2f. 2c 30 32 34  35 38 40

                           Effluent T-BOD (mg/J,)

        Fig.  10  Comparison of  T-BOD classified by effluent Kjeldahl
                 nitrogen  concentration
          As for the batch system, the  results  of  experiments at pilot plants
     and the Okinoshima plant showed that T-BOD did  not exceed 20 mg/£, and
     this system can treat wastewater stably.   At  the Okinoshima plant, the
     nitrification progressed sufficiently  except  for a certain period in
     winter, and the effluent concentration of  Kjeldahl nitrogen was 1.6 mg/jj
     on the average.  About 90% of the  data were less than 1.0 mg/£.
          According to the 24-hour investigations  at the Takane plant,
     effluent S-BOD with respect  to the changes of the effluent quality in
     time was in the range of about 2 mg/£  to 7 mg/£, and influent BOD was
     treated stably even when the hourly maximum flow was about 2.2 times of
     the design capacity.

3.2  Suspended Solid Removal

          As for effluent suspended solids  at each treatment plant, the
     maximum and the minimum were 26, 1 mg/£, respectively.  Therefore, if
     the oxidation ditch process  is operated under BOD loadings from 0.01 -
     0.07 kg-BOD/kg-SS/day, stable SS removal could be achieved.
          Fig. 11 shows the relationship between the overflow rate of the
     final settling tank and the  effluent suspended solid at the Takane
     plant.  The overflow rate in this  case refers to a value based on the
     total flow of wastewater and return sludge.  Fig. 11 shows that the
     overflow rate remained within the  range from  5 to 20 m^/m^/day, and
     the effluent suspended solids never exceeded  10 mg/Ji.  Also, the
                                     284

-------
     experiments  (experiments on the continuous treatment system)  by Lhe
     Public Works Research Institute showed the removal of  suspended solids
     was stable in the range from 6.9  to 26.1 m3/m2/<3ay of  the overflow
     rate.
                                                      24-hour test
                  20
                  15
                 = 10
                   5 -
                       Legend
                        o 12/21 Nitrification control mode;
                         MLSS 3,800 mg/i

                        o 3/6 Full nitrification mode;
                         MLSS 3,670 mg/J,
                        (Note)  The overflow rate includes the
                             amount of sludge returned
                                                O
                                              O   00
                                                          O
                                                          O
                                5          10          15

                                Overflow rate (m3/m2/day)
         Fig.  11  Relationship between the overflow  rate and effluent
                  suspended  solids in the final settling tank
          In the oxidation ditch process,  the MLSS concentration is
     maintained at a high concentration of 3,000 to 5,000 mg/£.   For this
     reason, zone  settling of activated sludge usually occur  in  the final
     settling  tank,  so that fine floes are held in sludge blanket.   These
     results show  that removal of suspended solids is excellent  if  the
     suitable  overflow rate is set  for the final settling tank and
     withdrawing of  activated sludge  is carried out appropriately.   The batch
     system especially exhibits this  characteristics because  of  the zone
     settling.
3.3  pH
          Fig.  12  shows the relationship between the alkalinity and pH in
     effluent  at three plants.
                                       285

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              7 -

    ""-"  o**
•"el •   o
                                          Legend
Mark
A
0
'
Treatment plant
Yufutsu
Takane (Full Nitrification)
Takane (Nitrification
control)
Okinoshima
                         50         100         150

                               Effluent alkalinity (mg/X.)
                                                        200
                                                                  250
        Fig. 12  Relationship between  the  effluent  alkalinity and pH
          pH never declined significantly because of sufficient recovery  of
     alkalinity by denitrification.
          At the Takane plant, distinctive difference was noticed between
     effluent pH in the full nitrification mode and that in  the nitrification
     control mode.  In the full nitrification mode, pH was a little low in
     the range from 7.1 to 6.6 because of full nitrification and partial
     denitrification.  In the nitrification control mode, however, due to
     complete denitrification of nitrate produced, pH remained in the range
     from 7.0 to 7.3.
          At the Okinoshima plant, the effluent alkalinity was considerably
     low compared to other two plants, and pH sometimes declined to 6.2 as
     shown in Fig. 12.  However, at this plant, the alkalinity in the mixed
     liquor changes with aeration time (nitrification and denitrification
     process) as shown in Fig. 13.  The average pH in the mixed liquor during
     aeration is much higher compared with effluent pH.
          Figs. 12 and 13 show that if pH decreases as nitrification
     progresses, the decrease in pH can be prevented by incorporating
     denitrification reaction in a ditch to recover alkalinity as required.

3.4  Nitrogen Removal

3.4.1  Nitrification

          The relationship between influent Kjeldahl nitrogen into the ditch
     and that of effluent of each treatment plant is shown in Fig. 14.
                                      286

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     80
     60
- 40


^



<
           Denitrification   .    -
           process	  Nitrification process
                                               Settling
                                      (Okinoshlma)
                                                       Super-

                                                       natant
                                                    	O
                    Aeration tame (hour)
Pig. 13   Changes in  the  alkalinity of  mixed liquor
          •  Takane  (Nitrificati

             control)
                                                           100
                                                           90
                                                         ;   80 S
                                                         -   70
                                                           60 i

                                                              S.
      0   10   20   3C   40   50   60    70   80   90   100  110



                Influent Kjeldahl nitrogen  (mg/4)




   Fig.  14   Characteristics  of  the nitrification
                             287

-------
         At the Takane plant, the removal of Kjeldahl nitrogen in the full
    nitrification mode were more than 90%.  The nitrification occurred
    sufficiently even if the temperature of mixed liquor was 6°C.  On the
    other hand, the removal efficiency of Kjeldahl nitrogen in the
    nitrification control mode was about 60 to 90%.  In this mode,
    nitrification progressed just partially because of a smaller aerobic
    portion in the ditch, so that the Kjeldahl nitrogen remained in the
    effluent.
         Observations on the Okinoshima plant (Batch type system) showed
    that the removal of Kjeldahl nitrogen both in summer and in autumn was
    more than  95%.  The removal efficiency in winter fluctuated
    considerably, and sometimes declined to about 80%.  The asterisk mark in
    Fig. 14 shows a case in which the aerator failed to raise the
    revolutions to the predetermined 39 rpm during the nitrification cycle
    and dissolved oxygen was not supplied enough to complete nitrification.
         Fig.  15 shows the variation of effluent soluble nitrogen from Nov.
    1981 to Feb. 1982 of the series III test (Batch type process) carried
    out by the Public Works Research Institute.
I

a 30
  20
  10
                                                  r\
                                                                        xlO

                                                                        16
12
      'HI 11/10  11/20   11/Jl)   12/10   12/20   J2/JO    '1)2 1/10  1/20    1/30

                                     Days


                Fig. 15  Removal nitrogen in the series III
         Soluble Kjeldahl nitrogen remained in the effluent after the middle
    of December 1981, and excess sludge was withdrawn to reduce MLSS in the
    ditch from 16,000 to 3,000 mg/£.  As a result, Kjeldahl nitrogen was
    seen to have converted into nitrate nitorgen.  This may be attributable
    to the increased dissolved oxygen in the mixed liquor caused by lowering
    MLSS.
         All these observations suggest that the amount of air supplied is a
    control factor to determine the degree of nitrification.
                                     288

-------
          The relationship between the water  temperature  and  the
     nitrification rate of Kjeldahl nitrogen  in  the  ditch is  as  shown in
     Pig. 16.
                 a 0.4
                  0.2
                                     Legend
Mark
A
•
T
Treatment plant
Yufutsu
Takane
Okinoshima
                                    A
                                     A
                               10         ;o   •      30

                               Water temperature in the ditch (°C)
               Fig. 16  Nitrification rate in the aerobic  zone
          The nitrification rate at the Yufutsu and Takane  plants  was
     calculated by using the amount of removed Kjeldahl nitrogen and aerobic
     ditch volume that is effective for nitrification.  In  the  case of  the
     Okinoshima plant, the nitrification rate was calculated  as the removal
     rate of Kjeldahl nitrogen in the ditch assuming  a  zero order  reaction.
     The nitrification rate was from 0.2 to 0.7 mg-N/g-MLSS/hr  and are
     considerably lower compared with that of nitrified liquor  recycled
     biological nitrification denitrification process (NLRB process), of
     which rate was 1.6 mg-N/g-MLSS/hr  (20°C).  It is considered that this
     low nitrification rate is caused by the low DO distribution in the ditch.

3.4.2  Denitrification

          The relationship between the removed Kjeldahl nitrogen
     concentration and the removed nitrogen concentration of  each  sewage
     treatment plant is shown in Fig. 17.
                                      289

-------
            100


             90


             80


             70
           I

             60
           3  50
           o
           I  40
           5
           i



             20
Legend

 *  Yufutsu plant

 o  Takane (Full nitrification)

 •  Takane (Nitrification
    control)

 •  Okinoshima Diane
                                   I
                                                    I
                               40   50   60   70   80   90  100

                       Removed Kjeldahl nitrogen (mg/£)

            Fig.  17  Characteristics  of denitrification
     At the Takane plant, almost no nitrite  or  nitrate remains in  the
effluent in the nitrification control mode.   In the full nitrification
mode, however,  nitrite and nitrate remain  in the effluent owing  to
nitrification  and the total nitrogen removal was smaller than  the
Kjeldahl nitrogen removal.
     At the Okinoshima plant which is operated in a batch mode,  nitrate
and nitrite nitrogen also remained in the  effluent 'throughout  the
observations,  because the settling and withdrawal cycles follows right
after the  nitrification cycle in the time  sequence.  Therefore,  the
amount of  removed total nitrogen was smaller than that of removed
Kjeldahl nitrogen.
     The relationship between the temperature and denitrification  rate
of the mixed liquor is shown in Fig. 18.
                                  290

-------
                   0.5
                 C 0.4
                   0.3
                 ~ 0.2
                   0.1
                                    AA
Legend
Treatment plant
A j Yufutsu
O


*
TaKane
[Full nitrifi-
cation)
(Nitrification
. control)
T :.-.ir.cshima
                               10
            Fig. 18  An  average  denitrification  rate  in  the  ditch
          In the case of the Yufutsu plant and the Takane plant,  the
     denitrification rate was calculated by using the  difference  between
     influent Kjeldahl nitrogen and the effluent total nitrogen,  and ditch
     volume in which DO is as low as about 0.5 mg/jK.   In the case of the
     Okinoshima plant, the denitrification rate was calculated as a removal
     rate of nitrate nitrogen.  The denitrification rate of the oxidation
     ditch process ranged from 0.1 to 0.3 mg-N/g-MLSS/hr, which is fairly
     slower than that of the NLRB process, the rate of 0.6 mg-N/g-MLSS/hr at
     10°C and 1.0 at 20°C.  However, the denitrification rate of  the NLRB
     process could be as low as 0.35 mg-N/g-MLSS/hr when the last portion of
     the nitrification tank with low soluble BOD (1-3 mg/jfc)  was used for
     denitrification.  Therefore, limitation of available BOD as  a hydrogen
     donor is considered to be the cause of the low denitrification rate in
     the oxidation ditch process.
          According to Fig. 18, the denitrification rate in the nitrification
     control mode is smaller compared with that in the full nitrification
     mode.  This may be caused by the difference of nitrate production
     between two modes.

3.4.3  Alkalinity balance

          Fig.  19 shows the relationship between the calculated alkalinity
     consumption and the measured alkalinity consumption.   These  values are
     expressed as following formulas;
                                     291

-------
       100
      3 50
                                             o     '
                                         X
                                                  X
                                                x    t-
                                               /    o


                                             g"9   °
                                                    o


                                             Legend
                               50

                       Caluculated value (kg/day;
               Pig. 19  Alkalinity  balance
AM
                (GAlin - cAleff>  * Q
                      - CAeff)  • 7.14 -  (CAin  - CNeff)
                                                3.57}
             Measured alkalinity consumption (kg/day)
             Calculated alkalinity consumption (kg/day)
             Alkalinity in influent  (mg/£)
             Alkalinity in effluent  (mg/£)
             NH| - N in influent  (mg/H)
             NHJ - N in effluent  (mg/^)
             N02 - N and NO^ - N in  effluent (mg/£)
               AC
               cAlin
               GAleff
               cAin
               GAeff
               cNeff

          Fig. 19 shows that  the measured values are almost equal to the
     calculated values.
          Alkalinity balance  obtained by  other  experiments was also the same
     as above.

3.4.4  Nitrogen removal

          The results of experiments at the  pilot plants (refer to Fig. 3)
     are sown in Table 11.
                            292

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                             Table  11   Results on the batch system at the pilot  plants

Influent


Effluent


periods
I
II
III
I
II
III

Average
Range
Average
Range
Average
Range
Average
Range
Average
Range
Average
Range
B^ATO
(rag/i)
121
73.4
- 160
119
68.0
- 202
250
126
- 480
3.6
1.2
- 7.4
1.1
0.3
- 2.7
3.1
0.3
- 20.2
CODMn

72.3
52.2
- 104
940
33.3
- 223
191
113
- 289
9.2
6.1
- 14.9
7.5
5.6
- 11.8
7.5
5.4
- 14.6
ss
(rag/*)
122
56.0
- 246
293
61.0
- 1040
604
277
- 2030
7.9
3.1
- 13.8
7.3
2.4
- 15.3
6.5
2.4
- 27.1
VSS
(mg/jei
75.9
31.0
- 170
144
36.0
- 458
412
154
- 824



TO
(rag/*)
19.1
12.4
- 28.7
23.3
7.67
- 49.8
45.3
12.8
- 74. 8
12.2
8.46
- 15.8
6.91
5.68
- 8.80
4.46
0.95
- 9.67
DN
(rag/*)
14.0
9.51
- 18.7
13.1
2.24
- 23.1
16.6
8.50
- 26.3
11.6
8.07
- 14.9
6.65
5.32
- 8.76
4.05
0.75
- 8.55
KN

18.2
11.7
- 28.2
22.4
6.46
- 48.9
44.1
12.2
- 72.4
1.21
0.58
- 2.78
0.91
0.41
- 2.28
2.24
0.51
- 9.64
DKN
(mg/JZ)
13.2
8.74
- 18.2
12.2
2.00
- 22.7
15.4
7.70
- 25.4
0.59
tr
- 0.98
0.65
0.36
- 1.03
2.04
0.28
- 8.52
NH4-N
(wg/je)
9.60
5.23
- 12.1
8.56
0.75
- 14.6
9.63
3.34
- 14.1
0.44
0.27
- 0.72
0.42
0.06
- 0.72
1.38
0.16
- 5.83
NO2-N
(»g/£)
0.11
0.06
- 0.20
0.16
tr
- 0.66
0.08
0.05
- 0.13
0.05
tr
- 0.11
0.07
0.02
- 0.12
0.01
0
- 1.16
N03-N
(mg/£)
0.71
0.02
- 3.01
0.76
0.03
- 3.59
1.23
0.29
- 3.55
10.9
7.09
- 14.3
5.93
4.30
- 7.96
2.02
0
- 6.33
Water tem-
perature (°C)
19.4
16.5
- 23.3
23.6
19.0
- 26.0
13.6
9.6
- 18.9
19.6
16.0
- 25.6
24.2
17.8
- 27.8
11.2
7.0
- 17.2
PH
(-)
7.36
7.12
- 7.50
7.33
6.99
- 7.53
4.49
7.13
- 7.77
7.51
7.30
- 7.70
7.44
7.05
- 7.82
7.23
6.78
- 7.62
Transparency
(cm)
5.0
1.8
- 8.5
4.B
1.5
- 12.8
2.6
0.8
- 5.0
32
- 50^
22
- 50<
- 50<
ro
10
CO

-------
     Although the average  removal  of  soluble nitrogen in the series  I
(continuous aeration) was  17.1%,  it rose to 75.6% in the series  III
(intermittent aeration).   Thus  the experiments proved that the removal
efficiency of total nitrogen  of the oxidation ditch process can  be
improved up to about 75% of the total nitrogen by incorporating  a
denitrification process in the  ditch.  Fig. 20 shows the relationship
between the removal and influent nitrogen concentration both at  the
Takane plant and at Okinoshima  plant.  At the Takane plant, the  nitrogen
removal was 70 to 90% in the  full  nitrification mode and 60 to 80% in
the nitrification control  mode.
          100
          50
                  Legend
                   o  Takane (Full nitrification

                   •  Takane (Nitrification
                      control)

                   •  Okinoshima (Summer)
                                                        100
80
                                                         60
                                50
                   Influent total nitrocer.  irtcr/xj
                                                   100
            Fig.  20   Characteristic of nitrogen removal
     Even  in  the  full nitrification mode, anoxic zone existed  in the
ditch.  Therefore,  this resulted in 70 to 90% of the removal of  Kjeldahl
nitrogen.  In the nitrification control mode nitrite and nitrate
nitrogen produced by  nitrification were completely denitrified,  but 20
to 40% of  influent  Kjeldahl  nitrogen remained in the effluent  because of
insufficient  nitrification.   According to the results of these two
modes, an  optical operating  condition would be between the conditions of
these two modes.
     At the Okinoshima plant,  the nitrogen removal 80 to 95% during
summer and autumn,  whereas the nitrogen removal declined to 70%  to 80%
in winter because of  both  insufficient nitrification and
denitrification.  Though the operating conditions did not change
                                 294

-------
     throughout the investigations (Fig. 8), there were signifcant difference
     of DO concentration among seasons, 0.2 to 0.3 mg/£ in summer, 0.7 to
     1.2 mg/j? in autumn and 0.6 to 3.5 mg/j? in winter.  In addition to the
     decrease of the nitrification rate in winter, the change of DO profile
     in the ditch, namely, decrease in anoxic zone, caused the lower removal
     efficiency of total nitrogen.


4.   OTHER PROPERTIES

4.1  sludge Settleability

          Settling of activated sludge differs depending on solid
     concentration.  Sludge settles with clear interface being formed when
     the solid concentration is high,  while causing hindered setting with
     unclear interface when the solid  concentration is lower.  Fig. 21 shows
     the relationship between MLSS and settled sludge volume after
     30 minute-settling (SV3g) of mixed liquor or its diluted liquor.   The
     SV30 is measured as sludge volume (in percentage)  settled after
     leaving the activated sludge full of 1 litter cylinder for 30 minutes
     (Analytical Methods for Sewage, Japan Sewerage Works Association).
     Fig. 21 indicates that the group  causing hindered setting has MLSS under
     3000 mg/j? and SV3g within the range of 20 to 45%.  On the other hand,
     the group forming a clear sludge  interface as soon as settling starts
     has MLSS over 2000 mg/j? and SV30  within the range of 70 to 99%.  The
     oxidation ditch process is normally operated under the condition that
     MLSS is over 3000 mg/.£, thereby causing settling of activated sludge
     with an interface being formed remarkably slow.
          To improve sludge settleability, an experiment was made to
     investigate the effect of slow stirring with a picket fence set in the
     acrylic settling tower (0200, H1200 mm).  The result of the experiment
     is shown in Fig.  22.   The figure  indicates that the setting velocity of
     the interface formed in the activated sludge was greatly improved owing
     to the picket fence.   This is because water paths are created due to
     stirring by the picket fence, thereby helping ascent of water in sludge,
     and improving settleability of the sludge interface.
          Based on the study by the Public Works Research Institute, Fig. 23
     shows the relationship between sludge consolidation ratio obtained by
     the picket fence method (represented by SV3Q_P)  and sludge
     consolidation tatio in the final  settling tank (svg = MLSS/return
     sludge SS).   The figure shows that SV30_p/SVs is below 1.0 in almost
     all cases,  and indicates that the picket fence offers more consolidated
     sludge than  that in the final settling tank.
          With the above mentioned reason,  it is desirable to provide  a
     picket fence  in circular  shaped final  settling tank for improvement of
     sludge settleability.
                                     295

-------
100

90


80



70


60

50


40




30




/--•jjjm, 	
/ O ^ O
/ MB
/ o ^
/a 3 •
1 ^O O
la A,
\ O 4l^
^-^ __c> 	 	

	 —
	

* \

a



kk







	 — -


\

\
I
a

s


\ Sedimentation of
\
-
Hindered settino
/
, 	 f Legend
-^ ^ O \
s ^S A A \

/H A B \
1 D '
IS A] 1
^ v-^ f~1 r~i i
1 ^ rrtTL Q Cn
'f^S 0 Hyp B;
' i^-^ 2 O vtkuk ^^
\c^ Q 4ffi£^ ^^-^
\ _. ^ —
20 r- ^__ — ""



10



0








Treatment
Researched
Document
Data
Document
Data
Document
Data
Document
Data
Document
Data
Document
Data
Document
Data
Voids are
dilution sa
interface





Plants

(Separate
Sewer)
(Separate
Sewer)
(Separate
Sewer)
(Separate
Sewer)
(Separate
Sewer)
(Combined
Sewer)
(Combined
Sewer)

spies.





vs/ss
•64-69%

•66-67%

362-63%

B79-81%

U60-69%

U66-68%

•^80-83%

^67-68%



























i i i i i
0       1,000      2,000     3,000       4,000     5,000     6,000




                        MLSS (mg/5,)
Fig.  21  Relationship between MLSS and SV
                                               30
                        296

-------
                     100

                      90


                      80

                      70

                      60


                   5  50

                   in  40

                      30

                      20


                      10

                       0
MLSS (1) 3,450 mg/£
    (2) 3,730 mg/£
  Legend
   	Sedimentation tower (<(i200xl,200)
        without picket fence
   	Sedimentation tower (i))200xl,200)
        with picket fence
   	Practical sedimentation lake (H=
        1,200, 1,400) without picket £en(
                                   (1)
                              10     20
                                                  40
                                                        50
                                  Time past (minutes)
             Fig. 22   Improvement  of settleability by picket  fence
                      sv
                        30-P
                                            °D
                                            a
                                    2,000       4,000
                                       MLSS (mcr/£)
                                                       6,000
                          Fig.  23  SV30_p/SVs and MLSS
4.2  Sludge Production
           At the pilot  plant of the  public Works  Research Institute, solid
     balance has been measured by  experiment  (continuous system)  with a
     sludge retention time of 56 days both in  summer and winter.   The
     volatile suspended solids (VSS)  of the influent was 70  to 75% of the
     suspended solids  (SS).  The experiment indicates that the sludge
     production was about 80% (in  summer) or about 75%  (in winter) of the
     removed BOD, and about 60% (in  summer) or  75% (in winter)  of the removed
     SS.   Another experiment in autumn for 3 months without  drawing out
     excess sludge shows that the  sludge production was about 50% of the
     removed BOD and abut 70% of the removed SS.
                                         297

-------
          Table 12  shows the sludge  production  during  3  months  in  autumn at
     Takane plant.   The  volatile  suspended solids  in the influent  at Takane
     plant was 81%  (62 to 89%)  of the suspended solids.   The sludge
     production was 73%  of the  removed BOD and  75% of  the removed  SS.
            Table 12  Soudge production at Takane treatment plant
Item
Quantity of BOD removal
Quantity of SS removal
Quantity of HLSS increased
Quantity of excess sludge
Sludge production ® • ©
© / © (kg/kg)
© / © (kg/kg)

© (kg)
© (kg)
© (kg)
® (kg)
+ ® (kg)


Calculated value
57.3 kg/day x 63 (days) = 3,610
53.1 kg/day x 63 (days) = 3,534
(4,030 - 3.48) mg/i x 1,320 m3
= 726 kg
10,300 mg/jj x 36 ra3 371
8,980 x 54 485
8,170 x 40.5 331
10,500 X 27 284
11,900 X 19 226
6,800 x 32.4 220
Total 1,917 kg
2,643 kg
2.643 / 3.610 = 0.732
2.643 / 3.534 - 0.748

kg
kg





          The oxidation ditch process, when used to treat the wastewater
     which has VSS/SS about 75 to 80% (similar to ordinary domestic
     wastewater), enables to keep the sludge production at about 70% of the
     removed SS,  which is smaller than that of the conventional activated
     sludge process.

4.3  Oxygen Consumption Rate

          Oxygen  consumption rate is an important factor for determination of
     the required quantity of oxygen.  Oxygen consumption rate is influenced
     by BOD and nitrogen in the mixed liquor, MLSS, and water temperature.
          Pig. 24 shows the relationship between specific oxygen consumption
     rate and water temperature in the ditch.  When NH^-N is over
     1 mg/jfc, the specific oxygen consumption rate depends on oxidation of
     BOD, nitrification, and sludge endogenous respiration.  In this case,
     the rate constant is under strong influence of water temperature:
     2 mg-02/g-MLSS/hour when water temperature is 10°C, and
     4 mg-O2/g-MLSS/hour when 20°C.  The rate constant measured after
     rinsing the sludge depends on sludge endogenous respiration.  In this
     case the influence of water temperature is small: 0.5 to
     1.0 mg-02/g-MLSS/hour when water temperature is within the range from
     10 to 30*C.   Nitrification was completed when NflJ-N is under
     1 mg/£, which seems to reduce the consumption rate.  In this case, too,
     the influence of water temperature is smaller compared with the case
     where NH^-N is larger.
                                     298

-------

Q)
-u
2
c 8
0
4J
'•n
K
o ~ 6
u
C J3
o-w
>, ra

0 s
U C7i 4
H X.
-t O
U 1
Qj G
CO ~*
2
Legend


-



~


NH4-N

over 1 . 0 mg/£

NH-N under l.Omg/S,
After

rinsing

raka.-
ne
•

Ofcino-
snima
O




0 j •
A



Yuf utsu treatment plant . . m







•

•
•

•




•

••
•
o • o
* • o Y>

£ f
                                        20
                                                 30

                                           ir. ditch (°C)
       Fig. 24  Water temperature vs. oxygen utilization rate constant
5.   CONSIDERATIONS ON DESIGN

          When designing the oxidation ditch process, the following need be
     considered.

5.1  Recovery and Supply of Alkalinity

          In the oxidation ditch process, which is the treatment process
     requiring a long sludge retention time nitrification usually takes
     place, which consumes 7.14 mg alkalinity to oxidize NH^-N of 1 mg
     to NO^-N.  Accordingly, pH of the mixed liquor falls, whereas the
     most appropriate condition for nitrifying bacteria is neutral to weak
     alkali.  The fall of pH results in deterioration of nitrification rate.
     Therefore, countermeasure to prevent fall of pH is required for the
     influent with low alkalinity.
          As a method of such countermeasure, recovery of alkalinity by
     biological denitrification shall be suggested.  Reducing 1 mg of
     NO^-N into nitrogen gas through denitrification produces alkalinity
     of 3.75 mg.  Estimates (calculated values)  of alkalinity balance
     considering biological nitrification and denitrification, as shown in
     Pig. 19, conforms to the actual values, which proves the relationship
     mentioned above.  Generally, buffer capacity becomes quite weak when
     alkalinity of water is below 50 mg/je, thereby causing fall of pH.  Thus,
     it is desirable, with consideration to nitrogen concentration (about
     30 mg/£)  and alkalinity (about 200 mg/£) of the Japanese general
     wastewater, to provide an anoxic portion so as to recover alkalinity.
                                     299

-------
5.2  Nitrification and Denitrification Rate

          To achieve biological denitrification in the oxidation ditch
     process, aerobic portion and anoxic portion need be set spatially or
     timed.   For this setting,  nitrification rate and denitrification rate to
     be considered at designing must be known.   Nitrifying and denitrifying
     rates at the practical facilities employing the oxidation ditch process
     are shown in Fig. 16 and Fig. 18.
          The nitrification rate shown here is  smaller compared to that of
     the NLRB process (1.6 mg-N/g-MLSS/hour when 20°C, about
     0.5 mg-N/g-MLSS/hr when 10°C).  This is because NHj-N of the mixed
     liquor is low and DO is not high enough for nitrification (about
     1.5 mg/£ or more) in the whole ditch.  The relationship between
     nitrification rate and DO indicates that DO is a critical factor over
     nitrification rate in the low DO (under 1  mg/£) zone.  When DO is
     0.5 mg/it then the nitrification rate is about 0.5 mg-N/g-MLSS/hr.  The
     result obtained from a bench scale experiment on the effect of ammonia
     concentration on the nitrification rate indicated that the nitrification
     rate was 2.6 mg-N/g-MLSS/hr when the NH^-N concentration was 10 to
     15 mg/H, and it decreased to 0.2 to 0.4 mg-N/g-MLSS/hr when NHj-N
     became under 5 mg/£.  Accordingly, the nitrification rate of 0.2 to
     0.4 mg-N/g-MLSS/hr will be adopted as a reasonable value.
          The denitrification rate is also smaller compared to that of the
     NLRB process (about 1 mg-N/g-MLSS/hr at 208C, and about
     0.5 mg-N/g-MLSS/hr at 10*C).  The reason of this seems to be the low
     soluble BOD.  The denitrification rate in the NLRB process could be as
     low as 0.35 mg-N/g-MLSS/hr (at 10 to 25*C) in the nitrifying tank
     because of a low soluble BOD in it which is only 1/2 to 1/6 of that in
     the denitrifying tank.  For the oxidation ditch process, denitrification
     rate of 0.1 to 0.2 mg-N/g-MLSS/hr will be adopted since the available
     BOD in the mixed liquor is low (about under 10 mg/jK).

5.3  Oxygen Supply

          The quantity of oxygen required in the oxidation ditch process is
     decided with consideration to consumption of oxygen by oxidation of BOD,
     nitrification, and endogenous respiration.  This could be expressed in
     the following formula:

          Required quantity of oxygen (kg-02/day)=
               {quantity of removed BOD (kg/day)
               - denitrified nitrogen (kg/day)  x m  x a + b x IMLSS
               + nitrified nitrogen (kg/day) x n   '

          Where;

          a: Quantity of oxygen required for unit BOD removal, which is about
             0.5 - 0.7.

          m: Quantity of BOD required for unit denitrified nitrogen, which is
             about 2.
                                     300

-------
          b: Quantity of oxygen consumed by endogenous respiration.
             24 mg-02/g-MLSS/day will be appropriate when the oxygen
             consumption rate after rinsing shown in Fig. 24 is used.

          n: Quantity of oxygen required for nitrification,  it is 4.57 when
             nitrification is to be expressed by the equation: NHj +
             202 — >- NOs + 2H+ + H20.
          When calculation is done using the following conditions (removed
     BOD: 180 mg/£, denitrified nitrogens 20 mg/S., MLSS: 3000 - 5000 mg/S.,
     nitrified nitrogen: 24 mg/S,, and hydraulic retention time in the ditch:
     24 - 48 hours), the oxygen consumption rate will be 2.4 -
     3.3 mg-02/g-MLSS/hr .  These values, compared with the measured values
     in Fig. 24, seem to be appropriate.
          Based upon the above mentioned theory, the required quantity of
     oxygen will be decided considering denitrif ication and safety factor of
     the design.

5.4  Control and Adjustment of Aerator

          Nitrification and denitrif ication have much to do with DO profile
     in the ditch.  Required quantity of oxygen in the ditch fluctuates
     according to the changes in influent, water temperature, and MLSS.  For
     example, oxygen consumption rate goes up as water temperature rises.
     Accordingly, quantity of oxygen supplied by the aerator need
     occasionally be increased to secure aerobic area required.  To prepare
     for such case, the number of rotations of the aerator and the number of
     running units need be designed controllable and the dip depth adjustable.
6.   CONCLUSION

          Through researches with pilot plant and full-scale facilities in
     service, it has been proved that removal of BOD and suspended solids
     could be done stably irrespective of seasonal, daily, and hourly
     fluctuations.  It has also been turned out that anoxic portion set for
     the oxidation ditch process effectively helps to remove nitrogen, to
     recover alkalinity, and to decrease required quantity of oxygen  (i.e.,
     decrease of demanded energy).  For sufficient nitrogen removal, it is
     necessary to provide the hydraulic retention time of 40 - 48 hours for
     the ditch capacity.
                                     301

-------
                     Tenth United States/Japan  Conference
                        on Sewage Treatment Technology
  PLANNING AND DESIGN MANUAL
                 FOR
 SMALL-SCALE SEWERAGE SYSTEM
The work described in this paper was
not funded by the U.S. Environmental
Protection Agency.  The contents do
not necessarily reflect the views of
the Agency and no official endorsement
should be inferred.
              S. Ohmori,
           Research Engineer
              M. Fukabori,
           Research Engineer
              K. Murakami,
         Dr. Eng., Deputy Director
Research and Technology Development Division
       Japan Sewage Works Agency

                 303

-------
                              TABLE OF CONTENTS
                                                                          Page
1.   BACKGROUND AND STATUS QUO OF SMALL-SCALE SEWERAGE SYSTEM 	     305
 1.1   Background	     305
 1.2   Status Quo	     309
2.   PLANNING AND DESIGN MANUAL FOR SMALL-SCALE SEWERAGE
     SYSTEM (DRAFT)  	     312
 2.1   Details of Manual preparation	     312
 2.2   Sewerage System Plan	     312
 2.3   Sewer Design	     313
 2.4   Design of Pumping Facility 	     316
 2.5   Treatment Facilities 	     317
 2.6   Model Works of Small-scale Sewerage System 	     319
3.   RESEARCH AND DEVELOPMENT OF FACILITIES FOR SMALL-SCALE
     SEWERAGE SYSTEM 	     319
 3.1   Outline of Development	;	     319
 3.2   Development of Collection Facility 	     320
 3.3   Development of Treatment Facility	     334
 3.4   Theme for Future	     340
                                      304

-------
1.   BACKGROUND AND STATUS QUO OF SMALL-SCALE SEWERAGE SYSTEM

1.1  Background

          Population served by sewerage system in Japan was 33% in 1983.   One
     hundred (100)  years had past from 1883 when it began to lay sewers in
     the ground.  Before the World War II and for ten years after the War,
     however, preparation of industrial basis such as roads and railways was
     mainly performed while only big cities dare to achieve sewerage works.
     During 1950's and 60's economy grew quite rapidly, and at the same time
     it caused environmental pollution.  The needs for environmental
     pollution control had promoted increase in the spending for sewerage
     works with the help of financial advantage thanks to the high economic
     growth.  In recent years, in spite of severe financial condition, 1.6 to
     1.8 trillion yen per year (0.6 - 0.8% of GNP)  is being invested for  the
     sewerage works.
          Deviation of population served from the national  average is quite
     large depending on areas or cities with their scale.   Fig.  1 presents
     the ratios of  population served by sewerage system of  Japanese cities
     classified according to population ranks.
          A city having population over one million,  such as Tokyo and Osaka,
     has been served very well,  about 80%.   This owes to the fact that the
     national and the local governments jointly made  effort to promote
     sewerage works since population and industries had centered therein
     causing severe environmental pollution.  While population served in
     large cities is relatively  high, that in small cities  with population of
     less than 50 thousand is only 4% on the average.   The  total population
     in the municipalities with  population less than  50 thousand is about
     36.6 million,  which accounts for about one third of the Japanese
     population. Most of these  people are not receiving benefit of the
     sewerage system.
          As for the number of cities carrying out sewerage works,  it is  all
     of the cities  having population over three handnsd thousand, and 80  to
     90% of the cities having population over fifty thousand.   However,
     talking about  cities having population under fifty thousand, it is only
     512 cities (18%)  out of 2,834 that have started  sewerage works.
     Further, it is only 157 cities that have sewage  treatment plants in
     operation.
          This does not mean that the cities with population under  fifty
     thousand have  their environments well conserved  and have no necessity
     for sewerage preparation.  According to the "Survey on the  Opinions  of
     Mayors Concerning Sewerage"  done by the Japan Sewage Works  Association
     in 1984, the mayors of smaller municipalities answered that the  quality
     of public waters such as rivers, lakes, and coastal seas has become
     worse than that  ten years ago.   Especially the mayors  of  the cities  each
     having population of ten to thirty thousand,  who answered that the
     quality of their  rivers,  lakes,  and coastal seas  deteriorated  show the
     highest rate.   Fig.  2 and Fig.  3 show their answers concerning the
     quality of public waters in  their  cities.
                                     305

-------
                                                        
[Major Cities]
90 -

80-

70-
Rate of 60_
population
served by
sewerage
system

30-

20-
10-


Scale of
population
Total populatio n

Population served
by sewerage
system
(unit: 10,000)

of cities
Number of cities
achieving sewer-
age works
Number of cities
having sewerage
in service
Tokyo, Osaka,
Kyoto, etc.

78%
r-^j^;j>~;;y,-v
<$$&? % **%l$0X
'?/\ *^&X$6£^&
-" /+°**^***^*^C**t*^
i*£+t *^"% ^V% ' $j& J>/!
"*>t vff ,V£* %J^»*t4^.4
* ^''"/V^ XV^c^o


'"-.^s^flJ^t
• ?? %'". ; •'"• ~r. vv^*
;-' > '.v-,,,:/<, ;~-<>»H
•»••*> v «»«*"'v>tfS>;<
1-v. / t.t^''>'*- ."*'.'
Over 1,000,000



1,820




10

10

Hiroshima
chiba
Sendai
Okayama
etc.


52%
' i? '°"?c'^ *<, *
.•:* \."..

fa^' V ' '
»/->''«'/ti-',«i
500,000 -
1,000,000



323


10

10

10

Shizuoka
Nligata
Nagasaki
Matsuyama
etc.





40%
^' N. •' ^ , '"
> '*• ^~
'/V^^vf
fv^'?A°A>;-:
^^'^'siJi'*'!
''/$ ''''A'?
*« '<.>''^y %^
300,000 -
500,000

'

581


38

38

37

Aomori
Akita
Maebashi
Miyazaki
etc.






35%
&> '•*" *.\ '„' ' * "„•
|>*;< o«°- ;.-,'-;;
S#°"°°°"" ?-*-f^ "'
PSC "? l'«- Vj-'/v^"- * " '
*;-s->^>«t-> ^t**^'0'' ' '
^!^- ^^ -'"V* <«"<-«•;
100,000 -
300,000
,
"

816


141

132

117

Takayama
Ohmi Hachiman
Zushi
Hon^o
etc.








21%
'\ ' , - ^
1'. °,y ' y,x«
*' ' *AV»;' V.* r, ,
rt'jX'r-'S?*",*?
50,000 -
100,000
cm
'

311


223

183

122

Hitoyoshl
Itakomachi
Tazawakoraachi
Akankomachi
etc.






Whole country 33%




4%
STS! :"&i:£'t i'C ^yis.,.'. •• ' .:.,. ,
Under 50,000



136


2,834

512

159



















Total



3,987


3,256

885

455

                                                            (Survey by the Ministry of construction)
1. Details of the total number of cities are as follows: 652 cities, 1,993 towns, and 611 villages.
        Fig.  1  Sewerage  in  service in Japanese  cities classified by
                 population rank
          Table 1  shows the priorities  (at present and  after 10 years)  among
     preparations  within the limited  budget, of public  properties such  as
     repetments of rivers, roads, and sewerage, etc.  The table tells that
     every municipality having population over thirty thousand and of higher
     ranks are putting priority on  sewage works both at present and after 10
     years.  On the other hand, the priority given to sewage works in cities
     having population under thirty thousand is the fourth (4th) at present.
     However, the  first (1st) priority  is given to the  sewage works after ten
     (10) years.
                                       306

-------
Improved fairly Deteriorated
No changes Deteriorated slightly badly
Improved slightly , .
0 - 10,000

10,000 -
30,000

EOOO -
100,001)

100,000 -
500,000

Over 500,000
54 199 396 515 155
4% 15% 30% 39% 12%
\ ^ /
46 192 179 448 158
4% 19% 17% ' 45% 15%
\\ " 	 	 	 ^~~~~ 	 --_ \
4y 141 65 146 63
11% 30% 1 14% 1 31% 14%
^"\-^ — -~-I::::::^rr— - — _ "\
38 86 1 14 I 25 32
22% 49% | 8% | 14% 7%
	 — -_ — "~^::::^r— ~J~\
10 8 1 1 1 ]
50% ' 40% 1 5% | b%

Average in
vhole country
197 626 655 1,135 3B8
7% 21% 22% 37% 13%
Improved fairly                No changes    Deteriorated slightly    Deteriorated
             Improved slightly                                   badly

  Fig. 2   Water  quality of  rivers  and lakes compared to
           that 10 years ago
Improved fairly

n - 10,000

100,01)0 -
30,000

10,000 -
100,000

100,000 -
500,000

Over 500,000
Improved slightly No changes Deteriorated
1
160 395
13% 31%
, . , , , Dnteriorated
slightly , ,,
badly
538 142
42% 11%
\ ^— ""~"~~'~"~ ^~^~^
146 155 457
15% 15% 45%
^\ ^~^~~~^ ^~"~\
40 96 61 157
9% 21% 13% 34%
221
23%
/
108
23%
^\ " 	 -~^Hr-~- -— -_ ^~~~~--\
26 60 17
15% 35% , 10%
~~ ~~^-^ ~^-^I
6 8
30% 40%

Average in 1
whole country
Improved fai
27 470 630 1,201
1% 16% 22% 41%
rly No changes Deteriorated si
48 21
28% 12%
r 	 _ /
21 3
10% 5% 15%

501
17%
ightly Deteriorated
badly
   Fig.  3  Water quality of small streams compared to
            that 10 years ago

                                307

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  Table 1  Best 5 of  priorities in  infrastructure  construction
            (classified by scale of  population)
^X^Priority
Scale of
populations^
0 - 30,000
30, 000 -
100,000
100,000 -
300,000
300,000 -
500,000
Over 500,000
1
Road
(8,833)
Sewerage
(6,953)
Sewerage
(1,571)
Sewerage
(1,864)
Sewerage
(530)
Sewerage
(497)
Sewerage
(165)
Sewerage
(145)
Sewerage
(84)
Sewerage
(84)
2
Cultural
facilities
(4,839)
Road
(5,070)
Road
(1,335)
Road
(1,139)
Road
(372)
Park, green
area, etc.
(336)
Road
(87)
Park, green
area, etc.
(85)
Road
(38)
Park, green
area, etc.
(43)
3
Park, green area
etc.
(3,427)
Park, green area
etc.
(4,214)
Cultural facilities
(1,027)
Park, green area
etc.
(1,011)
Cultural facilities
(275)
Road
(317)
Cultural facilities
(60)
Road
(64)
Park, green area
etc.
(35)
Welfare and medical
treatment facilities
(30)
4
Sewerage
(3,096)
Welfare and medical
treatment facilities
(3,429)
Park, green area
etc.
(826)
Cultural facilities
(694)
Park, green area
etc.
(257)
Cultural facilities
(216)
Park, green area
etc.
(55)
Welfare and medical
treatment facilities
(62)
Welfare and medical
treatment facilities
(29)
Traffic facilities
(29)
5
Welfare and medical
treatment facilities
(2,643)
Cultural facilities
(3,042)
Welfare and medical
treatment facilities
(515)
Welfare and medical
treatment facilities
(652)
Welfare and medical
treatment facilities
(178)
Welfare and medical
treatment facilities
(197)
Revetment of
watercourses
(45)
Cultural facilities
(59)
Cultural facilities
(20)
Road
(26)
    Notes values in parenthesis (  ) represent total evaluation point.  The total evaluation point
         was calculated with 5 points for the first:priority, 4 for the second, 3 for the third,
         2 for the fourth, and 1  for the fifth.

    Reference from the "Survey on  the opinions of Mayors Concerning Sewerage" as of 1984 by Japan
    Sewerage Works Association.



     The rate of population served by sewerage system  remains at a very
low level  in spite of  the quality of rivers and water  channels having
been deteriorated in small municipalities.   Therefore  such small
municipalities shall positively promote sewerage construction to meet
desires for urban life style such as flushing toilet as well as to

protect quality of public waters.
     The center of sewerage works which were mostly done for big  cities
and a  part of other cities, has been moving over to local mid and small
scale  cities through the  time the whole country has experienced the  high
economic growth.  In near future,  sewerage works in smaller
municipalities and/or  small communities around urbanized areas shall

become to  hold a great ratio.
                                    308

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          The Japanese sewerage technology has been developed as sewage works
     achieved in big cities and stored up as well.  The most appropriate
     technology and system have been pursued for big cities,  it is
     comparatively easy to secure personnel with high technology thereby
     introducing facilities which are benefitted with high technology rather
     economically thanks to the scale merit.  However, application of such
     technology to small-scale sewerage system may cause many problems.  For
     example, it will be difficult to secure high technical engineers even
     though treatment facilities employing high technology is established.
     In addition, cost per capita will be high owing to the scale demerit.
     As for pipe laying works, the cost will also be high because of lower
     population density which results in longer pipe per capita.   These
     factors cause initial cost per capita for sewage works to be increased.
     Further, such increase makes it more difficult for minicipalities to
     start sewage works since most of them are financially weak.
          To meet the needs of sewage works in municipalities, establishment
     of effective planning and designing process for small scale sewage
     system has been requested.  Therefore, the Ministry of Construction drew
     up the "Planning and Design Manual for Small-scale Sewerage System
     (draft)".  This manual (draft) is now tentatively applied so as to make
     its contents more accomplished.  Along with preparation of this manual,
     the Japan Sewerage Works Agency entrusted by the Ministry of
     Construction is performing researches and development of facilities
     which are appropriate for small-scale sewerage system.
          The outline of "Planning and Design Manual for Small-scale Sewerage
     System (draft)" and the researches and development achieved  by the Japan
     Sewerage Works Agency are described separately in Chpater 2  and
     Chapter 3.

1.2  Status Quo

          The sewerage systems for small communities include public sewerage
     systems (under jurisdiction of the Ministry of Construction),
     agricultural community wastewater treatment works (under jurisdiction of
     the Ministry of Agriculture and Fishery), and local community night soil
     treatment works (under jurisdiction of the Ministry of Health and
     Welfare).  (See Table 2).  In addition, joint treatment facilities
     managed by the residents of housing estates without any subsidy could be
     listed.
          Public sewerage systems can be classified into two:  public sewerage
     systems in  a narrow sense and specific environment protection public
     sewerage works.   The narrow-sense public  sewerage systems, whose scale
     is not specifically specified,  are applied to urbanized areas.   Specific
     envornment  protection public sewerage systems are to be applied to
     outside of  city palnning areas or to urbanization control areas having
     population  over  1,000 but no more than 10,000.
                                     309

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   Table 2  Classification of small scale sewage treatment works
Classification
Public sewerage
(in narrow sense)
Specific
environment
protection public
sewerage works
Agricultural,
community waste-
water treatment
works
Local community
night soil treat-
ment works
Population
planned for
treatment
-
1,000 - 10,000
1,000 or less
101 - 30,000
Object area
Urbanized
areas
Other than
city planning
areas or
urbanization
control areas
Agriculture
promotion
areas

Regulation Law
Sewerage law
Sewerage law
Waste Disposal
and Public
Classing Law
(Construction
Stnadardization
Law)
Law for Disposal
of Waste and
Cleaning
Jurisdictional
Ministry
Ministry of
Construction
Ministry of
Construction
Ministry of
Agriculture
and Fishery
Ministry of
Health and
Welfare
     Accordingly, small scale sewage works are mostly performed as
specific environment protection public sewerage.  The specific
environment protection public sewerage is divided into two:  nature
protection sewerage and rural village sewerage.  The nature protection
sewerage is prepared to protect the quality of water of rivers, lakes,
and reservoirs in national and seminational parks.  The other rural
village sewerage is prepared to avoid pollution of the public waters for
farming due to domestic wastewater from such villages.  The agricultural
community wastewater treatment works are applied to the area having
population scale under 1,000.  At the end of 1983, nature protection
sewerage works have been started at 34 places and rural village sewerage
works at 52 places in the whole country.  As for public sewerage works
in a narrow sense, 53 municipalities having population less than ten
(10) thousand have get started by the end of 19Si3.
     Table 3 shows the treatment plants in operation by the end of 1982
classified by capacity and by treatment processes.  As for the treatment
process employed at the secondary treatment plants, most of those
handling 5,000 m /day or more adopts conventional activated sludge
process or step aeration process.  The treatment process at each plant
handling less than 5,000 m^/day is principally the conventional
activated sludge process, which is employed by one second (1/2) of the
secondary treatment plants.  However, variety has been appearing in
methods such as extended aeration process, oxidation ditch, and rotating
biological contactor process.  This is because the small scale treatment
plants require processes which are easier to oprate and maintain.
Treatment processes tend to vary more in the treatment plants under
construction or planned, which means that each municipality is trying to
employ the technology that is appropriate for its own local conditions.
                                  310

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Table 3  Treatment plants classified by  capacity and treatment process
                                                            (As o£ the end of fiscal 1982)
I Treatment
\ process
maximum dry
weather flow
(unit:
1,000 mVday)
Under 5
5-10
10 - 50
50 - 100
100 - 500
Over 500
Total
primary
treatment
Plain
sedimentation
process
2
1
2



20
Semi-secondary
treatment
High-rate
trickling
filter
process
2
3
6
1
1

13
High-rate
aeration
process
2

14
3


19
Secondary treatment
Conventional
activated
sludge
process
37
45
121
69
88
10
370
Stepped
aeration
process
5
6
13
23
21
9
77
Extended
aeration
process
12
1




13
Contact
stabilization
process
1





1
Pure
Oxygen
Aeration
process
2

1

2

5
Oxidation
Ditch
6





6
Rotating
Biological
contactor
process
7
3
2
1


13

Total
76
61
158
96
112
19
522
Notes: 1. When two (2) types of treatment processes exist at a treatment plant, the method treating greater water flow is
      reflected in this table.
     2. Details of the total 522 treatment plants:
        public sewerage 	 460 plants
        River Basin-wide sewerage 	  41 plants
        Specific public sewerage 	  8 plants
        Specific environment protection public sewerage 	 13 plants
       Agricultural  village wastewater treatment works which are under
  jurisdiction of the Ministry of Agriculture  and Fishery are to be
  achieved for treatment of wastewater to prevent irrigation channels and
  other waterways from  being polluted.  Such works are applied in
  agriculture promotion areas, fishing port areas, and forestry promotion
  areas in principle.   Each treatment plant has  the scale below 1,000
  people in principle.   One hundred and thirty-one (131) districts have
  begun works by 1983 and thirty-nine  (39) of  them had already started
  servicing.  Approximately 70% of the treatment process employed for the
  plants which are already in service is soil  covered type contactor
  oxidation process. The remaining 30% is split approximately equally
  among methods such as the rotating biological  contactor process,
  extended aeration  process, and conventional  activated sludge process.
       The local community night soil treatment  works are under
  jurisdiction of the Ministry of Health and Welfare.  The works are
  constructed based  on  the plan concerning disposal of waste provided by
  munipality.  Domestic wastewater including excrement from a housing
  development and so on is treated by such facility that should be managed
  by local public bodies.  The government subsidy is to be applied for  the
  works which meet a certain requisite  (treatment capacity should be over
  101 people but no  more than 30,000).  According to the white paper on
  welfare, the local community night soil treatment works have been
  established at 869 places in the whole country by the end of fiscal
  1979.  Most of them have employed the extended aeration process or
  conventional activated sludge process.  The  criteria of the final
  effluent from these facilities is, based on  the structural guideline,
  BOD under 30 mg/j?, SS under 70 mg/H,  and coliform count 3,000
  organisms/cm3.  This  criteria is rather loose  compared to the criteria
  of Sewerage Law applied for the secondary  treatment  (BOD under  20 mg/£,
  SS under 70 mg/jj,  and coliform count  3,000 organisms/cm3).
                                   311

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2.   PLANNING AND DESIGN MANUAL FOR SMALL-SCALE SEWERAGE SYSTEM (DRAFT)

2.1  Details of Manual Preparation

          As the design manual for sewerage system in Japan, the "Design
     Criteria for Sewerage System" published by the Japan Sewage Works
     Association has widely been used.  Since the sewerage systems in Japan
     have been implemented mainly in large cities, various preconditions such
     as the population density, road conditions, underground facility status,
     load of the sewage treatment plant and fluctuation of quantity and
     quality over time are assumed mainly on the basis of the conditions in
     large cities.  As described in the preceding chapter, however,
     implementation of sewerage systems in small-scale cities in provincial
     districts is becoming an important theme for the future.  Therefore, the
     necessity of another manual for small-scale sewerage system in small
     cities is being recognized.  In small cities socioeconomical conditions
     such as the city characteristic, surrounding environment and financial
     standing are generally different from those in large cities, aside from
     the above technical conditions.  It is natural that the sewerage system
     planning and implementation methods are somewhat different.  For smooth,
     efficient execution of small-scale sewerage system construction works
     which will increase much more in the future, the Ministry of
     Construction has determined to prepare a new planning and design manual
     and entrusted the Japan Sewerage Works Association with the preparation
     job in 1981.  Japan Sewage Works Association formed a manual preparation
     committee consisting of the experts of the Ministry of Construction, the
     Japan Sewage Works Agency, prefectural governments and municipal
     governments, and finalized the "Planning and Design Manual for
     Small-scale Sewerage System (Draft)" in October 1984.
          The main features of this draft manual are explained below in
     comparison with the existing design criteria.  The Design Criteria for
     Sewerage System is hereafter called the "Design Criteria", and this
     Planning and Design Manual for Small-Scale Sewerage System the "Small
     Facility Design Manual".

2.2  Sewerage System Plan

     (1)  Scope of application

               As a rule sewerage system implementation has so far been
          executed only in DIDs (densely inhabited districts)  defined as the
          communities each with a pepulation over 5,000 persons and a
          population density over 40 persons/ha.  Therefore, the Design
          Criteria assumes sewerage systems in such communities.  On the
          other hand, the Small Facility Design Manual assumes the use for
          planning and design of sewerage systems in districts smaller in
          scale, or where the population is less than 5,000.
                                      312

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     (2)   Target year  for  planning

               The Design  Criteria  assumes  about 20  years  later.   Sewerage
          system will  have to be usable under  possible changes  in the future
          because sewers,  once laid,  are very  hard to be reconstructed.
               In the  Small Facility  Design Manual,  the current conditions
          are generally adopted because large  population change in the object
          district is  not  generally possible.

     (3)   Storm water  drainage

               Sewerage systems in  Japan are generally planned  as separate
          sewer systems.  The Small Facility Design Manual assumes use of
          existing drainage facilities as a rule for storm water drainage and
          does not include storm sewer planning except for a special case.

     (4)   Facility structure

               The Design  Criteria  assumes semipermanent reinforced concrete
          construction for facilities.  The Small Facility Design Manual
          assumes, simple  facility  construction as far as  possible.  It  lays
          stress on the economy of  construction investment and  adaptability
          to technical innovation and does not insist on semipermanent
          construction. For these  purposes, it recommends use  of
          prefabricated structures  and machinery and equipment  on the market
          while trying standardization of facilities.

     (5)   Basic thinking about operation and maintenance

               The Small Facility Design Manual basically  assumes no
          full-time operator for the  control of the pumping station and
          treatment plant, but the  patrol once or twice a  week  and adoption
          of the remote alarm system.  Therefore, the pumping station as well
          as the facilities in the  sewerage treatment plant are to be
          operated automatically.

2.3  Sewer Design

     (1)   Fluctuation  of sanitary sewage flow

               The Design  Criteria  assumes the ratio of the design hourly
          maximum flow to  the design  daily maximum flow to be 1.3 to 1.8.
               In a small-scale sewerage system, however,  the hourly flow
          fluctuation  is even greater.  Fig. 4 shows the water  supply data.
          When the daily water supply is in the scale of 1,000  m3/<3ay, the
          ratio of the hourly maximum to the daily maximum is 2 to 3. Since
          some storage retention in the sewer  can be expected in a sewerage
          system, the  Small Facility  Design Manual assumes the  ratio of  the
          design hourly maximum sanitary sewage flow to the design daily
          maximum flow to  be 2.
                                     313

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7
6
§ 5
a *
3 ,
e 3
>,
rH
M T
5
0 1.5
1
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•









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1 1 1 ! 1 t 1 , , 1 1 , , , 1 1 1 t III ,1 I I , 1 1
0 50 10° 500 1 , 000 5 , 000 10, 000 50 , 000 100 , 000
(mVhour)
1 1 1 1 1 1 1 1 t 1 1 1 1 1 1 1 I 1 I 1 1 1 1 1 1 1 1 1 1 ( | ! 1 1 1
      500
           1,000
                   3,000 5,000   10,00020,000   50,000  100,000200,000  500,000  1,000,000
                                   (m3/day)
                           -»- Daily maximum water consumption
Fig. 4  Ratio of hourly maximum water consumption to daily maximum
        water consumption at 60 water supply districts
         (general residential areas)  in 16 cities
(2)   Sewer cross-sectional shape and minimum pipe diameter

          The Design Criteria defines the sewer  cross  section to be
     mainly circular or rectangular, and the minimum pipe diameter to be
     200 mm.
          On the other hand, the Small Facility  Design Manual recommends
     circular or egg-shaped pipe as a rule, and  the  minimum pipe
     diameter of 100 mm.  Since the house density is small in a
     small-scale sewerage system, the sanitary sewerage  flow in the end
     branch is generally small.  Increasing the  dragging power by
     decreasing the pipe diameter has been considered  to be favorable.
     In adopting the 100 mm pipe, a verification test  was conducted by
     the Research and Technology Development Division  of Japan Sewage
     Works Agency as described later.
          Fig. 5 shows the cross-sectional view  of the egg-shaped high
     rigidity PVC pipe as an exmaple of egg-shaped pipes.

(3)   Laying position

          The Design Criteria specifies that sewer pipes should be laid
     under public roads and the minimum earth convering,  shoudl be 1 m.
          The Small Facility Design Manual does  not  limit the laying
     position to under public roads but allows laying  in private land if
     it is favorable.  It also recommends minimization of  the earth
     covering considering the load and allows exposed  sewers if
     necessary so as to economize the laying cost as far as possible.
     Fig.  6 shows the example of exposed sewers.
                                 314

-------
                                            Partial sectional
                                            view of pipe


                                            In case of circular
                                            holes
                                           In case of oval
                                           holes
    Fig. 5   Sectional view  of high-rigidity egg-shaped PVC pipe
               (i)
              (2)
                                   Cleaning port
                  Fig.  6   Example of  exposed sewer
(4)   Manhole
          The Design Criteria requires a manhole to be always provided
     at a curved portion of  the sewer.  The  minimum inside diameter of
     the manhole is 900 mm.
                                   315

-------
               The Small Facility Design Manual specifies that manhole may be
          omitted using angle pipes at a curved portion of sewer so long as
          it does not adversely affect the maintenance and operation.  In a
          section using small diameter pipes whose inside diameter is less
          than 150 mm, the simplified manhole with an inside diameter of
          500 mm as shown in Pig. 7 may be used.
                                Manhole cover
                                (e 500 mm)
                               55
                                      500
                                              55
    Fig. 7  Example of simplified manhole with inside diameter of  500 mm


2.4  Design of pumping Facility

     (1)  installation of pumping facility

               The Design Criteria specifies gravity flow as the basic rule,
          and installation of the relay pump as required.
               The Small Facility Design Manual evaluates the role of the
          pumping station more positively, and recommends pumping station
          establishment if it is favorable in view of the total construction
          and maintenance cost.  It also recommends positive study of
          pressure sewer adoption.

     (2)  structure

               The Small Facility Design Manual encourages adoption of simple
          pumping station.  Fig. 8 shows an example of simplified manhole
          type pumping station.  The screen and grit chamber for relay
          pumping station are not to be provided as a rule.
                                       316

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                             Plan view
                                       Cross
                                       section
                            Inlet
                            pipe
                                         Submersible
                                         mocor pump
               Fig. 8  Example of manhole  type  pumping station
     (3)  Pump type and minimum diameter

               The Small Facility Design Manual  specifies the use of
          detachable submersible pumps  as  a  rule.   The minimum pump diameter
          is 80 mm as a rule similarly  as  in the Design Criteria, but the use
          of 65 mm or smaller pumps is  allowed if  pumps clogging  by large
          floating substances can be prevented.

     (4)  Reserve pumps

               The Design Criteria specifies installation of  one  reserve pump
          in each pumping station.  The Small Facility Design Manual does not
          specify one reserve pump installation  for every pumping station but
          at least one reserve pump in  one treatment area.

2.5  Treatment Facilities

     (1)  Grit chamber, screen and primary sedimentation tank

               The Small Facility Design Manual  defines installation of no
          grit chamber as a rule for simplification of maintenance and
          operation.  Screens are provided for pump protection, but they are
          limited to one type as a rule.   If  the secondary  treatment process
          is of the fixed-film biological  reactor  type, the primary settling
          tank or substituting fine-mesh screen  is  to be provided.   If the
          secondary treatment process is of  the  suspended growth  biological
                                      317

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         reactor type, neither  the primary sedimentation tank or fine-mesh
         screen shall be provided as  a  rule.

    (2)  Wastewater treatment process

              The Design Criteria specifies only time-tested processes like
         the activated sludge process and trickling filters for which the
         design criteria have sufficiently been established.
              The Small Facility Design Manual, however, lays stress on  low
         BOD loading type processes featuring easy control,  it describes
         the sequencing batch reactor process and submerged fixed-film
         biological reactor process which have not much positive performance
         in the past.  Fig. 9 shows an  exaple of the submerged fixed-film
         biological reactor process.
                                                     Removed sludge
                                                     (to thickner)
       Grit
Screen  chamber
u /oji     JLDJ
                                                                      Chlorination tank
              Equalization
              tank
                                         Supernatant/     Thickened
                                         outlet         sludge
Sludge
                                                                  Thickner
         Fig.  9  Example of submerged fixed-film  biological reactor
     (3)  Sludge  treatment and disposal

              The  Small  Facility Design Manual recommends  the  non-heated
         anaerobic degestion, aerobic digestion, and sludge drying beed
         treatment process featuring relatively easy operation and
         maintenance.   It also describes the centralized processing of the
         sludge  collected from several treatment plants or the patrol
         maintenance system should first be studied.  Utilization for
         agricultural  purposes is especially recommended as regards sludge
         disposal.
                                     318

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     (4)   instrumentation system

               As described before, the Small Facility Design Manual
          basically assumes automatic operation for the pumping and
          wastewater treatment facilities.  On the other hand, it recommends
          that the instrumentation system should be as simple as possible,
          mainly consisting of alarms.

2.6  Model Works of Small-scale Sewerage System

          The Small Facility Design Manual adopts new concepts having not
     much past performance.  Model systems applied with this manual have been
     planned and executed at 6 places shown in Table 4.  Full application of
     this manual will start after checking the results.
    Table 4  Model municipalities applied with Planning and Design Manual
             for Small-scale Sewerage System
prefecture
Ibaragi
Niigata
Yamanashi
Gunma
Yamagata
Niigata
Municipality
Dejima-mura
Nagaoka-shi
Takane-cho
Yoshioka-mura
Hagurc—machi
Sumon-mura
Year of adoption
1984
1984
1983
1983
1978
1978
Design
population
(whole plan)
1,800
1,000
2,000
1,820
4,000
4,100
3.   RESEARCH AND DEVELOPMENT OF FACILITIES FOR SMALL-SCALE SEWERAGE SYSTEM

3.1  Outline of Development

          The Japan Sewerage Works Agency has been doing researches and
     developments of ficilities which are appropriate for small-scale
     sewerage system, while the preparation of the Small Facility Design
     Manual by the Japan Sewerage Works Association.
          The small scale sewerage must fit the natural and social conditions
     of local areas different from city areas.  Characteristics (such as
     living environments and state of public facilities) of agricultural
     villages, representing the area to which small-scale sewerage system is
     to be applied, are researched before development of facilities.  With
     consideration to the characteristics known from the research, the
     purpose of development has been set as follows: 1) efficient
     construction, 2) simple operation and maintenance, and 3) harmony with
     the local society.  The direction of development of each facilities was
     studied based on such purpose.
          Mian theme of this research was to improve the existing facilities
     and equipments and to develop new technologies.  Contents of the
     research are described hereinafter.
                                     319

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3.2  Development of Collection Facility

          Density of houses is low in the area to which small-scale sewerage
     is applied thereby requiring longer sewer per house.  The grade of the
     sewer shall be great since sanitary sewage flow is small thereby
     increasing earth-covering.  In addition, the number of manholes per
     sewer length increases because of narrow roads with many corners.  Thus
     the collection facility for the small-scale sewerage system tends to
     cost more per capita.  It is unavoidable to have longer sewer per
     house.  However, it is necessary to study measures to lessen
     earth-covering, to decrease the number of manholes, and to hold down the
     construction cost.

3.2.1  Branch pipe

          In a small community, very small quantity of sanitary sewage is
     expected within the sewer from the starting point to the point to which
     sanitary sewage from dozens of houses is collected.  Such sewer
     mentioned above was defined as "branch pipe".  The measure to decrease
     earth-covering of branch pipe is discussed below.
          When designing sewer, size and grade of pipe have been decided by
     calculation based on steady flow of the maximum hourly flow.  The Design
     Criteria specifies the minimum sewer size as 200 mm and the minimum
     velocity of flow as 0.6 m/sec.  The branch pipe, in which a small flow
     is expected, requires a steep grade to secure such velocity of flow.
     Accordingly, the branch pipe need be laid deep in the ground thereby
     increasing the construction cost.
          The sanilary sewage does not inlet continuously into the branch
     pipe from house drain equipments.  The flow in the branch pipe need be
     considered as unsteady-state flow.  Considering unsteady-state flow in
     the branch pipe the energy at the peak flow shall be used as dragging
     power thereby making the grade of pipe smaller.  Based on this idea, we
     studied about the minimum size of pipe and minimum velocity.  Egg-shaped
     PVC pipe of 100 mm and 150 mm have been studied considering
     connectibility with access pipe and maintainability.

     (1)  Hydraulic characteristics

               To clarify characteristics of flow in the branch pipe,
          measurement using an experimental equipment and simulation via
          computer were performed.  Fig. 10 shows the outline of the
          experimental equipment.  On the conditions of 15 a/time of toilet
          drain, 30 A/time of laundry drain 90 I/time of bathtub drain, flow
          in the pipe were measured at 25 m, 50 m, 75 m, and 100 m each from
          the draining point.
               The theoretical flow was computed via electronic computer with
          the same condition used in the experiment.  The following basic
          equations which are used for open channel unsteady-state flow were
          used as basic formula for computation:
                                      320

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Water
supply
tank
                   ©  Wash machine (304/tirae)

                   @  Bathtub (90£/time)

                   Q>  Toilet (158,/tirae  9S./tirae)

                                    100 m
                            KGf 0100. 0150
                            or VP I: 0 - 10%
                                            ir
                                          1
                                                       8 m
                                                               Support
                                                               frame
Ruc'ulVi ny
tdnk
           Fig. 10  Experimental facility for studying the hydraulic
                    characteristics  of  egg-shaped pipe
                Equation of Continuity

                   3A	JK3         n.
                   3t ~   9X   	  v  '

                Equation of Motion
                   3Q     IS   i£
                   at = ~ 3x ~ 3x +
                where;
                t:  time
                X:  distance
                i:  slope of pipe
                g:  gravitotional acceleration
                P:  water pressure
                A:  flow cross section area
                Q:  flow rate
                n:  roughness coefficient of Manning
                V:  flow velocity
                R:  hydraulic radius

                An  example of the results of experiment and computation is
           shown in Pig. 11.  The actual values  and computed values almost
           agree each other, which proves that hydraulic characteristics of
           the  branch pipe conforms to those of  open channel unsteady-state
           flow.  Prom the experiment and computation,  the following are known
           about hydraulic characteristics of the branch pipe.
                Decrement of the momentary maximum flow rate (£/sec) by the
           flowing  distance is greatly influenced by the quantity of drain.
           The  more flow rate is, the longer the distnace is before the
           momentary maximum flow rate is decreased.  For example, the flow
                                    321

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rate of 15  S. drainage  and 90 S. drainage and 90 Si  drainage is  nearly
the  same when measured at 15 m from  the draining  point.   However,
the  momentary maximum  flow rate of the 15  i drainage is  decreased
down to 0.25 £/sec when measured at  25 m from the draining point.
On the other hand, the 90 i drainage keeps the 0.25 jK/sec flow rate
even at 300 m from the draining point.
•w m
as -M ,
^  *
s °
0
                      100 aim, Q = 15 I, I = 3%
    A 15m
     3 25 i
        C 50
                  loom
                                      •Estimate  (Calculated value)
                                  	Value by experiment
                                   F 200m
 0 °     125   250    375    500 '  625 '  750  ' 875    1000  ' 1125 ' '-"  •-'-- '  --'-
                                                       1250  1375   1500
                           Time passed (seconds)
                      100 mm,  Q = 90 i, 1 = 7%
       125    25°   375   50°    625   750   875   1000   1125  ' 1250 '  1375 '  1500
                           Time passed (seconds) —*•
                      * 150 mm, Q =. 90 i, 1 = 3%
                        I  I   I   I  I	1	1	1	1   •  I	1	1	1	1	1	1
       125   250    375    500   625   750   875    1000   1125   1250  1375  1500
                          Time passed (seconds) —»•
               Fig. 11  Changes in  flow by time
                                   322

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     o The greater the slope is and the smaller the size of the pipe is,
       the longer the distance is before the momentary maximum flow rate
       decreases.

     o Water level and flow velocity have the same tendencies mentioned
       above.

(2)   Peces conveyance function (straight pipe)

          The study of hydraulic characteristics tells that water  level
     and flow velocity can be maintained in  the branch pipe pretty far
     down when having the momentary maximum  flow rate by the drain from
     bathtub.   In case a bathtub of 90  Si is  drained to a pipe of 100 mm
     with a grade of 3%, the flow velocity shall be about 0.5 m/sec. and
     80% of the initial water level can be kept downstream up to 100 m.
     The feces conveyance function by such momentary maximum flow  rate
     is measured by experiment using artificial feces.

     (a)   Method for experiment

               The same equipment used  for research of hydraulic
          characteristics were used. However,  pipe of 100 m extension
          was adopted,  with consideration to repeatability, the
          artificial feces are made of  sponge,  specifc gravity of  1.5
          when wet,  and weight 29 g/piece.  The shape is imitated  to the
          actual object.  Four (4)  pieces are discharged at a time by
          toilet flushing.
               The smaller the flow rate is, the more disadvantageous it
          is for feces conveyance function.   The most disadvantageous
          condition was supposed in the experiment: One house is
          connected to the branch pipe, four (4) family members living
          in the house.
               The relationship between size of pipe, slope, and feces
          conveyance function was studied with eight (8) patterns  of
          drainage supposing that the standard type toilet (15 £/flush)
          or water-saving toilet { £/flush), washing machine (30 Si) , and
          bathtub (90 8.)  are equipped in the house.

     (b)   Result of experiment

               Fig.  12 and Fig.  13 show result of the experiment.   The
          result clarifies the following:

          o AS shown in Fig.  12,  it is  advantageous to use a pipe  of
            100 mm compared to that of  150 mm under normal drainage
            condition where 30 A/time of laundry drain can be expected.
            For example in Pattern 5, feces  is conveyed down to 100 m in
            a pipe of 100 mm while that is conveyance only 30 m in a
            pipe of  150 mm.  Flow velocity and water level have much to
            do with  conveyance of feces.  As predicted with hydraulic
            characteristics of unsteady-state flow, the feces conveyance
            function is greater  when the size of pipe is smaller.

                                   323

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                    Feces conveyance  distance  (Weighted average)
            10       20        30      40       50       60       70       80
           —I	'	1	1	1	1	1	1	T
                                                                   © I - 34    ©1-7%
                                                                      15 i x      9 I x
                ©I- 54  ©I- 74  © I • 3% © I = 54         ©1 = 7%  © : - 5%        4 times      4 times
                  9K.X    9Hx     15 «. x   15 f. *           15 £ x    9 t " 4 times +   + 30 £ x     +30£*
                  30 times  30 times   30 times  30 times          30 times   30 I * 2 times   2 times      2 times
                      PP
                      /I
0)                 /   /
-P^  150 -            
-------
             Feces conveyance distance (Weighted average)
Pig. 13  Relationship between  slope  of  egg-shaped PVC pipe and
         artificial feces conveyance distance (Diameter: 100 mm)
    (a)  Method of experiment

              As sown in Fig. 14, curved pipes are set at four  (4)
        parts within the distance of 100 m.  Experiment was  done
        separately using a piece of 90° bend pipe at each part and
        using two pieces of 45° elbow pipe at each.
                 34 m
                                   34 m
                                                 34 m
                              Second
                              angle
Third
angle
                               First
                               angle
 Forth
 angle
        Fig.  14  Experimental setup for curved pipe study
    (b)   Result of experiment

              Fig. 15 shows the relationship between radius of
         curvature of the curved pipe and feces conveyance distance.
         Table 6 presents the comparison between conveyance distance  in
         straight pipe and that in curved pipe.  The following can  be
         known from the result:
                               325

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              Feces  conveyance distance (Weighted average)
       A   45° elbow

       O   90° bend

      A •  1.3%

      A O  1=5%
     	Q - 9 I « 4 tines + 30 I * 2 tim

     	 Q = 15 £ x 4 times + 30 £ * 2 ti.
Pig. 15  Relationship between average feces  conveyance distance in
         egg-shaped PVC pipe of  100 nun  and radius of curvature
  Table 5  Comparison of conveyance distance  in curved pipe with
           100 cm radius of curvature  and  straight pipe
Draining pattern
9«x7 + 30jex2

15«x4+30«x2

Slope
3%
5%
3%
5%
Feces
conveyance
distance in
straight pipe
51 m
80 m
83 m
100 m
Feces
conveyance
distance in
curved pipe
52 m
73 ra
74 m
84 m
Difference
- m
7 m
9 m
16 m
Difference
per bend
- ra
2 m
2 m
4 m
          o It is more advantageous to adopt greater radius of
            curvature.  However, the difference between conveyance
            distances of 100 cm radius of curvature and that of  150  cm
            radius of curvature is smaller than the differences  between
            that of 50 cm radius of curvature and that of  100 cm radius
            of curvature.  Judging from the viewpoint of processing  of
            pipe and work efficiency, the angle pipe with  100 cm radius
            of curvature seems to be proper.
                                 326

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          o As shown by (?)  and (9)  in Fig.  15,  the feces conveyance
            function is greatly improved if  a head of 20 mm is provided
            when there is a  waller  quantity of  sewer compared to that
            of (§)  and  @ . '$
                          - ,;f
          o There shall be '':ffe*ater difference between the feces
            conveyance function of the straight  pipe and that of  the
            curved pipe as drainage  rate and slope become greater.
            However, the conveyance  function per curved pipe with 100  cm
            radius of curvature does not have much difference compared
            to that of the straight  pipe.  (Table 5)   In addition,  it  is
            quite rare to use several curved pipes in such a short
            distance as adopted in the experiment.  Therefore, it shall
            be allowed to adopt curved pipe  with 100 cm radius of
            curvature or more and head of 20 mm.  This could be
            considered to have the same function as straight pipe.

(4)   Maintainability

          Prom the viewpoint of feces conveyance function, the pipe
     having size of 100 mm shall be  considered to have enough ability.
     However,  there is a possibility to have blockade in a pipe for some
     reason.  Experiment was done to check if any trouble may occur to
     remove the large substances clogging in the pipe of 100 mm.  Clog
     was artificially made in the experimental equipment containing
     curved pipes,  with artificial feces, paper  and cloth diapers,  etc.
     Then the  work to remove the clog was done using the Mini-Jet and
     Flexi-Rodder which are  usually  used for cleaning sewer.  Removal
     was achieved without any problem.
          Employing the pipe of 100  mm instead of the existing minimum
     size pipe of 200 mm may possibly cause  more clogging by large
     substatnces such as paper diaper.  On the other hand, it is  easier
     to know the cause of clogging since a fewer houses are assigned to
     a branch  pipe of the small-scale sewerage.   In addition,  residents
     of such communities do  not move often and 80% of the agricultural
     communities achieve road repair and trench  scooping in coopration
     (survey by the National Land Agency).  This represents the strong
     sense of  cooprative body.   Residents of such areas easily
     understand that draining of abnormal substances into sewer causes
     clogging  thereby bringing troubles to themselves.   Acordingly, it
     can be expected that they learn the use of  sewerage properly.   From
     this point of  view, it  also can be said that maintenance of
     small-scale sewerage sytem with pipes of small size in such
     communities is rather easier compared to that in city areas.

(5)   Maximum flow capacity

          The  minimum pipe size of 200 mm specified in Design Criteria
     has usually much room in flow capacity  compared to the planned flow
     rate.   Therefore,  designing based on steady flow did not cause any
     problem concerning flow capacity.  Now  that the size of pipe is
     100 mm, it is  necessary to design the maximum flow capacity  of the

                                  327

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branch pipe based on unsteady-state flow, as designing considering
sludge conveyance function.
     The momentary maximum flow rate of unsteady-state flow shall
be greater than that of steady flow.  However, the momentary
maximum flow rate made by each house shall occur within a very
short period of time, and there is little possibility for the
momentary maximum flow from each house to coincident.
     Therefore, design of branch pipe should be done based on the
theory of probability.  The study was done about the branch pipe of
0100 mm and the pipe of 0150 mm into which unsteady-state flow may
reach in case the branch pipe is short.

(T)  Computation method

          The simultaneous drainage probabilistic method used in
     plumbing facilities was adapted for the study mentioned
     above.  The basic equations are described below.
          Where w  (£) represents the volume of water drained from
     one unit at a time, and q (Si/sec) represents the flow rate of
     w flowing the pipe, then the time for draining t  (sec) is
     expressed as follows:
          The time ratio (P) shared by w from a certain time T to
     +    TQ» that is, during the time duration of TQ, can be
     expressed by the following equation:
              T0

          When w is drained from n plumling fixture units within
     the time duration Tg, then the time ratio    (the average
     number of simultaneously draining  uiits) shall be expressed as
     follows:
           M » n-p -


          In the case n is extremely big and p is small, the
     probability to have simultaneous draining is known to closely
     be approximated by the Poisson distribution.  The probability
     to have simultaneous draining from r units shall be expressed
     as follows:
                                328

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     From this equation, the total probability  (a) to have
simultaneous draining from more than m plumbing fixture units
can be expressed as follows:
      a=  z  P  (r) =  Z    rj
         r=m         r=m

     Then the maximum simultaneous drainage rate Q  (JJ/sec) can
be obtained by the following equation when the average number
of simultaneously draining units is y, and the maximum number
of simultaneously draining units for a is m.

     Q = m»q

     Sanitary sewage from each home includes bathtub drain,
laundry drain, kitchen drain, toilet flushing drain, etc.
Some or all of these possibly occur simultaneously as an
indenpendent events.  Sanitary sewage from each drainage unit
shall be considered as an indenpendent events with
consideration to safety.
     P (A) represents the simultaneous draining probability
from a certain number or more of a certain kind of plumbing
fixture unit.  P (A]_, A2, ..., AI) represents the
probability that each event of i kinds of plumbing fixture
unit occur simultaneously.  P (A-^, A2, ... A^) is
expressed as follows:

     P (A1, A2 ... Ai) = P (A^  x P (A2) x ... x P  (Ai)


     And when Q^, Q2, . • . Qj represent the maximum
simultaneous drainage rate of each kind of unit, then the
total maximum simultaneous drainage rate  (Q) that is caused in
case these drains are discharged simultaneously is expressed
as follows:

     Q = Q! + Q2 + ••• + Qi

     The number of units, that is, the number of houses can be
estimated by comparing the hydraulic flow capacity of pipe
itself with the maximum simultaneous drainage rate under a
certain probability obtained from these basic equations.

Condtions for computation

     The following conditions are defined for computation.

(a)  Plumbing fixtures concidered and volume of water per
     discharge

          To know the maximum simultaneous drainage rate,
     simultaneous drainage rates all of the drainage units

                             329

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     should  be obtained  and  totaled.  For  simplification  of
     computation, however, the units whose drainage  rate  is
     small were neglected.   That  is, computation of  the
     maximum simultaneous drainage rate was  done using bathtub
     drain and laundry drain.  The quantity  of  drainage per
     time from each drain was supposed 170 jK/time  and
     40 a/time based  on  the  actual measurement.

(b)   Draining time period

         For study of draining time period, drainage patterns
     of three (3) communities were researched.  The  research
     tells that the time period for bathtub  drain  and laundry
     drain is generally  divided into two:  in the morning
     and/or  in the afternoon.  Laundry drain occurs  more  in
     the morning, while  bathtub drain appears slightly more  in
     the afternoon than  in the morning.  Such drains are
     concentrated within eight  (8) hours a day.
         The draining time  period may incline  to  occur in
     either  of the morning or afternoon.   Therefore, the
     draining time period of four (4) hours  was adopted for
     computation.  In addition, the draining time  period  of
     two (2)  hours was used  for computation  because  there was
     occasionally a  tendency for  drainage  to occur
     concentrated in  two (2) hours.  These two  cases (2 hours,
     4 hours) are used for computation.

(c)   Pipe arrangement and density of houses

         The area to which  the small-scale  sewerage system is
     applied has population  of 49 heads/ha,  or  less.  So, the
     density of houses was supposed  to be  10 houses/ha,  based
     on the  standard. The model  was made  with  houses located
     under  such condition, with 15 m sewer extension from the
     draining point of each  house.

(d)   Momentary maximum flow  rate

         The momentary  maximum flow rate  of bathtub drain and
     laundry drain measured  at  15 m  downstream  from the
     draining point are  as follows.  They  are obtained via the
     simulation described  in Section 3.2.1.

         Bathtub drain  (170 Si):  q = 1.07  U/sec)
         Laundry drain  (40  H)  :  q = 0.44  (£/sec)

         The sewer extension from each  house to  each designed
     point  practically differs.   However,  the 15  m sewer
     extension, which is on  the safer  side,  was adopted for
     simplification.
                               330

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(e)  Excess probability

          To set some computing cases, the excess probability
     based on the Poisson's distribution was adopted as
     follows: excess probabilities from 1/100 (once per three
     months) to 1/10000 (once per three yeras)  were applied
     for each drain.

(f)  Hydraulic flow capacity of pipe

          When the maximum flow rate of sewer is set based on
     a certain excess probability, there is possibility a flow
     exceeds the flow rate set with the probability.  Such
     case does not necessarily cause an overflow at manhole
     and/or catch basin, because the flow shall be pressurized
     and go downstream in most of the case.
          The flow rate considered herein is a momentary flow
     rate.  Therefore, pressurized water flow should be
     allowed when having a flow rate over a certain
     probability.  The hydraulic flow capacity of pipe was
     computed separately for full pipe flow rate and
     pressurized flow rate to be compared with the maximum
     simultaneous drainage rate.

Results

     Table 6 shows the number of houses acceptable for
drainage depending on the excess probability, using a pipe of
0100 mm and 0150 mm were used with a grade of 3%.  In case of
100 mm and the draining time period of four (4)  hours with
excess probability of 1/1,000 for full pipe flow, for example,
then the number of houses acceptable is 50.  In case of excess
probability of 1/10,000 for pressurized flow, then the number
of houses acceptable is 42.  This capacity can be said enough
practically when considering the standard density of houses
(10 houses/ha.).
     In case a pipe of 150 mm is used and the draining time
period is four (4) hours with excess probability of 1/10,000,
then 135 houses can be accepted.  The model arrangement of
houses requires sewer extension over 1,000 m, thereby greatly
decreasing the momentary maximum flow rate genrated by drain
from each house.  This means that such design is further on
the safe side.
     As a result of the above-mentioned studies and
researches, the pipe of 100 mm can be used with a minimum
slope of 3% for small-scale sewerage system so as to decrease
the construction cost without causing any problem in large
substances conveyance capacity and maximum flow capacity.
                             331

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                             Table 6   List of maximum flow capacity  (number  of houses)
Total drain excess probability
Bathtub drain excess probability
Laundry drain excess probability
Type of pipe
diameter
(Degree of
grade)
Egg-shaped
PVO pipe
0100 mm 3%
Egg-shaped
PVC pipe
#150 mm 3%
Average
draining
time
period
7200 sec.
(2 hr.)
14400 sec.
(4 hr.)
7200 sec.
(2 hr.)
14400 sec.
(4 hr.)
Item
Number of houses
acceptable for
draining
Number oC houses
acceptable for
draining
Number of houses
acceptable for
draining
Number of hounon
acceptable for
draining
State of flow \
Full-pipe flow
Pressurized flow
Pull-pipe flow
pressurized flow
Full-pipe flow
pressurized flow
Full-pipe flow
Pressurized flow
1/100
1/1
1/100
70,
80
140
150
215
225
440
450
1/10
1/10
44
51
91
100
115
125
235
240
1/100
1/1
45
54
90
100
150
160
305
310
1/1000
1/1
1/1000
50
59
100
110
175
185
360
370
1/10
1/100
33
41
68
76
95
105
195
200
1/100
1/10
26
34
54
62
* 83
93
* 170
180
1/1000
1/1
* 25
35
* 50
60
105
115
210
220
1/10000
1/1
1/10000
38
48
76
86
145
160
300
310
1/10
1/1000
27
35
53
61
84
93
170
175
1/100
1/100
20
29
39
48
69
78
140
150
1/1000
1/10
16
* 25
33
43
63
* 72
125
* 135
1/10000
1/1
15
26
30
* 42
79
91
160
175
u>
U)
Ni

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3.2.2  Simplified manhole

          The inside diameter of existing manhole is 90 cm at the minimum for
     maintenance works of sewer to be done in a manhole.  Maintenance works
     of small diameter pipe with small earthcovering is considered to be done
     from the ground.
          Provided .that man would not enter manhole, the diameter of a
     manhole can be made smaller unless it does not cause any trouble to use
     flushing equipment therein.  Then, construction cost of manhole can be
     saved.
          Based on this theory, simplified manhole has been devised.  The
     peculiarity of this simplified manhole is that the frame of cover and
     the top slab are not directly attached to the vertical wall thereby
     conducting load on cover directly to the ground.  Such structure
     decreases the load to be conducted to the base slab, avoids settlement
     of sewer and reduces stress to the vertical wall.  Ready-made product
     shall be used as an invert at the bottom and installed by bonding.  To
     connect a sewer to the vertical wall, a combined saddle is to be used
     for maintainability.
          Strength test and study of maintainability were achieved using a
     prototype.  The loading test by the normal wheel load was applied to
     measure the stress at each part and settlement rate.  The result tells
     that the stress generated at each part in greatly under the strength of
     the part, that is, each part can bear the wheel load.  It is also proved
     that the settlement caused by full load does not cause any practical
     problems.  As for maintainability, pipe check (inside)  by a T.V. camera
     and cleaning by Mini Jet were done using the prototype.  It was proved
     that the manhole of 300 mm diameter does not give any troubles to the
     works using the T.V. camera and Mini Jet.
          It was also proved that small manholes have the following
     advantages in construction compared to the existing standard manhole:

     (a)   Requires the same excavation width with a pipe thereby decreasing
          earth works.

     (b)   Requires a very short time for construction thanks to unnecessity
          of concrete curing.

     (c)   The construction work is very simple thanks to employment of a
          ready-made product as an invert.

     (d)   Assemble and installation works can be done by man power thanks to
          the light material.

     (e)   There is a clearance between the vertical wall and the top slab,
          which allows delicate adjustment in setting the manhole cover
          height.
                                      333

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3.3  Development of Treatment Facility

3.3.1  Cost analysis

          As known from experiences,  the construction cost for  sewerage
     treatment facility becomes rather higher  considering  the scale when the
     treatment facility is smaller.   To hold the  construction cost for
     small-scale sewerage treatment facility,  the factors  rising the cost
     have been studied.
          The study does not include  the control  building  and sludge building
     which have been clarified so far.
          Three (3) ranks of scales were provided for comparison:
     1,000 m3/day, 500 m3/day, and 100 m3/day.  Three (3)  kinds of
     treatment methods were used: conventional  activated sludge process,
     extended aeration process, and oxidation  ditch  process.  As for
     computation method of cost, estimations done by several  sewerage
     facility makers were referred.   Basic factors and specifications of main
     facilities were presented to them.  As one of basic conditions, it was
     ruled that a grid chamber and a  private power plant should not be
     established.
          Fig. 16 shows construction  cost per  design flow  classified based on
     the scale and the treatment method.  This  figure shows that the smaller
     the scale becomes, the higher the construction  cost per  design flow
     becomes.  The ratio of construction cost  per design flow among
     1,000 m3/day and 500 m3/day is  1:1.3 - 1.2.   Such ratio  among
     facilities processing 500 m3/day and 100 m /day is greater, that is
     1:2.0 - 2.1.   Every cost item requires higher unit cost  when the scale
     becomes smaller.  Especially the facility processing  100 m3/day has
     greater rise in ratio.  As for  oxidation  ditch  process,  the ratio
     between the construction cost per design  flow among  facilities
     processing 500 m3/day and 100 mvday is 1:1.4 in construction
     facility and 1:2.6 in machinery equipment.  The rate  of  machinery
     equipment in the facility processing 500  nr/day is 40%,  while that in
     the facility processing 100 m /day is 51%.
          The reason for the rise in  construction cost of  machinery and
     electronic equipment per design  flow for  the facility processing
     500 m3/day or less is due to the limit in  minimizing  scale of each
     equipment.  This means that the  capacity  of  facility  does  not become
     smaller in proportion to the scale of wastewater treatment flow.
          As for aeration unit, the electric motor output  per 100 m3/day
     was compared among facilities processing  100 m3/day,  500 m3/day, and
     1,000 m3/day.  It resulted in 1.5 kw, 1.1  kW, and 1.1 kW at each
     facility.  The facility processing 100 m  /day requires the highest
     considering the scale.  The collector of  settling tank is  operated with
     the same power used for all the facilities processing 100 m
     500 m /day,  and 1,000 m /day.   Automatic  screen of  the same size is
     used for all the facilities.   This means  that the construction cost per
     design flow of the facilities  processing  100 m3/day is ten (10)  times
     of that of the facility processing 1,000  m3/day.  Main pumps provided
     for the facility processing 1,000  m3/day  are 2 units (5.5 kW)  and 1
     spare unit.   Those for the facility processing 500  m3/day are 1 unit
     (5.5 kW)  and 1 spare unit.  Accordingly,  the facility processing

                                      334

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    500 m /day cost much requiring more  spare unit considering  the scale.
         The ratio of  principle items  in the machinery equipment was
    studied.  Fig. 17  shows that of the  oxidation ditch process handling
    500 mVday.  The aeration unit, control  unit, and sludge  collector
    hold a grat portion.  As a result, it can be said that  improvement of
    these equipments serves effectively  to down the cost.
         The cost analysis has clearified that it is necessary  to develop
    the technology to  make construction  facility, machinery equipment, and
    electric equipment small scaled.   Especially the machinery  equipment
    need be small scaled.  Standardization of facilities and  study for
    practical use of sludge collector  and sludge dewatering bag have also
    been studied.  They are described  below.
  11,000 yen'

      400
376
C
135
(36)
E
48
(13)
M
193
(51)
\
\
184
96
(52)
15 (8)
73
(40)
\

x-

151
80
(53)
61
(40.5)
346
10
•T6.5)
C
168
(•49)
&
M
135
(39)
V,
12
(7)
10?
(60)
57
(33)
C: C
E: C
M: C
\ 143
	
	 — ^.
82
(57)
51
(36)
ost tor structures
ost for
10
"(7)
machinery equipment
312
C
134
(43)
E
35 (11)
M
143
(•46)
\ u«
\\ Z* \ 110
\\
V 	 \ (50)
14 61, >' 46
(9> (8) (42)
           100     500     1000


            Oxidation ditch process
100     500


Extended aeration process
             [m3/day]
Conventional activated
sludge process
            Note: Each value in ( )  indicates the percentage of the each item.
Fig. 16  Construction cost per  design flow of 1 m /day (prices as of 1982)
                    Fig. 17  Breakdown of machinery cost
                                       335

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3.3.2  standardization of facilities

          The small-scale sewerage treatment plant has greater scale demerit,
     and a great number of small-scale sewerage treatment plants are expected
     to be constructed in future.  The scale demerit in the construction cost
     shall be decreased by standardizing facilities thereby allowing mass
     production of parts.  In addition, mass production possibly allows
     simplification of construction, maintenance, and reduction of
     construction period.  Stadardization also omits designing work which has
     been done individually for each facility.  At the same time, design cost
     and office overheads can be cut.  Standardization is now in the work to
     consider mass product at factories.  The outline is described below.

     (1)  Basic policy

               The following were provided for one of standardizations:

          o The basic flow is shown in Fig. 18.  The objects to be
            standardized are screen, aeration tank, settling tank,
            hypochlorite contact channel, and thickner (part enclosed by
            broken line in Fig. 18).

          o Pump well is not included for standardization since it may not be
            required depending on geographical conditions, or its inlet sewer
            level and water head differ.  Sludge treatment facilities is also
            not included for standardization since sludge processing/disposal
            can be centralized from srveral plants and the treatment method
            differs depending on the disposal method.
Inlet
Pump
well
Aeration
tank
                     Scope of standardization
              Fig. 18  Basic flow and scope of standardization
                                      336

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     o Existing treatment plants have two (2)  series or  more to secure
       treatment ability.  In this standardization,  however, the
       teratment series shall be one (1)  from the economical
       view-point.   Accordingly, it is required to make  it possible to
       achieve check and/or repair without stopping  treatment.

     o Small-scale  wastewater treatment plant tends  to hold a great
       portion of personnel expense among maintenance cost.   To reduce
       the personnel expense, the facility shall be  designed to require
       patrols about two (2)  times a week instead of hiring full-time
       operators in principle.

          Based on  this theory,  standardization of oxidation ditch
     process has been tried at six (6)  ranks (300 m  /day -
     1,200 m3/clay)  which are within the range of scale set in the
     Small Facility Design Manual.

(2)   Structure

          When making a standard design,  the structure of each facility
     shall be based on the following theories:

     o Principally, civil engineering works shall not require landslide
       protection wall.  Facility load is small thereby  employing  the
       spread foundation as standard foundation type.  Foundation  type
       is required  to be designed somehow else in case pile foundation.

     o The aeration tank and the final  settling tank shall be the
       integrated concentric circle type which decreases the number of
       wall.

     o Base slab level of the aeration  tank and that of  the  final
       settling tank shall be the same, that is, the base slab of  the
       final  settling tank shall be flat without any taper.   This  will
       make the construction easy and reduce cost.  Sludge collection
       function of  a settling tank with a flat base  slab is  described
       later.

     o Field assembly using precast concrete parts or  employment of
       ready-made concrete products for buildings are to be promoted so
       as to encourage mass production  and commercialization.

(3)   Selection of equipment

          The points to be considered for selection  of equipment are
     shown as follows.

     o Automatic equipment will  maintenance free should  be positively
       adopted since it is operated by  patrol  system in  principle.

     o High technology of the operation and maintenance  shall  not  be
       needed since it is difficult to  secure  patrol man with such


                                   337

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            technology.

          o For easy storage of spare parts and replacement,  products on the
            market shall be used as far as possible.

          o The structure need be designed to allow check,  repair,  and
            replacement without stopping treatment, since only one  (1) series
            exists.

3.3.3  Simplified sludge collector

          Equipment of treatment plant has also been developed considering
     the standardization theory.  The simplified sludge collector devised
     during the development, is outlined below.
          The sludge collector used in the existing small-scale treatment
     plant has fixed rake and center pole.  This requires to  temporarily
     empty settling tank for check and/or repair of the sludge collector.
     Accordingly, they have two (2)  serieses.  To improve demerits  of such
     sludge collector, a simplified sludge collector has been designed which
     does not need to empty settling tank for check and/or  repair.
          Fig. 19 shows its concept.  Th rake is hanged by a  chain  from the
     arm which turns around the center pole by means of drive unit.  Sludge
     is collected by the turning rake.  The rake, hanged by a chain,  can be
     accessed for repair or replacement easily by hauling the chain,  without
     emptying the tank.  In addition, the weight of material  shall  be
     decreased since the parts are not fixed, thereby causing a cost
     reduction.
          Using this type of collector, experiment was done to confirm sludge
     collection function.  The base slab of the tank is flat  considering
     economical advantage and easy construction.  The rake is curved  so as to
     collect sludge stabilizedly.
          The experiment proved that the sludge collector of  such structure
     does not have any problem in its operation and ability.
    Roller
                                        Chain
                    Fig. 19  Simplified sludge collector
                                     338

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3.3.4  Sludge dewatering bag

          Though it was not mentioned in the section of cost analysis, it is
     known sludge treatment facility has a great scale demerit.  For example,
     expenses per sludge volume for dewatering by machine are higher in
     smaller-scale.  This is because the dephdrator of small-scale plant has
     sometimes greater capacity than that is required since the dehydrator
     has not been developed for small-scale plant.  In addition, experts in
     machinery and electrical engineering are required for operation and
     management.  The sand bed process has an advantage of cost reduction
     while requiring pretty much labor for removing dried sludge.
          In the "Small Facility Design Manual", centralized sludge treatment
     and disposal system is recommended to save energy and increase
     economical advantages for small-scale sewerage treatment plant.  When
     such centralized system is adopted, then the scale merit of sludge
     treatment facility shall be increased as well as opportunity to secure
     experts in machinery and electrical engineering.
          On the contrary, it requires each community to promote sewerage
     works at the same level, and there are other practical problems.  A
     simple method for dewatering is desired at least for present.  From this
     point of view, the Japan Sewerage Works Agency has studied
     practicability of sludge dewatering bag.
          Fig. 20 shows the concept of the sludge dewatering bag.  Excess
     sludge, after mixed with polymer, is put into the bag made of Tetoron or
     rayon to be left for a certain period for dewatering and drying.  The
     cloth of the bag plays the filtering role of sand of the sand bed.  The
     sludge shall be disposed as it is in bags when dewatering and drying is
     complete.
                   Feeding
                   sludge
— Polymer
                                                    Dewatering
                                                    and drying
                       Fig. 20  Sludge dewatering bag
                                    339

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          The construction cost is extremely  low since  hardly  any  equipment
     is required as mentioned above.   The required site shall  also be smaller
     compared to that is required for  sand bed  process.  Mechanical and
     electrical engineer are not needed either  because  of  such simple
     equipment.
          The excess sludge from the long-period aeration  process  was used in
     experiment to check the effect of sludge dewatering bag.   It  resulted
     that the sludge was dewatered to  70% moisture content after four (4)
     weeks drying.  Provided that a bag of W  100 cm x H 75 cm  can  treat
     sludge containing about 5 kg of dry solid,  then forty (40) bags are
     required in a week at the treatment plant  of 300 m3/day.   Considering
     the labor for feeding sludge and  carrying  bags, the sludge dewatering
     bag process is adaptable only at  a treatment plant of extremely
     small-scale.   It can be said the  sludge  dewatering bag process is easy
     to be employed as a temporary method until centralized
     processing/disposal system for a  wide area is prepared.

3.4  Theme for Future

     (1)  Collection facility

               It has been proved that the pipe of 100  mm  with a grade of  3%
          can be used when unsteady-state flow  in the branch pipe  is
          counted.  However, substitute sludge  made of  sponge  was  used and
          the draining patterns were limited  in the experiments.   Various
          objects such as toilet paper,  vegetable scraps,  cloth, vinyl as
          well as feces are disposed into the practical sewer.  In addition,
          there are other conditions which were difficult  to be checked by
          experiments (such as influences by  catch basins  or house connection
          pipes).   proof tests using practical  facilities  are  indispensable
          for practical use.  Practical laying  tests have  already  been
          started in a certain line.   In order  to prove practicality under
          various conditions, many practical  laying tests  are  being planned.
          After such checks and tests, a munual to help easy designing of
          sewer shall be prepared. As for simplified manholes, they are
          already under manufacturing  since no  trouble  was found in
          experiment.  Proof tests, however,  shall be performed at practical
          facilities with simplified manholes so that they can be  diffused.

     (2)  Treatment facility

               It has approximately been proved that the simplified sludge
          collector and sludge dewatering bags  can be practically  used.  Whe
          inconveniences found in experiments are improved, proof  tests need
          be achieved at practical plants.
               Through standardization works  for oxidation ditch process,  the
          basic theory of standardization of  small-scale sewerage  treatment
          plant could have been clarified. Technology  for small-scale
          equipment (such as simplified sludge  collector)  need be  promoted at
          each facility so as to improve maintainability and to decrease
          construction cost by standardization.
               In  preparation for increasing  needs for  small-scale sewerage

                                      340

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system, establishment of technology for standardization and mass
production need be promoted continuously as well as improving
conditions for such producton and marketing.
                             341

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                             Tenth United  States/Japan Conference
                                on Sewage  Treatment Technology
EFFLUENT REUSE IN AN URBAN RENEWAL DISTRICT IN TOKYO
         The work described in this  paper was
         not funded by the U.S.  Environmental
         Protection Agency.  The contents do
         not necessarily reflect the views of
         the Agency and no official  endorsement
         should be inferred.
              Kenichi  Osako, Yasuo  Kuroda
 Sewerage Bureau,  Tokyo  Metropolitan Government,  Japan
                          343

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1.  INTRODUCTION
                                CONTENTS






                                        	345
2.  AIMING AT FURTHER RELIABLE WATER SUPPLY 	  346




    (1)  Water workx expansion project  	  346




    (2)  Leak prevention	346




    (3)  Promotion of demand restriction measures 	  345




    (4)  Recycling of used water	3^7




3.  PRESENT SITUATION OF TREATED EFFLUENT REUSE 	  348




    (1)  Reuse in industrial water supply 	  348




    (2)  Reuse in sewage treatment plant. 	  349




    (3)  Reuse for restoration of water ways	349




    (4)  Reuse for others	3^9




4.  SEWAGE RECYCLING MODEL IN SHINJUKU URBAN SUBCENTER	350




    (1)  Outline of Shinjuku urban subcenter	350




    (2)  The aims of sewage recycling project	350




    (3)  Outline of Shinjuku sewage recycling project 	 351




5.  CONCLUSIONS	356
                                  344

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                             1.  INTRODUCTION
     The demand for water is constantly increasing along with the massive
concentration of population in Tokyo, the city's economic development and
modernization of city life.

     Water supply in Tokyo is expected with the maximum daily supply
reaching an estimated 6.89 million m3 in fiscal 1985, and 7.48 million
m3 in fiscal 1990.

     Tokyo's water works have now water sources, available to use, amount
to 5.63 million m3.  So development of water resources, such as reservoir,
is requested to implement.

     Meanwhile, the construction of new reservoirs is hampered, because of
the scarcity of exploitable sites, and the need for environmental pro-
tections.

     To ensure effective use of limited water resources, Tokyo Metropolitan
government has taken the following measures.
                                    345

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                2.  AIMING AT FURTHER RELIABLE WATER SUPPLY
     (1)  Water works expansion project

     Tokyo's water works takes most of its water from the rivers of three
water systems.  Those are shown in Fig.-l.

          a)  Tama River water system

          b)  Tone River water system

          c)  Sagami River water system

     In order to meet the growing water demand, the Fourth Tone Water Works
Expansion Project was launched in Fiscal 1972.

     The project is designed to (1) construct Misato purification plant to
expand installed capacity, (2) strengthen the pooling function of purifi-
cation plants through construction of pumping stations and communication
pipes, and (3) carry out emergency measures to ensure effective raw water
utilization through construction of a second intake facilities at the
Ogochi dam, an intake weir at ozaku and conveyance pipes.
To cope with this project, new reservoirs for raw water will be needed.

     (2)  Leak prevention

     Priority is given to leak prevention from the view point of effective
utilization of available water resources.
The leaks that occurred in fiscal 1984 accounted for an estimated 14.7
percent of total supplied volume.
Service pipes account for more than 90 percent of the leak repair.  To
drastically improve the pipe structure and material, stainless steel pipes
were used biginning in May 1980.

     (3)  Promotion of Demand Restricting Measures

     Water is essential for the preservation of city life.
In view of the current tight condition of water supply, the rational use
of water will be expected.

     In January 1973, the Bureau announced "Measures to Restrict Water
Demand".  The following actions have since been taken for this purpose.

          a)  Campaign for water conservation such as pamphlets and poster

          b)  Development and use of conservation-Type Equipments such as
              faucet, washing machine, flush toilet.

          c)  Water conservation through education of children.  Study
              materials are distributed to all fourth-graders of primary
                                    346

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              schools and first-year students of junior high school in the
              water supply areas in order to propagate a correct knowledge
              of water works through education.

     (4)  Recycling of used water

     Because of the difficulties in evacuation of residents, and development
of adjacent area, construction plan of new reservoirs have been delayed.
Therefore, the unit cost of water resources development will be rising.

     On the other hand, diffusion rates of sewerage for 23 wards of Tokyo,
reached to 82 percent in fiscal 1984, and the volume of sewage treated
amounts to nearly 6 million m3 per day.

     So, recycling of used water will be very important not only for solving
the shortage of raw water, but also preventing water pollution of water-
sheds of source rivers.

     And recent tendency has been for both city water rates and sewage
charges to increase greatly for large consumers.

     In Tokyo, total charges can amount to more than ¥600/m3.
For this reason, the augment for waste water reuse becomes very persuasive,
not with standing the fact that the cost of reuse has also increased.
                                    347

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              3.  PRESENT SITUATION OF TREATED EFFLUENT REUSE
     (1)  Reuse in industrial water supply

     The first attempt to reuse treated municipal sewage for industrial
water started in 1951, when treated effluent at Mikawashima sewage treat-
ment plant in Tokyo was sand-filtered and supplied as a trial to a cardboard
manufacturing factory.

     At the period 1960s, many factories served underground water for
industrial use.

     Of the total number of factories in the 23 special wards,  about one-
half are located in the industrial areas of Koto and Johoku.  Enormous
quantities of underground water were pumped up in these areas until rest-
rictions were imposed.

     The heavy intake of underground water has caused a conspicuous ground
subsidence in these industrial areas.  At one place the ground level has
dropped more than 4m during its past 60 years.

     The metropolitan government supplied substitute industrial water to the
areas in 1965 where restrictions are placed on the use of underground water
to prevent the sinking of the ground.
Alternative industrial water is supplied through two channels.   One is the
industrial water works in the Koto area.  The other is in the Johoku area.

     Thanks to these projects the ground sinking in the Koto and Johoku
districts has slowed markedly since the 1970s.  At present there is little
evidence of subsidence.
Thus the purpose of industrial water works-prevention of ground subsidence
- has been achieved.

     The source of Koto industrial water works is sewage which is treated
by the activated sludge process at the Mikawashima sewage treatment plant.
The treated sewage then undergoes sedimentation, filtration and sterilization
at the Minami-senju purification plant before being distributed to indivi-
dual factories.
On the other hand, Johoku industrial water works receives raw water from
Tone, and Tamagawa rivers.  Surface water from the Tone is led to Misono
purification plant, where it is treated through sedimentation.   Meanwhile,
surface water from the lower reaches of the Tamagawa is treated through
sedimentation and filtration at the Tamagawa purification plant, then send
to Misono purification plant.  At Misono, treated water from these two
sources is mixed at the ratio of 3 for Tone and 1 for Tamagawa.

     In the case of users downflow of Kohoku purification plant, an average
volume of 7000 m3 per day (normal time) from the Kohoku purification plant
is added to the mixed industrial water described above.
                                     348

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     At Kohoku, industrial water from Minami-senju, which originates from
 treated sewage, is further treated with activated carbon to improve quality.
 This water makes up  for  the shortages of river water.

     The demand for  industrial water is due to the Japanese economy's shift
 to  a period of slower growth, evacuation of industrial facilities following
 imposition of stringent  environmental restrictions, and internal use of
 reclaimed water.

     Given these limiting factors, demand has been diminishing.

     The bureau plans to use part of the industrial water for other mis-
 cellaneous purposes, such as cleaning at factories, scouring, and cooling
 at  sewage treatment  plant, car washing at taxi companies and toilet flushing
 at  housing complex.  Table-1 shows the proportion of usage of industrial
 water supply.

     (2)  Reuse in sewage treatment plant

     In 23 special wards of Tokyo, 10 treatment plants are in operation.
 In  these facilities, 250,000 m3 of water are consumed, for cooling, washing
 every day.  And among them, about 230,000 m3 are supplied by treated sewage
 after being filtrated.

     (3)  Reuse for  restoration of waterways

     Citizens in Tokyo have a great concern for improvement of urban
 facilities such as parks and waterfronts.

     The Tokyo metropolitan government commenced the project for the re-
 stration of waterways to improve the waterside environment.

     Tamagawa waterway and its diverted waterways which had supplied water
 for livelihood and irrigation for over 300 years, were stopped supplying
water in 1978, because of no need for irrigation.

     However, Nobidome watersupply, which  is a typical diversion of
Tamagawa watersupply, was restored in 1984, which tertiary treated water
began to flow into the waterway from the Tamagawa Joryu treatment plant at
 the rate of 20,000 m3 per day.   In near future other waterways will plan to
be restored.

     (4)  Reuse for others

     In addition,  tertiary-treated water is also used for washing Shinkansen
 (bullet train) carriage of the Japan National Railways.
                                    349

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          4.  SEWAGE RECYCLING MODEL IN SHINJUKU URBAN SUBCENTER
     (1)  Outline of Shinjuku urban subcenter

     Business firms, by nature,  tend to gather at a certain place because
they can benefit from mutual contract.   Particularly since Tokyo is  the
capital city of Japan, it has a  great number of central  government offices
and advanced research institutions which is  a major reason for  the con-
centration of business in the capital.

     Development of new traffic  and communication systems, has  served to
heighten the importance of central management of functions in business
firms encouraging independence of such functions.

     In order to cope with the situation,  The Tokyo metropolitan government
carried out urban renewal project in Shinjuku, where Yodobashi  purification
plant was located.

     Yodobashi purification plant is the first modern waterworks, put into
service in our city, in 1898, using slow sand filtration process. To meet
with the rapid demand of water,  Higashi murayama purification plant,
equipped with rapid sand filtration, went  into operation in 1960.
And the sites, involving Yodobashi purification plant, were planned  to be
used for urban renewal.

     Among the planned 96 hectares, 50 hectares are now  implementing  the
urban renewal project.  Since 1960, 12 high  rise building for hotel,  and
business offices, are constructed.

     And the population working  in this district will be expected to
300,000 in near future.

     (2)  The aims of the sewage recycling project

     Tokyo metropolitan government set forth the administrative guidance
for providing installation of recycling facilities at the time  of const-
ruction of large building or a housing complex.

     In this systems, individual buildings have their own sewage treatment
facilities and the treated water is reused for flushing  toilets within the
buildings.  (Table-2)

     After the announcement of establishing  of a water-saving society,
recycling systems in individual  buildings  are tending to spread gradually.
(Table-3)

     And recycling in the urban development  area began operation to  supply
reclaimed water to three building by Marunouchi Central  Heating Co.  in 1976.

     But recycling of used water in large scale has not  been established yet,
                                     350

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     Therefore, since 1978, suffering from the water shortage,  Tokyo  metro-
politan government intended to implement sewage recycling project as  a
model in the Shinjuku urban subcenter in order to clear the problems  in
employing water recycling system in large scale.

     And Tokyo metropolitan government set up a guideline for advising
citizens for recycling of water in 1984.

     On the other hand, water recycle systems in district wide works  and
individual building within the public sewerage area have a great effect in
reducing sewage discharge.

     Tokyo's first sewer system, "Kanda sewage works" laid down brick sewer
pipes in 1884.  So in some parts of public sewered area, the capacities of
sewerage facilities became shortage owing to the rapid urbanization and
changing in life style.

     Therefore, in this point of view, introducing large scale recycling
systems to this Shinjuku urban renewal district will be very effective
procedures for reducing the capacity of trunk sewer in this area.

     (3)  Outline of Shinjuku sewage recycling project

     In 1984, sewerage bureau with the aid of the Ministry of construction,
constructed dual supply system in Shinjuku urban subcenter.

     Among the 12 high rise buildings which were already in use, 9 buildings
were prepared for dual supply systems following to the advice of the  bureau.

          a)  Projected dual supply area

              Projected area was decided on the 50 ha of urban renewal
              district where the water consumption will be large and  rea-
              sonable usage of water will be expected.  (Fig.-2)
              The execution plan was devided into two stages.
              First stage is to supply sand-filtrated effluent to a build-
              ings in use, from Ochiai treatment plant located near to sub-
              center.  Second stage is to supply reclaimed water from the
              Recycling center located at Shinjuku Kokusai building to the
              whole consumers in the projected area.

          b)  Design capacity

              Planned capacity is 4000 m3/d for first stage, and 8000 m3/d
              for second stage.
              Construction programme was devided into two stages owing to
              the effectiveness of supplying systems.
              Capacity for first stage was planned according to the inform-
              ation submitted by the owner of buildings.
                                    351

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    The whole capacity  for the  second  stage was  calculated  using
    the water-consumptions by unit  floor  area  (m3/m2/d)  and
    accumulated office  floor space  (m2) which will be designed
    according to the city planning  law, and building code.
    (Table-4)
    The capacity for the  existing buildings  is  the same  as  that of
    first stage.

c)  Supply systems

    At first stage,  wide  area supply system was  applied  because
    of the small demand for used water.
    In future, accompanied with the development  of this  district,
    more waste water reuse will be  expected.  Therefore, at the
    second stage, district wide supply system will be  adopted,  in
    order to cover the  insufficient capacity of  existing sewerage
    pipes.

d)  Usage of reclaimed  water

    The usage of reclaided water have  to  be  decided reffering
    acceptability of citizens and safety.  Furthermore much volume
    of reuse should be  expected.
    Shared ratio for flushing toilet,  investigated in  the office
    of the Shinjuku urban subcenter, such as Shinjuku NS building,
    and Shinjuku Center building, were 43 ^  50  percentage.
    (Table-5)
    Meanwhile, the ratio  for car washing  and cleansing were very
    small.  And in this district, central heating and  cooling
    service will be planned to  introduce  in  future.
    On the other hand,  avoidance of use in direct contact with
    human bodies may reduce the possibility  of  sanitary  problems,
    and also the consumer may have  less feelings of resistance
    from the psychological viewpoints.
    At present, Ministry of construction  and Tokyo Metropolitan
    government suggested  a guideline to use  reclaimed water for
    flushing of toilet.
    In this sewage recycling project,  reclaimed water  was planned
    to be used for flushing toilet.

e)  Water quality for supply and treatment facilities

    The water quality for supply should be satisfied  the following
    points.

    (T)  To secure safety for  the health  of  consumers.

    (g)  The color and  the odor of  supplied  water is  not unpleasant
         for consumers.

    (5)  Dual water supply systems  should not  be interrupted by
         scalings and corrosions.


                          352

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         In these point of view, some water quality criteria were
         proposed.   Table-6 shows that  for  industrial water.
         Refeering  the "Sewage Effluent  Reuse Guideline" published
         by sewage  department of Ministry of construction, the
         water quality for supply was decided as following table.
               Items
         e col.

         residual  chlorine

         Color

         Odour

         PH
              Criteria value
              less than  10  N/m£

                   Maintained

                   Not unpleasant

                   Not unpleasant

                   5.8 ^ 8.6
         For treatment  process, in future, will be proposed "activated
         sludge process -> rapid sand filtration ->• chrolination".
         The proposed process is adopted because of it's effectiveness
         for producing  expected water quality  and economy.
         Table-7, 8 shows the effluent quality of Ochiai sewage
         treatment plant and sand filtrate.

     f)   Water supply facilities

         Flow sheet for first stage is as follows.
        Tap water	

  L-
-I jceive
                              	 Reuse
                              KWVAVtt* water
                                                    Pump Control
1	1/  Sewage
                                               | Water recycling center)
                         0 q
                   r i ii  iii

                                          Advanced treatment
                                          facility
                                  	SlnT TiltM tioVtinir      '"*>
                           Octitai treatment plant
                                353

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     For second stage,  following  sewage treatment facilities
     will plan to be installed in water recycling center.
                        Inflow pipe
 o>
 ao
 •a
 3
-a
 cu
 o
 <
L.
3 T51
4J ^3)
06 Ml
Chlorination
                              I
                      Grit chamber for
                      sanitary sewage
                           Pumps
                      Primary sediment-
                      ation tank
                       Aeration tank
                       Final sediment-
                       ation tank	
                            Pump
                         Rapid sand
                         filtration
                        Storage tank
                       Effluent pump
                       Effluent pipe
                              1
                                           Raw sludge
                    Reservoirs of buildings
                                            01 00
                                            a G
                                            M -H M
                                             en 4J
                                            (U ") CO
                                            OS » 3
                                                           Sludge storage
                                                                tank
                                                             Sludge pump
                                                               T
                                                                  I
                                                             Slurry  pipe
                                                Ochiai sewerage
                                                treatment plant
                                  354

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g)  Cost for the project

    Total cost for this project was estimated about 6 billion
    yen.  Among them, the cost for the first stage was about
    3.2 billion yen.
    The source of finance for the construction of the project
    is national subsidies, general obligation
    and service charges.
    The service charges are collected form the users in
    proportion to the volume of water consumed.
    Water rate is estimated 250 yen per m3.
    Among them, maintenance cost is 117 yen per m3 and capital
    cost is 133 yen.

h)  Cross connections

    To ensure safety, cross connections and misuse must be
    carefully avoided.
    In this project, following procedures were adopted.

    (T)  Main pipes and service pipes for reuse of sewage
         were covered with brown tapes.

    (5)  The lids of valves were labelled as reuse of water.

    (5)  Supply pipes in the user's building were also labelled
         as reclaimed water according to our suggestions.

    (4}  Users were adviced to detect cross connection in
         their dual supply systems using special dosage.
                         355

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                              5.  CONCLUSIONS
     Reuse of water means that suitable water quality is served for parti-
cular use.  And it represents the resonable use of energy and resources.

     In order to facilitate water reuse, the costs and the space for in-
stallation and operation of the treatment plant must be kept to a minimum.
Therefore, compactness in the size of equipment and easy maintenance are
required.

     To cover the shortage of water resources, and the insufficient capacity
of sewerage works, and to protect river from pollution, development of new
technology for sewage reuse is absolutely essential.

     If there is a technical break through in compactness of treatment plant,
manpower savings and reduced costs, the concept of waste water reuse may
become dominant among the general public.
                                     356

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          Hatyilo) Dank I3lm
          Cwictlr 175.000.000m1
                                                                                         Bamg planned c»ur>i(a,eo»alfucllo»


                                                                                          Compteled
Kanagawa Pial
                     Figure  1.   Water  Sources  for Tokyo
                                                  357

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   Table 1.   Proportion  of Usage



Koto area
(m3)
(%)
Johoku(m3)
area (%)

Cooling


37,005
51.4
54,763
41.5

Washing


25,027
34.8
33,875
25.7
Product
treat-
ment


4,163
5.8
18,070
13.7
Mate-
rials


1,220
1.7
4,955
3.8
Temper-
ature
regul-
ation

395
0.5
3,365
2.6

Boilers


64
0.1
6,960
5.3

Others


4,118
5.7
9,717
7.4

Total


71,992
100
131,705
100
Table 2.  Use of Water in Buildings
Type of building
Office
Hospital
Department store
University
Scale
Big
Small


Culture
Science
Flushing (%)
0.3 * 0.5
0.5 ^ 0.8
0.2 ^ 0.3
0.15 ^ 0.35
0.35 ^ 0.7
0.1 ^ 0.2
Cooling (%)

0.3 ^ 0.4
0.3 ^ 0.5

                 358

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          Table 2.   Domestic Consumption
                                           (unit: %)
Drinking




Bathing




Washing




Laundry




Cleaning




Flushing toilet




Car washing and sprinkling
20 ^ 30




15 ^ 20




 5 % 15




  25




 4^8




  20
      Table 3.   Recycling project undergoing
\ Items
Class if i-\
cation \
In operation
Under
construction
Planning
Total
Number
of
project
47
20
20
87
Total
water
consump-
tion
42,279
14,975
22,842
80,096
Recycling
quantity
9,931
2,926
6,857
19,714
Recycling
rate
23.5
19.5
30.0
24.6
Reference
2 district wide
recycling projects
(7 buildings)
1 district wide
recycling project
(2 buildings)
3 district wide
recycling projects
(15 buildings)
6 district wide
recycling projects
(24 buildings)
                       359

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                          /  £
                              Ochiaj. treatment
                              plant
                         -7s'   '.•/.,-.
                 \_ Shinjuku" jj
                 1 r-central park
            injukul]
       ,_  Cation1)'
       0 *=3WII
       iH fiO»':i  | !'
       'P   Jilllll'
       Afl —•/^  —
                     ~W
      Water Recycling Center
    «— Service pipe
    I  1 Buildings for supply used water
Shinjuku  Mitsui Building
Yasuda  Marine and Fire
Insurance Building
Shinjuku  Nomura Building
Shinjuku  Center Building
Shinjuku  Daiichi Life
Insurance Building
Odakyu  Century Building
Keio Plaza,  Hotel
Shinjuku  NS  Building
Shinjuku  International Building
        (a)  Constructed
1C))  Tokyo Dental University
11)  Nishi Shinjuku Jofuji District
L|>  Nishi Shinjuku 6-chome  East District
y)  Nishi Shinjuku 6-chome  South
    District
         Municipal sits
    Shinjuku  Central Park
             (b) Planning
          Figure 2.  Shinjuku Sewage Recycling Project Area
                                      360

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Table 4.  Water Consumption by Unit Floor Area
                                              (m3/m2/d)
Classifi-
cation
Office
School
Hospital
Department
Hotel
Factory
Mis cellaneous
Number
of
samples
50
51
42
42
22
22
16
16
6
6
32
32
37
37
Average
U/m2/d)
78.1
10.9
19.1
16.1
49.8
27.5
161.2
26.0
153.5
30.8
51.5
31.1
94.2
24.4
Maximum
U/mVd)
189.2
27.8
76.8
113.6
78.6
58.5
507.6
85.9
350.5
52.1
493.3
131.3
482.2
73.7
Minimum
a/m2/d)
19.2
3.1
1.2
4.8
11.8
13.1
37.4
8.5
29.3
12.3
1.2
2.3
1.6
1.7
Standard
deviation
U/m2/d)
43.9
5.6
17.6
17.4
18.2
12.4
121.8
22.4
112.6
14.8
96.8
29.2
120.0
18.7
Variance
0.562
0.510
0.919
1.081
0.365
0.451
0.756
0.863
0.733
0.481
1.880
0.934
1.274
0.766
, Upper: per unit sits ,
Lower: per unit floor area
                       361

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Table 5.  Water Consumption for Usage
                                        (unit:  m3/d)
Items
Flushing
toilet
Cooling
Car
washing
Sprinkling
Cleansing
Washing of
hands and
face
Steam
Bathing
Store
Pool
Mis-
cellaneous
Total
Shinjuku
NS
Building
641
0
39
25
19
178

515
65
0
0
0
1,482
Keio
Plaza
Main
Building
440
60
20
0
0
90

830
430
50
0
80
2,000
Keio
Plaza
Southern
Building
220
30
20
0
0
45

405
225
55
0
40
1,040
SS-7
719
0
24
0
0
124

1,253
533
0
74
0
2,727
Shinjuku
Center
Building
770
0
5
0
0
201

551
0
0
0
15
1,542
Yasuda
Marine
and Fire
Insurance
Company
452
0
4
6
0
177

333
0
0
0
0
872
Total
3,242
90
112
31
19
815

3,787
1,253
105
74
135
9,663
                  362

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Table 6.  Water Quality Standard of Industrial Water
Items
Water quality
Temperature
Turbidity
Hydrogen ion
Chlorine ion
Iron ion
Pressure
Koto area
Johoku area
less than 27 °C
less than 15 degree
pH 5.8.8.6
less than 1,500 ppm
less than 0.7 ppm
less than 200 ppm
less than 0.3 ppm
More than 0.5kg/cm3
                   363

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Table 7.  Daily Average Water Quality at Ochiai Treatment Plant
                                                       (1982)
Samples
Temperature
Transparency
PH
Vaporized residual
Furnace residual
Furnace reduction
D.S.
S.S.
BOD
COD (alkaline)
COD (acid)
Total-N
NH3-N
Organ! c-N
Chlorine
Content of normal
hexane extract
MBAS
Inflow
sewage
18.5
6
7.1 ^ 7.4
463
233
238
302
161
148
55
80
28.0
12.2
14.6
51
18.7
7.3
Primary
sedimented
effluent

7
7.1 ^ 7.4
391
208
182
301
88
110
46
63
27.0
12.8
1-3.7
52


Final
sedimented
effluent

37
7.0 ^ 7.4
281
198
84
270
12
14
14
17
21.6
11.9
7.0
52
1.0
0.7
                              364

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Table  8.  Water Quality of Sand  Filtrate
  Items
                            Value
Temperature  (°C)




Transparency




Turbudity




Color




Odour




     PH




     SS      (mg/£)




    BOD      (mg/£)




    COD




Chlorine




   MBAS      (mg/£)




Alkalinity   (mg/£)




Conductivity (ys/h)
          (mg/£)
 17.8




 75




 10




 15




 none




  7.3




  5




  7




 15




 52




  0.2




138




595
                          25 Oct.  1984.
                 365
    US GOVERNMENT PRINTING OFFICE 1986 - 646-014/40019

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