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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
-------
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
-------
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
-------
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.
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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
-------
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
-------
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
-------
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
-------
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
-------
(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
-------
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
-------
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
-------
(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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
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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
-------
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
-------
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
-------
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
-------
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
-------
©
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
-------
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
-------
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
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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
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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
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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
-------
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
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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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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»
__
"
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
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(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
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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
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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
-------
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
-------
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
-------
(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
-------
(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
-------
(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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
(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
-------
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
-------
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
-------
-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
-------
«-
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
(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
-------
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
-------
Cumulative frequency ('!,)
ro
-Pa
ro
n
§
n
ID
o
o*
rr
H-
ID
Ml
H
ID
•Q
hn> &
o M P
O O fD
n> tr h
WHO
wo cr
"^ D
d» H*
** C
3
ft
"
3s
• M
10 ^
VO 1-^ 1
1
u>
vo
vo
to o
CO IO
— •* o>
^^
on o
UI VO
— * 10
ro
to
U)
vo
U) O
UI H*
*— Ul
^
O O
•— ' en
H> 1 —
co f-t o
* 3 •
* H* <
-J - M
VO
CD
UI
U)
en
vo
to o
UI 10
«*]
*b O
IO OD
—• 00
M
to
U*
VD
U* O
-J (-•
^
0 0
*- UI
go
< 0
.
ui on M
— M
1
to
UI
H
vo
o o
m to
*— IO
on
OD O
00 W
*- to
M
U)
00
vo
o o
en M
*— u>
UI
00 O
— 00
ft C
•
— !-• IH
-J 1
to
UI
to
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VO
to o
vo 10
on
•J M
00 0
— * lto>
to
o
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VD
Ij M
*- ' UI
en
to o
—* ui
tfi C
•
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— HI 1
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UI
VD
^ o
on to
•*!
vo o
on vo
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to
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— ' UI
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If
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vo
o>
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"^ '
J^
f_l
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o o
o *».
^
00
to o
U> -J
*— UI
IO
UI
00
'oo
vo o
ui to
*•* UI
"^
on o
—• -J
n
jT
n
n
a
0 50
£ S
01
VQ
0>
•O » >
n A 3
o H QI
8 &a
m t— O
O O D"
H-
9
a a n
MOO
c rr a
0, t- <
*O < fl>
O 01 3
rf rr
« Qi O*
0 3
« M
a
S 2
»
ID
•O 0 >
n a 3
Q n »
Son.
ID cr n
ta M. o
m o tr
H-
i
a n n
MOO
C rt- 3
<2* <" ID
ID 01 3
rr er
8 a|
0 t-
co
a
c
ft
a
n>
C
3
ft
M
ft
§
?
•o
I
1
o
1
V
I
X
"•"
01
cr
O
n
t
p«
c
CD
1
o
M
O
(D
-------
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
-------
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
-------
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
-------
(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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
(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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
(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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
(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
-------
7
6
§ 5
a *
3 ,
e 3
>,
rH
M T
5
0 1.5
1
1
' •
•
•
•
»
•
•
»
••
•
•
-• '»-l
•
,•
[•_
•
,•"
•
•
-L
\
/.
•
/
/
**
»
JJK ^ 3.
.-•..-
. T
1124
i.:-
•
(-2-
124
•• ...
-9 1
-0
i™^
.0
•
85
0
•
B
K: Ratio
'
-• — .
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
-------
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
-------
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
-------
(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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
/ £
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
-------
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
-------
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
-------
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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