EPA
November 1978
EVALUATION OF "WITHIN VESSEL" SEWAGE
SLUDGE COMPOSTING SYSTEMS IN EUROPE
by
0- S.T. DiNovo, W.C. Baytos and L.M. Curran
ro Battelle's Columbus Laboratories
(P Columbus, Ohio 43201
r^~
If) H. Hartmann, U. Muller, H.J. Kinkel,
~ E. Steinsiek W. Wagner and H. Puchinger
•J Battelle's Frankfurt Laboratories
*° Frankfurt, Germany
r*~
J. Dartoy, 0. Miller and C. Shorrock
Battelle's Geneva Laboratories
Geneva, Switzerland
Contract No. 68-03-2662
q
J982
Project Officer
Atal E. Eralp
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
EJBD
ARCHIVE
EPA
~
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
QQ2 U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
" f- 1 " /
llBatteile
Columbus Laboratories
505 King Avenue
Columbus. Ohio 43201
Telephone (614) 424-6424
December 8, 1978 Telex 24-5454
Dr. Atal Eralp
Project Engineer
Ultimate Disposal Section
Municipal Environmental Research
Laboratory
U.S. Environmental Protection
Agency
Cincinnati, Ohio 45268
Dear Dr. Eralp:
Contract 68-03-2662
Enclosed are four copies of our second draft final report on the subject,
Evaluation of "Within Vessel" Sewage Sludge Systems in Europe. We have
made the corrections and changes as suggested from (1) the remarks made
in the reviews of the first draft final report, (2) our telephone conver-
sations, and (3) the comments which were offered during our oral presen-
tation in Cincinnati, Ohio, on November 27, 1978.
If there are any further suggestions or comments, please let us know.
Sincerely,
S. T. DiNovo
Program Manager
Chemical Process Development Section
STD:ms
Enc.
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Enviromental Protection Agency, and approved for publica-
tion. Approval does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
ii
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DRAFT
X
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DRAFT,
ABSTRACT
This study was conducted as a cooperative effort by Battelle Labora-
tories in Frankfurt, Germany; Geneva, Switzerland; and Columbus, Ohio.
The objectives were: (1) to update a review of the state of the art of
sewage sludge composting in Europe; (2) to evaluate a European-designed,
continuous, thermophilic, mechanical, aerobic, composting system in
Germany; and (3) to compare its costs to that of the U.S. Department of
Agriculture's ARS, Beltsville, static-pile, aerated composting system.
This report addresses the general characteristics of the European com-
posting systems and a bioreactor in Hochheim am Main, West Germany.
This report was submitted in partial fulfillment of Contract Number
68-03-2662 by Battelle's Columbus Laboratories under the sponsorship of
the U.S. Environmental Protection Agency. The report covers the period
February 1978 to June 1978.
iv
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DRAFF
CONTENTS
Disclaimer ii
Foreword iii
Abstract iv
Figures vi
Tables viii
1. Introduction 1
2. Summary 2
3. Study of European Sewage Sludge Composting Systems. . 6
State of the art of sludge composting processes. . 6
4. Evaluation of the BAV Hochheim am Main,
West Germany Composting Plant 39
Criteria for site selection 39
Technical details of the Hochheim bioreactor ... 43
Mechanical reliability of composter com-
ponents at the Hochheim am Main plant 45
Mechanical reliability of composter com-
ponents at five other BAV plants 48
Temperature profile and exhaust gas
components 50
Process analysis by chemical and
physical methods 50
Evaluation of odors emitted from composting process 56
5. Economic Evaluation of BAV Hochheim Composting Plant. 59
6. Conclusions 67
7. Recommendations 69
References 70
Appendices
A. List of European manufacturers and representatives. . 72
B. Summary of a composting study conducted on
the Triga system 76
C. The sewage treatment plant components
operational data 85
D. Analytical methods used in the evaluation of
the BAV plant in Hochheim, Germany 88
E. Organoleptic odor evaluation 92
F. Information for cost evaluation supplied
by Hochheim plant 100
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DRAFI
FIGURES
Number Page
1 Refuse flow of Switzerland 1975 15
2 Triga composting reactor 16
3 Schematic of refuse composting plant 21
4 BUhler refuse and sludge composting system 23
5 Schematic diagram of the Brikollare process 25
6 Brikollare material balance 26
7 "Schnorr" biocell system 29
8 Roediger and Fermentiechnik method 31
9 HKS method 32
10 Hazemag dumping process 34
11 Prat method 35
12 Kneer composting vessel 40
13 Location of the four candidate BAV composting plants
in relation to Battelle-Frankfurt Laboratories 42
14 Process flow diagram of the Hochheim am Main composting plant . 44
15 The BAV bioreactor at the Hochheim am Main, West
Germany Wastewater treatment plant 46
16 Volumetric flow diagram of Hochheim composting plant 47
17 Temperature profile at bioreactor Hochheim 52
18 Conceptual view of the Hochheim am Main bioreactor at time
of product removal mechanism failure, April 18, 1978 57
vi
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Number Page
19 Flow sheet of the BAV Hochheim composting process 60
B-l Temperature evolution 82
B-2 Water content 82
B-3 Organic matter evolution 83
B-4 C/N ratio evolution 83
C-l Hochheim am Main, West Germany wastewater
treatment plant layout 87
E-l Block diagram of the portable Kiel olfactometer TO-4. ... 94
E-2 Concentration of odorous substance in the main
direction of distribution 99
F-l System of components 106
DRAFT.
vii
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DRAFF.
TABLES
Number Page
1 European Sewage Sludge Composting Processes 3
2 Sludge Composting Plants in France 7
3 Sewage Sludge Production in the Federal Republic of Germany. . . 9
4 Location of Sewage Sludge Composting Plants in West Germany. . . 11
5 Sludge Composting Plants in Switzerland 14
6 Analysis of the Triga Compost 18
7 Analysis of Dano Compost at Schaffhausen, Switzerland 22
8 Composting Systems Classification 36
9 Process Comparison Rating by Battelle Geneva 37
10 Gas Composition of Bioreactor Exhaust Gas 51
11 Comparison of Feedstock and Composted Product of the Hochheim
am Main, West Germany Bioreactor, April 12 to June 2, 1978. . . 55
12 Chemical Composition Comparison of Feedstock and Composted
Product from the Hochheim am Main, West Germany Bioreactor,
April 12 to June 2, 1978 55
13 Throughput by Type of Material 61
14 Installed Equipment Costs for a 250 m3/Day Sludge Plant 62
15 Estimated Total Plant Investment of BAV Process
for a 250 m3 Sludge/Day (20.4 dt/d) Plant 63
16 Estimated Total Capital Requirement of BAV Process
for a 250 m3 Sludge/Day (20.4 dt/d) Plant 63
17 Estimated Annual Operating Costs of BAV Process
for a 250 m3 Sludge/Day (20.4 dt/d) Plant 65
viii
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DRAFT.
Number Page
18 Estimated Annual Maintenance Costs of BAV Process 65
19 Comparison of Total Annual Costs for Sludge Methods
(1st Quarter 1978 U.S. Dollars) 66
B-l N, P, K Analysis of Sludges as a Percent of
the Dry Matter Weight 77
B-2 Composition of the Mixtures 79
B-3 Characteristics of the MSW and Sludges 80
B-4 Characteristics of the Mixture 84
D-l Chemical and Physical Data Obtained at the Hochheim am Main,
West Germany Bioreactor, April 12 to June 2, 1978 91
ix
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DRAFF,
SECTION 1
INTRODUCTION
Composting is a well-established method of stabilizing organic wastes.
It is used to convert leaves, grass, and wood trimmings into a useable soil
product. In recent years, the Agricultural Research Service (A.R.S) of the
U.S. Department of Agriculture, with the support of the U.S. Environmental
Protection Agency, has developed a composting procedure for digested and raw
sewage sludges. This successful process utilizes an open pile of sludge
cake mixed with wood chips. Air is drawn down through the pile and into a
vacuum system where the gases are eventually discharged through a stable
pile of compost for odor control. The procedure is referred to as aerated-
pile composting and works well with a minimum amount of capital investment.
However, it requires considerable land and labor, and the process is con-
ducted out of doors.
To overcome the problems associated with open air composting, several
within-vessel, continuous composting processes have been developed and are
in use in Europe. Effective odor control, minimum labor, and low mainten-
ance are among the advantages claimed for these within-vessel continuous
composting processes.
To evaluate these and other claims, a review study of the status of
European practices on sewage sludge composting was conducted by Battelle's
Columbus Laboratories under a contract from U.S. Environmental Protection
Agency. The study had two main objectives: (1) identify the existing
composting practices in Europe and compile information on operating modes,
effectiveness, reliability, and costs; (2) obtain experimental data to
verify the efficiency and the reliability of one commercial, within-vessel
system. The results of the investigation are presented in this report.
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DRAFT.
SECTION 2
SUMMARY
Of the seven European countries surveyed for sewage sludge composting
practice, West Germany is the center of activity with more than 30 operating
plants. Sweden follows with 20 which are either in operation or in the
planning and design stage; Switzerland has nine which are mostly the Buhler
rotating drum process; France has five; the United Kingdom has one; while
Italy and the Netherlands have none. These data are for systems where sewage
sludge is the predominant waste component. If municipal solid waste inten-
sive systems are also included, the number of installations would be higher.
[References (1) and (2)].
The European composting processes identified in this study are classi-
fied into five categories, "within vessel, windrow, rotating drum, pressed
bricks, and fermentation cells". The processes described and evaluated
according to category are listed in Table 1.
The feasibility of composting sewage sludge mixed with a bulking agent
is now well established in Europe, but the future of ge'neral composting
technology in Europe appears to depend on the market economics and con-
tinued public acceptance, rather than on technological improvements.
From Table 1, in the "within vessel" category, the Biologische
Abfallverwertungsges, mbH & Company (BAV) process is the most common sew-
age sludge composting system in Europe. BAV has constructed at least 19
operating plants in West Germany and have at least 7 plants either in con-
struction or design. Thus, based upon the popularity of this process, the
BAV system was selected for detailed study as representing the European
"within vessel" sewage sludge composting method. A BAV-construeted, sewage
sludge composting plant at the Hochheim am Main Wastewater Treatment plant
was studied in detail to obtain an indication of the efficiency and relia-
bility of the process. Four BAV plants were visited for one day, but
limited time and funding prevented any extensive evaluations of these
other plants.
Evaluation of the Hochheim am Main sewage sludge composting plant was
based upon a two-month, on-site, detailed study in the following areas:
(1) reliability of the plant's mechanical components; (2) process parameters
which are influenced by the progress of the composting process, such as oxy-
gen and carbon dioxide concentration in the exhaust gas, temperature rise
and temperature profile within the vessel, and total retention time of the
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DRAFT.
TABLE 1. EUROPEAN SEWAGE SLUDGE COMPOSTING PROCESSES
Number of
Category Process Operating Plants
Within Vessel BAV ^ 19
Carel Fouche Languepin 1
Roediger/Fermenttechnik 1
Schnorr Valve Cell 2
Societe General
D'assainissement et de 1
Distribution (SGDA)
Triga 2
Weiss 3
Windrow
Rotating Drum
Pressed Brick
Fermentation Cells
BIO-Manure
Hazemag
PLM
Blihler
Dano
HKS
Brikollare
Prat
1
-
9
2
2
1
NOTE: Addresses of the manufacturers contacted in the course of this
study are listed in Appendix A.
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DRAFT
feed material; (3) measurement of the odors originating from the facility;
(4) chemical and physical characterization of the feed material and the
final product; and (5) cost information.
While Battelle-Frankfurt scientists were on-site and conducting the
research, the bioreactor's product extraction mechanism failed. This equip-
ment malfunction was attributed to the solidification of the composting
material within the vessel. This equipment malfunction has occurred four
times during the past 1-1/2 years since start-up. The manufacturer believes
the reactor can be redesigned to avoid this problem and can point to a num-
ber of other installations with a more favorable, though shorter, operating
history.
During the two-month evaluation period, the reactor produced a product
whose chemical and physical composition did not differ significantly from*
the feed material; did not maintain a constant internal temperature; pro-
duced a non-uniform carbon dioxide off-gas profile; and emmitted odors,
during the product discharging cycle, which were detectable several hundred
meters from the wastewater treatment plant. The most probable cause for
this sequence of events is attributed to compaction and solidification of
the fermenting mass which caused the air flow to channel. The reader is
cautioned, however, that these observations represent the experience at only
one plant and that this plant may or may not have been properly operated.
Furthermore, the Battelle-Frankfurt research staff did visit other 3AV-
constructed plants where the final product appeared more mature and odor-
free, although no data could be developed as part of this study to verify
this assertation.
The BAV process is capital intensive and the initial investment cost
would be higher in the U.S. due to adaptation or redesign of European equip-
ment specifications to U.S. equipment. The total annualized costs appear to
be higher than the USDA's ARS aerated, static-pile composting process or
landfilling, but are comparable to those for landspreading applications,
and could be lower than trenching. This cost summation is based on annual
processing cost; the income from possible sale of the compost is not in-
cluded. Further investigation would be required before a direct comparison
of the various processes/methods can be developed. The bioreactor capacity
of most BAV installations is for a population equivalent of 30,000. The
largest plant serves a population of 110,000 and uses two Bioreactors, each
of which can process approximately 350 m3 of sludge cake per day. The poten-
tial for achieving further economic benefits based on the use of even larger
bioreactors is thought to be limited due to the constraints on the reactor
design. These physical constraints are (1) the maintenance of uniform air
flow, (2) the removal of compost from the extremities of the vessel, and
(3) the compaction of product at the base.
The above process evaluation is based on observations made at the
Hochheim am Main wastewater treatment plant. To develop a more general
assessment of "within-vessel" composting, at least one additional BAV plant
and another process should be investigated. A good choice for a second
process is that offered by Triga. The Triga reactor design may have mini-
mized the aforementioned product extraction problem By using an external
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DRAFl
screw reactor and by recycling the fermenting mass 3-5 times during the 8-
10 day residence time. The product from a Triga plant in St. Palais, France,
appeared to be one of the best products seen at any of the 10 commercial
installations that were visited during the investigation. An experimental
verification of this observation about the product was, however, beyond the
scope of the study.
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DRAFl
SECTION 3
STUDY OF EUROPEAN SEWAGE SLUDGE
COMPOSTING SYSTEMS
The primary intention of this section is to report representative and
reliable information of the status of mechanical composting processes in
Europe. Since the technology is relatively new and is evolving rapidly, a
variety of sources for information, in addition to the literature, were
required. Information was obtained through discussions with composting
process inventors, license holders, plant manufacturers and plant operators.
Representatives from Ministries on Environmental Affairs from France,
Germany, Italy, The Netherlands, United Kingdom, Sweden and Switzerland were
interviewed to obtain current data on sewage sludge composting. In addi-
tion, site visits by Battelle-Geneva, Battelle-Frankfurt, and Battelle-
Columbus scientists to selected operating plants were made. These were
the Triga plant in Royan, France; Blihler plants in Pfamensthal and Biel,
Switzerland, and Leicester, England; and the BAV plants in Hochheim,
Kronberg, Ferndorfthal and Rosbach, Germany.
Eleven different sewage sludge composting processes are described and
classified according to type of process such as windrow, "within vessel",
rotating drum, pressed bricks and fermentation cells. These processes are
then rated according to five categories such as temperature control, air
distribution, residence time, homogenicity of recycle and mechanical reli-
ability.
The locations of each sewage sludge composting plant are listed by
country and town in this section.
STATE OF THE ART OF SLUDGE
COMPOSTING PROCESSES
Current Geographical and National Trends
France—
In 1977 about 12 million metric tonne (t) of MSW, 600,000 t of dry
matter from community sludges and 1,600,000 t of dry matter from industrial
sludges were generated in France. Seven hundred-twenty-five thousand metric
tonne of MSW were processed in 92 plants (3) (47 windrow and 45 "within
vessel" plants) to produce 380,000 t of compost. The development of sludge
composting in France is recent (1975) and at the beginning of 1978 there
were 5 plants processing sludge and one under construction (see Table 2) .
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TABLE 2. SLUDGE COMPOSTING PLANTS IN FRANCE
Location
Salon de Provence
Nantes-South
Montargis
Dreux
S t-Palais-sur-mer
Name of
Company
SGAD
EPAP
Triga
Triga
Triga
Process
BAV/SGAD
BAV
Triga
Triga
Triga
Type of
Wastes
Sludge + MSW
Sludge + sawdust
Sludge + MSW
Sludge + MSW
Sludge + Sawdust
Status
Operating
Operating
Operating intermittently.
an existing MSW composting
Operating
Operating
R&D in
plant
(Royan)
Montbeliard
Martigues
Carel Fouchd
Languepin
Sofitom
Carel Fouche"
Languepin
Brikollare
+ bark
Sludge + MSW
Sludge + MSW
Operating
Under construction, start-up
scheduled for 1979
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In France, compost is considered an organic soil conditioner and its
main competitor is cattle manure. The market is not very large and the
average selling prices for municipal solid waste (MSW) plus sewage sludge
compost ranged from 5 to 35 FF/dt in 1977 ($1.10 to $7.70) which is not
enough to finance the operating costs and amortization. On June 9, 1977,
the "French Committee for the saving of raw material" made the decision
to intensify and coordinate the marketing of organic wastes as soil condi-
tioners and to encourage fertilizer manufacturers to use the wastes as
organic sources in their production. The policy is to improve the quality
of the compost and try to obtain a selling price of 20 to 25 FF/dt ($4.40
to $5.50). Triga sells some of its sewage sludge mixed with bark compost
from St Palais to a fertilizer manufacturer at a price of 120 FF/t ($27/
t). From that point of view, sludge plus bark compost is better than muni-
cipal solid waste (MSW) plus sludge compost.
Germany—
The amount of sewage sludge produced, as a result of improved sewage
and effluent treatment, is given in the 1975 Waste Management Program of
the German Federal Government as 50 million m-* of sludge from municipal
treatment plants and 30 million m3 of sludge from industrial treatment
plants. Each sludge has a water content of 95 percent (4). The values
correspond to 4 million t dry mass of sludge.
From data originating from an enquiry undertaken by the Abwassertech-
nischen Vereinigung (Technical Association for Waste Water), the Umwelt-
bundesamt (Federal Environment Agency) has estimated total sludge dry weight
at approximately 1.7 million t at the end of 1974, which corresponds to
about 34 million ra3 of sewage sludge with a 95 percent water content (3).
From this survey, disposal and recovery processes for sewage sludge such as
incineration, composting, tipping (landfill), agricultural exploitation,
selective tipping of agricultural utilization, and other disposal methods
(tipping at sea) were evaluated.
This report concludes that in treatment plants with fewer than 20,000
inhabitants, agricultural application prevails, and in treatment plants
with more than 20,000 inhabitants, the sewage sludge is primarily tipped.
An overview of the quantitites of sludge taken from the survey mentioned
above, and of the respective form of disposal, is shown in Table 3.
Windrow composting with additives—Composting sewage sludge in win-
drows without additives (sawdust, straw, bark) is no longer carried out
in Germany although numerous attempts were made from 1930 until the
present. Sewage sludge, without additives, has both low porosity and a
high water content. These two factors, when combined, reduce natural
aeration and favor anaerobic digestion to proceed. Strong, objectional
odors develop during anaerobic digestion. Therefore, due to the strong,
objectional odors which develop, composting sewage sludge without additives
has been abandoned.
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TABLE 3. SEWAGE SLUDGE PRODUCTION IN THE FEDERAL REPUBLIC OF GERMANY
(4)
Size group Total sewage
(Nusfcer of ,*°Pulatioil sludge,, tonnes
, ._ .., . dry weight
inhabitants) pe* year=100%
2,000 31,230
- JSS
- J:S
. S:S »•»•"•
. S:S «.•».»
- ^r >••».»>
100,000
excluding 9,146,111
city states
Total 15,910.490
Extrapolated
to 100% of 18 million
connected
inhabitants
- 48 million 48 million
2,200
4,754
16,254
42,781
100,347
114,991
278,220
559.547
(100)
Incineration, Composting,
tonnes dry tonnes dry
weight per weight per
year year
733
( 2)
3,243
( 3)
8,567
( 7)
31,933
(11)
44,476
( fl)
1,108
( 3)
8,190
( 7)
9,298
h.7)
Tonnes dry-weight
1.678.640
33,572,800
133,428
Amount of
2,668,560
27,894
. . Agricultural
Tipping, utillsatlon,
tonnes dry _
. . tonnes dry
weight per . .
year weight per y'
501 1
(23)
1,057 2
(22)
1,480 9
( 9)
13,359 20
(31)
33,338 32
(33)
45.323 29
(39)
147,755 68
(53)
242,814 165
(43)
per year (in tonnes)
728,442 496
sludge corresponding to 5% dry-weight.
557,880
14.568,840 9,920
,272
(58)
.963
(62)
,128
(56)
,859
(49)
,569
(32)
.824
(26)
,726
(25)
i3o}
.000
in ra
.000
Tipping or
, ,,. Other pro-
agric. utilis-
, . resses, tonnes
ation, tonnes
. . . 3ry weight per
dry weight per
427
(19)
734
(15)
5,646
(35)
5,821
(14)
23,628
(24)
19,488
(17)
14,259
( 5)
70.00^
210,000
4,200,000
901
(2)
7,567
(8)
3,599
(3)
15,547
(0)
27,614
(5)
82,840
1.656,800
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DRAFT
Sewage sludge composting plants—In the last 3-5 years in the Federal
Republic of Germany, about 30 plants for the composting of sewage sludge
have been built or are under construction (Table 4). These plants have a
capacity equivalent to a population of 800,000. In most cases, composting
of sewage sludge occurs with the help of bulking materials such as sawdust
or straw. Currently, a research program is being conducted by the German
Umweltbundesamt, to determine whether these processes do indeed produce a
pastuerized and pathogen-parasite-free product. Preliminary results of this
research program, as yet unpublished, show that in some of these processes,
pastuerization is incomplete and indeed some final composted products do
contain both human and plant pathogens.
MSW composting plants—In 12 of the 19 existing sludge composting plants
in the Federal Republic of Germany, the sludge produced is composted to-
gether with MSW (1).
Considering both sludge and sludge/MSW composting together, it is esti-
mated that in 1977 the total amount of sewage sludge composted was only 3
percent of the total sludge produced.
Italy—
In 1978, there are 7 composting plants and 21 composting plus inciner-
ation plants in Italy, processing 3,600 t/d of MSW. None of these plants
process sewage sludge with the MSW and there is no sewage-sludge-only com-
posting plant.
Professor de Bertoldi of the University of Pisa is conducting research
on sludge composting sponsored by the CNR (National Research Agency). The
Danieli Ecologica Company S.p.A. (VSest Alpine process) could process sludge
with MSW.
The Novater Company has the license for Italy of the Renova process
(Portland Zementwerke Heidelberg) (7). Sludge could be added to the MSW
using this process as is done in the Blauberen plant (Germany).
The Netherlands (Holland) —
No sludge composting plant was found in the Netherlands during the
course of this study. MSW have been composted since 1929 with a windrow
composting system, the Van Maanen (VAM) process. The MSW from 110 commu-
nities are carried by train to two plants in Wijster and Mierlo. The
unground refuse is digested in open piles, 6 m high, for 120 to 180 days.
It is turned from time to time by grab crane for aeration. The product
is then screened and ground to different sizes (35 mm, 15 mm, 6 mm) accord-
ing to the end use. There are also two Dano plants in Rijenhout and Soest.
United Kingdom—
As of 1978, there is only one operating plant composting sewage sludge
and it is located at Wanlip, near Leicester (8). Although 10 to 15 years
ago, MSW composting in Dano rotating drums was common, most of these plants
have shut down. Recently, in 1974, the Wanlip reopened and now processes
1000 t of MSW mixed with 500 t of digested sewage sludge (5 percent solids)
each week. The product, packaged under the brand-name "Lescost", is mar-
keted with some success throughout Great Britain.
10
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DRAFT.
TABLE 4. LOCATION OF SEWAGE SLUDGE COMPOSTING
PLANTS IN WEST GERMANY
Process
Producer
Planes
BAV
BAV
Biologische Abvallverver-
Cungs
CeaeUschaft nbH & Co
Berliner Strasse 22
6369 Schoeneck 1
Tel: 06187/5004
Weiss Gebruder Weiss KG
Maschlnebau Abe. Umwelt-
technik
Kupferverkstrasse
6343 Frohnhausen/Dillkreis
Tel 2771/5066
Fa. Daabach Industrtean-
lagen GmbH
Abt. KISrtechnik
Postfach 1240
Adolf-Dambach-Strasse
Tel: 07225/1841
Method of Che firms Pa. Wilhelm Roedlger
Roediger/Femenccech- Induscriehafen
nik 6450 Hanau/Hain
Schnorr (Valve Cell
Method)
HKS-Mechod
Fa. IBP
International Euro fur
Projektentvlck-lung B.V.
Heerllen
Niederlassung Aachen
Monhelmasalle 51
5100 Aachen
Tel: 0241/30505
Lambsheim
Uinterberg
UuUhela (Teck)
Gartringen
Delbnick
Lubeck-Herrenvyk
Hochheim (Main)
Lollar
Oberes Perndorftal/Hilchenbach
Steinenbronn
Ralsdorf
Kronberg (Taunus)
Wllnsdorf
Schefflenz
Eddershelm
Rosbach v.d.H.
Kandel
Buchen
Brilon-Messinghausen
under construction
Vlotho
Hohr-Grenzhausen
Freigerichc
Waldenbuch
Schliichtern
Deldeshelm
Dettenhausen
Bad Liebenzell
Denkendorf
Rastatt
under construction
Gaggenau
Mittleres Wutachtal
Aachen (piloc plant)
11
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DRAFI
A review of two recent summary reports (9,10) on sewage sludge disposal
practices barely mentioned composting. However, underlying the apparent
instability and dissatisfaction with existing land and sea disposal methods,
there are some indications that composting could receive greater attention,
especially if an economically proven process were available.
In particular, there appears to be an increasing interest in organic
farming. There is also concern that plant and human pathogens and para-
sites can survive current land application and land filling sludge dis-
posal practice.
Sweden—
In 1975, the Swedish parliament passed a resolution whose objective
emphasizes recycling through better solid waste management. With this
resolution, 20 Swedish communities or regions are planning, or are in
the process of constructing, composting plants. At present, less than 1
percent of the total MSW and sewage sludge produced is recycled by a com-
posting technique. According to recent estimates by the Swedish National
Protection Board (SNPB), in the next two years approximately 7 percent of
the total MSW and sewage sludge produced will be recycled by composting
methods.
The S.NPB has been engaged in research on composting MSW mixed with
dewatered sewage sludge (11). The procedure was very similar to the ARS
process. This study is reviewed below.
Forced aeration pile composting study—The undigested mixture was
placed on a concrete tile, producing a set of paralled U-channels for
forced aeration. The parameters studied were the means and intensity of
aeration, distance between the channels, degree of size reduction of the
refuse, height of the compost heaps and influence of the climate over a
year.
Compared to traditional composting systems, the one examined has no
reactor for starting the process and no windrows for maturation. Instead,
the degradation occurs in large flat heaps. It is believed that this will
reduce the total cost and produce operating advantages.
The experiments have shown that this system may be used in a Nordic
climate even if the water content of the starting compost is 60 percent
or more. Due to the evaporation of moisture by the forced aeration, the
water content decreases to the point where the composting process stops.
Adding water to the composting piles is a necessary step to keep the com-
posting process active. It is also essential to turn the pile at least
once during the reaction period. This turning insures that the final pro-
duct will be homogeneous.
It is also important to change the aeration flow direction between
suction and injection. In periods with injection, the aeration rate must
be increased in order to maintain the C02 content below 5-6 volume percent
(vol %) (12). After 100 days, the material is stabilized, independent of
12
-------
DRAFT.
the size reduction of the refuse, such that it can be piled without further
aeration. A better result is achieved when the distance between the channels
is reduced from 2.0 to 1.5 m. From the temperature point of view, it is
better if the windrows are 3 m high rather than 2 m.
Switzerland—
Currently, there are 9 composting plants in Switzerland, the latest of
which went into operation in 1975 in Biel (13). All but one, in Uzwel, mix
sewage sludge with MSW (see Table 5). In most cases, incineration and com-
posting equipment are built side by side. The composting operation is used
to dispose of sewage sludge. The incinerator burns most of the municipal
waste and the rejects from the composting installation. Except for Biel,
where a Dano installation runs in parallel with a Brikollare installation,
all the plants use the Dano system for composting. The auxiliary mechanical
machinery, such as hammermills, conveyors and screens, is usually produced
by Buehler. A breakdown of the MSW flow in Switzerland is given in Figure
1 (13).
The construction of composting plants has practically stopped. Appar-
ently most operating plants have difficulties in marketing the compost at
a satisfactory price. Alternatives for the disposal of sewage sludge are
incineration or direct sales to farmers (sometimes with prior pasturization),
but these also pose specific problems. The presence of heavy metals and
glass particles is the most common objection to the use of refuse-derived
compost. It may well be, however, that careful operating of the plant and
better marketing could improve sales of the compost (see example of Leices-
tershire, Great Britain). It appears very unlikely that a number of com-
bined MSW/sewage sludge composting plants will be built in the near future.
One of the reasons is that the rejects of composting must be burnt (land-
filling is, for reasons of space, not feasible in Switzerland), therefore,
an incinerator is necessary in any case. Building a larger incinerator
instead of a combined system, generating only ash to be disposed, seems in
many cases the simpler solution. However, the better-quality product from
sewage sludge/sawdust only, might find better product acceptance in Europe.
Presentation of Sewage Sludge Composting Processes
Triga Process—
The Triga "Hygienisator" is an enclosed concrete, cylinderical tower,
approximately 5 m diameter and 8 m high, and is divided into 4 independent
compartments. With this design, the tower contains a 4 individual, indepen-
dent reactors. Each compartment, or reactor, has its independent aeration
and temperature and carbon dioxide measuring systems, but each compartment
shares the common screw extraction mechanism designed for both product
removal and subsequent product recycle. The screw extractor, located ex-
ternally, and at the tower's base, rotates axially and travels on a track
around the tower's circumference. Its movement around the circumference
can be controlled either manually, or automatically. Figure 2 is a diagram
of the Triga composting reactor.
The feed, raw dewatered sewage sludge plus bulking agent mixture, is
blended in a horizontal, mixing trough (Pug mill). The mixcure is blended
13
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TABLE 5. SLUDGE COMPOSTING PLANTS IN SWITZERLAND
Location
Horgeq
Mannedorf/Pfannenstiel
Biel
KraOchthal/Worblental
Olten
Beringen/Schaffhausen
Penthaz
Geneve/Villette
Company
Buehler
Buehler
Buehler
Buehler
Buehler
Process
Dano
Dano
Dano,
Brikollare
Dano
Dano
Dano
Dano
Dano
Type of wastes
MSW + sludge
MSW + sludge
MSW + sludge
MSW + sludge
MSW + sludge
MSW + sludge
MSW + sludge
MSW + sludge
Status
Operating
Operating
Operating
Operating
Operating
Operating
Operating
Operating
-------
Total refuse Switzer-
land 1975
1.84 mio t - 100%
Processed slag
for; road construction (0.05 mio tonnea)
1.14 mio t » 62%
incineration
Slag
0.33 mlo
t - 18«
5%
0.24 mlo
t - 13%
I
compost (0.99 mlo t)
combined Incineration/composting
0.2
mio t
•= 11%
sanitary landfill
0.26
mlo t
•> 14%
uncontrolled tipping
(litter)
Slag
(0.05 mlo t)
Landfill
1975
0.84 mlo t
46%
*mio = million
Figure 1. Refuse flow of Switzerland 1975 (13).
-------
DRAFT.
1-2-12 belt conveyors
3 feed port
4 water spraying nozzles
5 temperature probe
6 aerator
7 screw extractor
8 axis
9 trolley
10 rolling path
11 finish product exit port
12 finish product conveyor
Figure 2. Triga composting reactor.
16
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DRAFT,
continuously within the trough by means of a double-shaft-with-paddles
screws. From the mixing trough, the feed is conveyed to the top of tower
on a belt conveyor. One compartment of the tower is filled completely and
is processed as a single batch. Fermentation is started by pulling air
through the compartment's open bottom by a vacuum pump located at the
compartment's top. The air flow rate is adjusted according to the tempera-
ture in the bed; at the start of the 8 to 10 day composting period, the air
flow through the bed is adjusted to maintain the bed temperature at 70° to
80°C, but still at a rate sufficient to maintain a >10 percent oxygen concen-
tration in the exhaust gas. The bed moisture is maintained at 50 percent
and can be adjusted, if needed, with water from spray nozzles located
inside and at the top of each compartment.
Additional product aeration and bed loosening is accomplished by ex-
tracting the bottom fourth of the bed of each compartment, each day, with
the screw extractor, and by recycling the removed bed through the belt con-
veyor system and by returning it to the top of the same compartment. Thus,
by this method, product compaction at the bottom of the bed is minimized.
After the active fermentation period within the compartment, the entire
bed is removed and placed in a static windrow for a two-month curing period.
Triga plant—At the beginning of 1978, two raw sewage sludge/bulking
agent plants were in operation in France, although plants based on MSW have
been in operation for about 10 years.
Dreux plant—Originally this was just a municipal solid wastes com-
posting plant. This plant was modified in September 1977 for the combined
composting of sludge and MSW. The actual treatment capacity of this plant
is 60 t/d (as received) of MSW and 10 t/d of sewage sludge. The digested
sludge is flocculated with lime and FeClo and dewatered to 80 percent
moisture by a band filter "Press Deg". An analysis of the compost is
given in Table 6.
St Palais plant (near Royan)—This plant was designed for the com-
posting of the sewage sludge of the city of Royan (4,100 dt/yr) and began
operation in July 1977. The sludge is flocculated with a polyelectrolyte
and dewatered by a band filter "Press Deg". The bulking agent is sawdust
and/or bark which account for 1/3 by weight of the mixture. At the begin-
ing, Triga used the pulp of grapes as the bulking agent but they gave this
up because of the high price. The residence time in the reactor, based on
the original volume of the mixture of sludge cake and sawdust (or bark),
is 10 days. During that time, the mixture is recycled 3 to 5 times. The
curing time varies from 2 to 2.5 months. The compost production capacity
is about 4,000 t/yr. An analysis of the cured compost is given in Table 6.
Since the composition of the starting mixture was not reported, a compari-
son between feed and final product cannot be made. The investment for
this plant was 2 million FF (^$400,000), with about 75 percent associated
with equipment purchase. The two major components of the operating costs
are: power consumption 40 kWh/t of sludge; and labor; only one man oper-
ates the plant. Appendix B describes some other pertinent details on the
Triga system and studies undertaken on it.
17
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DRAFT
TABLE 6. ANALYSIS OF THE TRIGA COMPOST
(Analysis: C.D.L.P. Melun)
Plant
Mixture
Curing period
pH
C/N ratio
Analysis by weight
Moisture
Organic matter
Mineral matter
Carbon
Cellulose
Total Kjeldahl N
Total phosphorus (p2°5^
Total potassium (K O)
Total calcium (CaO)
Total magnesium MgO
Total S
Total Fe
Total Mn
Total Cu
Total Zn
Total B
Total Cr
Total Cd
Total Ni
Total Pb
Dreux
sludge/MSW
1.5 months
7.8
21.8
dry basis raw
I
% 49.2
£ 50.8
% 22.5
% 8.7
% 10.3
% 5.8
% 2
% 37.3
% 4.2
% 4.7
ppm 7009
ppm 792
ppm 294
ppm 1129
ppm 14
ppm 33
ppm 5
ppm 22
ppm 366
Saint Palais
sludge/pine sawdust
product
41
29
30
13.3
5.1
6.1
3.4
1.2
22
2.5
2.8
4135
467
173
666
8
19
3
13
216
1.5 months
8.2
32.9
dry basis raw
84.3
15.7
40.6
12.3
9.3
2
36.4
1.3
6.3
3294
104
203
532
13
9
3
10
61
product
54.25
38.55
7.2
18.6
5.6
4.2
0.9
16.6
0.6
2.9
1507
47
93
243
6
4
1
4
28
18
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DRAFT.
Carel Fouche" Languepin Process—
The Carel Fouche Languepin (CFL) Company has been building composting
plants since 1965.
Fermentation takes place in cells arranged in blocks comprising five
levels. A vertical set of five cells represents one fermentation unit (or
digester). Two blowers per digester can inject or draw air from each of
the five cells fitted with air distribution ducts. The top cell is charged
with the freshly pulverized MSW. Sludge can be added to the MSW before
feeding. The fermentation mass passes vertically down the digester in five
steps, and connection between cells is achieved by tilting floor gratings.
The residence time in the digester is approximately a week. The only CFL
plant which processes MSW and sludge is the Montbeliard plant which has
been in operation since mid-1977.
The daily capacity is 150 t/d (as received) of MSW and 5 t/d of sludge
with a water content of 80 to 85 percent.
Development of a new digester—CFL is just beginning a research pro-
gram aimed at the development of a new digester for the fermentation of
sludge. This research is sponsored by the French Environmental Ministry.
The pilot digester will process 1 m^/d of sludge mixed with carbonaceous
source and/or minerals and/or polystyrene spheres. The aim of this research
is to obtain a product similar to a peat because the French importation of
peat is expensive.
SGAD Process—
In 1975, the "Soci^te" ggn*5rale d'assainissement et de distribution"
(SGAD) built a plant in Salon de Provence under the BAV license to process
sewage sludge and municipal solid wastes. They had problems with the
extraction screw conveyor and modified this system. Now, they have their
own process which, in fact, is a "BAV modified" process. They have not
built any other plants in recent years.
Salon de Provence plant—SGAD operates this plant which processes the
municipal solid wastes and digested sludge for the population-equivalent
of 60,000.
The MSW is ground and screened. The larger-sized fraction is burned
in a rotary kiln and the smaller-sized fraction is sent for fermentation.
The smaller-sized fraction is mixed with digested sludge which has a water
content of 94 percent. This mixture is then fed into two reactors, 300 m-*
each. To equalize the flow rate between the mixers and the reactors, there
is a short-term storage bunker. The temperatures at different locations
and the C02 content of the exhaust gases are measured and recorded. The
residence time in the reactor is about 15 days. The mixture is then
extracted and formed into 2 m high curing piles. The curing time is
approximately 10 weeks, without any further turning.
19
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DRAFT.
Dano Process—
The Dano process is probably the most widely used MSW composting sys-
tem in the world. Approximately 180 units have been installed since the
late 1930's. Some of the older units have been retrofitted to process
sewage sludges with the MSW.
The key piece of equipment is a rotating drum about 25 m long and 3.5
m in diameter, equipped with knives in the interior which are designed to
shred the material. Ventilators aerate the drum with the exhaust being
forced into an underground earth filter outside the building. The input
refuse is sometimes treated first in a hammermill. The output is screened,
either by a separate vibrating screen or, in new plants, in the perforated
end section of the drum. The final product is usually stored in windrows
for further curing and screened prior to selling (see Figure 3, diagram of
refuse/sewage sludge installation).
Typical operating conditions are the following: one Dano drum will pro-
cess about 130 t/d as-received, refuse plus sewage sludge. Larger capa-
cities are treated by parallel units. Normal municipal refuse and sewage
sludge are mixed at a ratio so that the desired humidity is attained, e.g.:
• 100 t refuse + 30 t liquid sewage sludge, or
• 60 t refuse + 60 t sludge cake.
The residence time in the drum is 24 hours, but some units will main-
tain a residence time of up to 4 days, thus a more thorough decompostion
is achieved. The internal temperature cannot be directly measured, but 50°
to 60°C is the normal operating range, depending upon the operating condi-
tions. Ten percent of the feed is lost as carbon dioxide and water vapor
in the exhaust gas. The tumbling action of the drum not only provides a
suitable environment for biological activity, but also reduces the refuse
particle size through the shearing action of the internally positioned
knives.
The output is about 8 percent metal (separated before or after the
drum), 60 percent compost, and 30 percent rejects. The ratio of rejects
to compost is, of course, dependent on the mesh of the screen.
The compost is nearly always stored in windrows and Dano claims that
further aeration is not necessary. The storage time may vary from a few
days to several months, longer periods giving better quality compost and
allowing for seasonal changes in demand. According to Dano, 8 days of
windrow storage is required by the German state authorities in order to
eliminate any health hazard.
For the standard size Dano plant, 130 t/d, capital costs are about $1
million for the drum, machinery, electrical equipment, erection and start
up, about $0.5 million for the necessary civil engineering.
20
-------
Conveyor for rejects.
Conveyor for pulvtrited ma tennis
Figure 3. Schematic of Dano refuse composting plant.
-------
DRAFT.
The results of the compost analysis performed by the federal authority,
Swiss Federal Institute for Water Resources and Water Pollution Control
(EAWAG), at the composting plant of Schaffhausen (Beringen) are shown in
Table 7.
TABLE 7. ANALYSIS OF DANO COMPOST AT SCHAFFHAUSEN, SWITZERLAND
Source: Swiss Federal Institute for Water Resources
and Water Pollution Control Board
Analysis
wt %
H 0
Organic matter (dry)
N
P2°5
CaO
MgO
2
46.1
40.7
1.0
0.5
0.7
3.7
1.3
Compost Age, month
5
43.2
38.3
1.0
0.36
0.5
5.9
1.5
8
51.0
35.6
0.9
0.2
0.4
4.6
0.9
Dano considers the Swiss Market to be saturated and is concentrating
its efforts on southern countries such as Italy and South America. While
most Swiss plants were built in cooperation with B'uhler, a major manufacturer
of solid transportation systems, screens and hammermills, Dano tends to oper-
ate more independently in its ventures abroad. Their new concept is a
greatly simplified process with much less investment cost. They propose
using the Dano drum as shredder compactor without any prior milling of the
input refuse. The output is to be screened and used for landfilling. They
claim that this is an economical solution to dispose of ordinary refuse
and sewage sludge, for communities of about 20,000 inhabitants. The refuse
is claimed to be highly compacted, and the compost generated would be used
only to cover and recultivate the landfilling site.
B'uhler Process—
This process is similar to the Dano; in fact, the Dano rotating drum
is a mixing component for blending the raw refuse with dewatered and liquid
sludge. After blending, the mixture is placed in a roofed shed for fur-
ther windrow composting. After windrow composting, the product is further
screened and set aside for post-maturation prior to sale. Figure 4 repre-
sents the flow of materials in the BUhler process.
22
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DRAFT.
BUHLER
REFUSE AND SLUDGE COMPOSTING SYSTEM
1 grab crane
2 slat conveyor
3 hammtf-mitl
4 chain conveyor
5 discharger tor dewatered sludge
6 1st magnetic separator
7 conveyor
8 2nd magnetic separator
9 metal press
10 pump tor liquid sludge
i' al screen (without admixing of sludge), or
b) homogenizing screening drum, or
c) digester with screen
depending on the particular conditions
12 tan
13 earth compost filter
14 conveyor
15 chain convtyor
16 double-rotor fine mill
17 belt conveyor with movable
•ripper and reversible crossbeit
18 fermentation shed
19 automatic windrow-turnmg machine
20 sat conveyor feeder
21 chain conveyor
22 lump breaker
23 screen
24 dry destoner
25 chain convtyor
26 fan
input
A household refuse
commercial and bulky refuse
6 dewatered sludge
C liquid sludge
End products
D fresh compost, coarse
E matured compost, coarse
F fresh compost, fine
C matured compost, fine
H specially matured compost, 'me
Remark
The hard particles (giass, stones etc ! can either
be disintegrated in the double rotor fine mill (16)
or removed by dry destoner I 24)
J tramp iron bales
K screen rejects
L removed hard partcles
Remarks to fermentation system
I intensive fermentation
II matumg,, storing
HI post -maturing
Figure 4. Btthler refuse and sludge composting system.
23
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DRAFT
Brikollare Process—
The Brikollare process is a composting process offered by Industrie-
Werke Karlsruhe Ausburg AG (IWKA) in Karlsruhe, West Germany. Two plants
are operational, one in Schweinfurt, West Germany, the other one in Biel,
Switzerland, where it runs in parallel with a Dano installation. A third
plant is being constructed in Martigues, Southern France.
Strictly speaking, it is not a "within vessel" composting process.
The screened refuse is mixed with dewatered, digested sewage sludge and
pressed into bricks of 60 x 20 x approximately 15 cm size. These bricks
are stacked and stored in an open shed where the biological acitivity lets
the temperature rise up to 70°C. After 2 to 3 weeks, the biological acti-
vity ceases because the bricks have dried out to 20-25 percent H20. At
this stage, the bricks may be stored in the open for any length of time.
As required, the dry bricks are milled and screened to ready compost. IWKA
claims no further windrow storage is necessary (see schematic diagram and
mass balance, Figures 5 and 6).
For 7-hour operation, 240 days per year, IWKA claims the following per-
formances .
• 25,000 t/yr refuse (35% H20)
+8,000 t/yr sewage sludge (75% H20)
• 37,500 t/yr refuse (35% H20)
+12,000 t/yr sewage sludge (75% H20)
• 50,000 t/yr refuse (35% H20)
+16,000 t/yr sewage sludge (75% H20)
• 75,000 t/yr refuse (35% H20)
24,000 t/yr sewage sludge (75% H20)
equivalent to 100,000 inhabitants will yield
• 13,000 t/yr compost (25% H20)
• 8,500 t/yr rejects that must be disposed (25% H20)
• 12,000 t/yr are water evaporated during the fermentation of
the brick and reduction of organic substances.
A turnkey installation including buildings, without sewage sludge con-
centrator, scrap metal and rejects presses will cost about 7.5 million DM*
($3.75 M) (1976 costs).
*DM = Deutsche Mark ($0.50)
24
-------
1 concrete bunker
2 polyp crane
3 feed bunker
4 coarse mill
5 vibrating transporter
6 magnet
7 coarse screen
8 refuse intermediate storage
9 centrifuge
10 sludge intermediate storage
11 double shaft mixer
12 press storage
13 press
14 stacking machine
15 roller table
refuse;
sewage sludge
t-o
Ul
Figure 5. Schematic diagram of the Brikollare process.
-------
IWKA - MATERIAL F LOW COMDITIOH8
SEWAGE SLUDGE I 25 t
( 95 % HjO )
MATER
VAPOR
6 t
OUCT10N A.
ORGANIC <
IBSTANCES- M"
l.S t '
REDUCTION
or i
SUBSTANCES-
DOMESTIC REFUSE- 15 t
( 35 % HjO )
ROUOI MILL
MAGNET / SIEVE
11 t
(40 * H;0)
REFUSE and SEV.AGE
SLUDGE MIXTUPP.
16 t
( 55 % HjO )
PRESS
reRHElTATICI
BRIQUETTES :
8.5 t •
(20-25 X H20)
PULVERIZER
USD SIFTER
ROUGH COMPOST
nun. 7.5 t
DRAFI
SOI
COMPOSTAoLEi
IMX. 4 t
Figure 6. Brikollare material balance
(Source:
26
-------
DRAFT
• Required operating personnel: 6 men
• Operating costs per T refuse or concentrated
sludge: 25 DM ($12.50)
• Equivalent to an investment of 75 DM ($37.50) and
annual operating costs of 8 DM ($4.00) per inhabitant.
All of these figures are given by the manufacturer, IWKA.
A particular feature of this process is the utilization of straightfor-
ward mechanical equipment that should not pose any particular operational
problems. During a visit to the Biel installation on May 6, 1978, no opera-
tional problems were apparent.
Sales prices in Switzerland in 1977 were:
• Compost for vineyards (superior 15 mm) 9.50 fr*/t ($5.20/t)
• As piglet's earth 11 fr/bag ($2.80/bag) (24 1, 18 kg).
• Bark compost, 1 part bark, 2 parts compost sold in 75 liter
bags to the largest consumer products chain in Switzerland
at 3-4 fr per bag, the retail price at the supermarket is
7.20 fr/bag ($3.90/bag).
"Bio-Manure" Process—
This is a windrow composting system with additives.
Straw seems to be the most suitable additive. Though attempts have
been made to produce compost with mushroom mycelium poultry droppings and
"Biorott" (bacteria and fungus concentrate from the firm Dr. Heinrich Propfe,
Manneheim), these have not been adapted by commercial installations.
The process of producing compost from sewage sludge in windrows by
adding straw ("BlO-manure") was developed by the Hessische Landesanstalt fiir
Umwelt (Hessian State Institute for Environment). Mixing straw and sewage
sludge is extremely simple since it can be done with fertilizer spreader. A
layer of straw in the form of compressed bales is packed lengthwise onto the
rollers. This layer of straw is covered with sewage sludge, from which first
approximately 20 percent of the water has been extracted in a belt type sieve
press, in the required proportions (fresh sludge:straw = 1.25:1; digested
sludge:straw =1.5:1). It has proved practical to spread part of the straw
in a thinner layer on top to obtain an especially even mixing process.
Building up the windrows is then carried out by discharging the fertilizer.
The typical course of such windrow composting can be described as follows:
Phase I: Two to four days after the windrow has been set up, its tem-
perature rises rapidly. Temperatures of over 65°C are reached in the windrows.
*fr = Swiss Franc (($0.55)
27
-------
DRAFl
Phase II: The temperature level is retained for several days. Even
the outer surface of the windrow becomes more than warm to the hand. Rain-
fall can lead to a short-term drop in temperature and to the development of
steam on the surface of the windrow. These high windrow temperatures last
approximately 6 to 10 days.
Phase III: The temperature gradually decreases to 40°C. The entire
fermentation period lasts about 6 weeks. With an 80 hp tractor, a 6 t
fertilizer, and a Caterpillar loader with a 1.5 m3 shovel capacity, approxi-
mately 9 m3 dewatered sewage sludge can be processed to "Bio-manure" per
hour.
The profitability is largely dependent on the transport costs for
straw, sewage sludge, and the finished product as well as on the purchasing
price for the straw needed. To save transport costs, the processing of
straw and sewage sludge should, therefore, take place in the direct proxi-
mity of the sewage treatment plant or as close as possible to the place
where the compost will be used later.
To sum up, it can be said that the extent of sludge composting in win-
drows using additives is slight taken altogether (one plant in Pleidelsheim
near Ludwigsburg; one plant in Althausen in the Ravensburg district), even
though repeated attempts are being made to achieve an improvement. The
following factors can be cited as obstacles:
• Difficulties in handling the material,
• Difficulties in ensuring an even water content and
sufficient aeration,
• Problems in obtaining and mixing the additive substances,
• Dependence on the weather conditions leading to
uncertain hygienic results, and
• Large space requirement.
Schnorr Valve Cell Process—
The fermenting towers used in the valve-cell process shown in Figure
7 are 10 m long, 4 m wide and 15 m high and consist of ten tiers, one above
the other. The floor of each tier consists of perforated valves which can
be opened and closed hydraulically. The fermentation mixture is fresh
sludge with a solid content of 22-25 percent plus ground-up bark with a
diameter of 5-10 mm and is fed into the top tier. When the valves are
opened, the material falls onto the floor below.
At the start of the process, the towers are initially filled with an
equal mixture of dewatered sludge and ground-up bark. After the process
is established, a portion of finished compost is recycled back into the
system by mixing it with fresh sludge and bark in a 2:2:1 proportion. Thus,
the quantity of ground bark required for the process is reduced. The mixer
28
-------
DRAFF,
1 biocell reactor
2 distributor
3 conveyor
^ sludge container
5 returns container
6 coagulant container
7 discharge conveyor
8 dump conveyor
9 sawdust conveyor
10 pumps
11 sawdust bunker
Figure 7. "Schnorr" biocell system.
29
-------
DRAFT.
and the drag chain conveyor are located below the sludge and recycle compost
containers. The product (feedstock) from the mixer passes through a set of
rubber rollers before being conveyed to the top of the tower. The purpose
of running the feedstock through the rubber rollers is to further loosen the
material by breaking any lumps which may have formed. This tends to keep
the feedstock fluffy, and thereby increases the opportunity for aerobic
composting.
Every third day, the content of the tower is let down one tier at a
time by opening the floor valves so that a residence time of 30 days
results. Every second tier is aerated from the front and the alternate
tiers from the back. Directing the air in this way ensures that it flows
through the fermentation material and not past it. The fermentation mix-
ture is spread out in layers of 1 m deep in each tier, and, as it drops
from tier to tier, further mixing and loosening occurs. Temperatures of
70°C and above are reached during a two-week fermentation period; thus, the
sewage sludge is made completely hygienic. The temperature is utilized to
control air flow to the process. Temperature probes are attached at three
places in the fermentation towers.
Roediger/Fermenttechnik Process—
This process was developed by Professor Baader (Institute for Agri-
cultural Technique, Brunswick) for animal wastes and has been adapted for
sewage sludge (see Figure 8). Fa. Wilhelm Roediger Industriehafen has
constructed only one demonstration plant which is located at Mittleres
Wutachtal, West Germany.
Previously dewatered sludge is combined with dried returns in a double-
shaft mixer to obtain a mixture with approximately 50 percent water content.
The mixture is fed into the reactor by a vertical conveyor. Aeration in
the fermentation reactor is achieved by passing air through the floor
grating. At certain intervals during the fermentation process, the grating
is set in motion and the material falls through a catch funnel into a screw
conveyor fixed below it. The material is then fed back into the reactor
via the vertical conveyor. Air is blown through the grating at such a high
rate that excess oxygen is supplied. The fermentation process reaches a
disinfection temperature of approximately 72-74°C within 24-36 hours. The
circulation process mentioned above ensures that all the material passes
through this high-temperature zone several times during the fermentation
period. The material is then formed into pellets and dried.
HKS (Homogeneous Composting and Stabilization) Process—
In this process, the fermentation takes place in a rotating horizontal
drum rather than in a tower (see Figure 9). The sewage sludge, predried
by machine (or also wet), is mixed with returns and continuously added to
the compost material moving in the drum during the daily operating time. In
this way the fresh sludge is quickly absorbed. Except when the plant is
started up, no additives are used. The additives are then forced out by the
continuous extraction of the finished product and addition of fresh sewage
sludge. To provide oxygen, air is supplied from below along the whole length
of the drum. The air is pre-heated so as to draw off excess water from the
compost. The exhaust gas escapes via a drain.
30
-------
Sludge metering pump
1 ,
[sludge do»ataring J
Dryer
Dry TKileriol (broken)
Process flow sheol of the FERMENTECHNIK System
FERMENTECHNIK
for Environmental Protedion
EURAMCA INC.
Figure 8. Roediger and Fermentiechnik method.
-------
U) .
NJ
1 mechanical dewatered raw sludge
2 compulsory mixer
3 feeding conveyor
ll discharge conveyor
5 composting drum
6 air supply
Figure 9. HKS method.
7 air heater
8 blower
9 exhaust air
10 discharge compost
11 final fermentation
-------
DRAFI
Hazemag Process—
Household and industrial refuse is emptied out of the rubbish truck as
they arrive into a feeding hopper. It then goes into an impact crusher where
it is broken up and simultaneously mixed with the sewage sludge (see Figure
10). Windrows are then set up out of the roughly crushed waste material for
a six-month period which leads to an aerobic metamorphosis and to mineiali-
zation and disinfection. Then, levelling out and tamping down reduce the
original volume by about 80 percent. New wastes coming from the impact
crusher are set up in windrows on the levelled-out surface: after six months,
the process is repeated which means that a dumping area of only 100 m x 200
m per 100,000 residents is required. The raw product is sieved and can be
used as compost.
Prat Process—
In the Prat process developed in France, the incoming rubbish trucks
empty the household refuse into a bunker (see Figure 11). The outlet mecha-
nism is so constructed that plastic bags are torn apart and especially bulky
pieces are broken up. The refuse together with the sewage sludge is taken
from the bunkers on a transport belt into the fermentation cells which run
on rails. A travelling platform brings the cells to the entrance of a pre-
heating tunnel. The fermentation cells remain in the heating area about
24 hours. During this time, warm air (55°C) is forced into the substance to
promote the start of the fermentation and improve the conditions for the
propagation of the aerobic bacteria. From the preheating tunnel, the cell
trains are shunted into the fermentation hangar where the surrounding air
circulates convectively and ensures the supply of oxygen necessary for the
aerobic fermentation. The cells are taken out of the fermentation area after
24 hours. At the end of these 24 hours, temperatures of up to 65°C are
reached. The fermentation cells then remain for 48 hours in the area where
cold compressed air flows through them and care is taken that the temperature
of 65°C is not exceeded. On the fifth day, the cells are emptied and the raw
refuse compost passed into crushers which break it up. Metal scraps are next
separated from the rat* compost and it is sieved. Finally, it is stored in
windrows.
Process Comparison
Composting systems can be classified according to two criteria: The
main waste (sludge or MSW) and the type of process (see Table 8).
To compare these processes, we selected 5 criteria:
Temperature
Air distribution
Residence Time
Homogeneity/Recycling
Mechanical Reliability.
An evaluation of these criteria is given in Table 9.
33
-------
DRAFT.
refuse
sewage sludges
hopper
impact crusher
levelling and
compacting of fei?-
mented windrows
depositing further
material coming
from the impact
crusher on the
levelled area
I rotary screen
^^feaSSj
I
Figure 10. Hazemag dumping process,
34
-------
Ln
1 refuse collector
2 feeding bunker
3 compost bunker
A tank for chemicals
5 water addition
6 conveyor
7 fermentation cell
8 compressor
9 fermentation cell
10 cell tipping device
11 metering tank
12 hammermill
13 ballistic separation
14 conveyor belt
Figure 11. Prat method.
15 conveyor belt
16 magnetic separator
17 iron scrap
18 screen
19 hammermill
20 conveyor belt
21 conveyor belt
22 raw compost
a
-------
TABLE 8. COMPOSTING SYSTEMS CLASSIFICATION
DRAFl
Main Waste
Sludge
MSW
Minor Waste
MSW, sawdust, bark
Sludge
Process
Windrow
Within Vessel
Rotating drum
Briquetting
Cells
BIO manure
BAV
SGAD
Triga
Schnorr
Roediger
Weiss
HKS
Fa Hazemag
Carel Fouchg Languepin
Dane
Buhler
Brikollare
Prat
36
-------
TABLE 9. PROCESS COMPARISON RATING BY BATTELLE GENEVA
Process
BAV
Brikollare
Carel FouchS Languepin
Dano
Fa . Hazemag
Fa. Roediger
HKS
PLM
Prat
Schnorr
SGAD
Triga
Temperature
4
4
4
3
4
4
3
4
4
4 '
4
4
"ftir
distribution
4
1
5
3
2
-
4
2
-
4
4
4
Residence
time
4
5
3
2
N.A.
-
2
N.A.
2
5
4
4
Homogeneity
recycling
2
1
3
4
3
-
4
3
-
-
2
4
Mechanical
reliability
1
3
3
4
5
-
3
5
-
-
2
3
Arbitrary number scale 1-5: 1 = poor, problems, 5 = good, no problems, N.A. = not applicable
-------
DRAFI
Temperature—
The pasteurization effect is beneficial due to the increase in tempera-
ture to about 70°C which is generally sufficient to kill pathogenic microbes
(lethal temperature £60°C) such as Salmonella, Brucella, Shigella. Certain
insects and larvae will also be eliminated.
Thermophillic conditions in all of the processes described can be ob-
tained and maintained without any significant problems, and this has been
confirmed by direct temperature measurements. However, in the rotating drum
process, direct measurement of the internal temperature of the composting
mass has not been reported, but is assumed that thermophillic conditions are
reached and maintained. Temperatures reported in rotating drum processes
are measured at the outer shell of the drum and are reported at 50 to 65°C,
depending upon operating conditions.
Air Distribution—
A good air distribution within the reactor is necessary to create an
environment in which microorganisms will rapidly decompose the organic frac-
tion and to avoid local anaerobic conditions. Control of the air distribu-
tion is better in enclosed systems, especially in tower systems. In rotating
drum systems, the air does not flow very well inside the decomposing mass.
Residence Time—
The time required for digestion depends on the initial C/N ratio, the
initial moisture, the particle size, and the aerobic conditions. It is gen-
erally greater for sludge than for MSW. The residence time of 1-4 days in
the rotating drum systems is believed to be too short for complete stabili-
zation.
Homogeneity/Recycling—
The tumbling action in the rotating drum systems is good for the homo-
geneity of the product. The recycling of the mixture in the Triga process
ensures a better homogeneity of the end product. A good preparation of the
mixture is essential in the reactors where there is no mechanical mixing or
recycling.
Mechanical Reliability—
The windrow processes are better because there are very few mechanical
components. The BAV and SGAD processes seem to have mechanical problems at
the level of the extractor, especially in France.
Economics—
We do not have sufficient information to establish reliable comparisons
of these processes. However, the investment and operating costs per dry ton
of compost produced appears to be lower for the sludge composting processes
than for the MSW composting processes. When a plant is designed for com-
posting MSW, the additional cost increase for use of sludge may be generally
negligible.
38
-------
DRAFT
SECTION 4
EVALUATION OF THE BAV HOCHHEIM am MAIN,
WEST GERMANY COMPOSTING PLANT
The major objective of this section relates to the verification of the
efficiency and reliability of various composting processes. To restrict
the selection of processes to a workable range, only the process which has
the most plants in operation was considered. The Biologishce Abfallver-
wertungs, mbH & Company (BAV) process met this general requirement (see
Table 1).
Biologische Abfallverwertungs, MbH & Company has constructed at least
19 plants in West Germany within the past several years and has at least 5
additional plants being designed or under construction. Most BAV reactors
are designed for capacities equivalent to populations of 30,000. However,
BAV systems have been designed to service communities of 10,000 and to ser-
vice cities of 110,000. Table 3 lists the locations of BAV-constructed
plants in West Germany.
The BAV process has evolved from the general method that was patented
by F. Kneer (German patent No. 22 53 009, June 19, 1975). Essentially, the
process consists of aerating a mixture of dewatered primary sewage sludge,
sawdust, and cured compost in an open-top, cylindrical vessel. The dewatered
sludge, sawdust and cured compost mixture slowly descends, by gravity,
through the vessel's length in about 12 days. The descending mixture is
aerated by compressed air which is distributed at the base of the vessel.
The composting rate can be controlled, within limits, by the aeration rate.
A diagram of a general bioreactor vessel and its components is presented
in Figure 12. Because the reactants descend and the air rises within the
composting vessel, this process is sometimes called a "countercurrent venti-
lation process" (14).
A "conveying screw or mill is used to remove product at the base of the
vessel. This screw or mill rotates around the vessel's radius and brings
the compost product toward a center exit port. The product, after within-
vessel composting, is placed in windrows for a curing period.
CRITERIA FOR SITE SELECTION
To further restrict the selection and to remain within the time and funds
assigned for this evaluation, the following additional criteria were estab-
lished: (1) that only one composting plant be evaluated in great detail;
(2) that the plant be of average size, i.e., the plant should have a design
39
-------
DRAFT.
Raw Material Distribution Rake
Raw Material Feed Port
(15-20) Temperature Probes
Direction of Gas Flow
\flj[/M At \
Air
Distributor
Nozzles
Aerator
(11-13) Gas Sensors for
02 + C02
1 Insulated
Container
Multi-Point Recorder
16
iTemperature Recorder
Oxygen Cylinder
Finish Product Exit Port
Figure 12. Kneer composting vessel*.
* German Patent No. 22 53 009, Issued June 19, 1975.
40
-------
DRAFT.
capacity for processing the wastes produced by a population-equivalent of
about 30,000 inhabitants; (3) that the plant should be located in close
proximity to Battelle's Frankfurt Laboratory (this reduces travel time and
costs); and (4) that the plant should have more than one year of operating
history so that the confusion attributed to start-up is eliminated.
Four plants were considered and two appeared to fit the above criteria
The plants considered were at Hochheim am Main, Kronberg, Rosbach, and Lollar
(near Giessen). Figure 13 is a map of the Frankfurt, West Germany area,
scaled to show the distance relationships of the four candidate BAV com-
posting plants to Battelle's Frankfurt Laboratories. Each plant was visited
before the final selection was made. The Hochheim am Main city administra-
tion officials gave their permission to perform the planned evaluations at
their plant, but in view of possible expected problems in obtaining tem-
perature and oxygen concentration measurements at the Hochheim am Main
plant, permission to monitor the Kronberg plant was also attempted. At
the Kronberg plant, the temperature and oxygen measuring instruments are
already installed and in operation. Moreover, the Kronberg sewage treat-
ment plant appeared to operate more consistently; unfortunately, discus-
sions with the Kronberg city administrators were not favorable. The Lollar
and the Rosbach plants each are very new and had only a few months of opera-
tional history. Both plants started in January 1978. Therefore, the final
selection was reduced to the Hochheim facility.
In addition to the above site selection criteria, the Hochheira am Main
plant was constructed and started operations in 1976, which is the year when
the majority of BAV-designed plants were put into operation. In that year,
at least 15 of the 21 operating BAV-designed plants were-put on stream.
(The first BAV-designed plant constructed and placed into operation was in
1973.) Thus, overall, the Hochheim am Main plant is thought to be repre-
sentative of the BAV process, although this plant does not have all of the
more recent improvements such as data storage memory banks, bucket con-
veyors, or a vessel constructed of reinforced concrete.
A comprehensive evaluation of the BAV composting bioreactor was per-
formed on-site at the Hochheim am Main wastewater treatment plant from
March 2 to June 2, 1978. The process was evaluated according the the fol-
lowing items: (1) reliability of the plant's mechanical components; (2)
process variables which are influenced by the progress of the composting
process, such as oxygen and carbon dioxide concentration in the exhaust gas,
temperature rise and temperature profile within the vessel, and the feed
materials's total retention time; (3) measurement of the odors originating
from the process; (4) chemical and physical characterization of the feed
material and the final product; and (5) cost information.
On April 18, 1978, the bioreactor was shut down, due to the failure
of the product discharge mechanism. At the time, it was thought that down-
time would be minimized and that sufficient time would still be available
to obtain the desired data for assessing the process. Furthermore, the
decision to continue the in-depth, detailed study of the BAV process at
the Hochheim am Main plant was based upon the fact that changing to another
site would have required additional time and funds.
-------
DRAFT
Lollar
Figure 13. Location of the four candidate BAY composting plants
in relation to Battelle-Frankfurt Laboratories.
42
-------
DRAFT
TECHNICAL DETAILS OF THE HOCHHEIM BIOREACTOR
The sewage sludge composting plant, which is a part of the Hochheim
wastewater treatment plant, was planned in 1975 and has been in operation
since June 1976.
The reactor has a capacity of 230-250 m3 and was designed to serve a
community of 25,000 inhabitants. The details of the sewage treatment plant
design are listed in Appendix B. A process flow diagram of the Hochheim am
Main composting plant is shown in Figure 14.
Sewage Sludge Dewatering
The sludge from the sewage treatment plant consists of both undigested
primary and activated sludge waste. The combined raw/activated-waste sludge
is pumped into the thickener vessel (417 m^) which was originally intended
to be an anaerobic digestion chamber when the plant was constructed. In
this thickener, the solids content is increased from 0.8-0.85 percent to
2-3 percent. The thickend sludge is pumped into two horizontal decanter
centrifuges (Flottweg, 3500 rpm, 8.3 kW) via the sludge distribution equip-
ment. Before the sludge is centrifuged, the sludge is treated with a
cationic polyelectrolyte, Sedipus 50/60 C. Polyelectrolyte rehydration
ratio is 50 kg Sedipus to 12 nr process water and is prepared in either of
the two mixing units, 12 m-^ capacity each. The sludge is then mixed by
proportioning pumps with the polyelectrolyte, one part polyelectrolyte to
4.3 parts sludge. The centrifugation increases the solids content to 15-
17 percent.
Sewage Sludge/Sawdust/Recycle
Mixer and Conveyors
After thickening in the centrifuges, the sludge is transported to the
sludge holding bunker by way of a drag chain conveyor. There is a recycle
holding bunker for the bioreactor returns directly beside the sludge holding
the bunker. The fresh sawdust holding bunker is situated outside, in the
open, next to the bioreactor. A discharge mill chain (powered by a 7.4 kW
motor), fixed to a shaft in the middle of the sawdust/finished compost
holding bunker, carries the sawdust out to a drag chain conveyor, which
then takes it to a continuous, high-intensity, circular mixer, similar to a
Banbury Mixer. Thickened sludge and the bioreactor returns are trans-
ported directly to the high-intensity circular mixer by screw conveyors.
Each screw conveyor is powered by 10 kW motors and is installed in the
bottom of the two holding bunkers. The high-intensity mixer is powered by
an 11 kW motor and has a mixing capacity of 6 m-Vhr. The feedstock mixture
(33-1/3 percent sludge, 33-1/3 percent sawdust, 33-1/3 percent returns, i.e.,
6.25 m^/d sludge, 6.25 nrVsawdust, 6.25 nrYd returns), falls onto a drag
chain conveyor which takes it directly to the top of the bioreactor. The
sludge feedstock preparation usually takes about 2 hours per day. It
should be noted that the design for mixing was 50 percent sludge, 40 per-
cent recycle, and 10 percent sawdust.
43
-------
Polyelectrolyte
Mixing Units
n
\
Sludge
Holding
Bunker
1 acr«*
CoBtijBr"
t,
n -
i
Recycle
Holding
Bunker
Bcr.« J
Jtn
Y 1 1
CM11BVD
MU«r
i
Dr..
Cell
H
MB
Di
Sludge
-V^. Distributors
Proportioning
Pi mine
t
•jr«
.8
4
i
r
i
cl
>
k llr
1
Rake
Bloreactor
Mctrlbullanr
r
aree
^
f
•tin Hill
1
*
I
ft
r
fr
Freeh Sawdust/
Finished Compost
Holding Bunker
i™q
k
b
Centrifuges
Hydraulic
Pumps
Air
Supply
Not drawn to scale
Figure 14. Process flow diagram of the Hochheim am Main composting plant,
-------
DRAFF
The Bioreactor
The bioreactor is an 8 m high steel tower (diameter: 6 m; capacity:
230 m3) insulated with styrofoam and has an outer covering of corrugated
sheet metal. (Figure 15 is a recent photograph of the Hochheim bioreactor).
The reactor is covered with a roof 80 cm above the top of the reactor. A
service gangway runs across the diameter of the reactor. The sludge mix-
ture is mechanically conveyed to the top of the reactor at the rate of
18.75 m3/d. The surface of the sludge mixture is leveled out with an
equalizer (revolving rake).
Inside, and at the bottom of the bioreactor, there is a Fr'diser arm
discharge mill chain (powered by an 11 kW motor) and the air distribution
system. The FrMiser arm rotates and travels on a track around the reactor's
circumference. On this arm, there is a moving drag mill chain which brings
product toward the center and into the exit port. One of the two rotary
piston blowers (each 15 kW) directs approximately 600 m3 air per hour
through the compost material. The composting mixture is aerated approxi-
mately 22 hours per day. There are 3 temperature measuring probes and
one carbon dioxide measuring probe fixed at 30 cm off the inside wall, and
out of the path of the equalizing rake. All 4 probes are fixed at one
point directly beneath the bioreactor's feed conveyor. The temperature
measuring probes extend into the compost to 3 depths, 160 cm, 200 cm, and
240 cm, from the bioreactor's fill line. The single carbon dioxide measur-
ing probe is attached to the 200 cm temperature measuring probe. It should
be noted that the carbon dioxide probe was inoperative during this study,
and consequently, portable gas analyzers were used.
The compost is taken out of the reactor after about 12 days, based on
the input feed rate (18.75 m3/d) and assuming plug flow. Part of it is
fed back into the reactor as returns (6.25 m3/d) while the rest is com-
posted for 5-6 weeks in windrows. There are no values on fermentation
shrinkage during windrow composting. A flow diagram of the process showing
volumetric flow is presented in Figure 16.
MECHANICAL RELIABILITY OF THE COMPOSTER
COMPONENTS AT THE HOCHHEIM am MAIN PLANT
From observations during the on-site study of the composting plant from
April 12 to April 18, 1978, and according to reports by the sewage treatment
plant foreman and the Hochheim city engineer, it appears that components
most susceptible to failure at the Hochheim composting plant are (1) the
product discharge mechanism in the bioreactor (Fraiser arm with mill); (2)
the discharge mechanism in fresh sawdust/bunker (discharge mill, Figure 14;
and (3) the continuous, high-intensity, circular mixer. The sludge centri-
fuges, rotary piston blowers for the air supply, rake equalizer at the top
of the bioreactor, and the drag chain conveyors, on the other hand, can be
regarded as reliable and require only normal maintenance.
Since plant start-up, there have been four major failures in the bio-
reactor's product discharge mill. These failures caused plant shut-down
for 2 to 4 weeks, and during the shut-down and before repairs could be
45
-------
Figure 15. The BAV bioreactor at the Hochheim am Main,
West Germany wastewater treatment plant.
-------
2-3% solids
40 m3/d
raw sludge from the
sludge treatment plant
125 m3/d
exhaust air
raw compost
-
10.75 in /d
Figure 16. Volumetric flow diagram of Hochheim composting plant.
-------
DRAFl
done, the bioreactor had to be emptied manually. The causes of each
failure are recorded in the wastewater treatment plant's log and the
following explanations were given:
• Mill chain on Frasier arm broke apart
• Fraiser arm bent upright, shaft broke off (solidified
material on the floor of the reactor)
• Fraiser arm stopped (solidified material on the floor
of the reactor)
• Fraiser arm stopped (the fermenting mass solidified on
the floor of the reactor). This was attributed to the
fact that the direction of the air flow through the reac-
tor was reversed from normal operation. The moisture in
the outside air condensed and accumulated in the base of
the reactor. The condensed water reacted with the sludge/
sawdust mixture to form a solid mass.
The discharge mill in the sawdust bunker broke 3-4 times since start-
up. Each time the center shaft broke. Since the sawdust bunker is not
roofed, the sawdust absorbs rainwater readily, which in turn reacts to
form a solid mass. (However, this can be easily corrected by roofing the
bunker and using a courser screen fraction of sawdust.)
The motor in the continuous, high-intensity, circular mixer has been
replaced three times. The latest replacement is rated at 11 kW. The first
two motors (7.5 kW and 9 kW, respectively) were insufficient. In addition,
mixing blades broke when large pieces of wood in the sawdust entered the
mixer. In one case, these blades became wedged into the drag chain con-
veyor below the mixer.
MECHANICAL RELIABILITY OF COMPOSTER
COMPONENTS AT FIVE OTHER BAV PLANTS
To further assess the mechanical reliability of bioreactor systems,
operators of five other composting plants were interviewed. The result
can be summarized as follows:
Two plant operators give the plant positive ratings, two neither posi-
tively nor negatively, and one negatively. However, all operators cited
difficulties with the bioreactor's Fraiser arm discharge mill, three (in
contrast to Hochheim) with the drag chain conveyors, two with the high-
intensity mixer and one operator reported that no part of the plant was
trouble-free. One operator had difficulty with the discharge mechanism
in the returns and sludge bunker before the discharge chains were sub-.
stituted with screw conveyors. One operator reported that bridging formed
in the bioreactor during the product discharge cycle. The bridging is
characterized by a depression in the level in spots, indicating localized
high solids removal rates.
48
-------
DRAFT,
The difficulties with the drag chain conveyors and the the high-
intensity mixers were generally viewed as possible deficiencies in the
system which may require developments as initiated by BAV in newer plants.
These include:
• The breakload on the Fraiser arm mill chain has been
doubled to 24-25 tons from 12 tons.
• Plastic bucket conveyors and conveyor belts have replaced
the drag chain conveyor. The plastic bucket conveyors
now lift the feed input into the reactor (verticle move-
ment) while belt conveyors are used where product is moved
horizontally.
• Fresh sawdust, the bulking agent, is now stored by itself
in an independent bunker, rather than being stored with
the cured compost.
• Variable speed hydraulic motors are substituted for the
fixed-speed electric motors for powering the Fraiser arm
mill chain and the high-intensity mixer.
• The new bioreactors are to be made of reinforced concrete
and tapered at the top. With the wider bottom, the pro-
duct may fall more easily and thus decrease the product
bridging problem.
Overall, it may be difficult to judge the BAV system's mechanical com-
ponents' reliability for the following reasons:
• Most of the plants were built in 1976 and 1977 (one plant
in 1973,, two in 1974 and three in 1975; a total of 21 com-
pleted by 1977) and only six plants have been operating for
more than 2-11'2 years.
• It is during plant shake-down when the usual initial
difficulties appear.
• The operating personnel are gathering experience in the
day-to-day operation of the plant.
• Each composting plant has to be adjusted to the type of
sludge produced by the corresponding sewage treatment
plant.
49
-------
DRAFT.
TEMPERATURE PROFILE AND EXHAUST
GAS COMPOSITION
Longitudinal Temperature Profile
The temperature within the reactor is recorded on strip charts in the
control room. The three thermocouple probes extend into the compost at
approximately 160 cm, 200 cm, and 240 cm from the reactor's fill line at
one point. The temperature was recorded throughout the on-site evaluation
study period and is plotted against the data in Figure 17. The data showed
that the reactor temperature varied from over 45°C to 90°C, at the time when
the reactor was being operated. On April 18, the reactor product-discharge
mechanism failed. The reactor was emptied manually so that the discharge
mechanism could be repaired. The temperatures recorded and plotted during
that down period, April 18 to May 18, is that of the ambient air.
Exhaust Gas Composition
The exhaust air was measured at three locations on the top of the bio-
reactor: Point 1 is 80 cm from the center, Point 2 is 180 cm from center,
and Point 3 is 280 cm from center. Table 10 lists the concentrations of
oxygen and carbon dioxide as measured by DrMger tube method. The oxygen
concentration averaged 17.2 percent (2-month average) in the central cir-
cular area (80 cm radius) and 18.3 percent in the outer circular area, 80
cm from the center to the reactor's inside wall. The carbon dioxide concen-
tration followed a similar pattern; the highest concentration was measured
in the center of the reactor, 3.9 percent (2-month average). In the outer
ring, 80 cm from the center to the reactor's inside wall, the carbon dioxide
concentration averaged 2.2 percent (2-month average). The significance of
these findings is that this is indicative that air is channeling through
the reactor rather than diffusing uniformly throughout. Visual inspection
of the compost surface at the top of the reactor correlates with these
measurements. The compost in the reactor's center (80 cm radius) consisted
of a loose-textured material, while the compost in the outer zone was
solidified and crusted. Cracks propagated throughout this crusted area.
PROCESS ANALYSIS BY CHEMICAL AND
PHYSICAL METHODS
One method of evaluating a process is by chemical and physical analysis
of its input and output. To accomplish this evaluation, representative
samples of feedstock and composted product were analyzed. The samples were
collected over a two-month bioreactor operating period, during which time
a breakdown of the product extraction mechanism occurred. The repair of
the product extracting mechanism required manual unloading of the reactor
contents followed by the refilling of the reactor with freshly prepared
feedstock, with no removal of product until the vessel was filled. One
month elapsed from the time of breakdown, unloading, repairing, refilling,
and returning to normal operations. Thus this evaluation represents the
process performance at two stages of the plant's normal operation, (1) after
50
-------
TABLE 10. GAS COMPOSITION OF BIOREACTOR EXHAUST GAS
Ul
Date
0*i/12/78
Q'i/13/78
O^/l't/78
OV17/78
OVlS/78
05/29/78
05/30/78
05/31/78 (1)
05/31/78 (2)
06/01/78
06/02/78
Average
Measuring
vol.% 0
«.
16
-
17
19.5
20.5
17.0
18.0
16.0
15.0
15.5
17.2
Point 1
vol. % CO
cL
_
3.8
Q.k
2.0
0.6
2.0
k.O
0.2
6.0
10.0
10.0
3.9
Measuring Point 2
vol.% Q^
15
20
20
21
21
20
16.0
18.5
14.0
19.0
19.0
18.5
vol. % C02
2.0
0.6
0.1
0.1
0.2
0.6
7.0
'J.O
7.0
2.0
1.0
2.2
Measuring
vol.% 0_
-
18
17
20.5
20
-
18.5
18
18
14.0
19.0
18.1
Point 3
vol.ft C0g
-
0.9
0.3
0.2
0.3
-
4.8
1.5
0.8
9.5
0.6
2.1
Measuring point l:~ 80 cm from center
Measuring poont 2:~ l80 cm from center
Measuring point 3:^280 cm from center
relative error: 5-10
-------
Ul
to
Course of Temperature
from April 11 to 20, 1978
April 12
20
90
160 cm below equalizer
'. 200 cm below equalizer
• 240 cm below equalizer
10
Figure 17. Temperature profile at bioreactor Hochheim.
-------
Ul
Course of Temperature
from May 18 to June 2, 1978
Remar
: No registration at interrupted curvf
May 18 19 20 21 22 23 24 25 26 27 28 29 30 31 June 1
Date
90
80
70 H
60 "g
i-t
P>
50 £
H
to
AO *
30
20
10
o
Figure 17. (continued)
-------
DRAFT.
an extended period of operation, and (2) at the beginning of a normal period
of operation. The complete analytical data and methods of chemical analysis
are detailed in Appendix D.
Sludge Solids Analyses
The study of compost solids is a measure of (1) the amount of solid
material, (2) the proportion of organic matter, and (3) the mineral, or
the inorganic fraction. The organic portion is the food for the bacteria
associated with composting. The results of these analyses indicate the
progress of decomposition of the organic components. As decomposition pro-
gresses, the concentration of organics will decrease as the proportion of
organics is converted to gases and inorganics. Also, the proportion of
total solids will increase as water is depleted from the solids by evapora-
tion. Fresh raw sludge usually contains approximately 70 percent of the
total solids and is highly odorous. Well digested sludge as found in compost
usually has an organic content of less than 50 percent of the total solids
and is not odorous.
In the solids content study of the Hochheim am Main bioreactor process,
the organic constituents contents of the feedstock and the composted
product (both before and after the mechanism failure incident) were analyzed
at 76 percent of the total solids (Table 11). The total solids in the pro-
duct increased, and this was due to the evaporation of water. The data sug-
gest that the Hochheim plant does not stabilize sewage sludge completely.
Elemental Analysis
The intent for conducting this study was to obtain a heat balance
around the system, such as in a combustion chamber. However, the analyses
for carbon, hydrogen, nitrogen, oxygen, sulfur, and heat values show no
difference between feedstock and composter product (Table 12.)
Odor and Appearance of Final Product
Visual and odor tests showed no difference between feedstock and the
product. Both had highly putrid odors.
Operational Factors Affecting Data
After the reactor is filled and the composting process starts, the
temperature increases to 70-80°C. (This plant recorded 95°C on May 29.)
In the BAV process there is no provision for internal mixing; the compost
supposedly moves uniformly through the reactor by gravity.
At the composting temperature, the organic constituents gelatinize (or
at least remain "sticky"), and since there is no internal mixing, the compost
compacts. (The product removal mechanism failure of April 18 was attributed
to solidification of compost at the base of the reactor.)
-------
DRAFJ
TABLE 11. COMPARISON OF FEEDSTOCK AND COMPOSTED PRODUCT
OF THE HOCHHEIM AM MAIN, WEST GERMANY
BIOREACTOR, APRIL 12 TO JUNE 2, 1978
(a)
Feeds tock^ '
Composted produce
Total solids
at 105°C,
%
33.2
39.6
Organic solids
% of
total solids
75.9
76.5
Ash
at 900°C,
%
8.0
9.3
(a) Average of 7 samples, in duplicate.
(b) Average of 10 samples, in duplicate.
i Dry Solids - % Ash
% Dry Solids
% Organic Solids
x 100
TABLE 12. CHEMICAL COMPOSITION COMPARISON"OF FEEDSTOCK AND
COMPOSTED PRODUCT FROM THE HOCHHEIM AM MAIN,
WEST GERMANY BIOREACTOR, APRIL 12 TO JUNE 2, 1978
•
c
Feedstock (b) 46.1
(c)
Composted product 44.6
Chemical elements,
%
H N 0 S
5.7 1.4 36.5 0.22
5.5 1.5 36.3 0.28
Lower heat
value / a'
kJ/kg
16946
16671
(a) Total mass basis, including ash.
(b) Average of 7 samples, in duplicate.
(c) Average of 10 separate samples, in duplicate,
55
-------
DRAFT.
In addition, the product removal port at the base of the reactor is cen-
trally located under the feedstock filling conveyor, Thus, a natural pro-
pensity to form a cone is established.
Therefore, product flow outside the cone is restricted. A substantial
portion of the compost remains stationary. A conceptual view of the internal
condition on the day the product removal mechanism failed, as presented in
Figure 18.
Thus, the feedstock filled at day zero in time, is removed at some time
which is shorter than one would calculate from the empty volume of the reac-
tor and the volumetric feed rate.
The formation of a "sticky" mass is a key tenet in this explanation,
and this was observed quite strikingly at Hochheim, and to a lesser extent
at other BAV plants visited (Kronberg, Rosbach, and Ferndorftal (Siegen).
The propensity to form this mass was deferred relative to the proportion of
sludge used in the feed material. Furthermore, the use of unstabilized
recycle material would tend to aggravate this process. This may have been
the cause for the agreement between feed and product data obtained from the
Hochheim plant. However, if over-loading with insufficiently dewatered
sludge is the source of the problem, it is likely that increasing the mass
of bulking agent or properly stabilized compost will correct the problem.
However, throughput rate of fresh sludge will correspondingly be reduced.
EVALUATION OF ODORS EMITTED FROM
COMPOSTING PROCESS
The three major odor sources of the Hochheim am Main sewage treatment
plant appears to originate at the
• Activated sludge tank
• Bioreactor, and
• Windrovre.
The odor qualities were determined organoleptically and the odor intensities
were identified by determing the detection theshold level by human sense of
smell (see Appendix E). The most intensive odor emission was measured during
emptying of the bioreactor. This strong emission results from the evapora-
tion of the warm vapors steaming from the freshly processed compost while it
is transferred to the curing windrows. The odor intensities determined at
the windrwos and the activated sludge tank were 25 and 16 percent, respec-
tively, of the predominating odor emitted from the bioreactor. The emission
intensities and qualities vary, e.g., in seasonal and working-day cycles.
In Appendix E, a discussion of odor measurement technique and theoretical
considerations concerning odor distribution in the surrounding neighborhood
is described.
56
-------
DRAFT
Raw Material Feed Port
Lu^-i—^
r
Free- ;
~v
Solidified'Flowing Solidified
Mass ) Mass
) Zone
7.
I
,—ow—"
r-r r '
Qbi<==^
JrO
$ i "
4^-
Finish Product Exit Port
Figure 18. Conceptual view of the Hochheim am Main
bioreactor at time of product removal
mechanism failure, April 18, 1978.
57
-------
DRAFI
Odor concentration in the vicinity of the Hochheim plant depends on top-
ographic and weather conditions, especially on wind direction and speed and
on turbulence. The three odor sources or odor profiles are considered and
it is usually the odor from the bioreactor or a mixture from bioreactor and
windrow odor which predominates, whereas the odor from the activated sludge
tank is practically not perceived outside the plant area. As a result of
topographical factors, odor concentration zones may form whose characteris-
tic odor profiles may be temporarily perceived in an area of several hundred
meters.
58
-------
DRAFI
SECTION 5
ECONOMIC EVALUATION OF BAV HOCHHEIM COMPOSTING PLANT
Operating and maintenace costs and capital investment costs were esti-
mated for the BAV process on equipment specifications and process require-
ments supplied by the City of Hochheim. The Hochheim composting plant is
designed to process 250 m3 per day of sludge cake from the sewage treatment
plant which is equivalent to 20.4 t of dry solids/day and serves a popula-
tion of approximately 25,000. The plant throughput is currently 50 percent
of the design capacity or 125 m^ of sludge per day. Details of the process
which were supplied by the Hochheim City Engineer are given in Appendix F.
A flowsheet of the composting process is illustrated in Figure 19. The
capacities of each component in the process are listed in Table 13.
The installed costs for each equipment item were supplied by the City
of Hochheim in Deutsch marks (DM). These costs were converted to dollars
based on the exchange rate of 2 DM per dollar. An independent estimate of
the installed costs was then made using the equipment specifications sup-
plied by the Hochheim plant. These values of the installed equipment costs,
as well as the equipment specifications, are detailed in Table 14. The
estimated costs are 18 percent higher than the actual reported costs which
is within the accuracy of the cost estimate method used; the estimate of
the total installed costs is $816,000 compared to an actual installed cost
of $690,000. The estimated installed costs include instrumentation,
piping, electrical, concrete, steel, paint, and insulation. These items
are listed separately in the actual costs column. The estimated cost of
the general facilities is assumed to be equal to 10 percent of the total
installed cost.
Assuming a contractor's fee of 11.1 percent and contingencies at 15
percent, the estimated total plant investment of the BAV process is
$1,043,300 (see Table 15). Licensing, fees are based on the annual capacity
of the plant and for this capacity (20.4 t/d or 5100 t annually,), the fees
are $20,000 per year. The estimated total capital requirement is $1,225,800
(see Table 16).
Land cost is not included in the estimated total capital requirements
due to the variability in land price with location. Land cost should not
exceed 10 percent of the total plant investment. Because windrowing is
required, the BAV process requires approximately the same amount of land
as aerated piles.
59
-------
DRAFT
Pumps for raw sludge
Sludge thickener
Pump for sludge
Coagulant container/propor-
tioning
Decanter centrifuge
Drag chain conveyer
f 7J Sawdusc bunKer
Mill Chain/drag chain
conveyer
(7) Ihick-sludge
Discharge spiral
Returns bunker
Discharge spiral
Mary mixer
con\7ever
M5) Rotary piston blower
Mbj Bioreactor
1?) Discharge mill chain
l6\ Windrows
12. Raw cos^ost to be set
on windrows
Material (see
Table 13)
Component of the
- plant (see above)
Figure 19. Flow sheet of the BAV Hochheim composting process.
60
-------
DRAFT
TABLE 13. THROUGHPUT BY TYPE OF MATERIAL
Type of material
1. Primary sludge from the sewage
treatment plant
2. Water from sludge thickener
3. Dewatered sludge
*). a) Coagulant (in t/d)
b) Fresh water
5. Water from decanter centrifuge
6. Thick sludge from decanter
centrifuge
7. Sawdust
8. Recycled product
9. Mixed material
10. Air
11. Raw compost discharge
12. Raw coirpost to be set on windrows
Volume
m3/d
125
85
U
0.05
12.0
1.5.8
6.25
6.25
6.25
18.75
13.200
17.0
10.75
Solid natter content:
I of weight
0,8
0
2.5
0
0
16
80-90
36
32
0
36
36
61
-------
DRAFT
TABLE 14. INSTALLED EQUIPMENT COSTS FOR
A 250 m3/DAY SLUDGE PLANT
Item
Pimps for conveying
sludge to thickener
Sludge thickener
Pump-sludge feed Co
cencrifuges
Pipeline- thickener to
cencrlfuge
Coagulant container
( i-lch agltacor)
Proportioning punps
Pipeline to centrifuge
Centrifuges
Drag conveyor
Savdust bunker
Mill chain
Drag conveyor
Thick sludge bunker
Screw convevor
Return bunker
Screw conveyor
Rotary mixer
Bucket conveyor
Blovers
vent pipes
Bioreactor
Drag conveyor
Windrows
General facilities
Installation Coses
Gas measurement system
Buildings
Foundations
Electrical
Site preparation
Startup costs
INSTALLED COST
Note: D • diameter
No.
required
3
1
1
1
2
2
1
2
1
1
1
1
1
1
1
1
1
1
2
1
1
Design
basis
carbon steel
250 n3/d
0.8: solids
125 m3/d
concrete
concrete
1500 t/hr
6 m3/hr
6 m3/hr
concrete
6 m3/hr
6 D3/hr
concrete
4 m3/hr
concrete
3 m3/hr
6 m3/hr
6 m3/hr
600 D3/hr
rotary pistons
.95 cm
4.5 m3/hr
10.75 o3/d
~
H - height ID -
Unit size
or
capacity
83 m3/d
9.5 n D x 6 m H
12 si3
3500 rpm, 8.3 kW
35 m capacity
4.5 m x 4.5 n x 1.7 m H
7.4 kV motor
2mx2mx2o
2mx2mx2m
10 kW motor
11 kU motor
15 kW
15 kU
8 m H x 6 m ID
11 kW motor
15 m L. 5aW
—
Internal diameter
Equlpocnt Con'"'
Actual UV-HoeMielEi
I
13.700
17,800
5,300
12.500
4,500
5,600
5.400
88,400
26,800
13,000
4,800
Installed cost.
S
(Battelle estimate)
10,000
19,600
2,400
(costed as general
facility)
5,400
3,400
(costed as general
facility)
147,300
39,300
A, 300
—
51,800
(P«rt of 500
iuilll.rj rtciliti.e)
10,900
—
10,900
14,900
21,000
31,400
31,400
57,400
33,700
14,200
—
6,900
159,800
21,300
39,300
40,000
22.500
690,000
L • length
19,600
1.100
19,600
56,000
16,200
47,400
47,400
261 . 700
27,800
1,000
81,700
816,600
W - width
(a) These costs were obtained from the Hochhein City Engineer's Office.
62
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DRAFT
TABLE 15. ESTIMATED TOTAL PLANT INVESTMENT OF BAV PROCESS
FOR A 250 m3 SLUDGE/DAY ('20.4 dt/d) PLANT
Battelle Estimate,
$
Total installed costs 816,600
Contractor's fee (11.1 %) 90,600
Subtotal 907,200
Contingency (15%) 136,100
Total Estimated Plant Investment (TPI) 1,043,300
TABLE 16. ESTIMATED TOTAL CAPITAL REQUIREMENT OF BAV PROCESS
FOR A 250 m3 SLUDGE/DAY (20.4 dt/d) PLANT
Battelle Estimate,
$
Total plant investment (TPI) 1,043,000
Allowance for funds used during construction 93,900
(TPI x 1 yr x 0.09)
Licensing fees (annual cost/yr) 20,000
Startup costs (20% of total gross annual O&M costs) 47,000
Working capital
14-day inventory of raw materials:
sawdust (6.25 m3/d x d x $0.44/m3) 100
coagulant (60 kg/d x 14 d x $2.75/kg) 2,300
materials and supplies (0.9% of TPI) 9,400
net receivables (2-1/4 annual O&M costs) 9.800
Total Estimated Capital Requirement 1,225,800
63
-------
DRAFT
The estimated annual operating costs are $137,700 and the maintenance
costs are $97,200. Assuming a dry solids throughput of 20.4 t/d and 250
operating days per year, the O&M costs are $46.06 per t (Tables 17 and 18)
of solids per day or $41.76 per short ton of solids per day. This estimate
does not include the cost of transporting the sludge from the treatment plant
to the disposal site. In addition, no debit or credit has been taken for dis-
posal of the sludge.
The operating costs of the BAV process are relatively low due to the
small labor requirements of the process (1-1/2 men/shift plus supervision).
However, the BAV system is a capital intensive process; the total plant
investment for the BAV system is twice that required for an aerated pile
process of an equivalent capacity (15).
The largest plant now in operation is the Siegen plant which has two
reactors with capacities of 350 m3 of sludge per day and serves a popula-
tion of 110,000. A capacity of 350 m3 for the bioreactor could represent
a practical limit due to the restrictions in the design of the reactor.
The physical problem of drawing compost from the extremities of a vessel
of much larger diameter and maintaining air distribution are belived to be
the major problems which could prevent the use of larger vessels. There-
fore, the bioreactor itself may limit any economy which can be achieved
by increasing the size of the plant.
The annualized cost of the BAV process is compared to estimates of
several other disposal methods in Table 19. These values are listed for
purposes "of illustration and can only be considered "ball park" estimates.
They represent the best available estimates reported in the literature. To
establish a rigorous method of comparison, estimates should be made of the
other sludge disposal processes on the same basis at that used for the BAV
process.
The estimates for landfilling, landspreading, trenching, and incin-
eration are given as a range of values due to the cost variations reported
in the literature for these disposal methods (15). Estimates of capital
recovery, operating and maintenance costs have been included in the total.
In addition, a charge of $19.80/t has been added to account for dewatering
costs (16). Based on figures reported in the literature (17), the annual-
ized cost of sludge disposal by the aerated pile method has been estimated
for an equivalent capacity of 5100 t per year (14 t per day). (The aerated
pile method is operated 365 days per year.) Dewatering costs have been
included in the estimates. Transportation costs of the sludge to the dis-
posal site have not been included.
The estimate of total annual cost of the BAV process is higher than
the costs for landfilling and aerated piles. However, the estimate of the
BAV process falls within the range listed for landspreading and incinera-
tion of dewatered sludges. Trenching has a 30 to 50 percent higher total
annual cost than the BAV process.
64
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DRAFI
TABLE 17. ESTIMATED ANNUAL OPERATING COSTS OF BAV PROCESS
FOR A 250 m3 SLUDGE/DAY (20.4 dt/d) PLANT
Battelle Estimate,
$
Raw materials
sawdust (6.25 m3/d x 250 d x $0.44/m3) 700
coagulant (50 kg/d x 250 d x $3.3/kg) 41,400
•5
Purchased water (3000 m3 x $0.166/m ) 500
Electricity (173,500 kWh x $0.025/kWh) 4,300
Labor (1-1/2 men/shift x 2080 manhours/yr 25,000
x $8/manhour)
Supervision (20% of labor + supervision) 18,000
Supplies (30% of labor) 7,500
Local taxes and insurance (2.7% of TPI) 28,200
Wastewater disposal (32,700 m3 x $0.2179/m3) 7,100
Total Estimated Annual Operating Costs 137,200
TABLE 18. ESTIMATED ANNUAL MAINTENANCE COSTS OF BAV PROCESS
FOR A 250 m3 SLUDGE/DAY (20.4 dt/d) PLANT
Battelle Estimate,
$
Maintenance labor (0.6 x 0.06 x TPI) 37,600
Supervision (20% of maintenance labor) 7,500
Administration (60% of labor + supervision) 27,100
Supplies (0.4 x 0.06 x TPI) 25.000
Total Estimated Annual Maintenance Costs 97,200
65
-------
DRAFT
TABLE 19. COMPARISON OF TOTAL ANNUAL COSTS FOR SLUDGE
METHODS (1st Quarter 1978 U.S. Dollars)
( . Annual Processing Cost Annual Disposal Cost
Method^ $/t of Dry Solids $/t of Dry Solids
BAV processv/ 99.1
Landfilling(c) 46.8-82.2
(~\
Landspreadingv' 50.4-132.8
Trenching(c) 156.3-177.5
Incineration(c) 86.9-129.3
Aerated piles(d) 74.5
(a) These operating costs cannot be used for direct comparisons since
different end-products are involved. The BAV and aerated pile
methods produce a product for possible sales, whereas the others
involve disposal; the cited cost is for processing, and no credit
for sales has been included. Furthermore, landspreading is for
disposal of a liquid, whereas the other disposal method generally
involve solids. There are also significant differences in land
requirements for the different methods.
(b) These BAV methods cannot be compared directly to the other methods
because of the differences in scale of operation. The BAV method
has a reduced requirement for land compared to some of the others.
(c) Annual cost updated to first quarter 1978 (15); includes dewatering
cost of $19.8/t (16). No heat recovery is included in the incin-
eration method.
(d) Annual cost obtained from Reference 16, updated to first quarter
1978; includes dewatering cost of $19.80 (16).
66
-------
DRAFT
SECTION 6
CONCLUSIONS
The conclusions of this report will be presented in two parts. Part I
relates to the first objective of this study in which existing European
sewage sludge composting practices were identified and available information
gathered on their operating modes, effectiveness, reliability and costs.
Part II is related to detailed study performed at the Hochheim am Main
composting plant. The purpose was to obtain experimental data to evaluate
the effectiveness and reliability of the process as well as assess process
economics. Part Ila relates to the economics of the process at Hochheim.
Part I
1. The feasibility of composting sewage sludge mixed with a
bulking agent such as municipal solid waste (MSW), bark,
sawdust, etc., is well established in Europe.
2. The future of general composting technology in Europe
depends more on developing economic and-use markets and
on continued public acceptance rather than technological
process improvement.
3. In general, the quality of the compost produced from sludge/
sawdust of tree bark is better than the quality of the compost
produced from MSW/sludge. The better quality is due to the
amount of nondegradable material that exists in MSW/Sludge.
A. A condition for good composting of the sludge is that the
water content of the mixture must be kept at a level of
50-55 percent. A major problem in sludge composting is
the heavy metal content of the sludge, and this parameter
should be controlled carefully.
Part II
The following conclusions are based upon the data obtained only at the
Hochheim composting plant. These conclusions may or may not apply to other
composting units using the same process. Further studies would be needed
before any complete evaluation of the BAV system could be made. However,
the conclusions regarding the Hochheim am Main plant during the period of
the investigation are:
67
-------
DRAFT,
1. Effective use of the reactor volume available for stabili-
zation was not achieved during the investigation. The evi-
dence for this deficiency included:
• The compost product had an insignificant amount of
stabilization compared to the feedstock.
• The sewage sludge/sawdust/recycle mixture solidified
during processing.
• Analyses of exhaust gas compostion indicated that
aerobic composting occurred mostly in the center of
the reactor.
• Constant temperatures could not be maintained.
• Odor was noticeable several hundred meters downwind
when product was discharged from the bioreactor.
2. The product removal mechanism was not capable of handling the
solidified product produced during the investigation. This
mechanical problem was common to five other BAV installations
with the same type of reactor.
3. The most intensive odor from the sewage treatment plant was
emitted from the bioreactor itself during product discharge.
Part IIA
1. The BAV process is a relatively capital-intensive process
as compared to the USDA ARS aerated-pile system.
2. An installation built in the U.S. would most likely have a
higher investment than an equivalent European system due
to the redesign or adaptation of European equipment to U.S.
equipment specifications.
3. The BAV process may be amenable to only a limited economy of
scale due to the probable restrictions on air distribution,
product removal requirements, and compaction of solids at the
base of the bioreactor.
4. The total annualized costs for the BAV process are higher
than those for aerated piles and landfilling, based on the
best available data for comparison. The estimates of the
BAV process fall within the ranges given for landspreading
and incineration. The estimate for the BAV process is lower
than the cost estimated for trenching. These cost compari-
sons must be veiwed cautiously because it was not possible
to develop all the estimates on the same basis.
68
-------
DRAFT
SECTION 7
RECOMMENDATIONS
Based upon the results of this study, the following recommendations
are offered:
1. At least one other (or more) vendor(s) of mechanical
"within vessel" composting systems should be evaluated
in detail. It may be desirable to evaluate a system
which employs an externally-mounted product-removal
mechanism and which mixes the composting mass during
the active fermentation period. An example of this
system is the Triga-designed St. Palais sewage sludge
composting system at the Royan, France, wastewater
Treatment plant. Also, it may be desirable to evalu-
ate the Weiss "within vessel" system, since the manu-
facturer claims to have solved the composted product
extraction problem.
2. The Schnorr and Homogeneous Composting Stabilization
(HKS) processes should be evaluated and compared to
additional "within vessel" data.
3. The Swedish SNPD aerated-pile composting experiments
in arctic climates should be compared to the USDA ARS
system. The objective of the SNPD experiments is to
determine the combined effects of cold intake air
temperature with various types of contaminated sewage
sludge on the composting rate.
4. The effect of heavy metals in sludge composting systems
needs to be evaluated.
5. Economic evaluations of several different composting
methods should be conducted by a single source to pro-
vide a uniform basis of comparison.
69
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DRAFT.
REFERENCES
1. Mach, R., Composting Plants in Germany: Locations, Companies, Systems,
and Directions, Compost Science, 1977/4, p. 8.
2. Spohn, E. Recent Developments in Composting Municipal Wastes in
Germany, Compost Science, 1977/3, pp. 25-32.
3. B. Pommel and C. Juste, La valorisation agricole de dSchets: le compost
urbain, French Environmental Ministry, DPPN, 1977.
4. Bundesministerium des Innern, Abfallwirtschaftsprogramm 75 der
Bundesregierung Umweltbrief Nr. 13, 1976.
5. A. Thormann, Klarschlamm-Menge and Beseitigung in der Bundersrepublik
Korrespondenz Abwasser 7/77, 24 Jahr., 1977, pp. 212-214.
6. Enquiry of the Technical Union for Waste Water (ATV), Nov. 1974, and
Evaluation by Unweltbundesamt (FB III - 2.1).
7. Spoon, E. Recycling with Renova Method, Compost Science, 1972/2, pp. 8-11,
8. Hughes, E. G., Reviving and English Composting Plant, Compost Science,
1977/2, pp. 18-21.
9. Report of the Working Party, on the Disposal of Sewage Sludge to Land,
Department of the Environment/NWC Standing Technical Committee Report
No. 5, July 1977.
10. Sewage sludge disposal data and reviews of disposal to sea, Department
of the Environment/NWC Standing Technical Committee Report No. 8,
January 1978.
11. G. Hovsenius, L. Moreno and F. Setterwall, Composting pulverised
household refuse by forced aeration, Statens naturvardsverk,
Forsknings-skretariatet, SNV PM 1034, February 1978.
12. Dean, R. B., European Manufacturers Display Systems at Kompost '77,
Compost Science, 1978/2, pp. 18-21.
13. Wohin mit den Abfallen, Stand der Abfallbewirtschaftung und der
Keh'richtverwertung in der Schweiz, Aktion Saubere Schweiz + Schweiz.
Vereinigung fur Gewasserschutz and Lufthygiene, Zurich, November 1976.
70
-------
DRAFT
14. Wolf, H., Composting Sludge in Germany, Compost Science, 1974/6, p. 31.
15. Colacicica, D., et al., "Costs of Sludge Composting", ARS-NE-79,
February 1977.
16. Van Note, R. H., et al., A Guide to the Selection of Cost-Effective
Wastewater Treatment Systems, U.S. Environmental Protection Agency,
EPA 430 19-75-002, 1975.
17. Colacicia, D., and L. Christensen, "Sludge Composting: Costs and
Market Development", Proceedings of the Third National Conference
on Sludge Management Disposal and Utilization, December 14-16, 1976.
18. B. Parent, Etude de compostage commun de boues rSsiduaires fraiches
et d'ordures m£nageres, Techniques et Sciences municipales, Vol. 71,
No. 10, October 1976, pp. 425-433.
71
-------
DRAFT,
APPENDIX A
LIST OF EUROPEAN MANUFACTURERS AND REPRESENTATIVES
72
-------
DRAFF.
APPENDIX A
LIST OF EUROPEAN MANUFACTURERS AND REPRESENTATIVES
The following is a list of (1) the European manufacturers and their
European representatives of sewage sludge composting equipment and (2)
government environmental protection officials, city administrators, and
composting plant operators, who were contacted during the course of the
program.
DANO
Via alle Dobbie, 2
CH - 6924 SORENGO/LUGANO
Mr. V. Stahlschmidt
Gebruder Buhler AG
CH - 9240 UZWILL
Mr. H. Hofer and Mr. H. Weber
Industrie-Werke Karlsruhe Augsburg AG (IWKA)
Brikollare Process
Postfach 3409
D - 7500 KARLSRUHE 1
Mr. F. Beichel and Mr. H. Schriewer
TRIGA
33, avenue du Marechal Joffre
F - 92000 NANTERRE
Mr. G. During, General Manager, and Mr. B. Parent
Carel Fouche Languepin
55, rue d1Amsterdam
F - 75008 PARIS
Mr. P. Giloux, Manager DRU Department, and Mr. Roumens
S.G.A.D.
B.P. 20
F - 13267 MARSEILLE Cedex 2
Mr. Ch. Richaud
73
-------
DRAFT
P.L.M.
Pack
S - 20110 MALMO Sweden
Mr. B. Hansen, Vice President, General Manager Technical Activities
Ministere de 1'Environnement et du Cadre de Vie
D.P.P.N. - S.P.D.S.
14, bid du General Leclerc
F - 92521 NEUILLY sur Seine Cedex
Mr. B. Pommel and Mr. P. Godin
Agence Financiere de Bassin "Seine-Normandie"
10-12 rue du Capitaine-MSnard
F - 75732 PARIS Cedex 15
Mr. J. Bazin, Inspecteur Ge'ne'ral
Commission of the European Communities
Environment and Consumer Protection Service
Rue de la Loi, 200
B - 1049 BRUSSELS
Mr. L. Klein, Head of the Waste Management Division and Mrs. L. Pavan
Department of the Environment
2 Marsham St.
LONDON SW1P 3EB England
Mr. J.F.A. Thomas and Mr. Porteous
Water Research Center
Elder Stevenage
HERTFORDSHIRE SGI 1TH England
Dr. R. D. Davis and Dr. E. Cocker
Wanlip Composting Plant
Fillingate
Wanlip
LEICESTER England
Mr. Hughes, Plant Manager
The National Swedish Environment Protection Board
Technical Department
Pack
S - 17120 SOLNA Sweden
Mr. 0. von Heidenstam, Deputy Head of Municipal Division
74
-------
DRAFl
Republique et Canton de Geneve
Ddparteraent des travaux publics
Service Assainissement et contrble des pollutions
Rue D. Dufour, 5
CH - 1205 GENEVE
Mrf P. Spoerli, Head of the service and Mr. Kroepfli
Biologische ABF allverwertungsgesellschaft MBH Co,
(BAV)
Berliner Strasse 22
D-6369 SCHOENECK 1
Mr. Nemetz, and Mr. S. Schmidt
Representative in U.S.A.:
Josef Meyer
80 Thayer Road
Manhatten, L.I.
New York 11230
75
-------
DRAFT.
APPENDIX B
SUMMARY OF A COMPOSTING STUDY CONDUCTED
ON THE TRIGA SYSTEM
76
-------
DRAFT
APPENDIX B
SUMMARY OF A COMPOSTING STUDY CONDUCTED
ON THE TRIGA SYSTEM
RESEARCH ON THE INFLUENCE OF THE
CHARACTERISTICS OF THE SLUDGE
In 1975, Triga conducted a study, with the financial support of the
water agency "Seine Normandie", on the evaluation of the combined compost-
ing of MSW and sludge (18).
Four types of raw sludge were tested:
• Tests No. 1 and 2: sludge from the town of Montargis floc-
culated with lime and FeCl3 and dewatered by vacuum filtration.
Water content: 75 percent;
• Test No. 3: sludge from the town of Chateauroux flocculated
with a cationic polyelectrolyte "Fleurgey FC 250" and dewatered
by centrifugation. Water content: 72 percent;
• Test No. 4: sludge from the town of Montargis taken from the
primary and secondary settling tanks. Water content: 95 percent;
• Test No. 5: sludge from the town of Reims flocculated with
lime and Fed, and dewatered by pressure filter. Water content:
62 percent.
Raw sludge was preferred to digested sludge because its composting
ability is better according to the fertilizer value shown in Table B-l.
TABLE B-l. N, P, K ANALYSIS OF SLUDGES AS A PERCENT
OF THE DRY MATTER WEIGHT
N P2°5 K2° Organic Matter
Raw sludge
Digested sludge
3.5 to 4.5
2 to 2.5
2 to 3
1 to 2
0.5 to 1
0.2 to 0.5
60 to 80
40 to 65
77
-------
DRAFI
The procedure for these tests was as follows:
• the iron was removed from the MSW before the latter was
ground,
• sludge was then added to the MSW in order to get a mixture
with a 50 percent water content.
Table B-2 gives the composition of the different mixtures. Table B-3
gives an analysis of the MSW and the sludges used for the tests.
The mixture was then fed into the tower called "Triga Hygienisator".
During the tests, the following parameters were controlled:
• temperature,
• moisture,
• air flow rate,
• 02 and C02 concentration of the off-gases.
Mixing of the sludge and the MSW—The mixing of the sludge and the MSW
is directly linked with the water content of the sludge. There was no prob-
lem for Tests 1 to A. There were some difficulties in Test No. 5. The
sludge makes small flakes (1 to 3 cm) which do not mix very well with the
MSW. To ensure good mixing, the sludge and the MSW were passed 3 times
through a screw mixer (6 m long).
Within-vessel composting—The purpose of within-vessel composting is to
reach a temperature of 70 C as quickly as possible. This temperature is
reached after 4 days for the MSW alone. For the mixture (sludge and MSW) the
time depends on the composition of the mixture and the type of sludge.
Tests No. 1 and 2: digestion was carried out without difficulties in
2 days.
Test No. 3: the mixture stayed 10 days in the tower, and the tempera-
ture did not rise above 55°C. The high concentration of heavy metals such
as lead, boron and chromium could be responsible for the inhibition of ths
development of the microorganisms.
Test No. 4: the water content of the mixture was too high, and the
temperature rose too slowly.
Test No. 5: the mixture was not homogeneous and the transfer of the
sludge water to the MSW was poor. To adjust the moisture content of the
mixture to 50 percent a large amount of sludge was necessary. Thirty-six
percent of the dry matter came from the sludge. The result was a mixture
with a high density and therefore the forced aeration was difficult.
Curing—At the exit of the tower the mixture was screened to a size of
25 mm. The curing period was 3 months for mixture No. 1 and 4 months for
the others. During the first month, the mixtures were turned frequently and
water was added to keep the water content at a level of 45-50 percent.
78
-------
TABLE B-2. COMPOSITION OF THE MIXTURES
VO
Test no
1
2
3
4
5
Municipal Solid Wastes (MSW)
Weight tonnes
Water content %
Sludge
Weight tonnes
Water content %
35
35
25
75
61
33
35
75
21,5
36
17,4
72
63,4
39
(16 m3)
95
21,6
40
18,3
62
Mixture
Water content %
Sludge/MSW ratio %
(dry basis)
52
21
48
16
49,8
27
50
2
49,1
36
-------
TABLE B-3. CHARACTERISTICS OF THE MSW AND SLUDGES (Analysis: C.D.L.P. Melun)
oo
o
pH
C/N ratio
Water content %
Chemical analysis
(dry basis-% by weight)
Organic matter %
Carbon %
Nitrogen %
P-,CV %
2 5
K^O %
2
CaO %
Municipal Sludge
Solid tests
wastes 1 & 2
5.9 12.4
31.9 11.2
38 75
64.5 38.6
30.2 22.7
0.9 2
0.4
0.2
2.9 25.5
Sludge
test 3
6.8
15.3
72
63.8
38.4
2.5
3
0.17
5.4
Sludge
test 4
5.85
10.4
95.5
57.2
36.6
3.5
5.8
9.7
Sludge
test 5
14
12.3
61.5
12.6
1
1.3
0.09
33.7
-------
DRAFI
Figures B-l to B-4 give the evolution of the main parameters (temperature,
water content, organic matter, C/N ratio) vs. the time.
Conclusions of the study—Two conditions must be fulfilled to have good
aerobic digestion; the water content of the mixture must be kept at a level
of 50-55 percent, and the contribution of the dry matter of the sludge to the
total dry matter of the mixture should be less than 25 percent.
Sludge with a water content under 70 percent is difficult to mix with
the ground MSW.
A high concentration of heavy metals in the sludge could inhibit the
development of the microorganisms.
After 4 months of curing, the water content, C/N ratio, organic matter
content and pH are more or less the same for the 5 mixtures. Their values
are independent of the type of sludge, and the C/N ratio of 15 is such that
the humus can be applied to the soil without problem (Table B-4).
Sludge flocculated with polymeric organic chemicals is better than
sludge flocculated with ferric chloride and lime.
81
-------
DRAFT
T°C
\
30 60 90
Figure B-l. Temperature evolution.
120 Days
Testl
Test 2
Test 3
Test 4
Test 5
60 90 120 Days
Figure B-2. Water content.
82
-------
DRAFT.
O.M. as % of the
dry matter
30
30 60 90 120 Days
Figure B-3. Organic matter evolution.
Testl
Test 2
Test3
Test t.
Test 5
C/N
35
30
25
20
15
30
SO
90
120 Days
Figure B-4. C/N ratio evolution.
83
-------
TABLE B-4. CHARACTERISTICS OF THE MIXTURE (Analysis: C.D.L.P. Melun)
oo
Test
pH
C/N ratio
Hater content %
Chemical analysis
(dry basis-% by weight)
Organic Matter %
Carbon %
Nitrogen %
P2°5
CaO %
Before curing
123
6.8 7.8 6.6
28.3 28.1 25.3
45 43.7 40.5
47.7 47 40.5
23.1 23 24.8
0.8 0.8 1
0.9
0.3
8.9
4
5.7
31.5
54.2
56.2
28.7
0.9
0.8
0.1
3.7
5
7.9
27
47
34
22
0.8
1.1
0.3
4.3
After curing (4 months)
1 2
7.9 7.9
15.4 15.9
35.7 32
34.4 35
14.6 14.3
0.9 0.9
1.1
0.4
11.2
3
B
15
39.5
32.2
14.6
1
4
7.9
16.9
40
38.2
16.9
1
0.6
0.3
4.4
5
7.5
16
44
30.3
16.5
1
0.7
0.3
9
-------
DRAFT.
APPENDIX C
THE SEWAGE TREATMENT PLANT COMPONENTS
OPERATIONAL DATA
85
-------
DRAFT
APPENDIX C
THE SEWAGE TREATMENT PLANT COMPONENTS
OPERATIONAL DATA
The sewage treatment plant in Hochheim am Main comprises the following
components (see Figure C-l):
• roofed screening plant
• grit channel
• Venturi tube flow meter
• storm water tank
preliminary clarification tank
(volume: about 500 nH)
activated sludge tank (volume:
about 1000 m-*; with fine bubble
aeration
secondary sedimentation tank
(volume: about 3200 m3; over-
flow to the receiving water
course in the center)
sludge thickener (volume:
417 m3)
These three components form
one unit in a circular tank.
The secondary sedimentation
tank is in the middle, the
preliminary clarification
and the activated sludge
tank are arranged around it.
Analytical data from the laboratory diary-:
• Volume of sewage (mean value); about 5000 m /d
• Five days biochemical oxygen demand:
influent: 130-200 mg/S,
effluent: 13-18 mg/X,
• Settleable solids:
influent (preliminary clarification; after 2 hr) : 0.2-1.7 mg/SL
effluent (secondary sedimentation; after 2 hr): 0 mg/£
• pH value: 6.6 - 7.6
• Transparency (secondary sedimentation tank): 50-70 cm .
86
-------
DRAFI
Priaary
Clarification
v I
Secondary
Sedimentation
Ou all
MAIN RIVER
Figure C-l. Hochheim am Main, West Germany wastewater
treatment plant loyout.
87
-------
DRAFI
APPENDIX D
ANALYTICAL METHODS USED IN THE EVALUATION OF
THE BAV PLANT IN HOCHHEIM, GERMANY
88
-------
DRAFI
APPENDIX D
ANALYTICAL METHODS USED IN THE EVALUATION OF
THE BAV PLANT IN HOCHHEIM, GERMANY
SAMPLE COLLECTION AND LOCATION
Bioreactor feedstock and final product samples were collected simul-
taneously during the two-hour filling and emptying period. The feedstock
sample was collected at the point of entry, at the top of the reactor, while
the bioreactor product was collected off of the product discharge conveyor
belt. During the two-hour filling and emptying period, an aliquot of
material was collected at 30-minute intervals. These five aliquots were
composited into one sample, then thoroughly mixed, and from this composite
approximately one liter of material was reserved for the following labora-
tory analyses:
Determination of the Loss in Drying at 75°C
The compost was weighed in large beakers and dried in the drying chamber
at 75°C until it reached a constant weight.
Homogenization of the Compost
The dried samples (75°C) were broken up and homogenized in a laboratory-
sized hammermill.
Determination of the Loss in Drying at 105°C
The compost which had been dried at 75°C and homogenized was dried at
105°C.
Determination of Ash Content at 600aC
The compost sample which had been homogenized and predried at 75°C was
weighed into a porcelain crucible and reduced to ashes by heating in a
muffle furnace at 600°C until a constant weight was achieved.
Determination of Ash Content at 900°C
The same ash which was determined at 600°C was further heated in a
muffle furnace at 900°C until a constant weight was achieved.
89
-------
DRAFT.
Determination of C and H Content
The compost sample which had been dried at 105°C was burned by means of
semimicro-elementary analysis in a Heraeus combustion furnace and the H?0 or
C0_ resulting from combustion was gravimetrically determined.
Determination of N Content
According to Dumas
The sample dried at 105°C was burned in a Heraeus combustion furnace
using COo as a carrier gas and the resulting nitrogen was determined using
gas volumetric methods.
Determination of 0 Content
According to Unterzaucher
The sample, dried at 105°C, was decomposed in a Heraeous combustion furnace
using N2 as a carrier gas and the gases resulting from decomposition were
passed over coal heated at 1120°C. The resulting carbon monoxide was
idometrically determined following its reaction with iodine pentoxide.
Determination of S Content
The sulfur content was determined by burning the sample dried at 105°C
in an oxygen current, whereby the resulting sulfur dioxide was oxidized in
an absorption vessel containing HjQ? to form sulfuric acid which was then
conductimetrically analyzed.
Determination of the Calorific Value
The caloric value was determined using the sample dried at 105°C in a
bomb calorimeter. The water resulting from combustion was taken into
account in the calculation.
Analytical data are reported in Table D-l.
90
-------
TABLE D-l. CHEMICAL AND PHYSICAL DATA OBTAINED AT THE HOCHHEIM AM MAIN,
WEST GERMANY BIOREACTOR, APRIL 12 to JUNE 2, 1978
Dnte
04/12/78
04/12/78
04/13/78
04/13/78
O't/14/78
04/17/78
04/17/78
04/:8/73
05/29/78
05/30/78
05/30/78
05/31/7B
05/31/78
06/01/78
06/01/78
06/02/78
06/02/78
relntive
Average
S amp 1 c
entry-
exit
entry
exit
exit
entry
exit
exit
exx t
entry
exit
entry-
exit
entry-
exit
entry •
exit
error
entry (7)
exit (10)
J4 Weight Loss
75 °C
67.3
fa'i.l
65.9
66.2
•58.9
64.3
bl.9
57.3
50.7
64.8
58.0
65.2
54.3
66.4
56.3
64.5
51.5
+ Itf
65.0
(1.1)
57.9
(5.8)
105 °C
68.7
65.4
67.2
67.4
65.3
66.0
63.6
63.0
52.8
66.7
59.5
67.0
56.1
6b.4
58.0
66.1
52.9
+ 1*
66.8
(0.9)
60.4
(5.3)
9» Ashes
600 °C
8.37
9.27
5-98
7-88
8.52
6.'»3
9.79
8.26
7.06
10.51
9.«3
8.05
9.68
10.31
11.09
7.65
12.44
+ 15S
8.97
(2.0)
9.46
(1.5)
n
900 °c
8.25
9.12
5.93
7.76
8.46
6.39
9.68
8.18
7.81
10.27
9.73
7.87
9.57
10.26
10.75
7-31
11.83
*1*
8.04
(1.7)
9.29
(1.3)
*c'>
45.8
44.8
46.7
45.8
44. b
46.5
44.3
44.3
44.7
45.8
44.7
45-1
45.8
45.5
42.6
47.0
44. 't
+ 0,554
46.1
(0.7)
44.6
(0.9)
54 H *J
5.65
5.60
5.73
5.64
5-52
5.73
5.40
5.35
5.48
5.59
5.55
5.66
5.51
5.62
5.06
5.74
5.44
+ 1/4
5.67
(0.06)
5.46
(0.16)
% N *J
1.88
1.48
1.26
1.36
1.41
1.65
1.45
1.62
1.54
1.45
1.53
1.54
1.58
1.19
1.66
0.86
1.55
+ 554
1.4
(0.33)
1.5
(0.09)
XO'>
35.9
34.9
38.0
36.8
37.5
34.8
36.1
36.2
37.3
3.6.6
37.5
36.2
36.2
35.8
34.9
38.O
3b.o
+ 154
36.5
(1.18)
36.3
(0.95)
*s'>
0.31
0 . 4 1
0.23
0.29
0.27
0.20
0.30
0.27
0.27
0.21
0.24
O.20
0.24
O.22
0.23
O.l6
O.25
* lox
0.22
(.05)
0.28
(.05)
Hcnt
Value
1722'
1639<
l6'i7:
1729<
1658'
1743C
1653:
l6bll
1699C
1650'.
1637L
16977
Ib'i8:
l66b:
16636
17472
16806
* 2'i
16946
16671
*) Average value from double determination
-------
DRAFT.
APPENDIX E
ORGANOLEPTIC ODOR EVALUATION
92
-------
DRAFI
APPENDIX E
ORGANOLEPTIC ODOR EVALUATION
The composting plant comprises the following characteristic odor
sources:
• activated sludge tank
• bioreactor
• windrows (secondary fermentation) .
Organoleptic studies use the human nose as detector and analyzer and
sensory perception is the criterion for evaluation.
KIEL TO-4 OLFACTOMETER
In the present study the odor qualities were described and the thresholds
of typical odor profiles determined olfactometrically, using dilution methods.
In addition to the known scentometer 1-3 (Barnebey Cheney, Columbus, Ohio),
the Kiel Olfactometer TO-4 was used for this. The latter operates on pure
air or oxygen from commercial steel cylinders, and is used for mixing a con-
stant synthetic air stream with a controllable stream of ambient air (cf.
block diagram, Figure E-l) .
The pure air from the cylinder is passed through a pressure reducing
valve in an absolutely odor free tube and is used for operating a gas jet
pump. Via an adjustable throttle valve and flow meter this gas jet pump
draws in odorous ambient air and mixes it intensively with the odorless
synthetic air. The mixture flows through a tube to the breathing mask. The
mixing ratio of synthetic air or oxygen to ambient air at the odor threshold
is used as measure of odor intensity.
Care was taken that the olfactory cells could recover between measure-
ments .
The scentometer, Model 1-3, operates on the same principle as the Kiel
olfactometer, Model TO-4, except that the dilution air used is ambient air
which has been purified by passing the ambient air through a bed of acti-
vated charcoal. The activated charcoal bed is an integral part, and is
located inside of the scentometer.
93
-------
DRAFI
pesaure
reducing
valve
0 cylinder
expansion
bag
L
fine
adjustment
valve for
0_ volume
gas jet
pump
breathing
mask
Oxygen
Y///////////A Ambient air
Mixture
Principle: An adjustable stream of
ambient air is admitted to
a constant oxygen stream
pressure
gauge
adjustment
valve for
ambient air
volume
I
flow meter
ambient aii
I
dust
filter
Figure E-l. Block diagram of the portable Kiel olfactometer TO-4.
94
-------
DRAFT
ACTIVATED SLUDGE TANK
Characterization of the Odor Profile
Sensation: unpleasant
Intensity or order
Odor characterization of perception
• brackish-sweetish -H-+
• fecal ++
a rotten +
e sewers
a cabbage
• rakings
• suds
Odor Intensity (Olfactometric
Evaluation of Odor Emission)
(a) 1-3 (DT = dilutions to threshold): 1:350
(b) TO-4 (volumetric ratio of odorous to pure air): 1:33
BIOREACTOR (EMPTYING)
Characterization of the Odor Profile
Sensation: unpleasant
Intensity of order
Odor characterization of perception
• liquid manure, sweetish-sour +++
• ammonia ++
• peaty +
• earthy
• fermentation (silage)
Odor Intensity (Olfactometric
Evaluation of Odor Emission)
(a) 1-3 (DT = dilutions to threshold): 350
(b) TO-4 (volume ratio of odorous to pure air): 1:200
95
-------
DRAFT
WINDROWS
Characterization of the Odor Profile
Sensation: unpleasant
Intensity of odor
Odor characterization of perception
• ammonia, sourish +++
• fermentation, dung ++
• slightly earthy +
• henhouse +
• spoiled (degraded) potato
Odor Intensity (Olfactometric
Evaluation of Odor Emission
(a) 1-3 (DT = dilution to threshold): 350
(b) TO-4 (volumetric ratio of odorous to pure air): 1:50
Whereas the scentometer did not permit any differentiation between the
three odor sources to be made, marked differences in the emission from the
three sources were identified with the TO-4 olfactometer.
SURROUNDING NEIGHBORHOOD AREA
Characterization of the Odor Profile
Odor concentration in the vicinity of the Hochheim plant depends on
topographic and weather conditions, especially on wind direction and speed
and on turbulence. If we consider the three odor sources or odor profiles,
it is usually the odor from the bioreactor or a mixture from bioreactor and
windrow odor which predominates, whereas the smell from the activated sludge
tank is practically not perceived outside the plant area. As a result of
topographical and orographical factors, odor concentration zones or islets
may form whose characteristic odor profiles may be temporarily perceived in
an area of several hundred meters.
Odor Intensity (Olfactometric
Evaluation of Odor Concentration
In the immediate vicinity of the plant area the scentometer sometimes,
i.e., in the event of single gusts, recorded especially the odor from the
bioreactor at DT quotients between 350 and 31.
On the hillsides to the North odor concentration zones formed from time
to time between the buildings, depending on the prevailing air currents.
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DRAFT
Except in the event of inversion conditions, however, the odor was generally
carried off by relatively vertical currents of air.
Because of the specific, highly variable local conditions it is
impossible to record the different odor intensities in a general and
reproducible planimetric form and represent them cartographically.
To be able to make generally valid statements about odor concentration
in the vicinity of sewage treatment plants, the distribution of the odorous
substances involved must be calculated. Depending on the quality and quan-
tity of data available, this can be done with the aid of a conventional
Gaussian distribution model or, using a more sophisticated and more universal
numerical diffusion model.
The relatively simple Gaussian model uses the following equation for
computing the concentration of odorous substances:
y2 .,2
exP - TTTT^T exP 7TT77T
' 2nuoy(s)az(x)
where
C concentration of odorous substance [mg/m^]
x,y,z coordinates between odor source and recording point
Q . strength of odor source mg/a
U mean wind velocity
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DRAFT.
of the bioreactor be representative of the odor intensity
within the entire bioreactor (homogeneous distribution).
o
2. Let the air flow be constant at 600 m /hr.
Based on these two assumptions the odor concentration in the main
direction of distribution (i.e., as a function of the distance from the odor
source) was calculated for two different meteorological situations.
The results of these calculations are shown in Figure E-2. Odor concen-
tration is plotted as multiples of the odor threshold in this diagram. It
is noted that even under the most unfavorable distribution conditions (Case I)
the maximum value of odor concentration is as low as one-fifteenth of the
threshold value. At higher wind speeds and atmospheric layers of low stability
the maximum decreases in absolute terms and is located closer to the odor
source (Case II). These calculations do not consider the influence of local
topographical and orographical factors so that the experimentally determined
odor concentrations zones or islets cannot be identified with the simulation
model.
If the first of the two assumptions made is incorrect, detailed measure-
ments are required in order to determine the source strength per unit time.
Therefore, it is suggested to determine the emission strength of
individual key substances over an extended period of time (several days) by
measuring the gradient of the threshold value and correlate the throughput
of the bioreactor with the volume of odorous substance released. After
having thus determined the source strength by measuring the flow rate of
various odorous components, the distribution of the substance can be calcu-
lated with the above equation or, if detailed meteorological data are avail-
able, with a three-dimensional turbulent diffusion model.
A three-dimensional model of this kind (TRANSLOC) has been developed at
Battelle-Institut e.V., Frankfurt am Main. This model features the special
advantage that it can be used in the case of transient flow processes and
under weak-wind and inversion conditions.
98
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DRAFT
0.09
0.08
0.0?
'concentration
(multiple of the
odor threshold)
Case I: mean wind velocity
u = 1 m/s
stable temperature layers
( Klug category I )
Casell: mean wind velocity
u = 4.5 m/s
neutral temperature layers
( Klug category 111 )
Odor intensity at the source:
1 : 200
Air flow rate: 600 m /a
0.06
0.05
O.O3 -
0.02
0.01
100
500
10OO
distance from the source
Figure E-2. Concentration of odorous substance in
the main direction of distribution.
99
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DRAFT,
APPENDIX F
INFORMATION FOR COST EVALUATION SUPPLIED
BY HOCHHEIM PLANT
100
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
DRAPE
1. REPORT NO.
2.
3. RECIPIENT'S ACCESSION NO
4. TITLE AND SUBTITLE
EVALUATION OF "WITHIN VESSEL" SEWAGE
SLUDGE COMPOSTING SYSTEMS IN EUROPE
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
S. T. DiNovo, W. C. Baytos, L. M. Curran,
H. Hartmann. and J. Partoy
8. PERFORMING ORGANIZATION REPORT NO
G-7016-0001
9. PERFORMING ORGANIZATION NAME AND ADDRESS
BATTELLE'S COLUMBUS LABORATORIES
505 King Avenue
Columbus, Ohio 43201
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-03-2662
12. SPONSORING AGENCY NAME AND ADDRESS
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final Report
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This study was conducted as a cooperative effort by Battelle Laboratories
in Frankfurt, Germany; Geneva, Switzerland; and Columbus, Ohio. The objectives
were: (1) to update a review of the state of the art of sewage sludge com-
posting in Europe; (2) to evaluate a European-designed, continuous thermophilic,
mechanical, aerobic, composting system in Germany; and (3) to compare its costs
to that of the U.S. Department of Agriculture's ARS, Beltsville, static-pile,
aerated composting system. This report addresses the general characteristics
of the European composting systems and a bioreactor in Hochheim am Main, West
Germany.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Held/Group
Sewage sludge treatment & disposal
Composting
European composting methods
Sludge treatment &
disposal
Composting
ISTRIBUTION STATEMCNT
RELEASE TO PUBLIC
19. SECURITY CLASS (Tins Report!
UNCLASSIFIED
21. NO. OF PAGES
20 SECURITY CLASS (This page I
UNCLASSIFIED
22. PRICE
EPA Fofm 2220-1 (Re». 4-77) PREVIOUS EDITION is OBSOLETE
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DRAFT
APPENDIX F
INFORMATION FOR COST EVALUATION SUPPLIED
BY HOCHHEIM PLANT
The investment expenditures indicated below were taken from those bids
received by the Hochheim town administration in response to bid invitations
that were finally accepted.
The amounts have in part been estimated as the share of the composting
plant in the price quote for the entire plant (including the sewage water
treatment plant).
CAPITAL INVESTMENT ITEMS
Sludge Treatment and Composting Equipment
Price Total
per unit cost
No. (DM) (DM)
1. Pumps for conveying sludge to sludge
thickener 3 9,100 27,300
2. Sludge thickener (only cost of converting
an existing digestion chamber) 1 35,500 35,500
3. a) Pump for feeding sludge to centrifuges 1 6,600 6,600
b) Pipeline from sludge thickener to
centrifuges - ~ 24,900
4. a) Coagulant container (see Other
Installed Costs) 2
b) Stirring devices 2 4,500 9,000
c) Proportioning pumps 2 5,550 11,100
d) Pipeline to centrifuges - — 10,800
5. Decanter centrifuges 2 88,350 176,700
6. Drag conveyor 1 53,500 53,500
7. Sawdust bunker (see Other Installed Costs) 1
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DRAFI
Price Total
per unit cost
No. (DM) (DM)
8. Mill chain, delivered instead of the
planned belt conveyor ordered at the
same cost 1 9,600 9,600
9. Thick-sludge bunker (see Other
Installed Costs) 1
10. Screw conveyor 1 21,800 21,800
11. Return bunker (see Other Installed Costs) 1
12. Screw conveyor 1 21,800 21.800
13. Rotary mixer 1 29,700 29,700
14. Drag conveyor 1 42,000 42,000
15. a) Rotary piston blowers 2 25,400 50,800
b) Ventilation pipes - — 11,900
16. a) Bioreactor 1 120,000 120,000
b) Temperature measurement system 1 7,800 7,800
c) Level indicator 1 6,900 6,900
17. Mill chain 1 67,300 67,300
18. Windrows (see Other Installed Costs)
Total 745,000
Planned but not installed: gas measurement system (16 d) (13,700)
Other Installed Costs
Building for decanter centrifuges, including coagulant
container and foundations, and thick-sludge bunker
and return bunker 319,500
Foundations for bioreactor 22,000
Attendant cabin 20,500
Sawdust bunker 26,000
Excavation work 62,000
Electrical switchboard plant 33,500
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DRAFT
Other electrical installations (about 25% of the electrical
installation costs of the entire plant, including
sewage water 45,000
f\
Stone paving especially for windrows, 350 nr (DM 81,000 per
m2 including substructure) 28,350
Bituminous surfacing 18,000
Ancillary services (transport insurance for materials,
lodging for the workers during construction, training of
the operating personnel, initial operating materials,
start-up of the composting plant, warranty services for
the one-year perio'd, planning and contractor's fee) • 45,000
Total 619,850
There were additional costs which are not generally incurred for other
composting plants, especially for pulling down the existing sludge drying
equipment and the non-usable conveyor apparatus, and for special excavation
work which, however, was mainly for the sewage treatment plant.
Land Development Required
• Electric power supply about 80 kW
• Water supply
• Canal (if the plant is not located on the same plot of land as
the wastewater treatment plant)
• Telephone line installation
• Road construction
2
• Technique equipment 250 m
2
• Windrows (height of stored material: 1,5 m) 300 m
2
• Sawdust bunker, area for transportation, etc. 400 m
950 m2
Licensing Fee
The licensing fee, which is paid when the plant comes into operation,
is calculated as follows:
DM 20 per 1 kg solids content of the digested sludge per day .
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DRAFT
As its present throughput (about 50 percent of the planned throughput),
this would mean for the composting plant at Hochheim:
3
Volume of digested sludge: 125 m day
Specific weight: about 1,000 kg/m3
Solids content: 0.8 percent by weight .
Licensing fees:
125 (m3/d) x 1,000 (kg/m3) x x 20 (DM/kg/d) = DM 20.000 .
At full capacity, the licensing fees of the plant thus would amount to
DM 40,000.
OPERATING COST ITEMS
Labor Requirements (Excluding
Maintenance Staff)
One foreman (locksmith), full-time, with experience in wastewater and
sludge treatment (40 hours per week), and one assistant worker, half-time
(20 hours per week) are required.
The tasks of these persons include some repairs, lubrication, changing
of oil, cleaning of the rotary mixer, etc.
Materials Required
Expensive spare parts are not included. The main materials required
are:
• Sawdust: 6.25 m /d, 230-250 days per year; that is about
1,440-1,650 m3 per year
• Coagulant: 50 kg/d, 230-250 days per year; that is about
11,500-12,500 kg per year (in Germany the price
is about DM 2.80-3.40 per kg)
• Oil, grease: about DM 500 per year
• Not specially mentioned spare parts: about DM 500 per year .
Utility Requirements
• Electricity:
• engines without aeration: about 50 kW, 4 hours per day,
230-250 days per year, that is 46,000-50,000 kWh per year
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DRAFI
• aeration engines: one of the two engines (each 15 kW)
runs for 22 hours on 5 days a week, and 24 hours on the
other two days; that means about 123,500 kWh per year
2
• Water: good quality, to dilute coagulant: 12 m /d,
230-250 days per year, that is 2,760-3,000 m3'per year .
Waste Disposal Requirements
Wastewater from
• sludge thickener 85.0 m /d
3
• decanter centrifuge 45.8 m /d
Total 130.8 m3/d
3
230-250 days per year: 30,084-32,700 m per year .
MAINTENANCE COST ITEMS
Maintenance Requirements
The most expensive work, which can not be done by the workers of the
plant, includes the following:
1. Discharge mill chain of bioreactor (No. 1 in Figure F-l);
exchange of chain: once a year.
2. Drag-chain conveyor for the mixed input material of the
bioreactor (No. 14 in Figure F-l); exchange of chain:
every 3 years.
3. Additional different maintenance work at the electric
equipment, several times a year at irregular intervals.
Labor Requirements
1. Discharge mill chain (No. 17 in Figure F-l); 2 workers
with special experience are required for 3 days, i.e.,
6 man-days per year.
2. Drag-chain conveyor (No. 14 in Figure F-l); 4 workers
with special experience are required for 3 days, i.e.,
12 man-days for one exchange, or 4 man-days per year.
3. Electric equipment: 5 man-days per year of electrical
work are required.
Materials Requirements
1. Discharge mill chain
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DRAFT,
7. Sawdust
8. Hill chain / drag;
conveyor
1. Puirps for raw
sludge
Z. Sludge thickcrer
3. Purp for si Mice
5. Decanter centrifuge
6. Drag conveyor
9. Ihicl'-sludge bunker
iO. Discharge screw
conveyor
13. Rotary niter
4. Drag conveyor
16. Biorcactor
17. Discharge rill chain
16. V.indrows
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DRAFI
Materials Requirements
1. Discharge mill chain (No. 17 in Figure F-l)
2. Drag-chain conveyor (No. 14 in Figure F-l); ):
The price of one chain is about DM 10,000, that is
3. Different materials (work to be done by the staff
of the plant):
• Hydraulic system
- hoses: service life 2 years; 5 hoses per
year, price of one hose: DM 128, that is
- solenoid valves: about
Total
4. Parts for high intensity mixer (No. 13 in
in Figure F-l) (repaired very often):
5. Other spare parts: about
1,000 DM/year
3,333 DM/year
(640 DM/year)
(360 DM/year)
1,000 DM/year
4,000 DM/year
3,000-5,000 DM/year
107
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