Environmental Protection Technology Series
COMPLETE DISPOSAL-RECYCLE SCHEME
FOR AGRICULTURAL SOLID WASTES
Robert S. Kerr Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Ada, Oklahoma 74820
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-77-089
May 1977
A COMPLETE DISPOSAL-RECYCLE SCHEME
FOR AGRICULTURAL SOLID WASTES
by
Michael R. Busby
Greg Tragitt
Roland Norman
Kenneth Hillsman
Tennessee State University
Nashville, Tennessee 37203
Grant No. R802739
Project Officer
S. C. Yin
Source Mana'gement Branch
Robert S. Kerr Environmental Research Laboratory
Ada, Oklahoma 74820
ROBERT S. KERR ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
ADA, OKLAHOMA 74820
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DISCLAIMER
This report has been reviewed by the Robert S. Kerr Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publication.
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.
11
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ABSTRACT
With the advent of the 70's, there has been an increasing national concern
for the growing energy shortage as well as the problem of organic waste
disposal. These two problems, while at first glance appear unrelated, are
dealt with simultaneously by an anaerobic digestion process. Such a process
produces not only a useful fuel, methane, but also is a potential source of
a stabilized fertilizer and a nutritive supplement to animal diets. This
biological process has been used for decades, but the economic feasibility
of incorporating such a process on a typical small farm has not been clearly
established.
This investigation applied the anaerobic process to the production of
methane gas and a stabilized sludge from cow manure and farm clippings in
laboratory pilot plants as well as a full-scale (2,000 gal.) digester
system. The quantity and quality of gas produced, the biochemical and
chemical oxygen demands, and the nutritional value of the digested sludge for
both the laboratory and full-scale plants were evaluated.
111
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CONTENTS
Abstract iii
Figures vi
Tables viii
1. Conclusions 1
2. Recommendations 2
3. Introduction 3
Agricultural Waste Disposal 3
Energy Shortage 4
Purpose of the Study 4
4. Theoretical Considerations 5
5, Experimental Procedure 11
Laboratory Pilot Digester Reactors 11
Full-Scale Digester Plant 11
Analytical Procedures 24
6. Results 26
Pilot Plants 26
Full-Scale Plant 39
Operational Difficulties 39
Nutritive Value of the Anaerobically Digested Sludge . . 42
References 50
v
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FIGURES
Number
Page
1 Anaerobic stabilization of complex organics 5
2 Schematic of pilot plant digester 12
3 Pilot plant gasometer 13
4a EPA-CSRS-TSU anaerobic digester plant 15
4b EPA-CSRS-TSU anaerobic digester plant 16
4c EPA-CSRS-TSU anaerobic digester plant 17
5 Schematic of full-scale digester plant. 18
6 Schematic of digester tanks 19
7 Schematic of internal tank circulation system 20
8 Schematic of influent pumping arrangement 21
9 Digester tank heat exchanger system. 22
10 Schematic of digester monitoring equipment arrangement. . . 23
11 Laboratory pilot plant gas production 27
12 Biochemical oxygen demand for Unit I. 28
13 Biochemical oxygen demand for Unit II 29
14 Biochemical oxygen demand for Unit III 30
15 Chemical oxygen demand for Unit 1 31
16 Chemical oxygen demand for Unit II 32
17 Chemical oxygen demand for Unit III 33
18 Volatile solids for Unit I 34
VI
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Number Page
19 Volatile solids for Unit II 35
20 Volatile solids for Unit III 36
21 Pull-scale plant pH, temperature, and gas volume generation
rate 40
22 BOD and COD for the full-scale plant 41
23 Output gas handling arrangement. 43
Vll
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TABLES
Number
1 Growth Constant and Endogenous Respiration Rates 7
2 Composition of Dried Sludge and Mixed Liquor 37
3 Analysis of Heavy Metals (mg/kg dry weight) 38
4 Composition of Sludge Percent 44
5 Composition of Diets Percent 45
6 Summary of Growth and Feed Data 47
7 Summary of Dry Matter and Protein Digestibility Data ... 48
Vlll
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SECTION 1
CONCLUSIONS
An anaerobic waste treatment process was successfully operated in three
laboratory scale plants. A full-scale (two 2,000 gal. digester units) bio-gas
plant was designed and constructed to treat the agricultural wastes typical of
a small farm. Utilizing the experience gained in the laboratory, the full-scale
plant was operated over a six-week period.
Both the full-scale and laboratory systems functioned well, producing
methane and a stabilized sludge from feedlot cow manure by biological
degradation. The methane content of the dry gas produced was typically 62
percent and the full-scale plant gas volume generation rate varied from 3.5
to 5 ft. 3/hr. Csfc) after a fourteen-day retention time. In all samples, the
COD and BOD were reduced in the plant effluent as compared to the influent.
Both the pilot and full-scale plants were fed on a daily basis by wasting
digested material and adding an equal volume of fresh mixture. In the full-
scale plant the pH was controlled by the addition of lime, and mixture
temperature (104-112°F) was maintained by an internal cooper coil heat exchanger.
A nutritive study of the digested sludge was completed utilizing weanling
rats. It was found that feed conversion and digestibility of diets decreased
as the level of sludge increased. However, the experiment revealed that
anaerobically processed organic wastes are consumed readily and when incorpo-
rated into a balanced diet will support animal growth.
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SECTION 2
RECOMMENDATIONS
A full-scale bio-gas plant has been operated; however, several operational
difficulties were encountered. Specifically, mixing and pumping of the feeding
mixture and foaming of the supernatant in the reactor caused the gas outlets to
become clogged, presenting obstacles to plant operation. Only a small sample
of data has been taken from the large scale system. It became apparent that
environmental changes significantly affect the plant outputs. Therefore, before
any realistic evaluation of the economic feasibility of small farm operation
can be made, data must be collected over a long time period. This period should
include seasonal changes as well as day to day fluctuations in weather. The
Cooperative States Research Service (GSRS) has funded such an investigation for
a two-year period beginning in June, 1976. Data collected from this study
should establish a comprehensive basis for the economic evaluation of the
anaerobic process.
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SECTION 3
INTRODUCTION
There are many challenges which confront the United States in the mid 70's.
Among those are two problems which at first appear unrelated but upon closer
inspection are found to be complementary. The growing concern for a feasible
means of organic waste disposal and an increasing worldwide energy shortage may
be dealt with simultaneously by the anaerobic digestion process. The develop-
ment of an economical process to convert organic wastes into useable methane
gas would provide at least a partial solution to both these problems. In this
report only organic agricultural wastes will be considered.
AGRICULTURAL WASTE DISPOSAL
Farm animals were previously maintained at low areal densities, however,
now up to 20,000 beef cattle, 6,000 dairy cows, and 2,000,000 chickens are
confined in single locations (1). A high percentage of beef cattle spend
one-third of their life in feedlots for fattening, and nearly all dairy cattle,
swine, and poultry are restricted to a concentrated area during their entire
life. With at least one-half or more of the 1.2 billion tons of excreta being
defecated in feedlots and animal enclosures, an environmental problem has
arisen. An acceptable disposal scheme has become a necessity in order to avoid
surface and groundwater pollution, oxygen depletion, eutrophication of surface
waters, undesirable odors, and fly breeding. The problems of disposal are
aggravated by the marginal nature of the economics of the agricultural industry
in general and its consequent inability to treat its wastes satisfactorily.
Ecologically, land spreading is the best method of disposal to recycle
nutrients. Unfortunately, sufficient land is unavailable for this method of
disposal. The quantity of waste that can safely be applied to the land is
dependent upon soil vegetative cover, slope, climate, and distance to receiving
waters. While manure is being produced continuously, it can only be spread at
certain times due to crop covering, weather, etc.
Biological processes provide a means for treating large volumes of waste
materials (2). Their suitability is evidenced by the fact that their energy
requirements are minimal, the organic mass produced is negligible, methane gas is
a useful by-product, and a humus-like slurry for land reclamation is produced
after sludge stabilization (3).
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ENERGY SHORTAGE
In 1960 the total energy demand of the United States was 4.5 X 1016
BTU, 6 X 1016 BTU in 1970, and is expected to exceed 9 X 1016 BTU by
1980. The share of natural gas (methane) in this energy market was approxi-
mately 31 percent in 1968 (4). This total energy demand, and in particular
that on natural gas, cannot continue without exhausting the available fuels.
For example, gains in production of natural gas from 1947 to 1968 averaged
more than six percent per year with production growing from 5.6 to 19.3
trillion cubic feet. During the same period reserves increased on an average
of 2.5 percent annually, i.e., 165 to 282 trillion cubic feet. However, the
reserves-to-product ratio has declined from 29.5 to 14.6 years. Even with
optimistic views on reserves and future production, demand for gas will remain
greater than additions to reserves. In order to at least ease the inevitable
gas shortage, Bahn has estimated that anaerobic gasification of urban and
agricultural wastes would yield 30 trillion cubic feet of methane annually
(5). This quantity of gas would meet all of the present U. S. needs while
significantly alleviating the problem of animal waste disposal.
PURPOSE OF THE STUDY
Since the anaerobic process could be utilized effectively in the solution
of two of this country's problems, the present study was undertaken in order
to investigate the design and operating parameters for an agricultural waste
disposal scheme. Anaerobic digesters have been used for years to treat
domestic wastes but have not been used widely in the disposal of agricultural
wastes. Therefore tine primary objectives of this investigation were to oper-
ate pilot digester reactors in a controlled environment, to design and
operate a large scale plant, and monitor gas production and investigate the
feasibility of using the stabilized sludge as a food supplement for animals.
The overall objective of the project was to obtain data which could be uti-
lized by a small farmer for the construction and operation of a plant capable
of alleviating his waste disposal problems as well as providing significant
energy for farm operation.
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SECTION 4
THEORECTICAL CONSIDERATIONS
FUNDAMENTALS OF ANAEROBIC DIGESTION
The fundamentals of the anaerobic process have been excellently presented
by Pfeffer (6), and his discussion vail be given in this report for
completeness.
Anaerobic treatment of complex organic materials is considered to be
basically a two-stage process, as indicated in Figure 1. In the first stage,
a group of facultative and anaerobic bacteria, known as the "acid-formers,"
act upon the complex organics and change the form of complex fats, proteins
and carbohydrates to simple soluble organic materials. The end products of
this first stage conversion are primarily short chain organic acids, also
known as volatile acids, and small amounts of bacterial cells. This stage
accomplishes no stabilization of the waste material but it is an essential
prerequisite for the second stage in which the actual stabilization of the
waste matter occurs. It places the organic matter in a form suitable for the
second stage of treatment.
C02
C02
Complex
Organics
•
Acid
Formation
Organic
Acids
i
i
Methane
Formation
Cfy
+
C02
Figure 1, Anaerobic stabilization of complex organics.
In the second stage, the short chain organic acids are acted upon by a
strictly anaerobic group of bacteria, termed the 'taethane formers," and are
coverted to gaseous end products, methane and carbon dioxide. The methane
formed in this second stage, being insoluble in water, escapes from the system.
It can be collected for use as a fuel. The carbon dioxide involved partially
escapes in the gaseous form and partially goes into solution. It is in this
second stage that stabilization occurs through the removal of oxygen-demanding
material in the form of methane gas. Cell production is also minimal compared
to aerobic processes. This is a direct result of the high energy content of
the products, in particular methane (7). This is an advantage as the amount
of solids requiring ultimate disposal is minimized by eliminating any significant
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microbial protoplasm production in the process of stabilizing the organic
material.
There are several different groups of methane formers with each group
characterized by its ability to ferment only a specific number of compounds.
Therefore, several different bacteria are required for stabilization of the
organic material (8) . The most important of these methane formers, those
utilizing acetic and propionic acids for substrates, grow quite slowly and
for most organic compounds are rate limiting at the lower retention times.
For sewage sludge digestion, Pfeffer (9) found that in systems operating
with solids retention times of approximately ten to fifteen days, the rate
limiting step then becomes the hydrolysis of organic solids.
Tracer studies have indicated the major sources of methane (8).
One source is the direct cleavage of acetic acid into methane and carbon
dioxide. Most of the remaining methane is formed from the reduction of carbon
dioxide. Carbon dioxide, functioning as an electron accepter, is reduced by
hydrogen atoms enzymatically removed from organic compounds. The availability
of carbon dioxide in such a step is never a rate limiting factor as there is
always a large excess of it from the bicarbonate buffer system that is present
in anaerobic systems (8).
Organic destruction in anaerobic treatment is directly related to methane
production and vice versa. Buswell and Mueller (10) developed Equation 1
to predict the quantity of methane from a knowledge of the chemical composition
of the waste:
Ha % + (n - W - 7) H20 — -V (7 - 8 + 3) COa
na
(T + 8
nab.
- 4)
McCarty (8) showed that the theoretical methane production from the
complete stabilization of one pound of BOD or COD.was 5.62 cubic feet at
L
standard temperature and pressure. From this he forwarded Equation 2 for
estimating methane production from waste strength:
C = 5.62 (eF - 1.42A)
where: C = cubic feet of OU. produced ^er day (STP)
e = efficiency of waste utilization
F = pounds of BOD added per day
A = pounds volatile biological solids produced per day.
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The efficiency of waste utilization, e, should not be confused with the
stabilization efficiency. It is a factor designating the efficiency of the
conversion of the organic waste to both the gaseous form and to biological
solids. Whereas the former form represents waste stabilization, the latter
conversion does not. The pounds of volatile biological solids produced per
day, A, can be estimated from Equation 3 (11):
A = aF (3)
I + b (.SKTJ
where: a = growth constant
b = endogenous respiration rate
SRT = solids retention time in days.
Values for a and b are shown in Table 1 for various organic compounds (12).
TABLE 1. GROWTH CONSTANTS AND ENDOGENOUS RESPIRATION RATES
Substrate Growth Constant, Endogenous Respiration
a Rate, b
Fatty Acid 0.054 0.038
Carbohydrate 0.240 0.033
Protein 0.076 0.014
The percentage of added BOD which is stabilized, S, is given by Equation 4
(11):
S = 100C
5'62 F (4)
= 100(eF - 142 A)
F
The efficiency of waste stabilization is related to the solids retention
time. As the solids retention time decreases, the relative proportion of active
cells washed out of the system increases. If the solids retention time falls
below a certain limit, the micro-organisms responsible for anaerobic digestion
will be washed out faster than they can reproduce themselves and the result is
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failure of the process. The minimum retention time is dependent on the
temperature and the types of substrate being utilized. Though it is possible
to operate near the minimum retention times, efficiencies are low and process
dependability is poor. Solids retention times of at least two and a half
times the minimum are recommended (11).
While there are many different methane forming bacteria, there are also
many different acid-forming bacteria. For attaining good efficiencies of
waste stabilization, a proper balance among all these different organisms is
required. The establishment and maintenance of this balance dictates operation
under optimum environmental conditions. These are discussed in brief in the
next paragraphs.
Temperature is a very important operational parameter in anaerobic fermen-
tation process. As temperatures increase, rates of reaction proceed much
faster and this results in more efficient operation, and lower retention time
requirements (13). Two optimum temperature levels have been established.
In the mesophilic level the temperatures range from 30°C to 37.5°C and in the
thermophilic level, they range from 49°C to 51°C. Although the rates of
reaction in the thermophilic level are much faster than those in the mesophilic
level, the economics of most sewage sludge digestion systems have dictated
operation in the mesophilic level or lower (13). This steins from the fact
that the methane requirements to maintain thermophilic temperatures in most
digesters are excessive and uneconomical. This, in turn, is a result of the
inability to thicken the feed sludges sufficiently such that the organic loading
and the resulting methane production per unit digester volume are sufficiently
high to make such an operation economically attractive.
Another environmental requirement for anaerobic treatment is the mainte-
nance of anaerobic conditions in the digester. The methane formers are strict
anaerobes and even small amounts of oxygen can be quite detrimental to them.
This necessitates, in most cases, a closed digestion tank which is also
convenient because collection of the methane produced is facilitated.
The third environmental requirement for optimum operation is that for a
proper pH. McCarty (13) reports that anaerobic treatment can proceed
quite well with a pH varying from about 6.6 to 7.6 with an optimum range of
about 7.0 to 7.2. Beyond these limits anaerobic digestion proceeds with
decreasing efficiency until at a pH of 6.2 and lower, the acid conditions
become quite toxic to the methane formers and waste stabilization comes to a
virtual halt.
Control of pH should be exercised when the pH appears likely to drop
below 6.6. This is done by the addition of an alkali. In sewage sludge
digestion the use of lime for such control has been the most widespread,
but because of its many advantages over lime, sodium bicarbonate has lately
been receiving increasing attention as a substitute for lime for pH control.
The bacteria responsible for waste conversion and stabilization in the
anaerobic process require nitrogen, phosphorus and other materials in trace
quantities for optimum growth. Therefore, another important environmental
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condition is the presence of the required nutrients in adequate quantitites.
Municipal waste sludge usually contains all the required nutrients in
adequate quantities but other substrates, industrial and solid wastes in
particular, might not. If the nutrients are not present in the required
quantities, they must be either added or supplemented.
McCarty (8) calculated the nitrogen and phosphorus requirements based
on an average chemical formulation of biological cells of CsHgOsN. This
yielded a nitrogen requirement of about 11 percent of the cell volatile solids
weight and a requirement for phosphorus equal to about one-fifth of this figure.
Although these requirements should theoretically be based on the fraction of
waste removed during treatment rather than on the waste added, it is good
practice to base, them on waste additions (8). Other elements having stimu-
latory effects at low concentration include, but are not limited to sodium,
potassium, calcium, magnesium, and iron (14). All of these preceding elements
exhibit inhibitory effects at higher concentrations.
The fifth and final environmental requirement for successful anaerobic
treatment is that the waste be free from toxic material. This is particularly
true for concentrated organic wastes which, though normally are more suscepti-
ble to anaerobic treatment, are also more likely to have high or inhibitory
concentrations of various materials ranging from inorganic salts to toxic
organic compounds.
Some alkali and alkaline earth-metal salts above certain concentrations
exhibit degrees of inhibition and toxicity. The threshold levels vary,
depending on whether these metals act singly or in combination. Certain
combinations have synergistic effects, whereas others display antagonistic
effects.
Ammonia, particularly when in the ammonium form, is inhibitory when
present in high enough concentrations. At concentrations between 1,500 and
3,000 mg/1 and a pH greater than 7.4, the ammonia concentration can become
inhibitory. At concentrations above 3,000 mg/1, the ammonium ion itself
becomes quite toxic regardless of pH (14).
Other common forms of toxicity include those of sulfides, heavy metals
and toxic organic materials. Concentrations of soluble sulfide varying from
50 to 100 mg/1, can be tolerated in anaerobic treatment with little or no
acclimation, whereas concentrations up to 200 mg/1 can be tolerated with some
acclimation (14). Low soluble concentrations of copper, zinc, and nickel
salts are associated with most of the problems of heavy metal toxicity in
anaerobic treatment. Also, there are many organic materials that exhibit
inhibitory effects. These range from organic solvents to many common materials
such as alcohols and long chain fatty acids in high concentrations (14).
It is well to know that microorganisms usually have the ability to
acclimate to some extent to inhibitory concentrations of most materials if
the process is acclimated to the inhibitory substance. Also, it should be
recognized that only materials in solution can be toxic to biological life
(14). Control of toxicity or inhibition can, in general, be achieved by one
or more of three ways: (1) the removal from the waste stream or inactivation
9
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of toxic materials by such means as chemical precipitation, (2) the dilution
of the waste stream below the "toxic threshold" of the toxicity causing
material, and (3) the addition of an antagonistic material.
10
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SECTION 5
EXPERIMENTAL PROCEDURE
LABORATORY PILOT DIGESTER REACTORS
In the laboratory three anaerobic digestion pilot plants were fabricated
from plexiglass, as shown in Figure 2. Each unit had a volume of approximately
17 liters (15.24 cm dia X 91.44 cm). The top and bottom of each unit were
threaded, and plexiglass plugs were fitted and sealed with rubber "0"-rings.
A funnel - stopcock inlet arrangement was used for feeding the unit and a
drain for wasting was located at the bottom of the pilot digester. At the
unit top, a glass tube was located to provide a passage via a Tygon tube to
the gasometer. The entire unit assembly was mounted on a stand to facilitate
feeding and wasting.
The gas generated from the pilot unit was collected in a gasometer shown
in Figure 3. The apparatus consisted of an outer glass cylinder filled with
a sulfuric acid solution. An inverted inner plexiglass cylinder constituted
the gas collection system as shown. The cylinder would rise as the gas was
collected. The side of the gasometer was calibrated in cubic feet.
All units were housed in a room where temperature could be controlled.
The units were in a continuous, steady-state reaction, with a fourteen-day
detention time. Each plant contained ten liters of digestible material. The
units were fed every twenty-four hours with a 100 ml of fresh material being
added to each plant after 100 ml of digested material was removed. The digest-
ible material was made by diluting varying ratios of grass clippings and fresh
cow manure to 6 percent total solids. In Unit I the solids were 100 percent
cow manure; Unit II had 70 percent manure and 30 percent grass clippings; and
Unit III contained 50 percent - 50 percent mixture. The pH of the units was
maintained between 6.7 and 7.0 for all experiments with NaOH being added to
raise the pH to the desirable level.
FULL-SCALE DIGESTER PLANT
A full-scale anaerobic digester experimental plant was designed and
constructed on the Swine Area of Tennessee State University (Figures 4a, 4b,
and 4c). A schematic of the plant lay-out is shown in Figure 5. Two 7,570
liter (1.62 m dia X 3.66 m) digester reactors were constructed from cold-
rolled steel and mounted on concrete piers (Figure 6). The tanks were coated
inside and out with an epoxy paint which is resistant to the corrosive
properties of the waste slurry. The influent and effluent pipes are shown
in Figure 6. The tank's contents were circulated by pumping the
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Influent Inlet
I
\
Gas Outlet
r n
U U
n
s
/ •*
/ *
/ Effluent Outlet
•Plexiglass
Digester Ifait
(15.24 on dia X
91.44 on)
Unit Support
Stand
Figure 2. Schematic of pilot plant digester.
12
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Generated Gas Inlet
Gas
Reservoir
Sulfuric
Acid
Solution
Figure 3. Pilot plant gasometer.
13
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mixture through a manifold in the lower influent pipe, and extracting it from
the center influent pipe (Figure 7). The digestible material (feed-lot cow
manure and water) was mixed in a modified 189 liter stainless-steel coffee
urn and pumped into the digester through a series of valves as shown in Figure
8. Two gas ports and a manhole fitted with a rubber gasket are located on the
top of each tank (Figure 6). A flexible rubber hose was connected to a gate
valve at the effluent pipe to facilitate in digested sludge removal.
Platinum resistance thermometers were located in the sides of each
(Figure 6) to monitor the sludge temperature. In order to control the
mixture temperature, a heat exchanger, consisting of a copper tube (1.3 on
diam) coil, an external water heater and circulation pump, was fabricated and
positioned as shown in Figure 9.
Monitoring equipment was located in the utility shed. Two 63125 Precision
Scientific wet test gas meters, one for each tank,'were connected to the
digesters by 0.64 cm 0. D. copper tubing (Figure 10). The tank pressure was
monitored continuously by a strip-chart pressure recorder located in the shed.
A digital voltmeter was used to measure the output of the platinum resistance
thermometers. A schematic of the gas handling connections is also shown in
Figure 10.
The entire plant site was located on a 15.2 m by 12.2 m reinforced
concrete slab. A cyclone fence and gate arrangement insured plant security.
The typical procedure for charging the plant was as follows:
(1). Thirty gallons of water were mixed with 80 pounds of hammer-
milled dried cow manure in the coffee urn. The liquid was
throughly mixed by means of a Light in Mixturer (1/3 HP; ND-1
Model).
(2). The urn contents were then pumped into the digester. The
procedure was continued until the tank was approximately
70 percent full, i.e., 5300 liters.
(3). The proper valves were opened and closed and the tank
contents were continuously circulated.
(4). After a minimum of twenty-four hours of circulation, a sludge
sample was taken and the percent solids and pH of the mixture
were determined.
(5). Calculations were made to determine the required dilution or
solids addition to provide a 8 to 12 percent solids solution.
Also, the required amount of lime was calculated to assure a
solution pH of 6.5 to 7.6. The necessary additions were then
made.
(6). A fourteen-day retention time was required before ideal
operating conditions could be achieved. After this period
of time, equal amounts of digested sludge and new digestible
material were withdrawn and added (usually 303 liters) on a
daily basis.
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IS KtSEARC
PROJECT
ENVIRONMENTAL PROTECTION AGENCY
CuUPERATI \KST\TESRESEARCH
SERVICES•«
TENN STATE UN1URSITY
i
'
•-&*' * «^WH» -''' •'"' •
Figure 4a. EPA-CSRS-TSU anaerobic digester plant.
-------
Figure 4b. EPA-CSRS-TSU anaerobic digester plant.
-------
Figure 4c. EPA-CSRS-TSU anaerobic digester plant,
17
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T
15.2m
12.2m
oo
-Influent Dumping | |
^^. CT__ — j_ - — ^•••^
^ Scale
Digester
Unit
stem
o
o
Digester
Unit I
Instru-
ment
Shed
Concrete Slab
3.66m Gate
S~~ Cyclone Fence
Figure 5. Schematic of full-scale digester plant.
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"Manhole
Gas to Pressure Recorder
t
n
Plug
10 Effluent Drain
Platinu
Thei
Emergency
Drain-'
Gas to Wet Test Meter
t
n
Thermometer
-------
Influent Inlet
Digester
Tank
c
L
t=
3
•Platinum
Resistance
Thermometer
Figure 7. Schematic of Internal Tank Circulation System.
20
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"Digester Tanks
Sludge
Pump iHp-
3. Son diam
(Teel IP854)
PVC Pipe
5cm diam.
V
^-PVC Pip
3.8cm diam
Influent Inlet
(from urn)
Figure 8. Schematic of influent pumping arrangement.
21
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Circulation Pump (% Hp;Teel IP853)
CPVC
Pipe
(1.91 on
diam)
Make-up
WaterL
Inlet¥
4KW Water
Heater
•Digester
Tank
\_
Copper Coil
(1.3cm diam Tubing)
Figure 9. Digester heat exchanger system.
22
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Gas Outlet (Vent to Atmosphere)
Honeywell 702X,
0-10 psi, 7 day
\ Pressure Recorder
\ (Strip Chart)
Gas Inlet
Unit II
0.64cm ID Cu Tubing
•^"Needle
\Valve
Wet
Test
Meter
Gas Inlet #1-
•Gas Inlet
.#2
Wet
Test
Meter
Gas
Inlet
Unit I
Figure 10. Schematic of digester monitoring equipment arrangement.
23
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(7). Sludge temperature was monitored and adjustments were
accomplished by the heat exchanger. Tank pressures
were continuously monitored by the pressure recorder.
Total volume of gas generated and the gas generation
rate were monitored twice during a twenty-four-hour
period by utilizing the wet test meters.
ANALYTICAL PROCEDURES
EH
The pH of the pilot plants and full-scale digester mixtures were made
on a daily basis using a Becktnan Electromate pH Mster.
Alkalinity
A sample of the digester effluent was centrifuged and the supernatant
was then used for alkalinity determination according to the procedures
described in (15) p. 49. The solution was titrated with 0.02 N H2SO^ to a
pH of 4.5. All alkalinity reported are in mg/1 as CaC03
Biochemical Oxygen Demand (BOD)
The BOD's for the influent, centrifuged effluent, and mixed liquor were
determined by the procedure presented in Standard Msthods (15), p. 415. The
influent was the prepared manure or manure-grass mixture to be digested. The
mixed liquor was the digested material removed from the digester, and the
centrifuged effluent is the liquid portion of the mixed liquor. A secondary
influent from the Metropolitan Nashville Waste Treatment Plant was used for
seed in the BOD measurements. A DO meter was used for the dissolved oxygen
determination. The sample size in each case was 20 ml.
Chemical Oxygen Demand (COD)
COD's for the influent, mixed liquor, and centrifuged effluent were
determined according to procedures outlined in (15), p. 510. The sample size
for these cases was also 20 ml.
Ammonia Nitrogen
Ammonia nitrogen measurements in the mixed liquor for all three units
and the plant were by use of the distillation method described in (15),
p. 391.
Gas Composition Analysis
The generated gases were' analyzed using a Varian GLC gas chromatograph
with a thermal conductivity detector. An eight-foot Poropak Q column at
40°C was utilized to determine the carbon dioxide and methane content of
the sample. The instrument was calibrated using a standard gas mixture
containing 40 percent carbon dioxide and 60 percent methane by volume.
24
-------
The peak heights recorded on a strip chart recorder were used to determine
the concentrations o£ G02 and CH^.
Volatile Solids
The volatile solid measurements were performed by the procedure outlined
in (15), p. 425. The results are given in mg/1.
Heavy Metal Analysis
Sludge samples from the three laboratory units and a digested manure
sample were analyzed for Pb, Ca, Fe, Zn, Mn, Cd, and Al using an atomic
absorption spectrophotometer. Only a very small number of samples were
analyzed since the availability of the instrument was quite limited.
25
-------
SECTION 6
RESULTS
PILOT PLANTS
The pilot plants were operated over a two-month period and data were
taken on a daily basis. Typical experimental results are presented. The
three units were loaded and after a fourteen-day detention time, analyses of
the influent and effluent were begun. Gas production varied greatly from
day to day as shown in Figure 11. Units II and III produced considerably
more gas than Unit I. Gas production ranged from 8.5 to 17.0 liters per day
(0,3 to 0.6 ft. 3/day).
The biochemical oxygen demand (BOD) for the influent, mixed liquor,
and centrifuged effluent was measured during a fifteen-day test period. The
results for each unit are presented in Figures 12, 13, and 14. The BQD's
were reduced within all units, indicating that the dissolved Oxygen was
consumed by the microbial life while assimilating and oxidizing the organic
matter present. In Unit I the BOD was reduced from around 9,000 mg/1 in the
influent to nearly 3,000 mg/1 in the mixed liquor and 1,400 mg/1 in the centri-
fuged effluent (Figure 13). For the 50 percent-50 percent mixture in Unit
III, similar results were obtained, as shown in Figure 14.
The chemical oxygen demand (COD) was determined on various sampling days
for all three units. The experimental results are presented in Figures 15,
16, and 17. In all units there was a reduction in COD, indicating that
organic matter was being oxidized.
Volatile solids were also measured in the influent, mixed liquor, and
centrifuged effluent of each unit. As shown in Figures, 18, 19, and 20,
there was a reduction in volatile solids upon digestion.
A 400 ml sample from each unit was oven-dried to a constant weight at
100°C and ground in Wiley mill. Total nitrogen was determined by the Kjeldahl
Method and the crude protein content was calculated by multiplying the total
nitrogen by the factor 6.25. Carbon and phosphorus contents were determined
by the Walkley Black and Vanadomolybdophosphoric Yellow Color Mgthods,
respectively (16). The organic matter (O.M.) was calculated by multiplying
carbon by the factor of 1.72. The results of the analyses are presented in
Table 2. There was very little difference in the analyses of the dried
sludge taken from the three digestion units. The undigested manure, however,
had a higher organic matter content and a lower crude protein percent than
the digested samples. The ammonia nitrogen, pH and alkalinity of the mixed
liquor varied only slightly among the units. These quantities were maintained
within the range for optimal operating conditions as discussed previously.
26
-------
18
16
14
12
GAS PRODUCTION
UNIT III
UNIT II
10
UNIT I
t t I I i i I l
5 10
SAMPLING DAYS
Figure 11. Laboratory pilot plant gas production.
27
-------
10
o
o
o
BOD- UNIT I
INFLUENT
MIXED
LIQUOR
CENTRIFUGED
EFFLUENT
I I I I I
SAMPLING BAYS
10
Figure 12. Biochemical oxygen demand for Unit I.
28
-------
BOD UNIT II
12
10
INFLUENT
n
r« 6
*
MIXED
LIQUOR
CENTRIFUGED
EFFLUENT
I I I
5 10
SAMPLING DAYS
Figure 13. Biochemical oxygen demand for Unit II.
29
-------
14
12
10
* 6
BOD- —UNIT III
INFLUENT
MIXED LIQUOR
CENTRIFUGED
EFFLUENT
II I I i I I
J I I I I
SAMPLING DAYS
10
Figure 14. Biochemical oxygen demand for Unit III.
30
-------
o
o
o
CO
e
70
60
50
40
30
20
COD UNIT I
INFLUENT
MIXED
LIQUOR
10
I I
I I
I I
FUG]
CENTRIFUGED
EFFLUENT
J I
I
5 10
SAMPLING DAYS
Figure 15. Chemical oxygen demand for Unit I.
31
-------
70
COD—UNIT II
60
50
40
INFLUENT
MIXED
LIQUOR
30
20
10
CENTRIFUGED EFFLUENT
-o
o
•o
I I I I I I 1 I I I I I I I
10
SAMPLING DAYS
Figure 16. Chemical oxygen demand for Unit II.
32
-------
70 „
COD UNIT III
60
50
40
o
o
o
X
30
INFLUENT
MIXED
LIQUOR
20
10
I I
I I I
SAMPLING DAYS
10
Figure 17. Chemical oxygen demand for Unit III,
CENTRIFUGED
EFFLUENT
I ll L
33
-------
VOLATILE SOLIDS UNIT I
50
40
Influent
o
O
o
30
Mixed
Liquor
20
10
Centrifuged
Effluent
SAMPLING DAYS
10
Figure 18. Volatile solids for Unit I,
34
-------
VOLATILE SOLIDS —UNIT II
50
INFLUENT
40
30
MIXED LIQUOR
20
10
CENTRIFUGED
EFFLUENT
i i t i
l i i i i i
10
SAMPLING DAYS
Figure 19. Volatile solids for Ihit II.
35
-------
60
50
40
30
I?
20
VOUTILE SOLIDS UNIT III
'INFLUENT
CXED
LIQUOR
10
10 15
SAMPLE DAYS
20
•Q CENTRI-
FUGED
EFFLUENT
25
Figure 20. Volatile solids for Unit III.
36
-------
TABLE 2. COMPOSITION OF DRIED SLUDGE AND MIXED LIQUOR
Unit
I
II
III
Undigested
Manure
Dried Sludge (Percent)
O.M.
56.43
57.41
59.51
71.19
Fat
2.61
2.00
1.99
2.02
Crude Protein
13.44
13.86
13.63
10.56
Phosphorus
0.0247
0.0285
0.0266
0.0252
NH3-N (mg/1)
212.5
168.9
169.8
-
^ixed Liquor
pH
7.74
7.84
7.83
-
Alkalinity (mg/1)
8400
7404
7042
-
-------
TABLE 3. ANALYSIS OF HEAVY METALS frig/kg .dry weidit)
CM
00
Unit I
Unit II
Unit III
Undigested
Manure
Pb
42
50
52
48
Cu
33
45
80
22
Fe
3300
3600
3000
1800
Zn
320
240
300
480
Mi
380
380
340
280
Cd
1.5
2.7
7.5
1.4
Al
3100
3000
2700
1900
-------
Analyses for heavy metals were made with an atomic absorption spectropho-
tometer but there were no great differences among the units, with the exception
of higher Cu and Cd levels in Unit III (Table 3). All metal concentrations
were higher in the digested samples than in the undigested manure, except for
lead and zinc.
FULL-SCALE PLANT
Unit I of the full-scale plant was charged with 4765 liters of a mixture
composed of water and manure (2.8 percent solids). After a fourteen-day
detention time, seventy-five gallons of mixture were wasted and seventy-five
gallons of fresh mix were added to the unit. Data from this operation for
a six-week period are presented in Figures 21 and 22. The pH. of the mixture
was maintained above 6.5 by the addition of lime. The sludge temperature
varied from 40°C to 44.4°C, being controlled by the internal copper coil
heat exchanger. After a two-week detention time, the gas volume generation
rate was 3.5 ft. 3/hr. and eventually increased to 5 ft. 3/hr. near the end
of the testing period. Gas samples were analyzed in a gas chromatagraph.
Typically, the generated gas was 62 percent methane and 38 percent carbon
dioxide. The influent and effluent BOD and COD were measured. As in the
pilot plants, both these quantities were reduced upon digestion.
Unit II was charged with 6056 liters of a water and 30 percent farm
clippings- 70 percent manure mixture. However, operational difficulties pre-
vented continuous data acquisition for this unit.
OPERATIONAL DIFFICULTIES
Several operational difficulties were encountered when large scale plant
start-up was attempted. The coffee urn mixing arrangement was not satisfac-
tory. When the measured quantity of feedlot manure was placed in the urn and
mixed with water, the solution contained large lumps of manure and animal hair
which soon caused the pumps to become clogged. Several methods of straining
the mixture were attempted, but no feasible technique was found which could
handle a 5 on layer over the concrete pad of the plant and was allowed to
dry. The dried manure was then ground into a fine powder in a hammer mill
and stored in 190 liter barrels. When feeding the unit, the proper amount
of manure was weighed, placed in the urn with water, and the contents were
thoroughly mixed. The pumping and circulation problems were then solved.
Several days after the plant had been charged with a manure-water
mixture, foaming of the supernatant was discovered. This phenomenon was
possibly due to the lime which was added to insure the proper pH of the
solution. The foam clogged all gas lines leading to the pressure recorder
and wet test meter. On one occasion the tank pressure was well above 10
psig before the clogging was discovered. The situation was remedied by
decreasing the volume of the mixture to approximately 4765 liters and by
replacing the original 0.64 cm ID copper gas line with 1.3 cm ID tubing.
The 1.3 cm ID line was connected to a flask by a rubber stopper and a second
0.68 cm ID tube allowed passage of the gas to the recording instruments
(Figure 23).
39
-------
8
I
s
>-.
V
,110
f- 108
i—i
co
104
* >s
-------
If
5000
4000
3000
2000
••
o
o
o
8
70
60
50
40-
30
0
Mixture: 100% Cow Manure in Water to 2.8% Solids
Mixture Volume: 4765 liters
Manure Weight: 2040.17 Ibs
Gas Analysis: 62% CH4; 38% C02 Influent
BOD Measurements
COD Measurements
Influen£
Effluent
1234
TIME, WEEKS
Figure 22. BOD and COD for the full-scale plant.
6
41
-------
As the season began to change, temperature control became quite difficult.
Eventually the daily temperature was such that heat transfer losses were
greater than the heat exchanger could supply. In the new investigation, both
tanks will be insulated with styrofoam sheets, and thus, temperature control
should be easily maintained even in the colder months.
Measurement difficulties were also encountered. The gas chromatograph
and atomic absorption spectrophotometer at Vanderbilt University were found
in to inoperable. A division of the American Tobacco Company granted
permission to use their gas chromatograph. However, the number of samples
analyzed was limited. In the new investigation a GC will be purchased for
the University. Only one heavy metal analysis of dried sludge sample could
be made. The Varian Company was gracious enough to analyze the sample as an
equipment performance demonstration.
Equipment delivery and construction delays greatly hampered the comple-
tion of the full-scale plant. It was impossible to gather a sufficient set
of data. Fortunately, a two-year investigation to collect a comprehensive
set of data has been funded.
NUTRITIVE VALUE OF THE ANAEROBICALLY DIGESTED SLUDGE
In addition to methane gas another useful byproduct of the anaerobic
digestion process is the stabilized sludge. Specifically, the possibility
of supplementing animal diets with the digested material has been investigated.
Ruminants possess a uniquely high capacity for digesting cellulose and
hemicellulose of plant cell walls. However, 40 percent to 60 percent of
this potential energy source escapes digestion and appears in the feces. As
a result, millions of tons of undigested cell wall residues are excreted by
ruminants annually. Such materials represent a vast potential source of
energy for microbial fermentation. Anaerobic digestion of this excrement
makes it a potential source of nutrients for livestock.
42
-------
Gas and Foam
Inlet from Digester (1.3cm ID Cu Tube)
Ga.
s Ou
Gas Outlet (to Wet Test Meter
or Pressure Recorder-
n.64 on ID Cu Tube)
Rubber Stopper
1000 ml
Flask
Foam or Other Condensed
Matter
Figure 23. Output gas handling arrangement.
43
-------
The sludge used in this study was taken from three laboratory pilot
digestion units, (lJn.it I, 100 percent manure; Unit II, 70 percent manure and
30 percent grass; and Unit III, 50 percent manure and 50 percent grass) after
a detention time of fourteen days at approximately 35°C. The sludge was
dried to a constant weight at 105 C and ground in a Wiley mill, using a 2 mm
screen. Composition of the sludge is shown in Table 4.
TABLE 4. COMPOSITION OF SLUDGE PERCENT
Unit ffoisture Protein Fat Phosphorus Ash Cu Fe
I
II
III
6.25
6.16
6.69
13.44
13.86
13.63
2.61
2.00
1.99
.0247
.0285
.0266
34.54
34.52
34.47
.0033
.0045
.0080
.33
.36
.30
A fortified corn - soybean meal diet (Table 5) served as the basal diet.
Either 10% or 25% sludge from each unit was added to the diets at the expense
of corn and soybean meal. All diets were calculated to be isonitrogenous
(16% crude protein). Sixty-three female weanling rats weighing 40-70g were
randomly distributed into 7 groups (three rats per treatment). The trial was
replicated three times. All rats were individually caged. Feed and water
were offered ad libitum for 21 days.
Individual rat weights and feed consumption data were recorded at weekly
intervals. Average dai ly gain, average daily feed intake and feed per gain
were computed.
The rats were also subjected to a three-day digestion trial in which
the feces were collected and feed consumption monitored. The feed and feces
were dried and the percent dry matter digestibility was determined. From
this trial, the digestibility of protein was also determined. The feces of
three rats from each treatment (one from each replica) along with each feed
were analyzed for protein (Kjeldahl N x 6.25). The percent protein was
multiplied by the dry feces collected and feed consumed, and the protein
digestibility determined from the results.
The data from all trials were subjected to statistical treatment by the
analysis of variance as outlined by Fisher (17).
44
-------
TABLE 5. COMPOSITION OF DIETS PERCENT
Ration Number
Ingredient 1
Soybean Msal 22.0
Corn 70.0
Sludge Unit I
Sludge Unit II
Sludge Unit III
Lard 5.0
Calcium Phosphate 1.0
Limestone 1 . 0
Trace Mineral Salt 0.5
Vitamin Pre Mix 0.5
2
20.7
61.3
10.0
-
-
5.0
1.0
1.0
0.5
0.5
3
18.9
48.1
25
-
5
1.0
1.0
.5
.5
4
20.7
61.3
-
10.0
5.0
1.0
1.0
0.5
0.5
5
18.9
48.1
25.0
5.0
1.0
1.0
0.5
0.5
6
20.7
61.3
-
10.0
5.0
1.0
1.0
0.5
0.5
7
18.9
48.1
-
25.0
5.0
1.0
1.0
0.5
0.5
The results of this experiment are presented in Tables 6 and 7. Pats fed
ration 4 and 6 had similar growth rates to rats fed the basal ration; whereas,
rats fed ration 2 showed a growth depression (P < .05). Growth depression of
rats receiving 25 percent sludge (3,5, and 7) was highly significant (P < .01).
Average daily feed intake for all sludge treatments was higher than the
basal. Rats fed treatments 2, 5, and 6 showed an average daily feed intake
significantly higher (P < .05), and for rats fed treatments 3, 4, and 7 it was
significantly higher (P < .01) than for rats fed the basal ration.
Feed per gain ratios of all rats fed sludge treatments were significantly
higher than for rats fed the basal ration (P < .05) with the exception of rats
fed treatments 3 and 7 which had feed per gain ratios that were significantly
higher (P < .01) than the rats fed the basal ration.
Dry matter digestibility of diets decreased as the level of sludge was
increased in the diets. The digestibility of treatments 2, 4, and 6 were
significantly lower (P < .05) than the basal, and it was significantly lower
(P < .01) than the basal for treatments 3, 5, and 7.
45
-------
Protein digestibility of all diets with sludge treatments was significantly
lower (P < .01) than the basal. The protein digestibility of all sludge treat-
ments was similar with the exception of treatment 3, which was significantly
lower (P < .01) than the other sludge treatments.
Growth performance was not greatly reduced by the addition of 10 percent
sludge when compared to the control diet; however, 10 percent sludge did
considerably lower feed conversion and digestibility of the diets. Performance
of rats receiving 25 percent sludge was lowest of all treatment groups. This
included average daily gain, feed conversion and digestibility of dry matter
and protein. This reduction in performance agrees with the findings of Harmon
(18).
The lower protein digestibility of the sludge-containing diets may be a
consequence of a high proportion of non-proetin nitrogen, since microorganisms
are rich sources of non-protein nitrogen. The feeding of this sludge to
ruminant animals would be desirable, since the non-protein nitrogen fraction
would be utilized more efficiently than in non-ruminants.
The overall performance of the rats on the different dietary treatments
was in the following order:
1. Treatment 1 Basal
2. Treatment 4 10 Percent of 70-30 manure-grass sludge
3. Treatment 6 10 Percent of 50-50 manure-grass sludge
4. Treatment 2 10 Percent of 100 Percent manure-sludge
5. Treatment 5 25 Percent of 70-30 manure-grass sludge
6. Treatment 7 25 Percent of 50-50 manure-grass sludge
7. Treatment 3 25 Percent of 100 Percent manure-sludge
The results of the experiment indicate that:
(1) Ration with up to 10 percent anaerobically processed cow manure
and grass mixtures can be fed rats with results similar to those on non-manure
diets. This was probably due to increased feed intake by rats fed the 10
percent sludge diets.
(2) The use of anaerobically processed wastes resulted in less
efficient feed conversion.
(3) The addition of sludge did not reduce acceptability of the diets.
(4) The incorporation of sludge in the diets decreased dry matter
and protein digestibility.
(5) The poor overall performance of rats fed the 25 percent sludge diets
probably resulted from the inability of rats to efficiently digest the dry
matter and protein of these diets.
(6) The different sludges had very little effect on the performance
of rats. The slight difference favored Unit II followed by Unit III.
46
-------
TABLE 6. SUMMARY OF GROWTH AND FEED DATA
Treatments
Basal
100 Percent manure
Sludge
70 - 30 manure
Grass mixture
Sludge
50 - 50 manure
Grass mixture
Sludge
No.
CD
(2)
(3)
(4)
(5)
(6)
(7)
Percent
Sludge
10 Percent
25 Percent
10 Percent
25 Percent
10 Percent
25 Percent
Average daily
gain
(g)
4.31a
4.04c
3.86c
4.26a
3.91c
4.19a
3.80c
Average daily
feed intake
(g)
11.18a
12.63b
13.62c
12.90C
12.68b
12.91b
13.14c
g Feed/
g gain
2.59a
3.31b
3.52c
3.03b
3.24b
3.05b
3.46c
b Significantly different (P < .05) from a
c Significantly different (P < .01) from a
-------
TABLE 7. SUMMARY OF DRY MATTER AND PROTEIN DIGESTIBILITY DATA
Basal
100 Percent
manure
Sludge
70-30 manure
Grass mixture
Sludge
50-50 manure
Grass mixture
Sludge
Treatments Dry Matter
Percent Digestibility
No. Sludge Percent
(1) 86. 5a
(2) 10 Percent 81. 4b
(3) 25 Percent 73. 7c
(4) 10 Percent 76. Ob
(5) 25 Percent 73. 6c
(6) 10 Percent 79. 4b
(7) 25 Percent 73. 2c
Protein
Digestibility
Percent
86. 3a
81. 9c
75. 6c
80. Ic
80. 3c
80. 4c
79. 8c
b Significantly different (P < .05) from a
c Significantly different (P < .01) from a
48
-------
C7) There were no noticeable signs of sickness or abnormalities as a
result of consuming any of the diets.
Although feed conversion and digestibility of diets decreased as the
level of sludge was increased, this experiment reveals that anaerobically
processed organic wastes are consumed readily, and when incorporated into a
balanced diet will support animal growth.
49
-------
REFERENCES
1. Dugan, G. L., Young, R., and Takamiya, G. "Animal Waste Management in
Hawaii." Journal of Water Pollution Control Federation, 45, No. 4, April,
1973, p. 742.
2. Ghosh, S. and Pohland, F. G. "Kinetics of Substrate Assimilation and
Product Formation in Anaerobic Digestion." Journal of Water Pollution
Control Federation, 46, No. 4, April, 1974, pp. 748-759.
3. Graef, S. P., and Andrews, J. F. "Stability and Control of Anaerobic
Digestion." Journal of Water Pollution Control Federation, 46, No. 4,
April, 1974, pp. 66-683.
4. Anon. "Natural Gas: Worry About Supply." Chemical and Engineering
News, 48, No. 14, March 30, 1970, p. 8.
5. Ghosh, S. "Anaerobic Processes." Annual Literature Review - Journal of
Water Pollution Control Federation, 45, No. 6, June, 1973, pp. 1063-1074.
6. Pfeffer, J. T. "Reclamation of Energy from Organic Waste." EPA-670/
2-74-016, March, 1974.
7. McKinney, R. E., and Conway, R. A. "Chemical Oxygen in Biological Waste
Treatment." Sewage and Industrial Wastes, 29, No. 10, October, 1957,
pp. 1097-1106.
8. McCarty, P. 0. "Anaerobic Waste Treatment Fundamentals--Part One,
Chemistry and Microbiology." Public Works, 95, September, 1964, pp. 107-
112.
9. Pfeffer, J. T. "Increased Loadings on Digesters with Recycle of Digested
Solids." Journal of Water Pollution Control Federation, 40, No. 11,
November, 1968, pp. 1920-1933.
10. Buswell, A. M., and Mueller, H. F. "Mechanisms of Methane Fermentation."
Industrial and Engineering Chemistry, 44, 1952, pp. 550-552.
11. McCarty, P. L. "Anaerobic Waste Treatment Fundamentals--Part Four, Process
Design." Public Works, 95, December, 1964, pp. 95-99.
12. Speece, R. E., and McCarty, P. L. "Nutrient Requirements and Biological
Solids Accumulation in Anaerobic Digestion." Advances in Water Pollution
Research, 2, pp. 305-322. Eckenfelder, W. W., Editor. Pergamon Press,
New York, 1964.
50
-------
13. McCarty, P. L. "Anaerobic Waste Treatment Fundamentals--Part Two,
Environmental Requirements and Control." Public Works, 95, October,
1964, pp. 123-126.
14. McCarty, P. L. "Anaerobic Waste Treatment Fundamentals--Part Three,
Toxic Materials and Their Control." Public Works, 95, November, 1964,
pp. 91-94.
15. Standard Methods for the Examination of Water and Wastewater. Orland,
H. P., Editor. 12th Ed., American Public Health Assocation, Inc.,
New York, 1965.
16. Jackson, M. L. Soil Chemical Analysis. Prentice Hall, Inc. Englewood
Cliff, N. J. pp. 219-221; 153-154, 1958.
17. Fisher, R. A. Statistical Methods for Research Workers. 14th Ed.
Oliver and Boyd, Edinburough, 1970.
18. Harmon, B. G., Day, D. L., Baker, D. H., and Jensen, A. H. "Nutritive
Value of Aerobically and Anaerobically Processed Swine Waste." Journal
of Animal Science, 1973, 37, p. 510.
51
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-77-089
2.
4. TITLE AND SUBTITLE
A COMPLETE DISPOSAL- RECYCLE SCHEME FOR AGRICULTURAL
SOLID WASTES
7. AUTHOR(S)
Michael R. Busby, Greg Tragitt, Roland Norman, and
Kenneth Hillsman
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Tennessee State University
Nashville, Tennessee 37203
12. SPONSORING AGENCY NAME AND ADDRESS
Robert S. Kerr Environmental Research Lab. - Ada, OK
Office of Research and Development
U.S. Environmental Protection Agency
Ada, Oklahoma 74820
3. RECIPIENT'S ACCESSION-NO.
S. REPORT DATE
May 1977 issuing date
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1HB617
11. CONTRACT/GRANT NO.
R- 802739
13. TYPE OF REPORT AND PERIOD COVERED
Final (1/74-6/76)
14. SPONSORING AGENCY CODE
EPA/600/15
15. SUPPLEMENTARY NOTES
16. ABSTRACT
With the advent of the 70' s, there has been an increasing national concern for
the growing energy shortage as well as the problem of organic waste disposal. These
two problems, while at first glance appear unrelated, are dealt with simultaneously
by an anaerobic digestion process . Such a process produces not only a useful fuel ,
methane, but also is a potential source of a stabilized fertilizer and a nutritive
supplement to animal diets. This biological process has been used for decades, but
the economic feasibility of incorporating such a process on a typical small farm
has not been clearly established.
This investigation applied the anaerobic process to the production of methane
gas and a stabilized sludge from cow manure and farm clippings in laboratory pilot
plants as well as a full-scale (2,000 gal.) digester system. The quantity and
quality of gas produced, the biochemical and chemical oxygen demands, and the
nutritional value of the digested sludge for both the laboratory and full-scale
plants were evaluated.
17.
a. DESCRIPTORS
KEY WORDS AND DOCUMENT ANALYSIS
b.lDENTIFIERS/OPEN ENDED TERMS
Wastes, Anaerobic processes, Fertilizers, Farm wastes, Anaerobic
Methane, Nutritive value, Animal nutri- digestion, Energy,
tion
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
20. SECURITY CLASS (This page)
UNCLASSIFIED
c. COSATI Field/Group
02/C
21. NO. OF PAGES
60
22. PRICE
EPA Form 2220-1 (9-73)
£• II. S. GOVERNMENT PRINTING OFFICE: !977-757-056/6'i'i9 Region No. 5-11,
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