-------
AEROBIC TREATMENT
OF LIVESTOCK WASTES
This final report (SW-16rg) on work performed
by Purdue University under solid waste research
grant no. EC-00244 and by the University of
Illinois under solid waste research grant no.
EC-00245 was written by D. D. JONES, D. L. DAY,
and A. C. DALE and has been reproduced as
published by the University of Illinois.
U.S. ENVIRONMENTAL PROTECTION AGENCY
1972
-------
* U.S. GOVERNMENT HUNTING Of «CE : \ 972 O - 479-132
For Ml* by th« Superintendent of Docum«nu, U.S. Government Prlntinr Office
Wuhington, D.C. 20402 - Pnc* S& nnU
Stock Number 6602-00089
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FOREWORD
Urban America, dependent for nourishment upon
a remote agricultural industry, is largely unaware
of the complex nature of the food-producing process
or of the problems which beset the industry. A pre-
eminent problem concerns disposal of approximately
2 bill ton tons per year of agricultural wastes-
crop residues and animal manure—which constitute
57 percent of the Nation's total solid waste output.
Ironically, the problem of livestock waste
disposal is aggravated by the application of modern
technology to agricultural practices. The widespread
use and relative economy of chemical fertilizers,
for example, have resulted in a lessened demand for
animal manures to be used as fertilizers. And the
Increasing use of feedlots to raise livestock and
fatten them more rapidly for market produces enor-
mous and concentrated quantities of manures that can-
not be readily and safely assimilated into the soil,
as under conventional open grazing practices.
Under the authority of the Solid Waste Disposal
Act of 1965 (P.L. 89-272), the U.S. Environmental
Protection Agency has supported a wide variety of
agricultural solid waste research projects through
the grant mechanism. This report resulted from work
accomplished under two such grants: one to Purdue
University, entitled "Disposal of Dairy Cattle
Wastes by Aerobic Digestion," and the other to the
University of Illinois, entitled "Livestock Waste
Management and Sanitation," a project principally
concerned with waste from swine. The interface of
these two related projects was a natural subject for
a jointly-prepared report by the two grantees. The
information compiled in this report is valuable to
those who wish to design, develop, and implement
aerobic livestock waste-handling and treatment
facilities.
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THE NEED FOR A RIGOROUS STUDY of the aerobic biological method of
livestock waste disposal prompted the assembling of the information in
this bulletin. It should be of interest to anyone who wants to use the
aerobic method of livestock waste handling and treatment, and especially to
persons who design and develop such systems. Refer to Uniform Termi-
nology for Rural Waste Management (1969) for definitions of terms.
An abstract of this bulletin is included in the regional research bul-
letin, Farm Animal Wastes-1969, sponsored by NGR-67 (formerly NC-69)
Farm Animal Waste Disposal. Review and comments from members of
NCR-67, associates at the University of Illinois, Purdue University,
Cornell University, Thrive Center, Inc., and Fairfield Engineering and
Manufacturing Co. are greatly appreciated by the authors.
The cooperative authorship of this bulletin grew from previous co-
operation in NC-69 and the sabbatical leave that Dr. A. C. Dale of
Purdue University spent at the University of Illinois in 1965-66. Copies
of the bulletin may be obtained from either University.
Contents
LIVESTOCK WASTE PROPERTIES 4
THEORY OF AEROBIC TREATMENT 5
LABORATORY STUDIES OF AEROBIC TREATMENT OF WASTES 7
DEVELOPMENT AND MUNICIPAL USE OF OXIDATION DITCH 14
THE IN-THE-BUILDING OXIDATION DITCH FOR LIVESTOCK WASTES. . . 19
AEROBIC LAGOONS 41
AERATED LAGOON SYSTEM WITH IRRIGATION —
AN EXPERIMENTAL STUDY 47
SUMMARY AND CONCLUSIONS 50
REFERENCES 53
This bulletin was prepared by D. D, Jortes, formerly research assistant in the
Agricultural Engineering Department at the University of Illinois; D. L. Day,
associate professor of agricultural engineering, University of Illinois at
Urbana-Champaign; and A. C, Dale, professor of agricultural engineering,
Purdue University.
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OF LIVESTOCK:
LARGE VOLUMES OF MANURE have been produced on small land areas
since the advent of intensified confinement livestock systems. The
amount of wastes produced by livestock in the United States has been esti-
mated to be nearly two billion tons (Wadleigh, 1968). This is nearly ten
times the excrement produced by the human population of the United
States (Taiganides, 1967). However, there is much more dilution water
added to domestic wastes than to livestock wastes.
Until the last few years manure could simply be spread on the farmer's
field every few months. The farmer appreciated the fertilizer value, and
no one minded the odor. However, with the development of cheap,
efficient commercial fertilizer and the proximity of neighbors who object
to the manure odor, this is no longer the case.
It has been found (Van Arsdall, 1962) that "spreading solid manure
on cropland, rather than dumping it in a disposal area, is a profitable
practice because there is little difference between spreading and disposal
costs." But with liquid manure systems which are very popular in hog
confinement production, the report states: "The most profitable practice
for the farmer who raises hogs in confinement is to dispose of the liquid
manure in a lagoon and use commercial fertilizer on his fields." No doubt
the same would be true for producers who raise other types of livestock
in confinement.
The pollution of both surface and ground water supplies by animal
wastes is receiving the attention of various health and pollution control
agencies. In addition, land is not readily available during much of the
year for the immediate spreading of animal wastes. For these reasons,
farmers have begun looking for a low-cost, manure storage method which
will not give rise to intolerable odors and insect breeding (Dale, 1968).
They also want a method of storing manure for a longer period of time
and closer to the production unit.
As a result, researchers have concentrated a great deal of effort toward
developing a workable, odorless method of liquid waste disposal. One
of the simplest methods of odorless waste treatment is the aerobic bio-
logical treatment process. The two major forms of aerobic treatment
for municipal wastes are the activated sludge process and the trickling filter.
Extended aeration, a modification of the activated sludge process, has
primarily been used to treat livestock wastes aerobically. Two extended
aeration processes, the oxidation ditch and the aerated lagoon, will be
discussed in this report.
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LIVESTOCK WASTE PROPERTIES
The design and operation of any biological treatment unit depends
on the nature of the wastes to be treated. Wastes vary in concentrations
of biodegradable components, and appropriate bacterial cultures must
be developed to treat different organic compounds in the waste.
Housing and management conditions are unique for each type of
livestock and they influence the amount and nature of the wastes produced.
Differences in wastes are caused by differences in the size, diet, and
metabolism of the animals (Blosser, 1964). Swine and poultry consume
highly digestible rations and therefore produce a relatively small amount
of waste compared with cattle on high-roughage rations. Also, simple-
stomached animals such as swine produce excreta that is somewhat simi-
lar to that of humans (Loehr, 1968).
The manures from ruminants and herbivores, such as cattle and hogs,
are different. Ruminants tend to produce relatively large amounts of wastes
when compared with the amount of feed consumed. These wastes have
compositions different from wastes of simple-stomached animals. Urinary
wastes from herbivores tend to be more alkaline because diets are high
in compounds such as potassium, calcium, and magnesium. The bacteria
in the stomachs of ruminants utilize cellulose feeds. There are, however,
certain compounds such as lignin which accompany cellulose in plants
and which are difficult to digest in the rumen (Blosser, 1964).
Animals in confinement are fed a ration formulated to cause the
greatest weight gain in the shortest time. Highly efficient feed consump-
tion by the animal is required for continuous and rapid weight gain.
Wastes produced under these circumstances will contain more pollution
material than wastes produced by animals in which weight gain is less
important. When the nutritive content of a ration exceeds the optimum
Table 1. — Suggested Values for Manure Defecation Rates, per 1,000 Pound*
Live Wetghl in Confinement Animal Production (Farm Animal Watte* —1969)
Dairy Beef
cattle cattle
Raw manure (RM), Ib. per day.
Total solids (TS), Ib. per day. , .
Total solids, percent RM
Volatile solids (VS), Ib. per day.
Volatile solids, percent TS
BODs, Ib. per day
BOD*, Ib. per Ib. VS
BODj per COD, percent
Nitrogen, percent TS
Phosphoric acid, percent TS . . .
Potassium, percent TS
88
9
10
7
80
]
16
... 4
1
1
.2
.7
233
1
7
60
6
10
4.
80
1 .
9.
8
5"
252
8
Hens Pigs Sheep
59
17
30
12
74
4
28
11
.4
.9
.4
.338
.5
50
7
14
5
82
2
33
5
2.
1.
.2
.4
.9
.1
.363
6
,5
,4
37
8.4
22.7
6.9
82
.7
.101
1 Values (or beef were estimated by the authors.
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AEROBIC TREATMENT OF LIVESTOCK WASTES
LIVESTOCK MANURE
(ORGANIC MATTER)
DRY MATTER WATER
(SOLIDS)
VOLATILE NONVOLATILE
(ORGAN IC) (INORGANIC, FIXED, ASH)
BIODEGRADABLE NONBIODEGRADABLE
Components of livestock wastes important to biological treatment. (Fig. 1)
level, an animal will excrete more of the nutrient material. For example,
if the level of protein feeding is raised beyond a certain point, the protein
is less effectively digested and more passes into the feces (Loehr, 1968).
The composition of animal manure is dependent upon the animal's
environment and its level of productivity. Additives such as antibiotics,
copper, arsenic, grit, or sand in the feed also affect the biochemical proper-
ties and the physical characteristics of the manure (Loehr, 1968).
Livestock wastes added to oxidation ditches and aerobic lagoons are
often undiluted and do not contain bedding. There are only limited data
available on the properties of livestock wastes, so where possible the
livestock producer should have a sample of his specific waste analyzed
before constructing a waste treatment facility. The properties in Table 1
may be used when this is not possible (Farm Animal Wastes-1969). Also,
Figure 1 shows livestock waste components, and it may be helpful in
the following discussions of treating wastes biologically.
THEORY OF AEROBIC TREATMENT
Heterotrophic microorganisms need organic substrates as food to grow
either aerobicaJly or anaerobically, and livestock manure is a good food
source for many groups of bacteria. Aerobic bacteria (aerobes) require dis-
solved oxygen for metabolism, using oxygen as a hydrogen acceptor.
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Anaerobic bacteria use other hydrogen acceptors, such as sulfate and
carbon dioxide. Another group of microorganisms are facultative and
they gain energy by either the aerobic or anaerobic pathway. By either
route, the bacteria must have available carbon, nitrogen, and a supply of
various trace nutrients in the substrate. They must also be in an environ-
ment with a satisfactory pH and temperature.
Aerobic treatment for the removal of biodegradable organic matter from
liquid wastes is an odorless process and consists of two phases operating
simultaneously. One phase is biological oxidation that has by-products
such as carbon dioxide and water and it yields energy. The second phase
utilizes the energy from the oxidation phase for synthesis of new cells, as
shown by the following simplified equation: microbial'cells + organic
matter + O2 —> GO2 + H2O + NH3 + more cells. Oxygen must be sup-
plied continuously and the amount required depends on the quantity of
biochemical oxygen demand (BOD). Only that fraction of the wastes
which has been oxidized can be considered stabilized. The synthesized
microbial cells are not in the most stable form, but can be settled and
separated from the system if desired. Even with long detention times,
there will be in the system solids residue build-up (sludge) that must
ultimately be disposed of. The sludge accumulation rate in a municipal
activated sludge system is about 11 percent of the BOD removed per day
(Stewart, 1964).
BOD REMOVED
SOLIDS
DESTROYED BY
DIGESTION
VOLATILE
SUSPENDED
SOLIDS
OXYGEN CONSUMED
DETENTION TIME
RESIDUAL SOLIDS
FOR DISPOSAL
OXIDATION
AND
ENDOGENOUS
RESPIRATION
SYNTHESIS
TIME OF AERATION
The aerobic metabolism process.
(Fig. 2}
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AEROBIC TREATMENT OF LIVESTOCK WASTES 7
In a suitable environment (unlimited food supply, sufficient oxygen, and
so on) aerobic bacteria have a cycle that begins with a period of accli-
matization; then they reproduce at an exponential rate (logarithmic
growth period) as shown in Figure 2. During this period, the consumption
of oxygen increases sharply, food substrates (organic wastes) are oxidized,
and the mass of cells increases. An important parameter is the food-to-
organism ratio (F:M) and this is approximated by the pounds of BOD8
applied per day per pound of volatile suspended solids (VSS) in the
treatment plant (Ib. BODtt/day/lb. VSS) (Symons and McKinney, 1958).
The rate of reproduction and oxygen consumption drops if the suitable
environment is altered by such factors as depletion of the food or oxygen
supply or a buildup of toxic products, or when space for growth dimin-
ishes. The final stage of the cycle is endogenous metabolism wherein low
levels of oxygen and nutrients are needed. As available nutrients diminish
below the level needed for survival, then energy or other factors in the
environment become unsatisfactory for maintenance of life, and the
cells disintegrate, releasing nutrients for the survivors.
The complete bacterial cycle occurs when the system is batch fed.
However, if nutrients are supplied continuously, the cycle is in a con-
tinuous process with all phases occurring simultaneously. The predomi-
nance of any particular phase will depend upon the operation of the
particular system.
A maintenance of one to two milligrams per liter of dissolved oxygen
(D.O.) in the liquid wastes is sufficient to maintain aerobic conditions.
The air rate supplied for aerobic digestion is usually not a critical
parameter where air is used both as the source of agitation and for
microorganism growth, since experiments with municipal wastes have
shown that the air requirements for oxidation are usually small compared
with the amount of agitation needed to keep solids in suspension.
LABORATORY STUDIES ON AEROBIC TREATMENT
OF LIVESTOCK WASTES
Some form of aerobic treatment of livestock wastes appears certain to
be used in the future in animal production enterprises. Odor control alone
may be sufficient to make it a feasible operation. However, there are other
advantages that may add to its demand. Some of these are: (1) partial
decomposition of volatile (organic) solids into water and odorless gases
such as carbon dioxide, (2) destruction of most pathogenic organisms, (3)
reduction in the pollutional characteristics of the wastes, i.e., the lowering
of the oxygen demand, and (4) concentration of the minerals which may
be more readily applied to land by some system.
-------
In an effort to determine the effects of various aerobic treatment
methods and procedures, several laboratory experiments have been con-
ducted at the University of Illinois at Urbana-Champaign and at Purdue
University. These are briefly summarized under the following types of
livestock wastes.
Swine Wastes
Aerobic digestion of swine manure has been studied since 1964 at the
University of Illinois. The first laboratory study used batch loading and
resulted in a recommendation for an aerobic digester of 6 cubic feet of
liquid per 150-pound hog (Irgens and Day, 1966). This volume recom-
mendation is inversely proportional to a loading rate given as pounds of
daily BOD5 per unit volume of digester. It was also found that 2,500 cubic
feet of air was required per pound of BOD5 at 3 percent efficiency of oxygen
utilization.
In the laboratory treatment system, better results were obtained with
daily loading than when loads were added at weekly intervals. Thus, the
authors concluded that odorless aerobic treatment could be obtained under
the self-cleaning slotted floors of a confinement building by connecting the
ends of the liquid-manure gutters and adding a rotor aerator. This oxi-
dation ditch would keep the solids suspended, circulate the liquid manure,
and add oxygen. The first field tests in the fall of 1966, using volumes of 6
cubic feet per hog, however, gave poor performance and produced excessive
amounts of foam — indicating that more laboratory work was needed.
Further laboratory studies, using volumes comparable to 6, 8, 10,
12, 16, and 20 cubic feet per finishing hog (based on BOD5 of the waste
from a 150-pound hog) were designed by Jones et al. (1969B). The
earlier laboratory study used swine manure strained through one-eighth-
inch-mesh wire screen to remove grain particles, and this was diluted be-
fore being added to the digester. The waste in the second study was merely
collected and added to the digesters daily, with no prior straining or dilu-
tion. The volume was kept constant by drawing off a volume equal to the
volume added each day.
At the beginning of the study, waste from the liquid-manure pit under
a hog-finishing building was collected and frozen. The BOD5 (seeded) of
the waste was 17,500 milligrams per liter, the ultimate BOD was 54,000
milligrams per liter, and the BOD rate-constant (to the base e) was 0.08.
From this second laboratory study, the following observations were
made:
1. The digester with a volume of 6 cubic feet per hog consistently
foamed for two to three hours after its daily feeding. By the third week,
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AEROBIC TREATMENT OF LIVESTOCK WASTES
H.20
9.6O
a s.oo
6.40
g
o
> 4.80
3.20
1.60
OXYGEN UPTAKE
(LABORATORr EXPERIMENT-8/II/68)
DIGESTER 2 « 58.87 MG/L/MR
DIGESTER 3 » 45.36 MG/L/HR
DIGESTER 4» 29.11 M6/L/HR
DIGESTER 5 * 34.80MG/L/HR
DIGESTER 6 * 22.22 MG/L/HR
0 80 160 240 320 400 480 560 640 720
TIME (SEC.)
Oxygen uptake rates for the mixed liquor in the laboratory digesters after
13 weeks of operation. (Fig- 3)
it was obvious that this digester was heavily overloaded. Its operation was
discontinued.
2. After 13 weeks, the digesters had mixed-liquor BOD5's of 2,500,
2,400, 1,700, 2,100, and 1,700 milligrams per liter and supernatant BOD5's
of 45, 65, 40, 70, and 50 milligrams per liter, respectively, for volumes
of 8, 10, 12, 16, and 20 cubic feet per hog. Mixed-liquor BODB reductions
varied from 82 to 86 percent, with the volume of 12 cubic feet per
hog being the most efficient. The mixed-liquor total solids level after 13
weeks ranged from 2.1 percent at a volume of 8 cubic feet per hog
to 1.7 percent at a loading rate of 20 cubic feet.
3. After 13 weeks of operation, the digesters had oxygen uptake rates
of 59, 45, 20, 35} and 22 milligrams per liter per hour respectively for
volumes of 8, 10, 12, 16, and 20 cubic feet per hog (Fig. 3).
In contrast with the first laboratory study at the University of Illinois
(where the waste was strained before treatment), these results indicated
that volumes of 6 cubic feet or less per hog were not suitable for in-
the-building, oxidation-ditch treatment because of the serious foaming
problem. However, volumes of at least 8 cubic feet per finishing hog
resulted in good treatment and no serious foaming.
-------
10
100
o
H-
Q
111
-------
AEROBIC TREATMENT OF LIVESTOCK WASTES
11
CO
S 60r
40
u_ 30
o
| 20
o
a 10
K
VOLATILE SOLIDS REDUCTION
6 WEEKS
29
24
19
as
4%
3%
2%U 2%
1%
1/2%
VOLUME ADDED DAILY
Reduction of volatile solids in the chambers after six weeks of aeration. (Fig. 5)
added daily. The decomposition percentages of the volatile solids at the
end of six weeks and 24 weeks respectively are shown in Figures 5 and 6.
A plot of the trend throughout the 24-week period of the chamber to
S VOLATILE SOLIDS REDUCTION
j
0)
^50
h-
J40
0
£30
z
o
gio
a:
# 0
r 24 WEEKS
-
-
-
36
i
&3 40.8
I^^M
45.5
46.
IM^M
5
51
4%
1/2%
VOLUME ADDED DAILY
Reduction of volatile solids in the chambers after 24 weeks of aeration. (Fig. 6)
-------
12
BUILETIN 737
i
d I0°
to
UJ
U.
O
80
60
40
o 20
o
UJ
°= 0
DEGRADATION OF DAIRY CATTLE MANURE
46.5%
29%
42
77
182
TIME IN DAYS (TOTAL)
Reduction of volatile solids in the chamber with a daily loading of 2 per-
cent by volume throughout the experiment. (Fig. 7)
which 1 percent was added daily is shown in Figure 7; the 1 percent per
day rate is equivalent to the addition of 2.52 grams of dry matter per day.
Using the dry-solid basis, analysis of the solids after 24 weeks of aeration
for the 1-percent chamber was 25.6 percent ash, 2.65 percent nitrogen,
0.92 percent potassium, and 1.18 percent phosphorus. For the 4-percent
chamber the analysis was 18.3 percent ash, 2.06 percent nitrogen, 0.73
percent potassium, and 1.00 percent phosphorus.
An experiment to study the effect of temperature on the aerobic de-
composition of dairy cattle waste was conducted at Purdue University
(Bloodgood and Robson, 1969, and Robson, 1969). Aeration units at
temperatures of 4° C. and 24° C. were operated at loading rates of 60,
80, 100, and 120 grams of manure per day with an 85-percent moisture
content. Ground Holstein dairy cattle manure in slurry form was added
daily to each digester for 28 days.
Average reductions obtained were: for volatile solids, 42.3 percent
(at 24° C.) and 20.1 percent (at 4° C.); for COD, 53.6 percent and 24.5
percent; and for Kjeldahl nitrogen, 43.5 percent and 15.9 percent.
The following conclusions were drawn from these studies with aerobic
treatment of dairy cattle wastes.
1. The BOD0 may be reduced up to 98 percent if the wastes are di-
gested for a sufficient length of time.
2. Volatile solids can be reduced by 40 to 50 percent if the wastes are
digested for a sufficient length of time.
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AEROBIC TREATMENT OF LIVESTOCK WASTES
13
TEMPERATURE = 2 4 * C.
TIME (Days)
Comparison of the effect of two temperatures (4° C. and 24° C.) on volatile
solids reduction. (Pig- 8}
3. Temperature has an effect on decomposition rates and the final
decomposition obtained. At 4° C. about 20 percent of the volatile solids
of blended dairy cattle manure may be decomposed, as contrasted to a de-
composition of 43 percent at 24° C. (Fig. 8).
4. The breakdown of the volatile solids appears to be only slightly
affected by the higher loading rates.
5. Raw, unstrained cow manure does not decompose as rapidly as
manure from which coarse materials (stems, grains of corn, and so on)
have been removed.
Poultry Wastes
Ludington et al. (1969) conducted research to study hydrogen sulfide
production and degradation in the threshold between aerobic and
anaerobic treatment of chicken manure. The ORP (oxidation-reduction
potential) measurement responded to the presence or absence of aeration
and permitted continuous monitoring of conditions from aerobic to strictly
anaerobic. The ORP was incorporated into an automatic control system
to regulate aeration.
Tests were conducted with no aeration and with ORP controlled by
aeration at 0, -150, -300, and -400-millivolt (using a calomel electrode).
The tests were done in a room at 55° F. with daily feeding and no at-
tempt was made to control the pH of the chamber contents. Degradation
(reduction in volatile solids) of the waste is shown in Figure 9.
-------
14
«> REDUCTION OF VOLATILE SOLIDS
— ro o* * ui o>
o o o o o o o
DE
•
EGF
47.3
tm^^m
*ADA
TIC
36.6
•^^^•i
)N Of
i
r CHICKEN MANURE
39.3
35.3 35.9 |— |
OXIDATION REDUCTION POTENTIAL
Reduction in volatile solids of poultry manure as related to oxidation reduc-
tion potential. (Fig. 9)
Other tests were conducted to determine the time required for chicken
manure stored under controlled conditions of -350, -400, and -450 milli-
volts and no air to produce hydrogen sulfide after termination of aeration.
An average of only 12.8 cubic feet of air per day per chicken was required
to maintain an ORP of -400 millivolts and prevent the release of hydrogen
sulfide. Manure stored at -400 millivolts had a 35.9-percent reduction in
volatile solids. Chicken manure stored with aeration at zero ORP also
produced no hydrogen sulfide, but had a higher reduction of volatile
solids.
DEVELOPMENT AND MUNICIPAL USE
OF THE OXIDATION DITCH
The oxidation ditch was developed during the 1950's at the Research
Institute for Public Health Engineering (TNO) in the Netherlands as a
low-cost method of purifying non-pretreated sewage emanating from small
communities and industries (Pasveer, 1963). The oxidation ditch is a
modified form of the activated-sludge process and may be classed as an
extended aeration type of treatment. Aerobic bacteria use the organic
matter in the waste as food for their metabolic processes, thus reducing
the biologically degradable organics to stable material, with carbon dioxide
and water as byproducts.
-------
AEROBIC TREATMENT OF LIVESTOCK WASTES
I
TO DRYING BEDS
OR FIELDS
BAR
SCREEN
^SETTLED
^SLUDGE
-ROTOR
X
^OXIDATION
DITCH
RETURN
SLUDGE
PUMP
FINAL
SETTLING
TANK
SUPERNATANT
WATER
CHLORINATOR
,
EFFLUENT
INFLUENT
SEWAGE
A flow diagram of an oxidation ditch treatment plant for municipal wastes.
(Fig. 10)
The oxidation ditch is made up of two principal parts — a continuous
open-channel ditch, usually shaped like a race track, and an aeration rotor
that supplies the oxygen and circulates the ditch contents. A minimum
liquid velocity of about one foot per second must be maintained so that
the solids will be kept in suspension and will not settle out. Figure 10 is
a schematic drawing of a typical municipal treatment plant. Figure 11
Cage rotors for a municipal oxidation ditch. Rotor covers are removed.
(Photo courtesy of Lakeside Engineering Corp.) (Fig-
-------
II
A cage rotor in operation in an oxidation ditch in the Netherlands. Motor
cover raised. (Fig. 12)
shows typical cage rotors and Figure 12 shows one in operation. Berk
(undated) has summarized the principles of operation of the oxidation
ditch for sewage treatment.
The oxidation ditch is presently being used by several communities
in Europe and is being used to a limited extent in this country. The
oxidation ditch is only a part of the overall treatment process in a munici-
pal plant. There is normally no primary settling tank used; however,
the ditch is usually preceded by a bar screen to remove from the sewage
large floating debris which might damage the rotor. For the system to
operate at high efficiency of waste treatment, the sludge must have good
flocculating characteristics so that solids and supernatant can be separated
when quiescent conditions are provided (Fig. 13). Thus, the ditch is usu-
ally followed by a settling tank which allows the clarified effluent to
be drawn off and discharged into a water course after chlorination. In
many municipal treatment plants, the settling is accomplished by merely
shutting off the rotor for an hour or so and then drawing supernatant off
the top. Regardless of where the settling is done, the concentrated sludge
must still be disposed of. A large part of these sftlids actually consists of
bacterial cells (25 to 50 percent) and portions of the solids are always
retained in the ditch to help treat the incoming raw sewage. The oxidation
ditch is operated as a closed system and the net growth of volatile sus-
pended solids will increase so that it will be necessary to periodically remove
-------
AEROBIC TREATMENT OF LIVESTOCK WASTES
i^H
Separation of solids and supernatant after approximately 30 minutes of
quiescent conditions. (Fig. 13)
some sludge from the process. Removal of some sludge lowers the con-
centration in the ditch and keeps the metabolism more active. Excess
sludge may be dried directly on sludge drying beds or stored in a holding
tank or in a sludge lagoon for later disposal.
Because of the large volume of the aeration ditch and the fact that
suspended solids in the oxidation ditch are kept fairly high (4,000 to 8,000
mg./l.), the total amount of floe in the plant is from 10 to 30 times as
great as that in a municipal activated sludge plant. The rate of BOD5 load-
ing is correspondingly lower. Municipal oxidation ditches have a low F: M
ratio (about 0.05:1) compared with the ratio in municipal activated sludge
plants (about 0.5:1). It is evident that if a sufficient amount of oxygen is
provided at this very low loading rate, the floe will be in an advanced stage
of mineralization. As soon as there is a sufficiently high sludge content in
-------
18
the ditch, the operation should allow for regular removal of a quantity
of surplus sludge to maintain a constant suspended solids content. In
this manner, a suitable concentration of floe can be maintained and
excessive salt concentrations can be prevented. Pasveer (1960) makes
the following conclusions about the operation of an oxidation ditch:
1. The energy required for oxygenation will be greater than is the
case in a conventional activated sludge plant since the total quantity of
sludge in the ditch must be brought to an advanced state of minerali-
zation. However, the cost of the additional energy is still small compared
with the saving in capital costs.
2. The very large amount of floe in the system renders the process
insensitive to peak BOD-, loads.
3, It is to be anticipated that the purifying capacity of an oxidation
ditch will be even less susceptible to the influence of low temperature than
the conventional activated sludge process. Pasveer also states that in
the municipal oxidation ditch, the fresh sludge carried by the sewage and
the sludge formed in the purification process are mineralized to such an
extent that the surplus sludge can be dried without causing objectionable
odors. This means that a sludge fermentation tank is not needed. Further-
more, by selecting a suitable working method it is possible to avoid build-
ing a secondary sedimentation tank with a sludge return system. With a
loading rate of 89 cubic feet per pound BOD^, settled supernatant can be
removed from the ditch periodically in such a manner that all of the floe
(sludge) is retained in the system. According to Pasveer's observations in
municipal ditches, about 1 pound of dry sludge solids was produced for
every 2.5 pounds of BOD5 added to the ditch. The sludge had an ash con-
tent of 24 percent to 27 percent in the winter and 30 percent to 32 percent
in the summer.
The sludge taken from a municipal oxidation ditch dries to 10 to 12
percent solids after about one clay when spread four inches thick on a
sand bed (Pasveer, 1960). After six weeks, the sludge can be handled
with a pitch fork. If the soil is permeable under the sand beds, the
drying beds will not need to be drained. There are several alternatives
insofar as sludge disposal is concerned. The best method is probably to
place the sludge on the land to reclaim the fertilizer value from the waste.
The sludge may or may not be dried first. The physical structure of dried
sludge taken from a municipal oxidation ditch is greatly improved if
the sludge is left lying on sludge-drying beds throughout the winter. The
nitrogen content is high, about 6 percent of the dry solids, and the organic
matter is 65 to 75 percent of the dry solids.
Anaerobic digestion of the sludge from extended aeration has been tried
in municipal plants, both in digestion tanks and in lagoons (Pasveer, 1960),
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AEROBIC TREATMENT OF LIVESTOCK WASTES 19
The sludge does not decompose well, however, because of the high degree
of mineralization, as witnessed by the fact that only about half as much gas
is produced in the digestion of the sludge as compared with sludge from a
conventional activated sludge plant.
THE IN-THE-BUILDING OXIDATION DITCH
FOR LIVESTOCK WASTES
The success of the oxidation ditch in meeting the low-cost treatment
requirements of small communities has interested livestock producers.
The oxidation ditch may be a means of lessening anti-pollution pressures
from encroaching urban areas. In addition, the oxidation ditch appears
to meet the major requirements of a livestock waste treatment process:
decrease in labor requirements, reduction in volume of solids, reduction
of odors, and reduction of the pollution potential of the manure.
Approximately 200 oxidation ditches are now in operation in live-
stock buildings across the United States. Some of the reasons why the
oxidation ditch was selected over other possible treatment schemes are
as follows:
1. It is an odorless process, with the exception of small amounts of
ammonia at times and an earthy odor given off by the contents.
2. It has the ability to handle shock loads. Once the system is operating
properly, the ditch can absorb brief heavy loadings without upsetting the
biological process.
3. It fits well into the farmer's work schedule, requiring very little
attention or maintenance.
4. The process fits readily under the labor-saving slotted floor system,
eliminating extra pumping or hydraulic systems to move waste from where
it is produced to the treatment plant.
5. The oxidation ditch is a reasonably inexpensive process, both in
capital cost and in operating cost. The capital cost is low because the
manure collection gutter is usually already present and the only expenditure
required for the channel is to round the corners and connect the ends of
the gutter. Therefore, the main capital cost is the rotor itself, around
$300 per horsepower (including motor and drive) (Newtson, 1970).
The major operating cost would be the power source required to operate
the rotors (usually 2- to 5-horsepower motors).
Construction
The most common shape for a livestock oxidation ditch is in the form
of a race track (Fig. 14); however, several variations have been tried.
Probably any configuration could be used as long as a continuous loop
is maintained. However3 excess bends increase the frictional resistance
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20
"""— ROTOR
DITCH IS COVERED WITH
LIVESTOCK, SLOTTED FLOOR
Common shape of a livestock oxidation ditch made by dividing a manure
collection gutter. (Fig. 14)
and can retard the flow. A median width of 16 feet or greater is main-
tained in most municipal plants. For the sake of economy and because
of existing conditions, a median strip this wide is seldom used in live-
stock operations and 180-degree turns are common. Observations indicate
that the eddy currents caused by 180-degree turns may affect the flow after
the liquid passes the turn. Where such sharp bends do exist, it may be
necessary to install deflector vanes around the corners. However, solids
often settle out in the channel opposite the rotor after the flow has left
the deflectors. At any rate, the deflectors do prevent settling at the ends
of the channels, but more research is needed to lower the flow resistance
at corners. Also, better flow is obtained if the rotor is located in the middle
one-third of the straightaway rather than near a sharp turn.
Most livestock ditches are completely lined with concrete; however,
asphalt, plastic, and rubber liners may be used where the sides are sloped.
When the ditch is located under a slotted-floor building, the sidewalk
are generally vertical and lined with concrete.
There are two methods of discharging waste from the oxidation ditch —
batch or continuous flow. If the system is the batch-discharge type, mixed
liquor is allowed to accumulate in the ditch as raw waste is added. Then
the mixed liquor is removed periodically by pumping. The depth of the
liquid in the ditch is usually varied in this type of operation and requires
that the rotor be raised at intervals to prevent it from being too deeply
immersed. This requires some management and time on the part of the
operator, and livestock producers usually bypass it in favor of the continu-
ous-discharge method. With this method the liquid level is controlled
by an overflow and remains constant. The rotor is operated continuously
at a constant immersion depth. Most livestock producers prefer to simply
let the mixed liquor in the ditch overflow and discharge by gravity into
a lagoon or holding tank.
Start-Up
To start the aerobic process in the oxidation ditch, the empty manure
channel should be filled to the desired operation level with tap water.
The rotor can then be started at the desired blade immersion. Foaming is
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AEROBIC TREATMENT OP LIVESTOCK WASTES 21
often a problem during start-up. Initially, with a small microbial mass
in the ditch, there will be certain surface-active materials in the manure
which will not be readily metabolized and foam may result. This foam
is a very light fluffy type and can be controlled with antifoam agents
such as vegetable oil, petroleum oil, and various commercial products.
It can also be controlled with a water spray. Once the microbial population
increases to around 2,000 milligrams per liter of suspended solids, the
start-up foaming should subside (Day and Converse, 1967).
If possible, animals should be added gradually to the production
unit. After a few weeks of operation, the ditch can then be loaded to
design capacity. Another option would be to pump activated sludge from
an operating plant into the ditch to be started. Based on data obtained at
the University of Illinois, a continuous-discharge ditch may take up to
12 weeks to become acclimated to the waste loading (Day et al., 1969).
Therefore, it would seem that the ditch should probably never be com-
pletely flushed out, but rather a portion of the ditch contents should be
replaced with tap water when the solids or mineral concentration becomes
too high. At least 10,000 milligrams per liter of volatile suspended solids
should be maintained in the ditch when the ditch is in full operation.
It should be emphasized here that an oxidation ditch should never
be started when septic manure is in the ditch. This situation can give rise
to extremely dangerous gases, foaming, and odors. In general, when ma-
nure has been allowed to stf.nd in an oxidation ditch without aeration for
more than three days, at least half of the contents of the ditch should be re-
moved and replaced with tap water before starting the rotor, and even then
extreme caution should be taken to provide adequate ventilation for
animals and humans in the building. All ventilating fans should be
operating and doors should be left open for about 24 hours after starting
the rotor. If there is any doubt as to whether adequate ventilation can
be obtained in the building when the rotor is started, the animals should
be removed. Several animals have died in the last few years from gases
during agitation of septic manure, and also from foam inundation.
Operational Problems
The oxidation ditch is probably the simplest and easiest to maintain
of all waste treatment systems in use today. However, no waste treatment
plant is maintenance free. Every system must have regular maintenance
and good management if it is to function properly over an extended
period of time. The most critical period of operation for sftiy biological
system is start-up. Start-up problems were discussed above and will only
be mentioned here.
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22
If adequate oxygen is not maintained in the ditch, anaerobic bacteria
will develop and produce end products which are quite obnoxious and
odorous. Some anaerobic end products are also surface active so that
foaming usually accompanies the odor. Although it can be controlled
temporarily with antifoam agents, the foam is best controlled by adding
adequate oxygen to the ditch contents. If the mechanical system cannot
supply the needed oxygen, relief may be obtained by adding a hydrogen
acceptor such as ammonium nitrate or sodium nitrate (McKinney and
Bella, 1967). Once the system is completely aerobic, the foaming will
subside.
Some ammonia is often given off as urine drops into the ditch. In
a properly operating ditch, nitrification will convert the ammonia to ni-
trates. If the rotor is adding insufficient oxygen to the waste, the ammonia
may be liberated to the atmosphere. A slight odor of ammonia will
always be present in a building because of urine splashing against the slats,
but a strong ammonia odor may be a sign of insufficient oxygen in the
ditch.
Settled solids can be a nuisance to ditch operation. Not only do they
reduce the effective dilution of incoming wastes, but they may undergo
anaerobic decomposition and create foaming problems. Care should be
taken in the hydraulic design of the system to prevent solids accumulation
in the bottom of the ditch (see the section on ditch velocity).
McKinney and Bella (1967) tell of one of the operational problems
experienced at the Paul Smart farm, where the system was apparently
aerobic but was foaming significantly. It was found that solids were
settling out in the corners just before the rotor. These solids underwent
anaerobic decomposition and released their surface-active end products
to the upper water. Adequate oxygen prevented odors, but the material
hit the rotor before it could be metabolized and foaming resulted.
Removal of the settled solids eliminated the problem. McKinney and
Bella also state that "at no time has foaming ever been noticed except
at start-up and with anaerobic conditions. Foaming may be the best
indicator of trouble somewhere in the system." Also, cleaning detergents
and disinfectants must be used with discretion, as excessive amounts in the
ditch can cause foaming and other problems. Not only is foaming
an indication that the ditch is not treating the waste properly, but the
foam may rise up through the slats and endanger penned animals. There
have been reports of animal suffocation caused by oxidation ditch foam.
J. Stevenson has developed a foam switch as a safeguard to be installed
underneath a slotted floor. If foam rises to slat level, the switch stops the
rotor. This switch is available from Thrive Centers, Inc., Fairbury,
Illinois.
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AEROBIC TREATMENT OF LIVESTOCK WASTES 23
Oxidation ditches are simple in construction and operation. The
major problem in their operation is with the rotor bearings. It is essential
that the unit be easy to remove so bearings can be replaced. During normal
operation, the bearings must be lubricated at least once a week. Another
problem lies in the drive between the motor and the rotor (McKinney and
Bella, 1967). The belt drives have a tendency to absorb the shock of blade
contact with the water better than chain drives. It appears that the belts
slip slightly with each impact with a net result of less wear on the equip-
ment. The two major manufacturers of livestock oxidation ditch rotors
agree and have replaced all chain drives with belt drives.
Very little information is available concerning evaporation from an
oxidation ditch. An awareness that evaporation occurs is important to
the operator so he can determine the volume of ditch overflow and the
amount of salt buildup in the ditch. No doubt evaporation is increased
by the rotor throwing water into the air, since this will increase contact
between air and water; however, the amount of increase is not known.
In a beef confinement building at the University of Minnesota, Moore
(1968) found that make-up water had to be added to the oxidation ditch
to maintain the desired liquid depth, Those tests were run at ditch volumes
of 140 and 210 cubic feet per steer. Assuming a BOD5 production of 1.3
pounds per steer per day, this indicated 118 and 162 cubic feet of ditch
liquid volume per pound of daily BOD5 .respectively. Moore pointed out
that the ditch was about 75 percent exposed to the outside atmosphere
which possibly affected the evaporation rate.
Overflow did occur from a beef unit at the University of Illinois
where a volume of 50 cubic feet per 1,000 pounds of animal was tested
(Jones et al., 1969D). McKinney and Bella (1967) reported the need for
overflow collection basins for enclosed swine units where volumes of ap-
proximately 40 to 50 cubic feet per pound of daily BOD5 were tested
(computed by authors on basis of information given). It seems probable
that the amount of liquid lost by evaporation at the rotor will be less than
the manure added in most installations. However, since evaporation
tends to concentrate solids, make-up water may be necessary to maintain
a desired concentration of solids in the ditch.
Effect of Cold Climate
Even though locating the rotor inside causes increased moisture in the
building due to evaporation at the rotor, tjie advantages of this outweigh
the disadvantages of having the rotor outside. Where the rotor is exposed to
the weather, ice buildup can shut the rotor down during the winter. Rotors
can usually run year-round in all climates when placed inside the building.
The temperature in the animal unit is usually high enough to prevent any
serious icing problems.
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24
ROTOR
SOLID FLOOR
SCRAPED TO -0
OXIDATION DITCH
AGRICULTURAL ENGINEERING
UNIVERSITY OF MINNESOTA
ROSEMOUNT EXPERIMENT STATION
Oxidation ditch and buildings for beef cattle at the University of Minnesota,
Rosemount Experiment Station. (Fig. 15)
Ice formation in the ditch has been reported in beef operations in
Minnesota and Illinois, Studies at Minnesota by Moore et al. (1969) indi-
cate the oxidation ditch system can successfully treat beef cattle waste
in climates which experience extended periods of sub-freezing temperatures
even with about 75 percent of the ditch exposed to outdoor temperatures
(Fig. 15). Foam production was experienced on several occasions in
cold weather, and was often great enough to be a limiting parameter.
In one field trial in November, December, and January, the monthly
average waste temperature in the ditch was 36.8° F. An ice layer up
to 1 inch thick formed over part of the ditch. In one part of the ditch
the foam was found to freeze and provide an insulation blanket. A high
liquid velocity of 1.2 to 2 feet per steer was maintained in the ditch and
probably minimized the icing problems.
In a beef cattle unit at the University of Illinois at Urbana, up to
two inches of ice have been observed in the channels opposite the rotor
when the outside temperature dipped to 5° or 10° F. for a week (Jones
et al., 1969D). The velocities in this ditch, although not known exactly,
were not as great as in the Minnesota study. The insulation properties
of ditch foam that Moore et al. reported were observed in two sections
of this ditch.
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AEROBIC TREATMENT OF LIVESTOCK WASTES 25
Besides the mechanical operational problems mentioned above, there is
some evidence that biological activity in the ditch is also influenced by
cold climates. Pasveer (1954) reports difficulty in developing a good
quality of floe in the start-up of a municipal activated sludge plant at
temperatures of 7° to 9° C. At this temperature the nitrification process
begins slowly if at all. After the temperatures had risen to 13° C., there was
no difficulty developing a good quality of floe.
It may be concluded that an oxidation ditch will be able to continue
operation throughout the winter months when a small amount of ice is
present, although with slightly less efficiency. Efforts should be made in
cold climates to construct livestock buildings so they can be closed during
the winter, using minimum ventilation. This should conserve the heat
produced by the livestock and prevent the oxidation ditch contents from
freezing.
Microorganisms, Nitrification, and Denitriflcation
Researchers have found that oxidation ditches soon establish the
needed microbial populations even without seeding. McKinney and Bella
(1967) claim the major bacterial group that grows in the activated
sludge process is composed of common soil bacteria that easily enter the
system, many from the manure itself. They also noted that pathogens will
not grow in the oxidation ditch and will eventually die out unless they are
in the form of spores which can remain dormant. They found that bacteria
are the major microorganisms stabilizing the organic matter in the manure,
but protozoa and rotifiers also grow readily. Protozoa are very sensitive to
the lack of dissolved oxygen and will die within a few hours under
oxygen-deficient conditions. Likewise, stalked ciliates and rotifiers are
always present in a well-operated system. They help control the bac-
terial population and thus are useful in determining the extent of
treatment of the waste.
Baxter et al. (1966) found in their oxidation ditch trials with finishing
pigs that the biological activity varied widely. The numbers of protozoa
present in the supernatant liquor during a period of typical activity were
of the order of 20,000 per milliliter. Although the area around the
ditches was generally untroubled by insects, there was one short period
when a number of hover flies were present and their larvae were later
present in the oxidation primary ditch.
Nitrification is important in livestock oxidation ditches because it
prevents the release of ammonia into the building atmosphere. Nitri-
fication is the bacterial process of converting ammonia into nitrates, i. e.
nitrifying cells + NH3 + O2 (viaNCH NO3 + H2O + more nitrifying cells
-------
26
(Simpson, 1960, p. 5). Below a pH of 7 ammonia is in a combined
state and not readily released, but ammonia release increases with in-
creases in pH above 7.
Under aerobic conditions the nitrite formers convert ammonia to
nitrites. The nitrate formers then oxidize nitrites to nitrates. However,
under anaerobic conditions, nitrates and nitrites are both reduced by
a process called denitrification which liberates some .nitrogen gas to the
atmosphere.
Nitrification-denitrification can occur simultaneously in an oxidation
ditch. Nitrification occurs immediately downstream from the rotor where
excess dissolved oxygen (D. O.) is present. As the mixed liquor moves
around the ditch, D. O. is used up. In the absence of D. O., denitrification
can occur and prevent odorous conditions from developing until the
nitrates are used up. Of course, it would be a delicate design that would
operate in the nitrification-denitrification cycle and have the mixed liquor
reach the rotor for re-aeration just as the nitrates are used up. For the most
part, oxidation ditches operate with excess D. O. However, Scheltinga
(1966) performed experiments in the Netherlands that showed nitrification
caused ammonia nitrogen to be oxidized to nitrates, but a lack of nitrates
in the effluent indicated that denitrification was occurring.
McKinney and Bella (1967) report from their study in a farrowing
house that initially metabolic reactions converted much of the nitrogen in
the urine to ammonia, and some ammonia was released to the atmo-
sphere at the rotor since the pH of the mixed liquor was high (above 8).
Eventually, nitrification converted the excess ammonia to nitrates in the
presence of D. O. The data from the farrowing house indicated that
most of the nitrogen in the mixed liquor was tied up as organic nitrogen
in the form of microbial cells. A small portion existed in the ammonia
form, while a larger portion existed as nitrates. The most important
fact, however, was that the majority of the nitrogen was tied up with
the solids (sludge).
The release of some ammonia is typical during the^ first several weeks
of operation of a livestock oxidation ditch. This occurs until nitrifying
bacteria develop to complete the nitrification process of converting am-
monia to nitrates. A mixed-liquor pH slightly above 8 is also typical.
Sludge Accumulation
Not all livestock oxidation ditches have facilities for separate sludge re-
moval and in some cases it is not necessary if sufficient solids are being
removed in the overflow. A ditch in a farrowing house located south of
Fairbury, Illinois, operated for 2!/2 years with only mixed liquor overflow.
When sampled in July, 1969, the inorganic solids were about 27 percent of
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AEROBIC TREATMENT OF LIVESTOCK WASTES 27
,SLUDGE TRAP SLOTTED FLOOR BUILDING
. , X OVER OXIDATION DITCH
DISCHARGE-^-
An oxidation ditch with a sludge trap that utilizes the pressure differential of
the liquid immediately upstream and downstream from the rotor. (Fig, 16)
the suspended total solids, but the ditch was satisfactory with no odor and
a reasonably low BOD5 (mixed-liquor BOD5 was 3,000 milligrams per
liter).
The addition of a sludge trap should prolong the operation of the
system indefinitely. This would reduce the problems of poor treatment
and foaming during start-up procedures, since it would be started only
once. Sludge traps may be constructed along the side of the ditch channel
utilizing the pressure differential of the liquid upstream and downstream
from the rotor (Fig. 16). The trap is merely a small compartment through
which the flow rate can be controlled. The velocity in the trap is consider-
ably less than the velocity out in the channel so that solids are deposited
in the trap.
The particle size and amount of sludge to be removed can be con-
trolled by varying the size of the inlet and outlet of the trap, and there-
fore varying the velocity through the trap. The sludge collected must be
removed fairly often if the unit is to function properly. In municipal
plants this is usually accomplished with a small electric pump operated
on a time clock to pump the sludge to drying beds several times daily.
Something of this nature would be needed in a livestock ditch if it
were to be operated for an indefinite period; the procedure, however,
could be simplified somewhat, depending on the particular setup. The
trap would probably need to be operated only a few days a month since
some sludge is being removed continuously with the mixed-liquor effluent.
Possibly the inlet and outlet to the trap could be closed and the contents
emptied entirely. The sludge could be disposed of in the same manner
as the mixed-liquor overflow from the ditch. The mixed-liquor suspended
solids concentration in the ditch should be maintained between 10,000
and 20,000 milligrams per liter. Actually, the sludge trap is needed only
to maintain this level of floe in the ditch.
There is no research reported in the literature as to the best position
along the ditch for the sludge trap. Positions at one end of the channel or
-------
A 16-inch diameter rotor that operates at about 200 r.p.m. (Photo courtesy
of Fairfield Engineering and Manufacturing Co.) (Fig. 17)
in the straightaway just after the flow passes the rotor have been used
with about equal success. Since the rotor creates an inch or so of hydraulic
head, the inlet to the sludge trap can be placed in the ditch just after the
flow passes the rotor. If the outlet is then placed on the upstream side
of the rotor, flow should occur just opposite in direction to the flow in
the ditch proper. The small head will result in a low velocity and will
therefore cause settling. A simple method of removing excess solids may
be to dilute the ditch volume with water by one-third to one-half when
the concentration of solids becomes too high, thus flushing out solids with
the overflow.
Dale and Morris (1966) reported that an oxidation ditch operating
as a batch system with dairy cattle manure concentrated the minerals
and salts in the waste by about 80 to 100 percent. With the exception of
nitrogen lost to the air, practically all of the nitrogen, phosphorus, and
potassium in the incoming manure is contained in the oxidation ditch
effluent (Morris, 1966). It seems probable that the phosphorus and potas-
sium will be concentrated during the treatment process because of the nor-
mal evaporation which occurs in an oxidation ditch.
The concentration of nitrogen in the ditch will vary since some am-
monia or nitrogen gas may be given off, depending on whether nitrification
and denitrification take place in the ditch, Scheltinga (1966) measured the
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AEROBIC TREATMENT OF LIVESTOCK WASTES
29
A 27'/4-inch-diaineter rotor that operates at about 100 r.p.m. Front splash
cover removed. {Photo courtesy of Thrive Centers, Inc.) (Fig. 18)
nitrogen in the sludge as 6 to 9 percent of the dry matter. He also
measured sludge growth as 18 percent of incoming BOD5
The percent of ash in a livestock ditch may not be as high as in
a municipal ditch because of nonbiodegradable organic matter from undi-
gested feed particles in the livestock waste. However, ash contents from
20 to 25 percent are often obtained. Raw manure usually contains about 15
to 20 percent ash.
Rotors, Oxygcnation Capacity, and Liquid Transport
The oxidation ditch uses a cage rotor to aerate and move the liquid
around the ditch in a closed circuit so that the liquid passes the rotor at
regular intervals to renew its oxygen supplies. Cage-rotor aerators in
common use today are from 26 to 36 inches in diameter, although one
rotor being produced for agricultural applications is 16 inches in diameter
(Fie 17) (Linn, 1966). Cage rotors usually consist of approximately 12
blades radiating from and rotating about a horizontal axis, and the blades
are of a staggered-tooth design, with the teeth on successive blades occupy-
ing the voids in the preceding blade (Fig. 18). Blade design, oxygen
transfer and liquid propulsion capabilities vary from rotor to rotor
(Agena' 1968). Common rotation speeds are from 60 to 120 r.p.m.,
although speeds of up to 200 r.p.m. are being used. The length of the
rotor required will depend on the required oxygenation rate, the required
liquid velocity, and the channel configuration.
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30
The two main factors affecting oxygenation by rotor aeration in oxi-
dation ditches are rotor speed and rotor immersion. Where a biological
mass is present to exert an oxygen demand on the oxygen supply, the rate
of recirculation of the liquid is also important.
Five different cage rotors were tested by Jones et al. (1969C) in
manure gutters in livestock buildings. The rotors added from 1.3 to 1.9
pounds of oxygen per hour per foot of rotor at 6-inch immersion and
100 r.p.m. operating in a liquid depth of 25 inches. Based on the results
of ditch tests in finishing-pig buildings, it was concluded that although
immersions as high as 12 inches gave good results in tap water, much
less mechanical trouble was experienced when rotor immersion was limited
to around 6 inches.
Jones et al. also found that, as a general rule, adequate velocity and
oxygenation occurred when the immersion of the aeration rotor in the
waste was equal to approximately one-fourth to one-third of the liquid
depth. For instance, when the ditch contains 18 inches liquid, the rotor
immersion should be 4'/2 to 6 inches. When the rotor immersion is less
than this, some sedimentation may occur in the bottom of the ditch.
Therefore, if a 27I/2-inch-diameter cage rotor can be operated at a
maximum immersion of around 8 inches, the maximum liquid depth in the
manure pit would be around 32 inches, and preferably less than 24 inches,
to maintain proper velocity in the ditch. The actual ditch cross-section
can be calculated using the pumping capacity of the rotor.
Jones et al. (1969C) pointed out that rotor aeration efficiency increased
almost linearly with rotor speed and rotor immersion. The same type
of rotor was tested in two separate ditches having different lengths and
widths of channels, but the same depths. They found 30 percent variation
in the oxygen-uptake efficiency with the two different ditch configurations
tested. Figure 19 shows the oxygenation capacity for a rotor manufactured
by Thrive Centers, Inc., and tested in a ditch 5 feet wide and 64 feet
long (one way). These values, after being corrected for use in livestock
installations, will be used in the design criteria to be presented later in this
bulletin.
The main functions of an oxidation ditch rotor in addition to oxy-
genation is circulation of the liquid to keep solid particles in suspension
and to distribute oxygenated liquid throughout the ditch. Liquid trans-
port is often the limiting factor in the design of a rotor, even when
adequate oxygen is being added. The liquid velocity required in rotor-
aerated ditches depends on the weight, size, and number of waste particles
in suspension circulating through the ditch. Velocity is determined by
rotor and ditch configurations, liquid properties, ditch lining charac-
teristics, and rotor speed.
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AEROBIC TREATMENT OF LIVESTOCK WASTES
31
I-' (.50
U.
of
1.25
O
ffi
1.OO
Q.
O O.75
0.50
UJ
O
i
0.25
OXYGENATION CAPACITY
FOR
IN - THE-BUILDING OXIDATION
DITCH ROTOR
STANDARD CONDITIONS I 20' C, ATM. PRESS., CLEAN TAP WATER
ROTOR DIAMETER : 27{ IN.
ROTOR LENGTH : 46 IN.
TYPE OF BLADE I RECTANGULAR - 2^ X 6 IN.
INTER SPACE ! I $ IN.
POSITION OF BLADES ! STAGGERED
DITCH : ^340 GALLONS-Z4 IN. DEEP
DRIVE : DODGE 3-HP. MOTOR
ROTOR SPEED : 100 R.P.M.
BLADE IMMERSION (IN.)
Oxygenation capacity of a cage rotor manufactured by Thrive Centers, Inc.,
operating at standard conditions in tap water (Jones et al., 1969G). (Fig. 19)
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32
Very little research concerning liquid velocity required for solids suspen-
sion in oxidation ditches has been published. Pasveer (1963) found that
some sludge deposition occurred in municipal ditches when liquid velocities
were less than 1 foot per second in the middle of the ditch. On the other
hand, Babbit and Baumann (1958) state that a velocity of at least
0.5 feet per second will keep most organic matter in suspension. Knight
(1965) found that 0.5 feet per second was adequate to pick up and suspend
waste particles lying on the channel bottom. When suspended solid con-
centrations are as high as 20,000 milligrams per liter in livestock ditches,
then a minimum surface velocity of 1.25 feet per second appears necessary
(Day and Jones, 1970).
Knight (1965) measured velocities in an oxidation ditch with a
trapezoidal cross section 4 feet deep, 4 feet wide at the bottom, and 14
feet wide at the top. The ditch was 105 feet long with an 8-foot-wide
median strip. Using a 3-foot-long, 27'/2-inch-diameter cage rotor, he
measured the average liquid velocity in the ditch by averaging four read-
ings taken around the ditch. The average velocity was greater for higher
rotor speeds at 3-, 6-, and 9-inch immersion depths. At the 12-inch
immersion depth, the average velocity was greater for the lower rotor
speed (60 versus 100 r.p.m.).
Velocity transverses throughout the length of an oxidation ditch
channel are reported by Nelson et al. (1968). At the rotor discharge,
it was found that velocities were as much as six or seven times higher
in the top 4 inches of the channel, compared with the bottom 4 inches in
a 19-inch depth. However, 24 feet downstream from the rotor the velocities
were essentially uniform from within 2 inches of the channel floor to the
surface. Immediately after the turn, velocities at the center and outer
portion of the channel, with respect to the turn, were five to six times
greater than velocities at the inside of the channel. These measurements
indicated that sludge solids may accumulate in critical zones after a turn
even when mean velocity is adequate to transport the sludge.
The liquid flow in an oxidation ditch is produced by inertia and viscous
forces by the rotor and not by gravitational forces. Since the velocity
of the flow is dependent upon friction in the ditch, efforts should be made
where possible to eliminate or reduce friction. Most ditch walls in live-
stock buildings will be smooth concrete. When designing an oxidation
ditch, some thought should be given to using a wider median strip where
feasible to eliminate the sharp 180-degree turn commonly used. Straight
channels should always be used under the length of the building with no
jogs or turns in the channel to cause friction and turbulence, both of which
act to decrease the liquid velocity.
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AEROBIC TREATMENT or LIVESTOCK WASTES 33
In a model study at Oklahoma State University, Agena (1968) found
that, providing all other pertinent quantities were held constant, the mean
ditch liquid velocity:
1. Increased as rotor speed increased, with the rate of increase for a
given speed change being greater at lower speeds than at higher speeds.
2. Increased as paddle finger width decreased (while the inner-space
remained the same), with the rate of increase for a given change in finger
width being greater at smaller finger widths than at larger finger widths,
3. Increased as immersion depth increased, with the rate of increase
for a given change in immersion depth being greater at low immersions
than at high immersions.
4. Increased as liquid depth decreased, with the rate of increase for
a given change in depth being greater at small depths than at large depths.
The uniformity of flow across a section of that channel not contain-
ing the rotor decreased as the channel length decreased.
Design and Operational Criteria
McKinney and Bella (1967) discussed rotor design in an oxidation
ditch with respect to both liquid transport and aeration. They concluded
that only the fraction of water actually in contact with the rotor blade is
saturated with oxygen as a given volume of liquid passes the rotor. Thus,
in a ditch with 14 inches of liquid and 3-inch rotor immersion, only 21
percent of the flow is saturated. The turbulence created by the rotor helps
mix the oxygenated liquid with the non-oxygenated liquid so that the
mixed liquor in front of the rotor has a uniform oxygen content within
a relatively short distance. In designing oxidation ditches for livestock
confinement units, the oxygenation and pumpage by the rotor must be
balanced against the organic loading and the animal pen area above the
slats.
McKinney and Bella used the following example to illustrate their
point. In a farrowing house with a daily loading of 130 pounds of ultimate
BOD and with complete nitrification, the length of travel around the ditch
was 300 feet. With a one-foot-per-second ditch velocity, a single trip would
take 5 minutes. This is an oxygen demand of 0.45 pounds of oxygen in 5
minutes. The fraction of waste volume receiving oxygen would be calcu-
lated from the ratio of rotor submergence to liquid depth. The weight of
water in the system can be calculated from the area of the ditch, liquid
weight, and the specific weight of water. Multiplying all of these terms by
the oxygen of saturation in pouads per 106, or milligrams per liter, yields
the quantity of oxygen in pounds:
-------
34
-^-(2,470D) (6,214) (7.0/106) = 0.45, where
dr is the rotor immersion in feet or inches,
D is the ditch liquid depth in feet,
62.4 is the liquid density in pounds per cubic foot,
7.0 is the saturation value of waste, assuming 80 percent of the saturation
value for tap water in milligrams of oxygen per liter of wastes,
0.45 is the pounds of oxygen that must be added to the waste in the time
required for one complete trip around the ditch, and
2,570 is the surface area of the ditch in square feet.
Upon solving the equation, dr is equal to 5 inches. Based on ditch
observations, McKinney and Bella state that a 70-r.p.m. rotor with 3-inch
immersion can pump 1.2 cubic feet per second of waste per foot of rotor.
They believe that the volume of flow can be increased proportionately by
increasing the rotor speed to at least 100 r.p.m. or by increasing the depth
of rotor immersion to about 9 inches (Knight, 1965). Therefore, using a
dr of 5 inches, the rotor would have a pumpage of about 2 cubic feet per
second per foot of rotor. With a 1-foot per second velocity, this will pro-
duce a liquid depth of 24 inches in the example above.
McKinney and Bella (1967) note that it is not realistic to design on
the maximum possible oxygen demand, including nitrification. For practi-
cal purposes, it is possible to design on the basis of carbonaceous BOD5.
In the example above, this is only 0.24 pound of oxygen supplied during
each 5-minute loop. The rotor immersion in this case would need to be
2.7 inches with a liquid depth of 13]/2 inches. This was verified in a field
trial with 3-inch immersion and 14-inch depth with good results. The
building was actually loaded to only 80 percent of capacity in this trial so
it might be necessary in practice to modify this design slightly.
Livestock waste added to oxidation ditches is usually undiluted and
does not contain wash water or bedding. It will be assumed that this is
the case for the ditch design calculations presented later. It must be kept
in mind that there are only limited data available on the operation of
livestock oxidation ditches. The general design procedures to be followed
here will be based on experience from existing operations. Results from
three oxidation ditch studies with swine and two ditch studies with beef
cattle will be used as a basis for the design criteria.1 Table 1 presents the
amount and composition of the wastes from common farm animals. These
1 These studies were mentioned earlier: Baxter et al. (1966) ; McKinney and
Bella (1967); Jones et al, (1969A); Jones et al. (1969D);and Moore et al.( 1969).
-------
AEROBIC TREATMENT OF LIVESTOCK WASTES
35
§
o
I
•
Z
15
"
13
'2
"
K
LU
o 10
Q.
RO
1 1 1
GROSS ROTOR POWER
TECHNICAL DATA
r
TYPE I CAGE ROTOR.
DIAMETER : 27^ m.
SPEED: 100 R.P.M.
BLADES : 2 y X 6 IN. RECTANGULAR PLATE
LIOU
-
-
/
/
ID DEPTH:
/
Y
24 IN.
j
Y
/
/
jS -
-
-
-
-
6
ROTOR BLADE IMMERSION (IN.)
Typical operating costs of a cage rotor operating in a livestock oxidation
ditch, based on 2 cents per KWH (Day and Jones, 1970). (Fig. 20)
values will be used in the design procedure. All designs are based on daily
BOD5 production. An oxidation ditch volume of 30 cubic feet of mixed-
liquor volume per pound of daily BOD5 is used for livestock ditch design.
This results in detention times of 40 to 80 days. With these loading rates
and starting with tap water in the ditch, one could expect to operate a
-------
36
PUMPING AND OXY6ENATION
CAPACITY FOR AN IN-THE -
4.0
K
O
U.
O
SO
2.0
O
<
Q.
<
O
O
z
(L
1.0
BUILDING OXIDATION DITCH ,
CAGE ROTOR
ROTOR DIAMETER • 27^ IN.
ROTOR SPEED • 100 R.P.M.
ASSUME 0 C. » 80% OF 0. (
STANDARD CONDITIONS
/
/ .
/ /
'
/
//
/
0
/
0*"
/
/
:. AT y
+7
/
c
^
*•
^
-40.0
0
X
-30.0 fi>
m
5
O
O
•20.0 °
-1
r
o
0
-10.0 ?<
•n
H
«»•
0
3456
BLADE IMMERSION (IN.)
Typical oxygenation and pumping capacities of a cage rotor operating in
a livestock oxidation ditch. The oxygenation capacity curve is 80 percent of
the tested performance of the rotor in clean water corrected to standard
temperature and pressure (Jones et al., 1969C). The pumping capacity curve
was calculated using data reported by McKinney and Bella (1967). (Fig. 21)
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AEROBIC TREATMENT OF LIVESTOCK WASTES 37
continuous-overflow oxidation ditch for an indefinite length of time if
the volatile suspended solids in the ditch were kept at the 20,000-milligrams-
per-Iiter level by the addition of water as required to flush out solids.
Two requirements must be met when selecting a rotor for a specific
livestock building: the oxygenation capacity must be equal to twice the
daily BOD5 added, and there must be a pumping capacity capable of
moving the waste at an average minimum surface velocity of 1.25 feet per
second. The rotor manufacturer may be able to supply oxygenation, pump-
ing, and power requirement values for his rotor, but the values presented in
Figures 20 and 21 for a cage rotor (27!/2-inch diameter operated at 100
r.p.m.) may be used in lieu of this.
The oxidation ditch design criteria can be summarized as:
1. Minimum liquid volume per pound of daily BOD5 loading equa.1
to 30 cubic feet,
2. Rotor oxygenation capacity equal to twice the daily BODS loading.
3. Rotor pumpage sufficient to maintain a liquid velocity of 1.25 feet
per second.
4. Rotor operating power requirement is approximately 1 KWH per
pound of daily BOD5 loading.
5. Evaporation losses should be made up with tap water to maintain
the required liquid depth. This may be more of a problem with sheep
and poultry wastes because the moisture contents of these wastes are con-
siderably less than swine and cattle wastes (see Table 1).
6. Volatile suspended solids level in the ditch of around 20,000 milli-
grams per liter. This is not an absolute value, but rather a recommended
average maximum concentration depending upon how the effluent is
handled.
7. The maximum ditch distance between rotors should be about 350
feet.
8. Freeboard clearance between the top of the liquid and the bottom of
the slats or beams should be equal to at least 1 foot or ¥t of the liquid
depth, whichever is larger.
Steps for Designing an In-The-Bullding Oxidation Ditch
1. Determine the maximum daily BOD6 loading, use Table 1 if values
for the particular wastes are unknown.
2. Compute the ditch volume by multiplying the approximate loading
rate of 30 cubic feet per pound of BOD5 by the total daily BODB.
3. Determine the ditch liquid depth. The surface area of the pit will
be determined from the floor plan of the building and the penned area.
To maintain low-odor conditions, it is desirable to use the minimum floor
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38
Table 2. — Design Recommendation* for In-the-Buildlng Oxidation Dllchet
Animal
unit
Swine
Sow with litter. . . .
Growing pig
Finishing hog
Dairy Cattle
Dairy cow
Beef Cattle
Beef feeder
Sheep
Sheep feeder ....
Poultry
Poultry feeder
Weight,
Ib. per
unit
375
G5
150
. .. . 1,300
. , . . 900
75
4..r)
Daily
BOD6, '
Ib. per
unit"
.79
.14
.32
2,21
1 .35
. 053
.0198
Daily
req. oxy-
genation
cap., Ib.
per
unitb
1.58
.28
.62
4.42
2.70
,11
. 0396
No. of
animals
per ft.
of rotor,
units per
foot0
Hi
91
41
G
10
230
650
Ditch
vol.,
cubic
ft. per
unit'1
23.7
4.2
9.6
66
40
1 .6
.6
Daily
power
reqmt.,
KWH
per
unit"
.83
.15
.33
2.33
1 .42
.06
.021
Daily
cost,
cents
per
unit'
1.66
.30
.66
4.66
2.84
.12
.042
B From Table 1. Use specific production data when known,
h Twice the daily BODr,.
T Based on 25.5 pounds of C)a per foot of rotor per day (Fig. 21 at 6-inch immersion*).
11 Based on 30 cubic feet per pound of daily BOD,-,.
e Based on 1.9 pounds of Oa per KWH (Fi«;s. 20 and 21 at 6-inch immersion).
1 Based on electricity at 2 cents per KWH.
space necessary for each animal and to use totally slotted floors. The ditch
width and the ditch length will also be determined from the building floor
plan and pen layout. This leaves one parameter to be determined — the
ditch depth. The depth can be determined by dividing the ditch volume by
the surface area of the ditch.
4. Determine the rotor length required for oxygenation. Using the
blade immersion at which one wishes to operate, find the daily oxygenation
capacity per foot of rotor (Figure 21). To minimi/e capital expenditures,
use the deepest blade immersion recommended for the rotor. Since the
daily oxygenation capacity must be equal to twice the daily BODr,, multiply
the daily BODn by two and divide this by the daily oxygenation capacity per
foot of rotor to obtain length of rotor needed.
5. Make certain the rotor immersion depth used for oxygenation is suffi-
cient for pumpage. To determine the blade immersion required for pump-
ing, multiply the ditch cross-sectional area by a minimum velocity of 1.25
feet per second and-divide by the length of rotor \o be used. The maximum
distance between rotors should not exceed 350 feet. The blade immersion
required for this much pumpage can then be found from Figure 21. The,
blade immersion required for oxygenation (step 4) and the immersion
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AEROBIC TREATMENT OF LIVESTOCK WASTES 39
required for pumpage should then be compared and the larger value should
be used.
6. Check power requirements and operating costs.
7. A method of disposing of the mixed-liquor overflow must be selected.
Direct discharge by gravity into an aerobic lagoon is probably best for
operator convenience. Other alternatives are hauling directly from the
ditch or from an overflow holding tank.
An example follows to help clarify the design procedure.
Example: Oxidation Ditch for Swine
Given, A building with slotted floors to house 500 finishing hogs
(maximum average weight of 150 pounds).
Problem. Specify an in-the-building oxidation ditch to treat the waste
and eliminate objectionable odors. Assume the ditch is operated at a con-
stant liquid depth by using an overflow.
Solution. Experience has shown that there must be a totally slotted
floor to produce the needed ditch volume with the shallow depth that is
required for circulation to prevent settling. Use a floor area of 6 square
feet per finishing pig (Muehling, 1969). Assume a slat nominal length of
8 feet and a ditch width of 7.5 feet. Thus, a ditch length of 0.8 feet will
be needed for each pig.
Step 1. Daily BOD5 loading (assume as in Table 1) = 500 hogs X
150 Ib. each X . n"1 ' „ ' - = 158 pounds of daily BODS.
1,000 Ib. Hogs r '
30 rn ft
Step 2. Ditch liquid volume = 158 Ib. BOD0 X .. „"!"' = 4,740
• • / Ib. BOD*
cubic feet.
Step 3. Total ditch length = . l" X 500 hogs = 400 ft. Assume
the building is 32 feet wide and 100 feet long with two complete
ditch circuits. The surface area of the ditches down and back, will be
4 X 100 feet X 7.5 feet = 3,000 square feet. The ditch depths will
therefore be;
4,740cu. ft. . _ , ,„ . ,
— 1.6 feet or 19 inches.
3,000 sq. ft.
Step 4. Assuming an operating rotor blade immersion depth of 6 inches
(Fig. 21 ), the daily oxygenation capacity per foot of rotor is 25.5 pounds
of O2 per day per foot. The length of rotor required will then be:
1581b.BOD5/dayX2
25.5 Ib. 0,/day/ft.
-------
40
Use two rotors (one in each circuit) about 8 feet long, assume the actual
blade length of each is 7 feet,
Oxygenation required per foot of actual rotor length is:
158 Ib. BQD5/day X 2 Q0
7-7-7 = 22.6 Ib. Oa per day per foot.
14 it.
Rotor blade immersion depth, from Figure 21, should be about 5 inches.
Step 5. The ditch liquid cross-section area is 1.6 feet X 7.5 feet =
12 square feet and required flow rate will be:
1.25f.p.s. X 12 sq.ft. = 15 c.f.s.
The rotor pumping capacity required is:
15.0 c.f.s. _ c.f.s.
7 ft. ~ ft.
From Figure 21 the rotor blade immersion depth required for the
pumping capacity in this problem is 3.7 inches. However, a rotor blade
immersion depth of 5 inches is required for oxygenation, so use a 5-inch
rotor blade immersion depth, the greater of the two requirements.
Step 6. Power requirements for the rotors are approximately:
1 KWH 158 Ib. BODt day
Ib. BOD6 day 24 hr.
A motor with a rating of 5 horsepower would probably be used on each
rotor. Operating power cost (Figure 20) is:
12.2 KWH ^0^,,_ 2i _.,
Step 7. Assume the mixed liquor will overflow into an oxidation
pond. The daily loading is assumed to be 10 percent of the daily loading
of the ditch, i.e., assume 90 percent BOD5 reduction in the ditch. From
Table 3, lagoon volume for an oxidation pond is (using 10 percent of
tabulated value):
10% X 1U8^' X 500 (1501b. hogs) = 60,000ft.3.
ID. 01 nog
At 4 feet deep, this is 0.34 acre. This oxidation pond sizing is for ideal con-
ditions. The size should be increased accordingly for non-uniform loading,
freezing conditions, and if the BODS is reduced less than 90 percent in the
oxidation ditch (an alternative would be to use an aerated lagoon). Surplus
water and sludge can be removed as required by irrigating when convenient.
Table 2 was computed for use in estimating design requirements for
livestock oxidation ditches using BOD5 production data from Table 1.
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AEROBIC TREATMENT or LIVESTOCK WASTES 41
Specific BOD5 production data should be used when known. Note, these
design recommendations have been verified in laboratory and field experi-
ments for finishing hogs only. The other recommendations are extrap-
olated from hog research data, but should serve as a guide until further
data are obtained.
Professional help should be obtained when designing oxidation ditches.
Manufacturers of rotors for livestock ditches are a source of such help.
AEROBIC LAGOONS
Aerobic lagoons may be divided into two classifications, dependent upon
the method of aeration: oxidation ponds (naturally aerated lagoons), and
aerated lagoons (mechanically aerated lagoons). It is generally assumed
that both will be aerobic and therefore will not produce highly odorous
gases. However, this assumption is based on the premise that sufficient
oxygen will be supplied to the system to insure the maintenance of an
aerobic condition.
The reactions that take place in an aerated lagoon are similar to those
in the oxidation ditch. The biodegradable portion of the organic wastes is
stabilized and the sludge is mineralized to such an extent that objectionable
odors are eliminated. The main differences between the aerated lagoon
and the oxidation ditch may be in the size and shape, and in the tempera-
ture variations, since the lagoon is not likely to be enclosed. An aerated
lagoon may have essentially the same detention time as an oxidation
ditch of the same size. An oxidation pond would have a considerably
larger surface area than either the oxidation ditch or the aerated lagoon.
The temperature of a lagoon or an oxidation ditch located outside is
likely to be near the average air temperature.
The exact waste disposal procedure one wishes to use determines the
final layout of a lagoon system. If a mechanically aerated lagoon is used to
take the place of an oxidation ditch, it can be operated in a similar manner
with the same approximate sizes or detention times. In such a case, a
second lagoon, probably an oxidation pond, may be required to receive
overflow from the aerated lagoon. The second lagoon may be operated
in a similar manner as those receiving overflow from an oxidation ditch.
Liquids may be discharged in the usual manner with solids dried on a
sand bed. However, a system of irrigating mixed liquors and suspended
solids on adjacent cropland has been found to be highly successful at
Purdue University. This desludges the lagoon and removes excess li-
quids, thereby providing space for additional livestock wastes. Evapora-
tion from lagoons in the Illinois and Indiana areas is about equal to the
rainfall. Therefore, lagoons cannot be expected to "dry out" over a period
-------
42
of time. Also, excess liquids must be removed by discharging into an ac-
ceptable channel or irrigating onto some acceptable land area.
If one is going to use a lagoon system for the disposal of livestock
wastes, consideration must be given to the entire system. Some means
of routine flushing of the wastes into the lagoon must be provided. In most
installations, daily flushing is mandatory, and more frequent automatic flush-
ing may be required to prevent odor production that results from
shock loads. When adequate water supplies are not available for
channel or floor flushing, arrangements may be made to use the water from
the lagoon. Drainage from the collection channels to the lagoon should
be by gravity if at all possible. If this is not possible, all channels and floors
should be drained to a centrally located sump provided with an auto-
matically activated pump which discharges into the lagoon.
The actual layout of the lagoon is variable and would depend in part
on the available area. A round or oblong shape, depending on the aeration
method to be used, would be the most desirable for raw waste distribution.
The lagoon should probably be located near the livestock area to limit
piping maintenance and problems of stoppages.
Another factor that should be considered in the location of the lagoon
is the soil characteristics. The lagoon should be located in a tight, prefer-
ably clay, soil to prevent leakage and subsurface water contamination. If
such a soil is not available, arrangements should be made to waterproof
the lagoon. Sodium carbonate mixed with clay soil has been found to be
a good waterproofing mix. The use of soil cement or the installation of
a plastic lining are also accepted practices in lagoons.
Loading of the lagoon is a critical factor in the maintenance of proper
operation. Unusually large loads (slugs) of waste materials change the
pH and other environmental factors, deplete the dissolved oxygen, and
often result in what is called a "shock load." The digestion process is there-
fore upset and the lagoon does not function as it should. The most
desirable loading system is one that feeds the lagoon (bacteria) with a
steady, continuous feed in such a quantity so as to balance the feed, the
microflora, and the oxygenation capacity. The minimum loading times
per day is about two for satisfactory operation, but more frequent feeding
is desirable.
Oxidation Ponds
An oxidation pond (naturally aerated lagoon) is usually a shallow
basin 3 to 5 feet deep for the purpose of treating sewage or other
waste water by storage under climatic conditions (warmth, light, and
wind) that promote the introduction of atmospheric oxygen and that
favor the growth of algae. Bacterial decomposition of the wastes releases
-------
AEROBIC TREATMENT OF LIVESTOCK WASTES 43
Table 3. — Volume Required for Oxidation Pond* Receiving Raw Llvettock Wastes1
(Recommended Depth; 3 to 5 Feet)
Livestock Volume for each pound
of livestock
Poultry 17 cubic feet
Swine , 8 cubic feet
Dairy cattle 7 cubic feet
Beef cattle 6 cubic feet
» Computed using daily BODs productions from Table 1 and a loading of 45 pounds of daily
BODs per surface acre.
carbon dioxide which promotes heavy growths of algae. Ammonia and
other plant-growth substances are used up by the algae and dissolved oxy-
gen is kept at a high level. The driving force in this type of self-purification
is photosynthesis, supported by a symbiosis between saprophytic bacteria
and algae.
If oxidation ponds are properly constructed and hold the wastes for a
sufficient time, a good destruction of coliform organisms and a satisfactory
reduction of BOD5 occur. The effluent is usually high in dissolved oxygen;
often supersaturated during the daytime. Loadings in the vicinity of 45
pounds of BOD5 per acre are generally acceptable (Symons and McKinney,
1958). Oxidation ponds may require cleaning after an interval of several
years and weeds must be kept under control.
For livestock waste treatment, some modifications have been made in
the recommended loading rates, Clark (1965) suggests that an acre of
lagoon 5 feet to 6 feet deep would handle the wastes from 275 to 300 head
of 150-pound feeder pigs. This is a loading rate of about 96 to 105 pounds of
BOD5 per day per acre. If the lagoon is 5 feet deep, this is an average
of slightly less than 750 cubic feet per hog or about 5 cubic feet of capacity
per pound of hog. However, the present recommendations of the Midwest
Plan Service (Lagoon Manure Disposal, 1966) is 2 cubic feet per pound
of swine for an anaerobic lagoon with no particular limits on the depth.
In much of the Midwest, Clark's early recommendations would likely not
provide an aerobic system if the lagoon receives all the wastes.
Table 3 gives recommended sizes for naturally aerobic lagoons for
livestock. The size can be reduced by removing the settleable solids, using
a settling basin or septic tank. It is estimated that up to one-half of the
BOD5 might be removed in a settling tank which would proportionately
reduce the size of the lagoon or permit it to handle the waste from more
livestock.
Because of the large surface area required, oxidation ponds have not
-------
44
Table 4. — Volume Required for Mechanically Aerated lagoont Receiving Raw Livestock
Wattei (800 Days Detention Time)
Livestock Volume for each pound
of livestock
Poultry 75 cubic foot
Swine 1.00 cubic foot
Dairy cattle 1.25 cubic feet
Beef cattle 75 cubic foot
found favor with livestock producers. Their use has been essentially
limited to receiving effluent from anaerobic lagoons and other treatment
units. In this application, they provide additional treatment for the wastes
with a reduced surface area. Some producers have used oxidation ponds
to store anaerobic lagoon effluent for eventual disposal by land application.
Aerated Lagoons
In aerated lagoons, oxygen is furnished by means of some type
of mechanism that "beats" or blows air into the water with a portion
of the oxygen being dissolved. The lagoon is therefore not dependent on
the wind or algae growth for the oxygen supply. Therefore, the design
criteria (surface dimensions and depth) differ greatly from those of the
oxidation pond.
Satisfactory aerobic treatment of livestock wastes has been obtained in
aerated lagoons that have a volume of approximately 50 times the daily
manure production. However, if the aerated lagoon is considered as a
final or long-time storage of the waste residues, a much larger size is
needed. If one intends to de-sludge the lagoon yearly or more often,
the size may be reduced. Otherwise a detention time of two to three years
is recommended (Table 4).
For continuous operation, a mechanical aerator that will provide an
oxygenation capacity of 1.5 times the total daily BODS loading is the mini-
mum size recommended to obtain stabilization. If the operation is to be
intermittent (off in the extreme cold months such as December, January,
and February), the aerator should have an oxygenation capacity of at
least twice the daily BODs loading.
For complete odor control, the aeration (oxygen) requirements are not
greatly different from those required for stabilization. However, for partial
odor control, an oxygen supply of one-third to one-half the daily BOD0
will be of some benefit. The low rate of aeration stops the release of many
of the volatile acids and the accompanying gases such as hydrogen sulfide
and some of the mercaptan gases (Ludington et al., 1969). Generally
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AEROBIC TREATMENT OF LIVESTOCK WASTES 45
ammonia production is not stopped and the odor is still detectable. Al-
though it is not clearly understood, the pH is raised with the low aeration
rate and this prevents the release of H2S. However, ammonia release will
be increased.
There are numerous methods for aerating lagoons. However, it is not
clear which may be the "best." Floating aerators appear to be satisfactory,
but other schemes such as compressed air entering through diffusers (perfo-
rated pipes), rotating aerators, and rotary blowers may also work satisfacto-
rily. Some manufacturers of floating aerators guarantee an oxygenation
capacity of about 3.2 pounds per horsepower hour at a standard condi-
tion of 20° C. in clean water at a given percent of saturation of dissolved
oxygen in the water. An oxygenation capacity of this quantity is probably
the maximum that can be expected, but in many cases, it may be lower.
The mechanically aerated lagoon should be aerated continuously, be-
cause aerobic conditions thrive when oxygen is freely available. When
oxygen is not available, the aerobic bacteria are inhibited in their growth
and reproduction with the result that anaerobic conditions develop. If
this condition persists, the whole system is "upset" and considerable time
is required to return to the normal aerobic condition once the aerator is
restarted. Part of this problem comes from the fact that a large storage of
dissolved oxygen in water is impossible, since the oxygen saturation range
is only about 6 to 9 milligrams of oxygen per liter of water. After satura-
tion, additional oxygen is not held by the solution and further aeration is
of little use and would add unnecessary expense. The ideal system then is
one in which oxygen is being supplied at a rate equal to the oxygen demand.
The rate of decomposition is slowed as the temperature decreases. It
appears that below 40° F. bacterial action is greatly reduced and below
35° F. there is little activity. On this basis, it appears that little decomposi-
tion is accomplished by operating exposed aerators in extremely cold
weather. However, the aerator should be started as soon as the temperature
begins to warm up in the spring so that aerobic bacterial action can be re-
established. Some objectionable odors can be expected during the start-
up period.
A two-horsepower floating aerator operating in a 6-foot deep lagoon
at the Purdue University Dairy Farm did not freeze up during the winter
of 1967-68, but there was little evidence of bacterial activity during that
period. Ice piled up around the aerator and its efficiency probably was
impaired. A deeper lagoon would probably have helped, but the evapora-
tive cooling, as well as the other heat losses, would have lowered the
temperature below 35° F. A similar situation was observed at the Univer-
sity of Illinois during the 1968-69 winter.
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46
Removal of Sludge and Surface Water
Considerable decomposition of the organic solids occurs in aerobic
lagoons. Although the rate of decomposition is greatly reduced after some
30 days, decomposition does continue, and it is believed that in a period
of IVi to 2 years the volatile solids may be reduced by as much as 60 to
70 percent.
However, even with good degradation, solids (sludge) will eventually
build up in the lagoon until removal is necessary. The rate of sludge
buildup depends upon the size of the lagoon in relation to the manure
added and the breakdown that occurs. This sludge will contain consider-
able nutrients and may be removed and applied directly on cropland if
desired. Otherwise, it may have to be discharged onto a sand or gravel
bed for de-watering and drying. Late fall appears to be a good time for
removal of sludge from lagoons. The solids are the most stabilized at that
time and the odors are low if the lagoon has been well aerated during the
previous seven to eight months. A vacuum pump or other sewage pump
will remove sludge from the bottom of a lagoon. If the sludge has com-
pacted too much, an auger may have to be used for stirring and mixing.
When disposal of excess water is needed, irrigating mixed liquor from
an aerobic lagoon has worked satisfactorily (Dale et al, 1969). Sludge
buildup was not a problem, since suspended solids were removed by the
irrigation unit. However, if surplus water is not a problem the non-over-
flow lagoon with regular sludge removal may be satisfactory.
The continued operation of a system requires that the mixed-liquor
total solids content not exceed some maximum value. It is not known at
the present time just what this value is. In a mechanically aerated lagoon,
the aeration device can only operate effectively in liquid of a certain con-
sistency. In an oxidation pond, a solids concentration that is too high
will result in settling and anaerobic conditions. Also, the irrigation
system can handle only a limited amount of solid material. One might
estimate the upper limit of total solids to be about 20,000 to 30,000 milli-
grams per liter, or 2 to 3 percent in the completely mixed system. Addi-
tional water, if available, may be helpful in reducing solids concentrations.
Degradation can reduce the total solids by 20 to 40 percent, wljich should
provide a mixed liquor of not more than 2 to 3 percent solids content.
This material containing 2 percent of solids can be removed by irrigation,
thus leaving only a small part that may settle to the bottom of the lagoon.
For a mechanically aerated lagoon, some hydrolysis and anaerobic de-
composition may take place in the bottom of the lagoon, thus reducing
some of the solids. The products of anerobic decomposition are then fur-
ther degraded in the upper aerobic levels of the lagoon. This process has
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AEROBIC TREATMENT OF LIVESTOCK WASTES
47
FACILITIES
OXIDATION DITCH
OVERFLOW \—
IRRIGA-
TION
AREA
\ INLET — 7
A
/
ERATOR^ /
o —
p LAGOON
^m
' \
PUMP
INST.
BLDG.
DAIRY CATTLE
HOUSING AREA
CONCRETE CATTLE
FEEDING YARD
LIQUID MANURE
('STORAGE TANKS
SLOPE'
DOSING
TANK
Layout of facilities at the Purdue University dairy farm.
(Fig. 22}
been referred to as a two-stage lagoon, anaerobic in the lower portion and
aerobic in the upper portion.
AN AERATED LAGOON SYSTEM WITH IRRIGATION
AN EXPERIMENTAL STUDY
When excess water must be removed from a mechanically aerated
lagoon, irrigating the mixed liquor seems desirable. Sludge build-up is
not a problem since suspended solids are removed by the irrigating unit.
Essentially all criteria for operation of the aerated lagoon apply to a lagoon
operated in this manner. For example, the loading rates, temperature ef-
fects, and the need for continuous operation are no different. The main
difference is in the de-sludging which is accomplished by the irrigation
system. As a check on this system, an experiment was performed by re-
searchers at Purdue University (Dale et al., 1969). A similar study using
anaerobic lagoon effluent was conducted at Iowa State University by Koel-
liker and Miner (1969).
A lagoon studied at the Purdue Dairy Center had received runoff
from a dairy cattle concrete feeding floor for approximately 12 months
prior to the 87-day study. The floating aerator had been in intermittent
operation during the spring and summer prior to the start of the test. The
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Mechanically aerated lagoon with the dairy housing in the background.
(Fig. 23)
lagoon had an average volume of 18,000 cubic feet and was approximately
six feet deep.
The aerator was a nominal 2 horsepower for the initial period to day
44 and 5 horsepower from that day to the end. Effluent from this lagoon
was withdrawn with a centrifugal pump and applied to adjacent land
through an irrigation sprinkler system. A plan of the dairy layout used
in this study is shown in Figure 22. Pictures of the lagoon and irrigation
system in operation are shown in Figures 23 and 24.
Irrigation system in operation adjacent to the mechanically aerated lagoon.
(Fig. 24)
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AEROBIC TREATMENT OF LIVESTOCK WASTES
49
10
20
30
DAYS
40
FROM
50 60
START OF
70
LOADING
80
BOD- of the lagoon mixed liquor and cumulative (BOD5 input minus
BOD- irrigated). (Fig. 25)
Based on laboratory tests, manure having BOD5 of approximately 75
pounds and a chemical oxygen demand (COD) of approximately 225
pounds was placed into the lagoon daily for the last 30 days. The initial
reaction after the daily loading was a rapid drop in the dissolved oxygen
level in the lagoon within 15 to 20 minutes. The oxidation reduction
potential (ORP) followed, although not so quickly, until it reached a
low level. The dissolved oxygen and ORP remained at low levels for
several hours and then returned to their previous values.
Odors were measured only by the human nose, but were not noticed
at the lagoon except when the ORP reached —100 mv. or lower (using a
hydrogen electrode). At this ORP a slight urine odor was noticed. No
hydrogen sulfide odor was observed at any time. No odors were present on
the grassland being irrigated.
Sludge material from the bottom of the lagoon would often rise to the
surface and be dispersed by the action of the aerator. There was not an
excess of gas with such material, but rather small gas bubbles amid finely
divided black particles. A device for measuring bottom sediment was used
but very little was found, only about one-half an inch.
As the lagoon was being loaded with manure, any bubbles present on
the surface disappeared and any bubbles generated by the floating aerator
travelled only four to five feet. The disappearance of the surface bubbles
seemed to follow the reduction in dissolved oxygen.
-------
50
_ 50r
co 30
o
o
to
u, 20
_)
6
d io
VOLATILE SOLIDS
VOLATILE SOLIDS
MIXED
LIQUOR
'10 20 30 40 50 60 7O
DAYS FROM START OF LOADING
80
90
Volatile solids in the lagoon mixed liquor and cumulative (V.S. added minus
V.S. irrigated). (Fig. 26)
By plotting the actual mixed-liquor values of BOD8 and volatile solids
in the lagoon versus the cumulative value of the same parameters, a pic-
ture of what took place in the lagoon is obtained in Figures 25 and 26.
The cumulative values on the charts are the dosage quantities minus the
quantities removed by irrigation. Irrigation removed 11 percent of the
BOD and 14 percent of the volatile solids. The remaining differences
therefore were attributed to stabilization and decomposition by oxidation.
Volatile solids reductions of approximately 50 percent were obtained in
the lagoon.
SUMMARY AND CONCLUSIONS
This report emphasizes the aerobic method of storage and treatment of
livestock wastes (manure) primarily because of the low level of odors
associated with aerobic treatment. An introduction to the theory of aerobic
treatment is presented along with several laboratory experiments at the
University of Illinois and at Purdue University. These laboratory experi-
ments verified the use of the aerobic method for livestock wastes. From
these experiments two methods of aerobic treatment were studied and the
results were summarized. These were (A) the in-the-building oxidation
ditch and (B) the aerobic lagoon (oxidation pond and aerated lagoon).
However, work on some of these methods was simultaneously being con-
ducted at other research stations in the United States and in Europe. Some
of this related work is also discussed.
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AEROBIC TREATMENT OF LIVESTOCK WASTES 51
The oxidation ditch has proven itself in the field to be capable not
only of eliminating objectionable odors from manure pits, but of reducing
the BODB pollutional value of the waste by about 90 percent. In addition,
the volatile solids can be reduced about 40 to 50 percent (admittedly,
it is difficult to run accurate BOD and solid balances in fiehd installations).
With gravity overflow to a lagoon, the system can be operated with very
little labor. There will, however, be digested sludge and surplus water to be
removed.
Recommendations for designing in-the-building oxidation ditches for
livestock are presented. However, since only the recommendations for finish-
ing hogs have been thoroughly tested, the recommendations for other live-
stock are to be used only as a guide until they have been further tested.
Also, the oxygen supply recommendations are based on that required to
satisfy the BOD5 demand. If reduction of odors is the primary objective,
less oxygen supply can perhaps be used, but there is insufficient data to
make recommendations to meet some desired degree of odor control. Also,
severe foaming can result from the use of insufficient oxygen.
Without further treatment, the effluent from an in-the-building live-
stock oxidation ditch should not be discharged directly into a receiving
stream. Oxidation ditch treatment tends to concentrate plant nutrients
and mineral salts and therefore the ditch effluent would disrupt the
biological balance of a natural body of water. Even though a 90-percent
reduction in the oxygen demand of the waste is possible, the ditch effluent
will usually have a demand greater than raw domestic sewage. It also
has a reddish-brown color (like weak tea) which makes it undesirable to
discharge it into a stream. Hauling or irrigating with or without further
treatment is a practical alternative to stream discharge. In this way,
the moisture, as well as the nutrient value of the treated waste, can be
utilized while avoiding the odor problem of spreading raw manure or
anaerobic liquid manure.
The in-the-building oxidation ditch with a continuous discharge is
recommended for operator convenience. In this method the manure pit
beneath slotted floors is divided into a continuous channel (or channels)
for circulating the waste with an aeration rotor (or rotors). This prevents
rotor freezing problems and keeps the range of liquid temperature variation
to a minimum. Also, the continuous discharge method uses a constant
liquid depth and a constant rotor immersion depth (within smaJl variations
for minimum power usage). Having the mixed liquor overflow into an
aerobic lagoon is also convenient for the operator. The lagoon can have
a fluctuating depth so that surplus water can be removed at a convenient
time. The simplest method is by use of irrigating equipment.
The method above is a system having practically no odors from manure
pit to field. Of course, there may be some objectionable odors in the live-
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52
stock pens where manure splatters. Proper floor and pen design can help
prevent odors in the pens by not allowing manure to accumulate in low
spots or beneath pen partitions. Also, proper feeding and ventilation
methods can reduce odors in the pen area.
The aerobic method can also be utilized in buildings without in-the-
building oxidation ditches if some method of periodically flushing the
fresh manure into an aerobic lagoon can be devised. The fresh manure
must be flushed often enough to keep odors in the pen area to a tolerable
level (probably at least two times per day and more often if possible). The
aerated deep lagoon allows much less surface area and better temperature
control than the oxidation pond. Irrigating mixed liquor from the aerated
lagoon removes both sludge and surplus water.
With the variety of methods mentioned above, some form of aerobic
treatment should be possible for any livestock setup. There will, of course,
be operating expenses involved, but these methods should be attractive
alternatives to intolerable odors.
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AEROBIC TREATMENT OP LIVESTOCK WASTES 53
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