EPA-660/2-74-047
MAY 1974
Environmental Protection Technology Series
A Waste Treatment System for
Confined Hog Raising Operations
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established* to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
degradation from point and .non-point sources of
pollution. This work provides the new or improved
technology required for the control and treatment
of pollution sources to meet environmental quality
standards.
EPA REVIEW NOTICE
This report has been reviewed by the Office of Research and
Development, EPA, and approved for publication. Approval does
not signify that the contents necessarily reflect the views
and policies of the Environmental Protection Agency, nor does
mention of trade names or commercial products constitute
endorsement or recommendation for use.
Tor nh> by the Superintendent at Documents, U.S. Government Printing Office, Washington, P.O. 20402 - Price $1.20
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EPA-660/2-74-047
May 1974
A WASTE TREATMENT SYSTEM FOR
CONFINED HOG RAISING OPERATIONS
by
William R. Park, P.E.
Project No. 13040 EVM
Program Element 1BB039
Project Officer
Ronald R. Ritter
Chief, Grants Administration
U.S. Environmental Protection Agency
1735 Baltimore
Room 249
Kansas City, Missouri 64108
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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ABSTRACT
A waste treatment system was installed in conjunction with an exist-
ing confined swine feeding operation at Schuster Farms, Gower, Missouri.
The system consisted of a concrete aeration tank equipped with mechani-
cal surface aerators, followed by a settling pond. Wastes from the
1,000-hog feeding operation were flushed through a gutter in the con-
crete feeding floor into the aeration tank, where they were aerobically
digested. All aeration tank discharges were retained in the settling
pond where the liquids evaporated.
The waste treatment facility operated continuously and dependably over
a 2-year period, with treatment efficiency averaging 90% to 95%. The
system effectively controlled objectionable odors and insects, contained
all liquid runoff emanating from the feeding operation, and left only
a dry, inert residue suitable for land disposal.
Installation cost for the system was $12,000. Net operating costs, in-
cluding amortization of capital costs, were $7.33 per day. Thus, total
environmental control was achieved at a cost of approximately $1.00 per
hog, or 1/2 cent per pound (1.1 cent per kilogram) of weight gained
while on the feeding floor.
ii
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CONTENTS
Abstract ii
List of Figures iv
List of Tables v
Acknowledgments vi
Sections
I Summary and Conclusions 1
II Introduction 2
III The Waste Treatment Facility 8
IV Chronological History of the Demonstration Project 42
V System Design 55
VI System Operation and Economics 60
VII Appendix 68
iii
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FIGURES
No. FaRe
1 Swine Waste Management System at Schuster Farms 9
2 Plan View of Demonstration Site Showing Location and 14
Direction of Photographs
iv
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TABLES
No.
1 General Design Parameters for Proposed Swine Waste 57
Treatment Plant at Schuster Farms, Gower, Missouri
2 Raw Waste Characteristics 61
3 Performance of Swine Waste Treatment Facility at 62
Schuster Farms, Gower, Missouri
4 Minimum Recommended Tank Size and Equipment Requirements 66
for Swine Waste Treatment
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ACKNOWLEDGMENTS
This demonstration swine waste treatment system was built and operated
at Schuster Farms, Gower, Missouri. The farm is owned and operated by
Mr. Lee R. Schuster. Funds for the demonstration were provided in part
by the U.S. Environmental Protection Agency, under Project 13040 EVM.
Mr. Ronald R. Ritter, Chief of Grants Administration, Region VI,
Environmental Protection Agency, served as Project Officer.
In addition to Mr. Schuster, Mr. Gary Ellington and Mr. Don Farr of
Schuster Farms assisted in operation and evaluation of the waste treat-
ment system.
Technical aspects of the operation, including specification of design
and operating characteristics, startup and testing of equipment, per-
formance monitoring, and evaluation of system performance were the
responsibility of Midwest Research Institute. The Midwest Research
Institute program was directed by Mr. William R. Park, P.E. Dr. Ross
McKinney, University of Kansas, and Dr. William Garner, formerly of
MRI and presently of the U.S. Environmental Protection Agency, assisted
in system design.
vi
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SECTION I
SUMMARY AND CONCLUSIONS
The project described in this report was undertaken to demonstrate the
feasibility and effectiveness of a swine waste treatment concept suit-
able for use with existing confined feeding operations. The demonstra-
tion was conducted at Schuster Farms, Gower, Missouri. The demonstration
site was Schuster's Feeding Floor No. 7, a 70 ft by 220 ft (21 m by 67 m)
partially enclosed concrete floor, having a capacity of 1,000 feeder
pigs ranging in size from 30 to 225 lb (14 to 102 kg).
The heart of the treatment system consists of a 20 ft x 40 ft x 13 ft
(6.1 m x 12.2 m x 4.0 m) deep reinforced concrete aeration tank equipped
with two 7.5 hp bridge-mounted, gear-driven, mechanical surface aerators.
Wastes are scraped from the concrete feeding floor into a gutter, where
they are flushed down into the aeration tank with water drawn from a
nearby pond.
Biological reactions in the aeration tank convert some 90% to 957. of
the organic wastes into water, bacterial cells and harmless gases.
Any overflow from the tank is retained in a 75 ft x 125 ft (23 m x 38 m)
settling basin where liquids evaporate, leaving only an inert, odorless,
humus-like granular residue which can harmlessly, even beneficially, be
returned to the environment via land spreading.
The total cost of the system was $12,000. Annual costs, including both
capital charges (depreciation, interest, etc.) and operating expenses
(chiefly electric power), were $11.62/day, lowered to a net cost of
$7.33/day by the labor savings made possible by reduced manure handling.
This^amounts to roughly $1.00 per hog, or 1/2 cent per pound (1.1 cent
per kg) of weight gained while on the feeding floor, an amount that
must eventually be passed on to the pork consumer at the retail level.
This demonstration waste management system, in summary, provides for
total environmental control—of liquid runoff, odors, and solid wastes—
at a cost that should be acceptable to both pork producers and pork
consumers.
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SECTION II
INTRODUCTION
THE PROBLEM
As every feedlot operator knows, the handling and disposal of pig
manure can be a real problem in a large-scale swine operation. Tradi-
tional waste disposal practices have frequently led to lawsuits and/or
large expenditures for labor, equipment, and facilities; and even with
substantial investments, in many cases control practices have failed to
achieve the expected results in terms of solving air, water and solid
waste pollutional problems.
While the environment can assimilate small quantities of raw pig manure,
large amounts of this pollutant can have disastrous effects. During
periods of intensive rainfall, great quantities may wash into receiving
waters. This in itself is serious enough; but, unfortunately, the possi-
bility that these contaminants may reach an otherwise unimpaired water-
course has greatly increased as a consequence of recent changes in the
scale of hog raising operations.
In the past, hog growing operations have presented relatively few prob-
lems from a water pollution standpoint. Hog raising has traditionally
been carried out on a small scale, and since it has been a widely
scattered activity, the raw manure could be left on the land without
posing any serious environmental threat. Hog raising is, in fact,
still a widely scattered activity, although a definite trend toward
confined feeding is becoming increasingly evident.
In the future, more and more hogs are certain to be raised in confine-
ment. This trend will result in far greater quantities and concentra-
tions of wastes than have yet been encountered, with the accompanying
possibility of serious health hazards and costly stream pollution unless
the wastes are stabilized in an environmentally acceptable manner.
Large quantities of raw pig manure are extremely objectionable even
when large land areas are available for their disposal. However, hog
wastes are readily biodegradable, and their stabilization can be
accomplished effectively by means of relatively simple and inexpensive
biological treatment systems.
The effectiveness of aerobic stabilization of hog wastes has been demon-
strated in confined hog raising operations that employ slotted concrete
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floors. The defecated material passes through the slots into an oxi-
dation pit below, where aerobic digestion takes place.
The slotted-floor concept, while proven effective in newly constructed
facilities, cannot easily be adapted to existing operations. Therefore,
a real need exists for an economical waste treatment system that can be
employed in conjunction with established hog raising operations.
As in cattle feeding, mush and wetness in the hog pens are an economic
liability. Foot rot and other diseases are a direct result of damp-
ness , while the energy expended by the animal working through mush or
across slick concrete floors detracts from the weight-building body
processes. For this reason, concrete-floored animal pens are scraped
clean rather than flushed clean. Hydraulic cleaning and carriage of
manures may seem attractive from a sanitary engineering viewpoint, but
the attendant wetness in the pens would be most objectionable for the
hog raiser.
The problem, then, is to stabilize large quantities of a highly putres-
cible semisolid and thus eliminate the potential of stream deterioration
from this material.
Because of the physical nature of the manure, it defies composting.
Anaerobic digestion is both difficult to control and aesthetically
objectionable. Thus, the desired restraints on the system are:
1. Mechanical cleaning of the pens;
2. Mechanical or hydraulic movement of the manure to a treatment
site.
3. Aerobic-liquid stabilization;
4. Separation of the stabilized solids; and
5. Dispersal of the stabilized solids on adjacent croplands.
As in any waste disposal problem, the ideal solution would be to
achieve complete recycling of all materials--in effect, a "closed-loop"
system. For example, cropland produces grains used in feed for hogs;
each 3 unit weights of feed results in roughly 1 unit weight gain and
2 unit weights of waste material. The waste material can then be
collected and distributed on the cropland as fertilizer to grow more
grain to feed more hogs and produce more waste. Thus, the cycle could
continue almost indefinitely.
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However, this situation, while possible, is not economically feasible.
The scale of hog raising operations, the economy and convenience of
chemical fertilizers, and the use of processed and concentrated feeds
have all combined to decrease the relative economic value of hog manure
as a soil nutrient. However, while the potential for economic reuse of
hog manure is negligible, its potential for polluting nearby streams
is increasing rapidly as disposal goes on as cheaply as possible--
usually by dumping without regard to possible effects on water quality.
The overall problem of returning hog wastes to the environment in a
nonpollutional and environmentally acceptable manner can be divided
generally into three phases: (1) collection; (2) stabilization; and
(3) disposal.
The collection phase is by far the simplest, although it offers a number
of interesting possibilities. Except in new installations utilizing
the slotted-floor concept, mechanical cleaning of pens is generally
required, for the reasons previously cited. Existing facilities,
where hogs are confined outdoors on concrete slabs, usually involve
scraping the manure from the floor, either mechanically or manually,
and dumping it downwind or downstream. If a waste-stabilization faci-
lity were available, the manure could be dumped in it with perhaps
even greater convenience. Or, a system of open collection sewers or
lined trenches could be installed inexpensively, so that material
scraped from pens could be directed into the trenches and carried
hydraulically to the central treatment facility; the water used for
transporting the wastes could be drawn from either a pond or from the
treatment facility itself. Such is the waste collection system de-
veloped for the demonstration project.
For stabilization of swine wastes, aerobic biological waste treatment
systems have proven to be effective. However, many of the systems
currently in use are suitable only for newly constructed facilities.
In some of these, the hog confinement area is, in effect, built around
or over the waste treatment plant.
The primary interest of the hog raiser, however, is in raising hogs
and not in treating hog wastes. An acceptable treatment system must
recognize this fact and offer the operator a convenient and economi-
cal means of handling the substantial quantities of waste material
generated by the confined hogs.
Only when disposal by means of treatment becomes more advantageous to
the hog raiser than disposal of the raw wastes—that is, when there is
a proven, direct, measurable economic benefit accruing to the operator
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from the waste treatment process—will such treatment become an
accepted part of the hog raising business.
THE SOLUTION
Schuster Farms initiated the extensive pollution control program
described in this report. This waste management system solves many
of the costly environmental problems commonly associated with con-
fined feeding operations. The program, incorporating waste handling,
treatment and disposal operations, virtually eliminates all pollu-
tional threats to the surrounding land, air and water.
The project involved a three-way cooperative effort between Schuster
Farms, Midwest Research Institute (MRI), and the Environmental Pro-
tection Agency (EPA). The system design, monitoring and evaluation
were MRl's responsibility; Schuster Farms built and operated it; and
the demonstration project was partially financed by EPA.
The demonstration project was carried out at Schuster Farms, located
in Gower, Missouri. The hog feeding operations are located on Missouri
State Road DD, about 50 (80 km) north of Kansas City.
Schuster Farms has one of the largest integrated (farrowing and finish-
ing) swine facilities in the United States, with yearly sales of 15,000
butcher hogs. At full capacity, there are ample facilities for 1,600
sows, 1,500 pigs in weaning pens, and 7,000 hogs in finishing pens, with
300 farrowing beds'and parlors housing 1,600 pigs.
The demonstration system described herein has been designed, constructed
and operated to accommodate the wastes from hogs of known characteristics,
confined in an existing building housing from 700 to 1,000 feeder pigs.
The treatment facility consists of a separate, outside, aerobic biologi-
cal system, capable of producing a biologically stabilized effluent
from raw hog wastes. This system is readily adaptable to both existing
and new hog raising operations.
Because of the restraints on system design and since the effectiveness
of aerobic biological treatment of hog wastes has already been proven,
this type of system was selected for the demonstration. In order to
conserve space and, at the same time, to provide a relatively high
degree of treatment at minimal cost, a surface-aerated complete mixing
activated sludge system was employed.
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This approach offers several distinct advantages over the more conven-
tional slotted-floor, oxidation ditch concept.
I. It can be used with existing confined hog feeding opera-
tions, as well as with newly constructed facilities.
2. It avoids the additional cost of slotted concrete floors
(approximately $1.10 per square foot ($11.84/m2) more than
smooth floors), thus reducing the total cost of confined
feeding and waste treatment operations.
3. A single treatment facility can be sized to treat wastes
from a number of different buildings, thus affording
economies of scale and eliminating the necessity for having
several small, separate treatment systems.
4. Maintenance problems are significantly reduced by having
fewer, more readily accessible parts requiring repair or
replacement.
The demonstration project described in this report was carried out in
several distinct phases:
1. The engineering phase, which included actual laying out
of the demonstration site; detailed system design in view of
the effluent requirements; construction; and startup.
2. The operational phase, during which time the system was
operated and data collected. Samples were taken periodi-
cally at various points in the system, over a 1-year period.
At the same time, pertinent economic data were compiled,
including the costs of operation and maintenance and all
other expenses incurred in handling and disposing of the
wastes.
3. The analysis phase, wherein the collected data were
analyzed, guidelines for future use were developed, and
the results of the project were carefully documented—both
from a technical and economic viewpoint.
The entire project has been result-oriented, with the primary aim of
demonstrating that waste treatment can be accomplished at reasonable
cost and with a minimum of inconvenience to the producer.
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The success of this demonstration project is evidenced by both the
results achieved at the demonstration site and by the application and
adoption of the resulting knowledge and techniques to major swine
operations in other areas.
In summary, it is believed that the many lessons learned in connection
with this demonstration project constitute a major contribution to
knowledge in the area of agricultural pollution control. The techniques
developed at the Schuster Farms demonstration site will prove invaluable
to farmers throughout the United States, and, properly applied, will
aid in achieving the goal of improved environmental quality at minimum
cost.
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SECTION III
THE WASTE TREATMENT FACILITY
THE CONCEPT
The concept of the demonstration waste treatment system installed by
Schuster Farms is quite simple. Figure 1 shows the general layout of
the facilities involved.
The waste treatment facility consists of a concrete tank equipped with
mechanical aerators. When the pens are cleaned, wastes are flushed
through a gutter and into an aeration tank where biological reactions
remove some 95% of the pollutants. The treated wastes flow from the
tank to a small pond, where the remaining solids settle out and the
liquid evaporates, leaving only an inert humus-type material for
spreading on cropland as a soil conditioner.
The basic unit in the treatment system is a 20 ft x 40 ft x 13 ft deep
(6.1 m x 12.2 m x 4.0 m deep) aeration tank, designed to handle the
wastes from a maximum of 1,000 hogs weighing 220 Ib (100 kg) each.
This aeration tank is connected to the feeding floor by an 11 in. wide
x 6 in. deep (28 cm wide x 15 cm deep) gutter system that runs the entire
length of the building. The building was converted from a cattle feed-
ing barn, which shows the adaptability of this system to almost any
existing facility. There are four individual pens measuring 70 ft x
55 ft (21 m x 17 m), each equipped with self-feeders and automatic
waterers. Below the aeration tank is a 75 ft x 125 ft (23 m x 38 m)
settling basin that catches any overflow from the tank.
The cleaning of these pens now consumes the efforts of two men for
1.5 hr every other day. The only major piece of equipment is a four-
wheel-drive Melroe Bobcat front-end loader. The loader is used to
scrape the manure from the pens into the gutter. The second man
scrapes around the feeders and waterers with a shovel and assists the
Bobcat operator. Water is pumped from a nearby pond into the gutter
at a rate of about 25 to 30 gal/min (95 to 115 liters/min) in order to
flush the wastes down the gutter and into the tank.
Biological reactions taking place in the aeration tank are the key to
the system's effectiveness in eliminating pollution. In a properly
operating aerobic waste treatment system—one where plenty of oxygen
8
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Water for
Flushing
Bypass for Use When
Disinfecting Pens
Raw Wastes to
Aeration Tank
11 "Wide by 6"
Deep (28cm x
15cm). Gutter,
Running Entire
Length of Floor
Concrete Feeding Floor with
Four 70'x 55' (21 m x 17m)
Pens Equipped with Self
Feeders & Automatic Waterers
20'x40'xl3' Deep
(6.1m x 12.2m x 4.0m)
Reinforced Concrete
Tank with Two 7.5Hp
Mechanical Surface
Aerators Mounted on
Steel Bridges
Treated Wastes Overflow
to Settling Basin
Figure 1 - Swine waste management system at Schuster Farms
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is available—the wastes are eaten by bacteria and converted into bac-
terial cells, along with several inoffensive by-products: water (HoO)j
carbon dioxide (CC^), and ammonia (NH3). The C02 and NH3 enter the
atmosphere as harmless gases, leaving only water behind. Basically,
the reaction that takes place in a properly engineered waste treatment
process like this is:
Organic Wastes + Bacteria -f Oxygen * More Bacteria + H20 + C02 + NH3
Within an hour, these bacteria can eat more than 907. of the waste materials
dumped in the tank. Then, instead of the tank being full of water and
manure, it contains primarily water and bacterial cells. If the bacteria's
food supply (the manure in this case) stops, the bacteria will slowly
starve to death, shrinking to only about a fifth of their original mass.
These dead bacterial cells form the inert humus residue from the system
that ends up in the settling basin.
For these reactions to take place, it is essential that sufficient
oxygen be available. Otherwise, the aerobic bacteria cannot function,
and the system will turn anaerobic, or septic. Should this happen,
methane and hydrogen sulfide will be generated as by-products instead
of C02 and ammonia, and the waste will stink. This commonly happens
when a rotor breaks down in an oxidation ditch beneath the slotted
floor in totally confined indoor swine facilities, or when an aerated
lagoon is overloaded because of poor design or inadequate aeration
equipment.
MECHANICAL EQUIPMENT
A great deal of care must be exercised in selecting aeration equipment
to be used in treating swine wastes. Most commercially available
aerators are not designed for this type of waste, and are physically
incapable of supplying oxygen at the rate required, regardless of the
claims made for "oxygen transfer" by sales engineers! There are few
manufacturers of aeration equipment that can effectively and economi-
cally do the job required in this type of system.
In the Schuster system, two 7.5 hp bridge-mounted mechanical surface
aerators (manufactured by Smith & Loveless in Lenexa, Kansas) were in-
stalled. They run continuously, 24 hr/day, 365 days/year, to insure
that there is plenty of oxygen in the tank at all times. The system
design is such that a single aerator, mounted in the center of a 20 ft
x 20 ft x 10 ft deep (6 m x 6 m x 3 m) module will handle the wastes
10
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from 500 full-grown hogs. Thus, a 1,000-hog operation uses two
aerators in a 20 ft x 40 ft (6 m x 12 m) tank, and a 1,500-hog opera-
tion could be easily handled just by adding another module (with an
aerator) to the tank, making it 20 ft x 60 ft (6 m x 18 m); to handle
the wastes from 2,000 hogs, a 20 ft x 80 ft (6 m x 24 m) or 40 ft x
40 ft (12 m x 12 m) layout could be used. Any tank configuration is
acceptable, just so it is built in 20 ft x 20 ft (6 m x 6 m) modules
having a 10 ft (3 m) liquid depth and an appropriate aerator mounted
in the center of each module.
GENERAL ECONOMICS
The total cost of this particular system ran $12,000, of which about
half was for the two aerators and bridges and the remainder was for
construction of the tank and settling basin, wiring, grading, pipe,
etc.
Operating costs, including electric power, maintenance, and depreciation
and interest on the tank and equipment are $4,200 annually. However,
savings in manure handling over the old scrape, haul and dump method
previously used, amount to nearly $1,600 yearly because of the require-
ment for less labor and equipment, so the net additional cost of this
system is actually less than $2,700/year, or $7.40/day. This is roughly
1/2 cent per pound (1.1 cent per kg) of weight gain, or $1.00 in addi-
tional costs on each hog, spread over its time spent on this feeding
floor.
It must be realized, however, that even though this system is about
the cheapest way to provide complete environmental control in swine
raising operations, the extra dollar added to the cost of each market-
ready hog represents a substantial portion of the profit in that hog.
Eventually, the dollar will have to be passed on to the pork consumer
as his cost of environmental protection.
ADVANTAGES TO THE FEEDLOT OPERATOR
As a direct result of implementing this program at Schuster Farms, the
pen cleaning operation is now a faster, more efficient operation than
before, and provides total pollution control at a cost that can at
least be lived with.
The system has proven to have a number of advantages, some of which are:
11
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1. It requires little change of existing facilities. If a
gutter can be put somewhere in, or by, an existing building,
this is the only structural change needed.
2. It requires a small amount of land. The tank uses a 20 ft x
40 ft (6 m x 12 m) area. A lagoon to handle the same amount
of waste could require as much as 20 acres (8 hectares). This
is very important when land sells for $400 or more per acre
($989 per hectare).
3. Cleaning can be done in any weather or season. It is not
necessary to wait until crops are out to spread, or to wait
for a field to dry sufficiently so it can be driven on.
4. It requires less time, men, and equipment than a conven-
tional system. In this case, cleaning requires an hour
less than before, one less man than was used previously,
and a truck, manure spreader, and tractor are no longer
needed to dispose of the waste.
5. There are no mechanical parts in hard-to-service areas.
With an oxidation ditch or manure drag chain, there are many
moving parts in contact with manure at all times. The aeration
tank has only two rotors that revolve in the top 6 ft (2 m) of
the tank.
6. There is no runoff to area streams or adjoining farms. Run-
off is a problem that has closed down many large-scale opera-
tions in the past.
7. There is no air pollution. There is essentially no odor
from the tank; this will become increasingly important as
cities expand closer to the livestock feeding areas.
8. There is no solid waste buildup. Huge waste piles serve as
breeding grounds for flies and other disease carriers.
Disease spreads quickly in high density populations and every
control measure can mean the difference between profit and
disaster.
9, The control measures employed comply with every existing
federal and state law governing feedlot waste removal. With
zero runoff, no odor, and no solid waste buildup, this sys-
tem can pass the most stringent laws now on the books or
proposed for the next 15 years concerning feedlot waste.
12
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At a cost of 1/2 cent per pound (1.1 cent per kg) gain this system has
proven to be an efficient and economical solution to Schuster Farms'
waste disposal problems.
PICTORIAL DESCRIPTION OF SYSTEM OPERATION
The following 27 photographs describe the operation of the demonstra-
tion swine waste treatment facility, along with some of the problems
encountered and overcome during the evolution of the system as it now
functions.
Figure 2, a plan view of the general layout, shows the approximate
location and direction in which each photograph was taken.
13
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SETTLING
POND
N
AERATION
TANK
FEEDING FLOOR
Figure 2 - Plan view of demonstration site showing location and direction of photographs
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Photo 1. Herein lies the problem. A feeder pig eats between 3 Ib
and 3-1/2 Ib (kg) of food for every pound (kilogram) of weight it
gains. This means, in simple terms, that for every pound (kilogram)
of pork, two or more pounds (kilograms) of pig manure are generated.
15
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Photo 2. At present, most pig manure is discharged into the environ-
ment in an uncontrolled manner, often causing serious environmental
damage.
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Photo_3. Schuster Farms, located at Gower, Missouri, recognized the
problem and felt a responsibility to do something about it. This
site—Schuster's Feeding Floor No. 7--was chosen as the location for
a demonstration waste management system. The pond in the foreground
supplies water to the feeding floor.
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Photo 4. Feeding Floor No. 7, the demonstration site, consists of
an old cattle barn converted to confined swine operations.
18
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* p~ % "
i E-
Photo 5. The facility consists of a concrete feeding floor of some
15,400 sq ft (1,430 m2), fenced into four 70 ft x 55 ft (21 m x 17 m)
pens, each equipped with self-feeders and automatic waterers.
19
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Photo 6. Each of the four pens has a capacity of some 250 feeder
pigs. Pigs are placed on the floor at about 30 Ib (14 kg) and
marketed when they reach around 200 Ib (91 kg), after some 14 weeks,
20
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N^£
Photo 7. An 11 in. (28 cm) wide by 6 in. (15 cm) deep gutter runs
the entire length of the floor, sloping down continuously from east
to west (right to left).
21
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Photo 8. The pens are normally scraped clean at least two or three
times weekly during the summer and once weekly during the winter.
The cleaning process employs one man operating a small front-end
loader and another man on foot with a shovel, pushing the wastes
into the gut ter.
22
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Photo 9. Water pumped from the pond into the gutter carries the
wastes through the gutter to the west end of the feeding floor,
where they flow into a small concrete collecting trough.
23
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Photo 10. At the end of the trough, there are two routes that the
wastes can follow. The drain on the bottom bypasses the aeration
tank. By putting the plug over the bottom drain, wastes are directed
into the aeration tank.
24
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Photo 11. Here, the plug is in place and the wastes flow into the
open end of the pipe.
25
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Photo 12. The wastes flow from the collecting trough through this
pipe . . .
26
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Photo 13. . . . and into the aeration tank,
27
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Photo 14. The 20 ft x 40 ft x 13 ft deep (6.1 m x- 12.2 m x 4.0 m
deep) reinforced concrete aeration tank is equipped with two of
these 7.5 hp, bridge-mounted mechanical surface aerators. Only the
aerator blades come in contact with the water.
28
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, -^_ifm
tSfwe^
*vu.
v
Photo 15. The rotating blades on the aerators throw the tank's
contents into the air, thoroughly mixing incoming wastes with the
mixed liquor already in the tank.
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Photo 16. The wastewater thus thrown in the air absorbs oxygen from
the air, necessary for the desired biological reactions to take place.
30
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Photo 17. Each aerator is located at the center of a 20 ft x 20 ft
(6.1 m x 6.1 m) section of the 20 ft x 40 ft (6.1 m x 12.2 m) tank,
assuring good, continuous mixing characteristics thoughout the tank,
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Photo 18. The aerators operate continuously, 24 hr/day, 365 days/year,
Overall treatment efficiency falls generally in the 90% to 95% range.
However, since no wastes whatsoever are discharged to the environment,
treatment efficiency has only minor significance.
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Photo 19. The waste treatment facility is relatively inconspicuous.
It is free of odor and insects, and its electric motors operate
quietly.
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Photo 20. The liquid in the tank must be maintained at a constant
level to achieve maximum aerator efficiency. The overflow pipe on
the west side of the tank is set to maintain the optimum liquid
level. As additional raw wastes are flushed into the tank, an equal
quantity of treated wastes will flow out through the overflow to
be retained in a settling pond for additional stabilization and
ultimate disposal.
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Photo 21. The system has now operated dependably for more than 2 years.
It requires practically no maintenance, causes no nuisances, and need
only be checked occasionally by farm personnel to make sure the liquid
level in the tank is adequate. Here, the system designer Bill Park (left),
and Schuster Farms' waste management specialist Gary Ellington (right),
discuss the project, obviously unmolested by noise, odors or insects.
The clean, quiet, odor-free operation is one of the system's most
important features.
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Photo 22. The first aeration tank was constructed of concrete block
by farm personnel.
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Photo 23. The concrete block tank was completed, the bridges were
mounted on the tank, and the aerators were attached to the bridges.
Then the process of filling the tank with water began.
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Photo 24. The tank filling process ended shortly after it began.
With the water depth at about 4 ft (1.2 m), a lack of structural
integrity was noted in the west wall of the tank.
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Photo 25. Fortunately, the large cracks that developed in the block
wall permitted rapid evacuation of the tank's contents and thereby
averted further disaster. Had the wall collapsed, the mechanical
equipment would have crashed onto the concrete floor below, per-
haps causing irreparable damage. As it was, however, the equip-
ment was unaffected, remaining in place atop the fractured wall.
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Photo 26. It was decided that, rather than attempt repairs on the
concrete block walls, a new reinforced concrete tank would offer a
better long-range solution. Consequently, the equipment was removed,
the block walls were demolished, and the new tank was built by a
contractor on the original foundation and floor slab.
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Photo 27. At first, a major area of concern was the possibility of
freezing during winter operation. Freezing often adversely affects
mechanical surface aeration systems. Here, however, the problems
were minimal even during the coldest weather, with the equipment
functioning normally throughout extended periods of extreme cold.
Floating foam sometimes froze, blocking the overflow pipe, but the
problem was quickly corrected.
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SECTION IV
CHRONOLOGICAL HISTORY OF THE DEMONSTRATION PROJECT
JUNE 1970 THROUGH NOVEMBER 1970
Development of design criteria and parameters for the proposed waste
treatment plant, to provide a basis for evaluation of aeration equip-
ment, constituted the first major task in the demonstration project.
Available aeration equipment was carefully evaluated from manufacturers'
literature and from discussions with manufacturers' technical representa-
tives. Equipment that appeared to be capable of satisfying the specified
design criteria received further evaluation from three standpoints:
1. Technical. The oxygen transfer capacity and fluid pump-
ing characteristics of the equipment were of primary
importance in evaluating the expected performance of the
various types of equipment under operating conditions.
2. Economic. Since a major objective of this project was
to demonstrate an economically feasible approach to waste
treatment for the farmer, the expected cost of aeration
equipment to farmers who might wish to use it in their
own future operations was an important consideration.
3. Convenience. The ease of installation and maintenance,
and the adaptability of the aeration equipment to a wide
range of operating conditions, made up the third important
consideration.
Based on these considerations, bids were obtained from manufacturers
of the aeration equipment believed most suitable for the purposes of
the demonstration project. After receiving the bids, recommendations
were made regarding the specific equipment to be purchased.
The equipment ultimately selected for the project consisted of two 7.5 hp
bridge-mounted, mechanical surface aerators, manufactured in Lenexa,
Kansas, by the Smith & Loveless Division of Ecodyne Corporation.
The necessary reagents and equipment for performing the chemical and
biochemical laboratory analyses to be used in monitoring the plant
operation were also prepared at this time.
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It was decided that established laboratory analysis routines would be
adequate for making initial studies of the startup operations. Then
laboratory studies of the analytical techniques that were made would
permit modification of the routines to meet specific requirements of
the sampling and analytical program best suited to the conditions of
actual operation of the treatment unit.
At first the aeration tank was to be built of reinforced concrete, and
located at the west end of the finishing floor. These original plans
were, however, altered as follows:
1. The aeration tank would be located 50 ft (15 m) west of
the end of the finishing floor, instead of adjacent to it.
The purpose of this move was to allow additional flexibility
in handling slug loads when the pens were cleaned. Should
a sudden influx of organic material cause foaming or other
problems, there would be sufficient room available to build
a surge basin at the floor drain outflow. In this way, the
waste flow to the aeration tank could be leveled out.
2. Instead of using reinforced concrete for the aeration tank
walls, concrete blocks would be employed. This substitution
was believed to be desirable for several reasons.
a. Most farmers are accustomed to working with
concrete block, which can be handled without
special equipment and with a minimum of out-
side help.
b. Concrete block is substantially cheaper than
reinforced concrete for this size structure in
a remote location.
c. By eliminating the need for form work and
reinforcing steel, construction could be
greatly simplified and could proceed at the
farmer's conven ience.
3. In the original concept for this system, it was proposed that
mixed liquor would be drawn from the aeration tank and pumped
to the top (east) end of the finishing floor drain to provide
for hydraulic carriage of manure down the drain and back into
the tank. At Floor No. 7, the mixed liquor would have to be
pumped some 200 ft (61 m) against a 25-ft (7.6-m) head, re-
quiring considerable pumping capacity. To minimize pumping
requirements and reduce costs, it was decided instead to draw
flush water from a pond above and northeast of the pens.
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Meanwhile, with construction under way, all necessary laboratory prepara-
tions were completed.
Tentative procedures for analyzing samples taken from the several pro-
cessing stages in the operation of the waste treatment unit were developed.
The procedures were adaptations of the "Standard Methods of Water and
Wastewater11 techniques which incorporate appropriate modifications for
handling the types of samples to be available from the process units.
These modifications included sampling techniques, methods for sample
preservation and minor details of analytical procedures.
The nature of the operation and the distance to the Midwest Research
Institute laboratory where analyses were to be made required that samples
be preserved and transported in a manner that would retain sample integrity,
A tentative sampling schedule was devised for securing, preserving, and
transporting samples, and reagents and equipment for sampling the opera-
tions and conducting the analyses were stocked.
DECEMBER 1970 THROUGH MAY 1971
During the first part of this period, weather problems hampered con-
struction of the aeration tank at Finishing Floor No. 7, while delivery
problems delayed fabrication of the aeration equipment.
According to Dr. Ross E. McKinney, project consultant, the delays were
probably beneficial. Dr. McKinney felt that biological treatment systems
such as this should not start up during cold weather, since the necessary
bacterial activity could not evolve.
By starting the system during March, the biological loading in the
aeration tank should be built up to its normal operating level in late
April. This should provide ideal conditions from an operating standpoint.
Smith & Loveless reported that the delay in equipment fabrication was
caused by their gearbox supplier. Consequently, they changed gearboxes
and obtained all necessary components. The bridges were completely
fabricated, painted, and ready for delivery, and the aeration units
were to be assembled and ready for shipment on March 8, 1971.
The waste treatment facility was actually completed in May. The aeration
equipment was delivered, the steel bridges were mounted on the aeration
tank, and the aerators were installed on the bridges. All electrical
wiring was completed, the switchgear connected, and the mechanical
equipment tested. A drainage system was devised to permit discharge of
wastes directly from the finishing floor into the tank, with provision
for bypass of wastes should problems arise. Oxygen transfer tests on
44
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the completed system were scheduled for June 2, 1971. These initial
tests were to be conducted by the Research Division of Clow Corporation.
The west wall of the aeration tank gave way on June 1. Fortunately,
the large cracks which developed in the concrete block wall permitted
rapid evacuation of the tank contents, thereby avoiding any more serious
damage. The mechanical equipment was not damaged and remained mounted
atop the tank, though with less than optimum structural stability.
This temporary setback will provide a valuable lesson to others who, in
their own pollution abatement programs, might otherwise be tempted to
merely duplicate the facility installed here. The mishap which occurred
clearly demonstrated the importance of sound structural design, accom-
panied by good construction practices. While economy in construction
is desirable, it should not be achieved by sacrificing structural in-
tegrity. This small-scale structural failure may well have averted
some future large-scale structural disaster.
Consequently, in order to minimize the possibility of similar problems
occurring in the future, specific tank design and construction details
were developed, clearly delineating all dimensions, construction mate-
rials and reinforcing details.
To restore the damaged treatment facility to an operable condition would
have entailed the following steps:
1. Remove bridges, mechanical and electrical equipment and
appurtenances.
2. Remove the damaged portions of the tank walls.
3. Thoroughly flush the tank, and divert the waste stream
around the tank.
4. Drill holes in the floor slab so that a new wall could
be firmly anchored.
5. Pour additional concrete footings for supporting pilasters.
6. Replace walls and construct pilasters with reinforced
block, providing for firm bonds between floor slab,
pilaster footings, pilasters, and walls.
7. Install vertical reinforcing in block holes.
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8. Pour a 4-in. (10-cm) reinforced concrete cap, tied to the
block wall and allowing for a strong structural connection
between the tank and the steel bridges.
9. Reinstall the bridges, electrical and mechanical equipment.
Because, at best, the above procedure would have resulted in a patched-
up tank certain to cause considerable mental anxiety among designers,
builders, operators and observers, it was decided to completely scrap
the block walls and arrange with a contractor for construction of a
reinforced concrete tank, as originally envisioned.
JUNE 1971 THROUGH NOVEMBER 1971
The first half of this period could best be regarded as a period for
reconstruction, consolidation and reflection on the valuable insights
gained during the preceding period.
Probably the most important points demonstrated thus far in connection
with the project concerned the many and diverse problems that a typical
livestock producer might be expected to encounter in constructing a
waste treatment facility. To briefly review just a few of the delay-
causing highlights:
1. Rock was encountered during excavation for the aeration
tank, which necessitated some revision in the original
plans. This could pose a serious problem for many farmers
in constructing below-grade facilities of this type.
2. Concrete block was substituted for the originally planned
reinforced concrete walls, to reduce costs and to permit
the work to be performed by farm personnel. While a
reinforced concrete tank may be somewhat "overdesigned"
in terms of the anticipated structural loadings, an
ordinary basement foundation-type concrete block structure
might be considered equally "underdesigned" in terms of
its structural stability.
3. Delays in the fabrication and delivery of aeration equip-
ment were experienced. This, of course, could be expected
in almost any type of project.
4. The tank broke as it was being filled, strikingly empha-
sizing the importance of sound structural design and good
construction techniques. Thus, between the original design
46
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and the actual construction, the problem was "bracketed,"
with both overdesigned and underdesigned structures identi-
fied. The reconstructed tank represents a near optimum
point between these two extremes.
In summary, a number of important points were clearly demonstrated that
must be considered in the planning and construction of a livestock waste
treatment facility. While there was admittedly some disappointment felt
in having encountered so many problems, it was far better to have ex-
perienced them in connection with a pioneering demonstration project
where the results can greatly benefit those who follow.
Finally, the reconstructed waste treatment facility became fully operable
and evaluation of the system's operating characteristics and equipment
performance commenced.
Preliminary oxygen transfer tests were conducted on November 17 with
Smith & Loveless research personnel familiar with the equipment. Some
minor problems were encountered in the tests and the results were incon-
clusive, though impressive.
Some dilute swine wastes were present in the aeration tank, washed in by
rain during the preceding week. The oxygen uptake rate in the tank, as
determined by Smith & Loveless in their laboratory, was 102 nag/liter/hr.
The aerators raised the dissolved oxygen (DO) level in the mixed liquor
from 0.5 part per million (ppm) to 5.5 ppm in 8 min, an average net gain
of 0.6 ppm/min or 37.5 ppm/hr. During this time, the motors were each
drawing 6.5 actual horsepower.
Simply adding the oxygen uptake rate in the waste (102 mg/liter/hr) to
the net oxygen transfer rate (37.5 ppm/hr) gave a gross transfer rate
of 139.5 mg/liter/hr in the dilute waste. For the 50,000-gal.
(189,250-liter) tank, this represented a total oxygen transfer of
approximately 59 Ib/hr (27 kg/hr), or 4.5 Ib (2 kg)/hp-hr. Since
the equipment was rated by its manufacturer at only 4.0 Ib (1.8 kg)/hp-hr
in tap water, these results were not at all disappointing, however crude
crude the methods by which they were obtained.
Flushing of swine wastes into the tank was scheduled to begin in mid-
December. Although cold weather is admittedly a poor time to begin
operation of a biological treatment system, this schedule would facili-
tate a gradual buildup of organic material in the tank and allow observa-
tion of the mechanical performance of the system throughout the winter
season.
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DECEMBER 1971 THROUGH MAY 1972
Cold weather set in before the treatment system's operating characteris-
tics could be fully evaluated. Clow Corporation research personnel
attempted some oxygen transfer tests on December 1 and 2, but below-
freezing temperatures prevented their obtaining any useful results.
While biological activity in the waste treatment system was essentially
nil during cold weather, the mechanical performance of the system was
outstanding. It is difficult to visualize any worse weather conditions
than those that were encountered during the winter of 1971-1972. Tem-
peratures at the demonstration site reached 17 degrees below zero, and
below-zero temperatures prevailed over an entire week. Nevertheless,
the equipment continued to operate and the tank contents did not freeze.
Only a few minor problems were encountered during the first 3 months of
operation, most of them related to the weather and none of them serious.
Considerable foaming occurred as the tank was filling with wastes. This
is to be expected during the startup of any mechanically aerated bio-
logical waste treatment system and corrects itself as warmer weather
permits the bacterial action necessary to metabolize the organic mate-
rials in the waste.
A second problem was brought about by the sudden cold weather, which
quickly froze the foam that was floating on top of the water in the tank.
The frozen foam then plugged the overflow drain. Then, as additional
liquids flowed into the tank, the aerator motors became overloaded and
were shut off by the circuit breakers. The situation was temporarily
rectified by pumping some liquid out of the tank, dropping the level to
where the aerators could function normally. A variable-level discharge
device could provide a permanent solution to this problem.
Everything considered, the system operated quite successfully over an
extremely difficult period. Sampling and laboratory analysis began as
soon as the weather permitted.
Initial oxygen transfer tests on the aeration equipment indicated an
oxygen transfer rate of approximately 3 Ib (1.36 kg)/hp-hr in the waste.
The addition of a 2-day accumulation of wastes to the tank over a 1-hr
period lowered the dissolved oxygen level in the mixed liquor from
9.4 mg/liter to 6.3 mg/liter. Thus, it appeared that the system would
accommodate considerably heavier loadings than it was currently experi-
encing.
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The sampling and laboratory analysis program was initiated on April 27.
Samples were taken prior to, during, and after pen cleaning, as follows;
1. Raw waste samples were scraped from the feeding floor at
10 random locations. The sample included whatever was on
the floor and could be expected to end up in the aeration
tank—manure, spilled food, straw, dirt, etc.
2. A sample of the mixed liquor in the aeration tank was drawn
from near the center of the tank at about a 5-ft (1.5-m)
depth.
3. While the pen was being cleaned, samples were drawn from the
wastes flowing into the tank. These samples were taken at
1-min intervals during the time that cleaning was under way.
When cleaning was completed, a sample was taken from the
composite mixture.
4. After the waste inflow to the tank stopped, another sample
of the mixed liquor in the aeration tank was taken at the
same location as before (in Sample 2).
All samples were then placed in an ice chest and brought directly to
MRI for laboratory analysis.
The laboratory tests encompassed both the manure characteristics and
the treatment system's operating characteristics. The following tests
were performed:
1. Manure Characteristics (Sample 1)
a. Moisture content
b. Ash
c. Manure strength
(1) BOD
(2) COD
(3) Organic nitrogen
(4) Ammonia nitrogen
2. Treatment Efficiency (Samples 2, 3 and 4)
a. BOD
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b. COD
c. Suspended solids
d. Volatile suspended solids
e. Soluble solids
f. Volatile soluble solids
g. Organic nitrogen
h. Ammonia nitrogen
i. Nitrite nitrogen
j. Nitrate nitrogen
The early tests, while inconclusive, did indicate that the system was
functioning satisfactorily, with some 967. of the BOD removed in the
aeration tank.
JUNE 1972 THROUGH NOVEMBER 1972
Sampling and laboratory analysis continued on a weekly basis throughout
the first 3 months of this period, with interesting results.
The 14-week sampling period was divided into three parts, covering the
first four, middle six, and last four weeks. This allowed comparison
of waste characteristics and treatment plant performance between the
different periods as the hogs increased in size from a 50 Ib (23 kg)
average during the first period, to 100 Ib (45 kg) during the second,
and 175 Ib (79 kg) during the final period. Average hog weight over
the 14-week period was approximately 110 Ib (50 kg).
Waste samples, scraped from random locations on the feeding floor,
ranged from fresh to 3 days old and included manure, spilled feed,
dirt, straw, and whatever else might be on the floor. The average
5-day BOD of these raw wastes was 152,500 rag/liter, substantially
higher than values reported in the literature.
These raw wastes, diluted with pond water used for flushing, made up
the influent to the aeration tank. From 1,500 to 2,700 gal. (5,700
liters to 10,200 liters) of water were used for flushing the wastes
through the gutter, the amount depending on how long the floor-scraping
process took.
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The raw waste's 152,500 mg/liter average BOD was diluted to 46,440 mg/
liter by the time it entered the treatment tank. The average effluent—
actually an average of the mixed liquor in the tank before and after
the floor cleaning operation--was 1,680 mg/liter, representing a re-
duction of 96.47=.
Similarly, over the 14-week period, COD was reduced by 91.7%; suspended
solids by 89.3%; and total nitrogen by 89.67..
All sampling techniques and laboratory analyses were conducted in
accordance with Standard Methods, and the week-to-week results were
remarkably consistent throughout the test period.
Additional experimentation was planned for the following period, employ-
ing a new type of aerator. A single, 7.5 hp, floating aerator (manu-
factured by Roycraft Industries, Kansas City, Missouri), was supplied
and installed totally at the manufacturer's expense for evaluation. It
was believed that 7.5 hp would provide sufficient mixing and oxygen
transfer for these wastes; the system would thus benefit in several ways:
1. Energy costs would be cut in half.
2. The capital tied up in equipment would be approximately half.
3. The floating unit would maintain optimum performance regard-
less of the level of liquids in the aeration tank.
In terms of system economics, then, it was hoped that this new approach
would constitute a major breakthrough. Instead of the $1.00/hog, 1/2 cent/
Ib (1.1 cent/kg) of pork cost estimated for the original system, costs
could drop perhaps to the $0.60 to $0.70/hog, 1/3 cent/lb ($0.73/kg) level.
This, of course, would make it far more desirable from the farmer's stand-
point.
The original system was nevertheless considered an outstanding success
as a demonstration project, both technically and in terms of the amount
of favorable publicity it received in newspapers and farm magazines.
The two bridge-mounted aerators were moved to the ends of the aeration
tank and disconnected, and the single floating unit moored in place at
the center of the tank.
The new installation functioned smoothly for some time without major
incident, proving generally satisfactory in performance and dependable
in operation. Several shutdowns occurred, all of which were handled
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promptly by the manufacturer, Roycraft Industries, Inc., of Kansas City,
Missouri. Most of the mechanical difficulties experienced could be
considered normal "startup" type malfunctions, for which the necessary
modifications were made.
Sampling was discontinued with the advent of cold weather when little
biological activity was taking place, pen scraping was irregular, and
fewer pigs were on the feeding floor.
Several observations were worth noting on the overall system performance.
Mechanically, both the bridge-mounted and the floating aerators performed
dependably and continuously even during the coldest weather, with ambient
air temperatures remaining well below freezing for prolonged periods,
and frequently droping below 0* F (-18° C). The tank contents did not
freeze.
The floating unit was far less sensitive to variations in the liquid
level in the aeration tank than the fixed, bridge-mounted equipment.
However, the floating aerator was anchored to the tank sides with cables,
and when the liquid level dropped more than about 2 ft (0.6 m), the
aerator was suspended in the air by its cables, hanging above the water.
This could cause considerable damage to the motor.
In contrast, however, the bridge-mounted aerator allows a maximum vari-
ation in liquid level of only a few inches; even a 1 in. (2.5 cm) fluctua-
tion affects treatment efficiency by as much as 17%.
It appeared, therefore, that in an operation where equipment care and
maintenance must be kept to an absolute minimum, the floating aerator
might be preferable to the fixed unit,.especially when there is no
continuous inflow to the aeration tank. The remaining question dealt
with the relative treatment efficiency of the two types of aerators.
DECEMBER 1972 THROUGH MAY 1973
Che treatment system continued to function well during late 1972 and
early 1973, with several short shutdowns occurring; .these, however, were
handled by the equipment manufacturer without incident. They switched
to a different and reportedly more dependable motor and experimented
with different components in order to find the combination best suited
to this operation.
During late fall and winter when pen cleaning operations were conducted
less frequently than in the summer, the liquid level in the aeration
tank tended to drop substantially, necessitating the addition of water
to keep it at a satisfactory level. Thus, the treatment facility was
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found to be not only zero-discharge, but negative-discharge; fresh-
water had to be added just to keep the mixed Liquor at a constant
volume. There was, of course, no discharge of any kind reaching any
rivers or streams at any time. Tank overflows, when they occurred,
were retained in the settling pond.
There were no complaints of objectionable odors from the treatment
system.
In all, the treatment facility continued to demonstrate that environ-
mental protection could be compatible with existing confined livestock
feeding operations.
The floating "Aerolator" was in service throughout this 6-month period.
Sampling of waste influents and effluents during the time that the equip-
ment was functioning properly indicated highly satisfactory performance
and treatment efficiency, with from 90%-95%of the pollutants removed
in the aeration process.
However, some serious mechanical problems developed in early spring
which eventually led to abandonment of the floating aeration unit.
Blocks of wood (2 in. x 4 in. (5 cm x 10 cm)) frequently found their
way into the aeration tank and were drawn into the aerator, causing
severe damage on several occasions. The source of these boards was
never found, nor was the means by which they gained entry to the tank.
Possibly, the boards were dislodged from the fence by the pigs and
subsequently washed down the gutter and into the tank. Or, they could
have been thrown or dropped in the tank.
Nevertheless, the problem recurred frequently enough to be quite trouble-
some, both for the operator and the manufacturer. While the equipment
was shut down, solids would build up in the tank and objectionable odors
would develop. Consequently, it was decided to return the two Smith &
Loveless bridge-mounted aerators to service.
Still there was no doubt that the floating aerators could do an adequate,
dependable job, especially if they were incorporated during the design
phase of a project. The tank configuration at the demonstration site
was specifically designed for the bridge-mounted units, and the problems
associated with the floating aerator should in no way be considered a
reflection on the equipment.
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JUNE 1973 THROUGH NOVEMBER 1973
With the original Smith & Loveless aerators back in service, the waste
treatment system has operated continuously, dependably and efficiently.
The results can be considered nothing less than 100% effective.
The small quantity of wastewater flowing from the aeration tank to the
settling pond dries into a granular substance that has absolutely no
odor. Surprisingly, there are no flies around the entire tank area.
The system has effectively eliminated all air, water and solid waste
problems commonly associated with confined hog raising.
In summary, the demonstration project has proven remarkably successful
from a technical standpoint. And economically, the system appears to
offer at least a reasonable solution to what could otherwise become an
expensive problem.
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SECTION V
SYSTEM DESIGN
PHYSICAL DESIGN
The waste treatment plant design was based on a hog population of 1,000,
ranging in size from 30 Ib to 225 Ib (14 kg to 102 kg) and averaging 100 Ib
(45 kg) each. Waste flow, consisting of urine, manure, spilled food and
water, was estimated at 1,500 gal. (5,700 liters) daily. The 5-day bio-
logical oxygen demand (BOD) of the raw waste was expected to be around
33,000 mg/liter.
By way of comparison, the hydraulic waste loading would be comparable to
that generated by only 15 people, while the organic loads on the treat-
ment facility would exceed those produced by more than 2,400 people. The
raw wastes going into this treatment plant are more than 100 times as
concentrated as the inflow to most municipal treatment plants.
In terms of treatment efficiency, the equivalent of conventional second-
ary treatment was desired. For a completely mixed aerated lagoon, treat-
ment efficiency is related to detention time, and to achieve the desired
95% BOD removal attainable in a well designed municipal treatment plant
requires that wastes be held in the aeration tank for some 30 days.
The detention time and daily waste flow, then, set the minimum tank size
at 1,500 gal. (5,700 liters)/day x 30 days - 45,000 gal. (171,000 liters).
It was decided to use a 50,000-gal. tank.
To obtain good mixing and fluid flow in this type of system, the tank
should be set up in square or round modules, each with a depth of about
half its length or diameter. Square, rectangular and circular configura-
tions were examined.
The dimensions required in these various shapes were found to be approxi-
mately as follows:
Square: 24 ft x 24 ft x 12 ft deep (7.3 m x 7.3 m x 3.7 m deep)
Round: 26 ft diameter x 13 ft deep (8 m diameter x 4 m deep)
Rectangular (two square modules): 19 ft x 38 ft x 9.5 ft deep
(5.8 m x 11.6 m x 2.9 m deep)
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These three designs should perform equally well. However, it was felt
that the depth should not exceed 10 ft (3 m) for several reasons, the
most important one being that a thick layer of rock was encountered at
about that depth. Also, the smaller module offers better adaptability
to a wide range of operating conditions, and permits the use of smaller
aeration equipment. Each 19 ft x 19 ft x 9.5 ft (5.7 m x 5.7 m x 2.9 m)
module can accommodate the wastes from 500 hogs, and any size hog raising
operation can be handled by adding modules.
In this case, the aeration tank dimensions were finally set at 18 ft x
38 ft x 13 ft deep (5.5 m x 11.6 m x 4 m) (allowing for a 10 ft (3 m)
liquid depth plus 3 ft (1 m) of freeboard); outside, the tank measures
a convenient 20 ft x 40 f t x 13 ft (6.1 m x 12.2 m x 4 m).
For reasons noted earlier in this report, reinforced concrete construc-
tion is strongly recommended for the aeration tank. Dimensions and rein-
forcing details are included in the Appendix.
BIOLOGICAL DESIGN
In order for the desired biological reactions to take place in the aeration
tank, the system design must provide for the transfer of adequate quanti-
ties of oxygen from the atmosphere to the wa'stewater.
This oxygen transfer requirement, in turn, imposes certain mechanical
requirements on the pumping capacity of the aeration equipment.
The raw waste, with a 5-day BOD of 33,000 mg/liter and an average oxygen
uptake rate of 43 mg/liter/hr, required the transfer of 21.5 Ib (9.8 kg)
of oxygen per hour at 20° C. Alpha, the ratio of oxygen transfer efficiency
in the waste to that in pure water, was estimated at 0.8; beta, the ratio
of the oxygen concentration in the waste when fully saturated to that
in tap water, was estimated at 0.7. The ambient oxygen concentration in
the mixed liquor was set at 2.0 mg/liter. The general design parameters
for the proposed swine waste treatment plant are summarized in Table 1.
Given these parameters, the oxygen concentration of the wastewater at
saturation is found to be 6.23 mg/liter.
The oxygen transfer rate in wastewater (1^, in pounds of oxygen per
horse power -hour) could then be calculated from the following equation:
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Table 1. GENERAL DESIGN PARAMETERS FOR PROPOSED SWINE WASTE
TREATMENT PLANT AT SCHUSTER FARMS, GOWER, MISSOURI
Average population
Average hog weight
Average waste flow
Raw waste BOD5
Aeration tank size
1,000 hogs
100 Ib
(45 kg)
1,500 gpd
(5,700 liters/day)
33,000 mg/liter
20 ft x 40 ft x 10 ft
(6.1 m x 12.2 m x 3.1 m)
Average oxygen transfer requirement
Average oxygen uptake rate
Design temperature
Alpha
Beta
Oxygen concentration at saturation (tap water)
Ambient oxygen concentration in mixed liquor
Tank turnover time (KLa)
Required pumping rate
21.5 Ib/hr
(9.8 kg/hr)
43 mg/liter/hr
20° C
0.8
0.7
8.9 mg/liter
2.0 mg/liter
12.7/hr
762,000 gal/hr
(2,880,000 liters/hr)
57
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where
R « the oxygen transfer rate in tap water
Cgw = the oxygen concentration of the wastewater at saturation
Ce « the ambient oxygen concentration in the mixed liquor
Cgt • the oxygen concentration of saturated tap water
t = the ambient temperature
This equation yields the following results;
R__ = (0.8) (4.0) (6.23 - 2.0^ x (1 Q) „ 1>52 ib/hp-hr
\ 8.9 )
- (0.8) (1.816) (6-23 " 2'°| x (1.0) = 0.69 kg/hp-hr
\ 8.9 /
and the required horsepower is found to be:
so two 7.5 hp mechanical aerators were recommended.
Based on these design parameters, it was determined that the aeration
equipment, in addition to transferring 21.5 Ib (9.8 kg) of oxygen per
hour, should be capable of pumping at least 635,000 gal/hr (2,400 m3/hr)
of the liquid, thus "turning over11 the aeration tank's contents at a
rate of 12.7 times per hour, or once every 4.7 min.
EQUIPMENT SELECTION
For mechanical surface aerators rated at 4.0 Ib (1.82 kg) of oxygen
transfer per horsepower-hour in tap water (as most are), actual oxygen
transfer in the mixed wastes under design conditions will be far less.
Here, only about 1.5 Ib (0.68 kg) of oxygen transfer per horsepower-
hour is expected, thereby requiring some 15 hp of installed aeration
capacity. Since the system is set up in two modules, two 7.5 hp units
were specified.
Only two mechanical surface aerators were available at the time that
appeared capable of satisfying both the oxygen transfer and fluid pump-
ing requirements of the proposed system. One was made by Clow Corpora-
tion, the other by Smith & Loveless. Both claimed oxygen transfer of
4 Ib (1.82 kg)/hp-hr in tap water at 20° C; both were rated at well over
the required pumping rate—the 7.5 hp Clow unit at 5,600 gal/min (21,100
liters/min) and the comparable S&L aerator at 20,000 gal/min (75,000
liters/min).
After carefully reviewing the performance characteristics of both manu-
facturers1 equipment, the Smith & Loveless aerator was selected largely
58
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on the basis of its higher pumping capacity; its lower price (approxi-
mately $1,000 per unit); and the proximity of the manufacturer to the
demonstration site. This last point was considered especially import-
ant for a demonstration project employing a relatively new and unique
concept, although it should not normally preclude consideration of
other potentially acceptable units.
59
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SECTION VI
SYSTEM OPERATION AND ECONOMICS
OPERATING RESULTS
The most significant result of the operation of the demonstration waste
treatment plant over a 2-year period was its clean, dependable, odor-
free operation, conducted without interfering with the normal farm
procedures. It has provided complete environmental control at nominal
cost and with no inconvenience to the farmer-operator.
Treatment efficiency, important when wastes are discharged into receiving
waters, has little significance in this case. Nothing is discharged to
the environment except the harmless gases (chiefly ammonia and carbon
dioxide) generated by the biological reactions in the aeration tank.
Solids are retained in the settling basin, drying to an inert, odorless
granular consistency having no particularly objectionable characteristics
and suitable for land disposal. Liquids simply evaporate. Should the
settling basin fill because of unusual amounts of rainfall, another pond
will be built and used until the first one dries out. In terms of over-
all environmental effects, therefore, the treatment efficiency is
100%.
Table 2 shows the characteristics of the raw swine wastes being accommo-
dated by the treatment system. Over the 14-week life span of a hog on
the feeding floor, the 5-day BOD averages just over 150,000 mg/liter;
the COD is 264,000 mg/liter; and the total nitrogen content averages
18,000 mg/liter.
The next table (Table 3) summarizes the effectiveness of the treatment
process over the hogs' life cycle, as they grow from about 30 Ib to
over 200 Ib (14 kg to 91 kg), with corresponding increases in their
production of manure. As shown in Table 3, 8005 reduction averaged
96.4%; 91.7% of the COD was removed; suspended solids were reduced
by 89.37.; and 89.6% of the total nitrogen was dissipated.
In terms of conventionally measured treatment efficiency, then, this
system operates at a level comparable to the best, most expensive,
modern, sophisticated treatment plants.
60
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Table 2. RAW WASTE CHARACTERISTICS
First 4 weeks Middle 6 weeks Last 4 weeks 14-week
(4/27-5/18) (5/25-6/29) (7/6-7/27) average
BOD (5-day) (rag/liter) 109,500 175,700 160,500 152,500
COD (mg/liter) 263,100 233,600 309,500 263,800
Moisture content (%) 67.5 66.1 66.9 66.7
Ash (%, wet basis) 5.0 5.6 5.7 5.5
Organic nitrogen (mg/liter) 13,900 13,320 11,680 13,020
Anmonia nitrogen (mg/liter) 6,930 5,430 4,350 5,550
Total nitrogen (mg/liter) 20,830 18,750 16,030 18,570
Average hog weight (lb(kg)) 50 (23) 100 (45) 175 (80) 110 (50)
61
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Table 3. PERFORMANCE OF SWINE WASTE TREATMENT FACILITY
AT SCHUSTER FARMS, GOWER, MISSOURI
First 4 weeks Middle 6 weeks Last 4 weeks 14-week
(4/27-5/18) (5/25-6/29) (7/6-7/27) average
Average hog
weight (lb (kg))
BOD (5-day)
influent (ing/liter)
effluent (mg/liter)
percent reduction
COD
influent (ing/liter)
effluent (mg/liter)
percent reduction
Suspended solids
Influent (mg/liter)
effluent (mg/liter)
percent reduction
Total nitrogen
Influent (mg/liter)
effluent (mg/liter)
percent reduction
50 (23)
21,695
746
97.6
40,650
5,250
87.1
42,025
3,570
91.5
5,124
632
87.7
100 (45) 175 (80) 110 (50)
50,538 64,125 46,400
2,112 1,967 1,680
95.8 96.9 96.4
94,400 164,750 99,100
7,358 12,453 8,210
92.2 92.4 91.7
80,542 102,520 75,800
8,002 12,886 8,130
90.1 87.4 89.3
6,618 8,616 6,760
605 920 703
90.9 89.3 89.6
62
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But, to once more emphasize the most important operational characteris-
tics of the demonstration plant:
1. There is no objectionable odor; and
2. There is no pollutional discharge to the environment.
SYSTEM ECONOMICS
Construction of the aeration tank and purchase of the mechanical equip-
ment account for the bulk of the capital outlay in a system of this
type. The total plant investment for a comparable system should run
about $12,000.
Electric power for the two 7.5 hp motors constitutes the major operating
expense, totaling $2,445 annually at a rate of 2.5 cents per kilowatt
hour. Electric rates will, of course, vary widely among different
utilities and geographic areas.
Here is an approximation of the overall system economics:
Capital Costs;
Construction of Tank
Equipment
Aerators (2 at 7.5 hp)
Bridges
Wiring, tubing, etc.
Total
$5,000
4,600
1,600
800
$12,000
Operating Costs:
Power--264 kwhr/day at 2.5 cents
= $6.60/day or
Maintenance and miscellaneous
equipment
Amortization (12 years at 8%)
Total Annual Cost
Savings in Manure Handling
6 hr/week (one man plus one truck)
at $5.00/hr - $30.00/week
$2,445/year
200
1.600
$4,245/year or $11.62/day
or $4.29/day
63
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Net Cost:
$11.62 - $4.29 = $7.33/day
Time on feeding floor: 140 days
Weight gain: 195 lb/hog (88.5 kg/hog)
Net Waste Treatment Cost Based Upon Full Capacity
of 1,000 Hogs:
! 000— " $1.026/hog, or roughly $1.00/hog
Si 026
f - $0.0053/lb, ($0.00116/kg), or roughly 1/2 cent/lb
These costs are believed to be within the limits of economic feasibility
for most large swine producers, and the demonstration project can be
generally considered a success from an economic as well as technical
standpoint .
Profit margins in pork production hold the. key to the acceptability to
the producer of these costs and of the complete waste management concept.
The $1.00/hog incremental cost of waste treatment may constitute a sub-
stantial percentage of the farmer's net profit. This additional cost
must eventually be passed on to the consumer.
There is little doubt that society will pay for pollution control
through higher costs at retail, but this is small comfort to the man
currently confronted with making a capital investment. In other words,
currently, as he markets his livestock, he will not find in the competi-
tive market place that his pigs are worth one cent more for having been
produced in a facility with zero runoff.
The initial impetus for construction of similar facilities, then, is
likely to come from fear of urbanization, from fear of the neighbor's
lawsuit, or from fear of a governmental agency.
Thus, the results of this demonstration offer a ready solution to the
livestock man in trouble. Here is a system which can be adapted
readily to variable terrain or livestock population. Waste material
can be guttered or hauled to the tank, and dedication of land is minimal.
Modification to existing facilities likewise is minimal. The demonstra-
tion and design, then, become practical, workable, and flexible — and
perhaps most important, salable to the livestock man in trouble.
64
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GENERAL APPLICATIONS OF THE SYSTEM
While the swine waste treatment plant described herein was specifically
intended for the operation at Schuster Farms' Feeding Floor No. 7, it
can easily be adapted to virtually any confined swine feeding operation.
The treatment plant itself—consisting of the aeration tank and the
settling basin—will accommodate the wastes from approximately 1,000
feeder pigs, ranging in size from 30 lb (14kg) to 225 Ib (102 kg) and
averaging 110 lb (50 kg).
Collection of the wastes is a separate function and must be adapted
to a particular feeding operation. Gutters, sewers, conveyors, or
trucks may constitute an appropriate means of transporting raw wastes
to the treatment facility, depending on the local situation.
The aeration system demonstrated at Schuster Farms has proven itself
more than adequate. Two 5-hp units would, in fact, probably provide
sufficient aeration capacity for most 1,000-hog operations.
Table 4 shows the minimum aeration tank dimensions and aeration equip-
ment specifications recommended for various hog populations. These
are intended only as rules-of-thumb, based on a tank retention period
of 30 days and a total waste flow of 1.5 gal/day/hog (5.7 liters/day/hog).
Either fixed or floating aerators can be used equally well, but the
manufacturer should be consulted regarding the test shape and type of
aeration tank.
The settling pond into which the aeration tank discharge flows should
be sized according to local rainfall/evaporation relationships. Properly
sized, the pond will evaporate as much water as it receives. The pond
should, in general, be from 3-5 ft (1-1.5 m) deep, allowing about 1 acre
(0.4 hectare) of surface area per thousand hogs—less in dry areas, more
in wet regions.
65
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Table 4. MINIMUM RECOMMENDED TANK SIZE AMD EQUIPMENT REQUIREMENTS FOR SWINE WASTE TREATMENT
Aeration tank
Hog
population
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
W^dth
ft
18
23
26
29
25
26
28
29
30
m
5.5
7.0
7.9
8.8
7.6
7.9
8.5
8.8
9.1
dimensions
Length
ft m
18 5.5
23 7.0
26 7.9
29 8.8
50 15.2
52 15.9
56 17.1
58 17.7
60 18.3
Depth*
ft
9.5
11.5
13.5
14.5
12.0
13.5
13.5
14.5
15.0
m
5.9
3.5
4.1
4.4
3.7
4.1
4.1
4.4
4.6
Number
of units
Aeration eauipment
Horsepower
Pumping capacity
Rpm
1
1
1
1
2
2
2
2
2
5
10
15
20
12
15
17
20
22
.0
.0
.0
.0
.5
.0
.5
.0
.5
6
12
18
24
30
36
42
48
54
,000
,000
,000
,000
,000
,000
,000
,000
,000
m /min
23
45
68
91
114
136
159
182
204
a Allow additional depth for freeboard, depending on equipment manufacturer's recommendations.
-------
ESTIMATED COSTS FOR SYSTEMS OF VARIOUS SIZE
Aeration Tank
The estimated cost of constructing a reinforced concrete tank having
the general specifications and features of the design given in the
Appendix is
C » 500 -»• 0.4 d3 + 24 d2
( C - 500 + 14.1 d3 + 258 d2)
for a square tank, and
C - 500 + 0.8 d3 + 40 d2
( C - 500 + 28.3 d3 + 431 d2 )
for a rectangular tank, where C = the cost in current (1973) dollars,
and d = the liquid depth in feet (meters).
A 20 ft x 20 ft x 10 ft (6.1 m x 6.1 m x 3.1 m) tank, then, would cost
$3,300 and a 20 ft x 40 ft x 10 ft (6.1 m x 12.2 m x 3.1 m) tank $5,300.
The depth (d) will be half the width; for rectangular tanks, the length
will be twice the width.
Aeration Equipment
Surface mechanical aerators capable of doing the necessary job both
in oxygen transfer and fluid pumping currently cost about $1,700 plus
$170/hp, including controls. A 5-hp unit, then, would be expected to
cost about $2,550; a 10-hp aerator, $3,400; and a 20-hp unit, about
$5,100. Costs are essentially the same for bridge-mounted and floating
aerators, the cost of a steel bridge being roughly comparable to a
good flotation collar.
Operating Costs
The total annual cost of a waste treatment system of this type amounts
roughly to the electric power cost plus 20% of the capital outlay (to
allow for depreciation, interest, maintenance, etc.).
The power cost will be approximately $0.50/day/hp, with the electric
rate at 2 cents per kilowatt-hour. For other rates, the cost would be
directly proportional.
67
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SECTION VII
APPENDIX
The Appendix covers the construction details of the reinforced concrete
aeration tank installed at Schuster Farms' demonstration site. As al-
ready described, it will accommodate the wastes from 1,000 feeder pigs,
ranging in size from 30 to 225 Ib (14 to 102 kg).
It must be emphasized, however, that the aeration tank described here
was designed specifically for the Smith & Loveless aerators; different
tank configurations may be required for other units, and manufacturers
should be consulted regarding the optimum tank shapes and dimensions
for their equipment.
THE AERATION TANK
Figure A-l is an elevation view of the tank installation at Schuster
Farms' Feeding Floor No. 7. The tank is located 50 ft (15 m) west of
the west end of the feeding floor, connected by tile drain pipe. The
slope of the drain is about 5 ft in 50 ft, or 1 in 10. This slope pro-
vides adequate velocity for hydraulic transport of the manure and other
wastes.
Figure A-2 is a perspective and sectional view of the tank. The tank
installed at the demonstration site also has a concrete beam across its
width at the center, connecting the two long walls for additional
support; this is not really necessary, but after the mishap with the
concrete block walls, no chances were taken.
Figure A-3 is a sectional view of the tank, locating the inlet and out-
let. The outlet height must be determined experimentally, since the
aerators push large volumes of water toward the sides. An adjustable
outlet structure is therefore recommended, so that the liquid level
can be kept at the top of the rotor blades when the equipment is operat-
ing.
Figure A-4 is a plan view of the tank and a logitudinal section.
Figure A-5 covers the reinforcing details and shows how the tank walls
should be keyed into the floor slab.
68
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r*4l
Tank
Outlet
VO
Liquid Level
•50'± (15m)
Tank Inlet
5* (1.5m)
10'-9" (3.3m)
\
ELEVATION VIEW
Existing Floor
Existing Drain Outlet
Figure A-l - Location of aeration tank with respect to existing facilities
-------
AERATION TANK
18'x38'xl3'Deep Inside
20lx40'xl3'Deep Outside
(5.5m x 11.6m x 4.0m Deep Inside)
(6.1m x 12.2m x 4.0m Deep Outside)
SECTION THROUGH TANK
Figure A-2 - General configuration of aeration tank
70
-------
1
OUTLET < \~
R
I
(
10'
(312
\
— LIQUID LEVEL ~
i
-3« 10'-
cm) (328
i
-9"
cm)
1
a
INLET
INLET & OUTLET: 6" (15.2cm) Set at Center of Long
(40'; 12.2m) Sides at Heights Shown
Figure A-3 - Location of aeration tank inlet and outlet
-------
t
L.
SEE DETAIL
J
SEE DETAIL A
PLAN VIEW
SECTION A-A
Figure A-4 - Plan view and section of aeration tank
-------
r-8"
(50.8cm)
-r-8"—
(50.8cm)
2" (5cm)
8" (20.3cm)
_ 4 _
4 2"
'4 BARS
DETAIL B
(15.2cm)
'5 BARS-
•*5BARS(8"O.C.)
(20.3cm)
*4BARS (2'-0" O.C.)
(61cm)
.*4BARS(10"O.C.)
(25.4cm)
(20.3cm)
,(5cm)
4-8"
(50.8cm)
6"x6" -10/10 MESH
.,— (15.2cm x 15.2cm)
3"(7.6cm) 4" (10cm) /
A / t L
(50.8cm) (15.2)
REINFORCING DETAILS
Figure A-5 - Aeration tank reinforcing details
73
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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
11. Report No.
2.
• 3. Accession No.
w
4, Title
A WASTE TREATMENT SYSTEM FOR CONFINED HOG RAISING OPERATIONS
5, KepvrtDat*
6,
8. t rforating Or gar. i zatiott
7. Aathor(s)
Park, William E.
9, Organization
Midwest Research Institute
425 Volker Boulevard
Kansas City, Missouri 64110
10. Project No.
13040 EVM
Contract I Gtatst No.
13040 EVM
12. Sr -nsorin ~ Organ1' it/on
13 Type ^-i Repot <. and
Period Covered
U. S. Rmrirnnmgntal protection Agency
15. Supplementary Notes
Environmental Protection Agency report number, EPA-660/2-7U-OU7, May
16. Abstract
A waste treatment system was installed in conjunction with an existing confined swine
feeding operation at Schuster Farms, Gower, Missouri. The system consisted of a
concrete aeration tank equipped with mechanical surface aerators, followed by a settling
pond. Wastes from the 1,000-hog feeding operation were flushed through a gutter in the
concrete feeding floor into the aeration tank, where they were aerobically digested.
All aeration tank discharges were retained in the settling pond where the liquids
evaporated.
The waste treatment facility operated continuously and dependably over a 2-year period,
with treatment efficiency averaging 90% to 95%. The system effectively controlled
objectionable odors and insects, contained all liquid runoff emanating from the feeding
operation, and left only a dry, inert residue suitable for land disposal.
Installation cost for the system was $12,000. Net operating costs, including
amortization of capital costs, were $7.33 per day. Thus, total environmental control
was achieved at a cost of approximately $1.00 per hog, or 1/2 cent per pound (1.1 cent
per kilogram) of weight gained while on the feeding floor.
17a. Descriptors
Hogs, Waste treatment, Aeration, Settling pond
17b. Identifiers
Odor control, Economics, Surface aerators, Flushing gutters, Aerobic digestion
l~c. COWRR Field & Group
05D
18. Availability
19. Security Class.
(Repot.)
">!}. SecirityCJ 5s.
(Page)
21. ffo.of
Pages
J3. Pr/cs
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
US DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 2O24O
Abstractor
WRSIC 1O2 i«£V JUNF 197 !'•
| Institution
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