Environmentally Friendly Large
Scale Animal Operations
Jack Sheaffer, Ph.D.
Chairman, Sheaffer International, Ltd.
Paul Anderson, Ph.D.
Professor, Illinois Institute of Technology
Stuart Ellis, P.E.
Chief Engineer, Sheaffer International, Ltd.
Vice President, Sheaffer International, Ltd.
Livestock production in the United States has undergone a dramatic change in structure over the past twenty years. Led by the poultry industry, livestock production has adopted the vertically integrated production structure. The poultry industry pioneered this concept and it is now being rapidly adopted by the pork industry and elements of it are showing up in the beef and dairy industries.
In this vertically integrated structure a single entity or closely coordinated partnership or alliance control all aspects of production from birth to slaughter to processing. This structure works best where production can be concentrated with many large-scale, live production facilities in a relatively confined geographic area, so that economies of scale may be realized. This results in an efficient production structure where fixed costs are spread over many production units and allows an efficient use of feed mills, live production facilities, transportation and processing plants.
However, the concentration of large numbers of livestock on individual farms and significant numbers of these farms in a geographic area, raise challenges in the management of the livestock wastes that are generated. In particular, wastes that are handled in a liquid form (hogs and to some extent beef and dairy) have generated a large amount of controversy regarding the possibility of these liquid wastes polluting area water bodies and the associated odors that are present when the wastes are land applied.
Typically, large-scale farms employ an anaerobic lagoon or slurry pit to store and partially digest the wastes generated. The anaerobic lagoon will provide a marginal level of treatment to the wastes and reduce the solids content somewhat by anaerobic treatment, but in doing so, the lagoon itself will produce odorous compounds such as hydrogen sulfide and ammonia.
Periodically, the lagoon or slurry pit is pumped out and the waste is land-applied by irrigation, honey wagon or knifed into the soil with a special applicator. This partially treated waste will generate complaints when it is land applied as the odorous compounds volatilize.
The waste will also be rich in nutrients. If the waste is being knifed into the soil or spread with a honey wagon, it will be difficult to achieve a precise delivery of nutrients balanced with crop needs. Typically, the waste will be applied to deliver the full nitrogen need of a given crop all at once. Since the crop will not need all the nitrogen at once, and in fact, may not consume much of the nitrogen for some weeks, the nitrogen is vulnerable to climatic events that will cause nitrogen loss to the atmosphere, surface water or groundwater.
The anaerobic lagoon, while achieving a partial breakdown of solids, will often break them down at a slower rate than that at which they are received. This results in a limited life span for the lagoon as the solids accumulate. Eventually, the accumulated solids will have to be pumped out and land applied. This will also result in a serious odor management challenge.
There is a better way.
By using a combination of anaerobic and aerobic treatments in sequence, odors can be eliminated, solids handling minimized, nutrient loads greatly reduced and surface and ground water protected.
The Sheaffer Modular Reclamation and Reuse System
(MRRS) has been successfully employed for almost twenty years to reclaim and reuse domestic wastewater in an aesthetically pleasing odor free manner without the generation of sludge or
biosolids. Since the water and nutrients are reused there is no discharge. Its principles can be applied to the handling of wastes from large-scale animal operations.
The MRRS technology employs two deep treatment cells (25 feet deep) and a storage reservoir. The waste stream first passes through a comminutor to macerate the waste stream, it is then discharged into the bottom of the first treatment cell. The bottom five feet of the treatment cell contain an anaerobic treatment zone where, with extended treatment times, a breakdown of organic matter is achieved. Space is built into the anaerobic zone for the storage of inorganic substances (sand, grit, plastic particulate). This space is adequate to hold the inorganic material for approximately 25 years when it will be removed via a floating dredge.
At the five-foot level, large amounts of compressed air (2,500 cubic feet per pound of
BOD) are blown in through static tube aerators. This heavily aerated zone provides both treatment of the suspended BOD as well as oxidizing odorous gases produced by the anaerobic zone (e.g. hydrogen sulfide) into non-odorous compounds (e.g. sulfate). Due to the heat of compression, the delivered air is approximately 95-100 degrees F and warms the aerobic zone. This cap of warm water insulates the anaerobic zone, maintaining a temperature that stimulates anaerobic digestion, which breaks down the organic solids into soluble gases.
The system can be designed to operate on off- peak power rates. By ensuring an adequate amount of water is added to the raw manure, aeration can be scheduled on an interruptible or off-peak basis. The water acts analogous to a battery or bank, storing the oxygen for use during the off line period.
The total treatment time is usually 42 days and is evenly divided between the two cells. The cells are identical except that less air is required in cell two due to a reduced load of BOD resulting from the treatment in cell one. This process provides an anaerobic/ aerobic/anaerobic/aerobic sequence of treatment. While the heavy aeration converts ammonia to nitrate in cell one, the subsequent time in the anaerobic zone of cell two produces substantial
denitrification. After treatment in both cells and residence time in the storage reservoir, a 75% reduction in the total nitrogen content of the waste stream is generally achieved. This allows a substantial reduction in the amount of land and crop production required to take up the nitrogen when the reclaimed water is land applied.
Depending on the characteristics of the local water supply and feed inputs and their content of iron, calcium and aluminum, a significant amount of phosphorous will be precipitated out of the waste stream during treatment. This will accumulate with the non-biodegradable substances in the bottom of the treatment cell. The precipitation of phosphorous in treatment also reduces concerns about overloading the soil profile with phosphorous during land application.
By conveying the reclaimed water from the second treatment cell to the storage reservoir, the reclaimed water can be stored and programmed for reuse in synthesis with climatic and agricultural conditions. The best way apply the reclaimed water, and nutrients, is to utilize center pivots for irrigation. Center pivots allow the reclaimed water to be applied in stages to a growing crop, preventing drought stress (ideally maintaining soil moisture at >80% of field capacity) and applying the nutrients in frequent, small doses that minimize the potential for loss to groundwater or surface runoff.
The high quality of the reclaimed water makes it very suitable for other uses. The most practical use may be to recycle it back as flush water in the live production facility. Approximately two thirds of the required flush water could be made up of reclaimed water. Some fresh water must be added to the flush water to avoid a continuous build up in nitrogen content. The reclaimed water will have very little, if any, ammonia. This is an advantage over systems that recycle out of anaerobic lagoons for flushing. Such systems can actually increase ammonia levels in live production facilities, whereas using reclaimed water from a MRRS facility should allow frequent flushing, and lower ammonia levels in the live production facilities.
Frequent flushing with reclaimed water should be preferred over pit recharge systems and deep pit storage. There is a tendency to prolong the intervals between draining the pit recharge system. This causes the system to go anaerobic and increase ammonia levels in the live production facility. The deep pit storage has similar problems.
When the economic benefits generated by a MRRS facility are compared with the costs of operating the system on off peak power, there is a favorable benefit/cost ratio. This means that a system which makes a large scale animal operation environmentally friendly also makes it financially feasible. Economics and environmental protection are supportive rather than mutually exclusive.
A MRRS facility can make large scale animal operations environmentally friendly by eliminating odors, eliminating the periodic handling of odorous solids, reducing the overall nutrient loadings from the waste stream, and timing the delivery of water and nutrients with the needs of the crop and climatic conditions. A MRRS facility will reduce the labor requirements involved in the conventional handling of manure produced by large-scale animal operations. When large scale animal operations are designed to eliminate odors, sludge and discharges to streams, society will view these operations as desirable, efficient producers of food that bring economic benefits to a community.
In the mean time, we will continue with research to further optimize to cost effectiveness of the MRRS technology, particularly in the area of extracting the heat absorbed by the water from the compressed air. Efficient water to water heat pumps may make this an attractive source of heat in nursery operations.