Solids Separation of Animal Manure Ron Sheffield 1, Jim Barker 1 & Diana Rashash 2 1

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1 Solids Separation of Animal Manure Ron Sheffield 1, Jim Barker 1 & Diana Rashash 2 1 Extension Specialists, Biological & Agricultural Engineering 2 Area Specialized Agent There are several methods of improving or enhancing the handling and treatment of animal wastes. Many of these methods involve the separation of solids and liquids within the animal waste system. Producers will benefit from the lower cost of sludge and solids removal from lagoons, decreased nitrogen concentrations in wastewaters and the increased flexibility in the land application of wastes depending on the enhancement method used. BENEFITS OF SOLIDS SEPARATION Removal of fresh solids from manure slurries will reduce the nutrient content of manure, prolong the life of storage structures, improve the effectiveness of biological treatment, and minimize odors. Beneficial uses of the recovered solids include bedding materials, animal feed supplements, composts, and soil amendments. Mechanical Separation Mechanical separators of animal waste include: inclined screens, vibrating-screens, belt presses, and screw presses. Manure is collected in a sump sized to store the largest combination of flush tank capacities or pit storage accumulations. A submersible or stationary bottom-impeller lift pump mixes the manure and liquids into a slurry and pumps it across the separator where the liquid drains off. These devices are effective in solids while producing a product with a moisture content between 60 and 70 percent (Table 1). Separators with few moving parts, such as inclined screens and vibrating-screens, are more effective when large amounts of water are moved through the devices, such as in flushing systems. Most mechanical separators require daily cleaning and flow adjustments. Screens will need to be replaced periodically when the solids removal is decreased. SCREEN SEPARATORS The shape and size of particle are used tin the separation of manure solids by one or more fine layers of mesh or filter materials. Screening separators typically remove less than 25 percent of the total particulate matter from the waste stream. The percentage of digestible solids and nutrients removed is even less, because the digestible solids and particulate nutrients are largely represented by the very fine particles that go through the screen or filter opening. Screen separators (Figure 1) usually receive manure that has been pumped from a collection pit. These separators can be installed on frames above the ground to allow for the piling and stockpiling of separated manure. Piles can either form on a constructed concrete pad (with drainage back to the collection pit), into a manure spreader or transfer truck or specialized container for additional processing. BELT-PRESSES Belt filter presses (Figure 2) are continuous-feed solids dewatering deceives that involve the application of chemical conditioning, gravity drainage, and mechanically applied pressure to dewater manure and sludge. The belt filter press was introduced in the US in the early 1970 s has become the predominant sludge-dewatering device used to handle municipal wastewater sludge. Many variables affect the performance of belt filter presses: manure characteristics, method and type of chemical conditioning (if any), pressure developed, machine configuration, belt porosity, belt speed and belt width. A properly operated press may be able to produce a material that is % moisture.

2 Table 1. Performance of Mechanical Separators. Adapted from: Zhang, R.H. and P.W. Westerman Solid Separation of Animal Manure for Odor Control and Nutrient Management. Transactions of ASAE. 13(5): Separator - Animal Screen Size (mm) Total Solids in Raw Manure (%) Separation Efficiency (%) Total Solids COD Total Kjedhal Nitrogen Total Phosphorus Stationary Screen Swine Dairy Vibrating Screen Swine Dairy Rotating Screen Swine Belt Press Swine Centrifuge Swine

3 Figure 1. Stationary and Vibrating Screen Separators. Figure 2. Belt-Filter Presses for Separating Animal Manure. CENTRIFUGE SEPARATORS These type of separators function similarly to a centrifuge to dewater manure and rely on the differences of density between solid and liquid material. Since solid material is denser, it will settle out in an applied sedimentation field. Centrifuge separators are in general more efficient in dewatering manure than other mechanical separators. Two types of centrifuge separators have been used to dewater manure: centriseives and decanters (Figure 3) also known as screw-presses. However, centrifuge separators function best with liquid slurries (5-8% solids) compared to more liquid wastes. Gravity Separation A gravity settling basin (Figure 4) may be less costly while removing 50 percent or more of the solids from liquid manure. Solids can be settled and filtered by a shallow basin (2 to 3 feet deep) with concrete floors and walls and a

4 porous dam or perforated pipe outlet. Basins should allow access by a front-end loader to remove solids every 1 to 2 months. An alternative is an earthen settling basin for 6 to 12 months storage of solids. The basin top width should be no more than 100 feet with a length-to-width ratio near 3:1 and a liquid depth of 8 to 10 feet. The basin contents should be thoroughly agitated and removed for land spreading either by liquid manure spreader or slurry irrigation. If an earthen basin is used, the operator must make the necessary inspections discussed earlier in this chapter for anaerobic lagoons. The dam structure and waste level must be constantly monitored, and the dam structure maintained to allow visual inspection for structural deterioration. A third alternative consists of a large rectangular metallic or concrete settling tank with a 3:1 length-to-width ratio with an 8-foot depth. Tank volume depends on a peak-flow wastewater detention time of 10 to 30 minutes. Most solids in livestock manure settle in about 10 minutes although some additional settling occurs for hours. Tank inlets and outlets are baffled and solids are removed by automated skimmers and scrapers. Unless substantial solids storage is added to the settling tank volume, tank cleaning will need to occur frequently. Figure 3. Centrisieve and Decanter (Screw-Press) Separators. 1=Manure Slurry, 2= Liquid, 3= Separated Solids) FIGURE 4. CONCRETE SETTLING BASIN FIGURE 5. CONCRETE SETTLING BASIN

5 Flocculents & Polymers The use of polymers or other flocculents comes up frequently in discussions about solid separation of animal manure. This is especially true from frequent flush or pit recharge swine houses due to the liquid nature of swine manure and the dilution by flush water. Chemical treatment of wastewater involves the addition of chemical flocculents and polymers to alter the physical state of dissolved and suspended manure solids to increase the percent removed by solid separation equipment. Chemicals can be added to wastewater to react with phosphorus and other metals to coagulate dissolved particles into small visible floc. Flocculation then further adheres the coagulated floc upon the addition of a polyelectrolyte that adheres the particles into larger separatable particles. Many natural polymers, such as starches and chitoson, a product from shellfish, and synthetic polymers, such as those derived from polyacrylamide (PAM), are commercially available as flocculents. Solid separation of manure prior to entering the lagoon can provide significant reductions in lagoon nutrient concentrations. This benefit can be enhanced by the use of various polymers. Decisions about whether to use a polymer should consider the cost of the polymer and additional equipment requirements, such as mixing devices and metering pumps that may be needed for polymer addition. Bench-scale separation evaluations of an inclined bed screen separator indicated that a 1/32 screen would be a more efficient choice, than a 1/16 screen, for situations either with or without polymer additions (Table 2). Some questions that producers may want to consider include: Why is polymer use being considered? Will solids separation alone suffice? Do the costs of the polymer and the additional equipment outweigh the anticipated benefit? Table 2: Solids removal effected by screen size and polymer concentration. Screen Size (inches) Polymer Added (mg/l) Solids Removal (%) 1/ / Results are for an inclined bed screen separator utilizing flushed swine manure. OPTIONS FOR SEPARATED SOLIDS Separated manure solids can be utilized several ways: land application, compost, refeeding, and off-farm products. The easiest options for most producers will be to land apply separated solids. Solids can easily be spread with most side-discharge manure spreaders. Manure solids can be utilized in areas off the farm, are too far away to be irrigated or in portions of irregularly shaped fields that can not be covered by an existing irrigation system. When land

6 applied, manure solids must be sampled with in 60 days of application and be applied in accordance with the farm s certified waste utilization plan. To minimize odors after spreading, producers should consider incorporating manure solids into the soil as soon as possible. Composting can be used to minimize the odor of manure solids following spreading. Composting is a natural process that biologically stabilizes manure solids. Composted manure solids can be more easily handled, shipped and applied while producing significantly fewer odors than raw solids. To compost any material, a balance must be struck between the amount of water, carbon, nitrogen and air space in the composting material. Generally, material should have a moisture content of 50 60%, and a carbon to nitrogen ratio of 30 40% in order to provide a good environment for composting microorganisms. Research trials have been successful in producing compost by combining 1 part of separated solids to every 2 parts, by volume, of shredded wood. Additional time and equipment will be required to successfully manage a compost system. For more information on composting, contact your local extension office. The direct refeeding of manure solids and the development of off-farm products are two areas that are receiving a lot of attention n the past several years. Refeeding of separated swine manure to cattle has been conducted for many years because of the high protein content of the solids. Current research is focusing on developing methods to reduce the amount of pathogens that may be found in the manure solids. Both, fermentation and acid stabilization have been successfully performed and managed on commercial operations in North Carolina. Turning seperated manure into a more valuable off-farm product is a major goal of the Animal and Poultry Waste Management Center at NC State University. Not only would this remove nutrients off the farm, but it would also be an additional revenue source for producers and livestock integrators. SUMMARY The use of solid/liquid separators will improve the waste handling and treatment efficiencies of many livestock operations. With the removal of manure solids, the storage life of a structure will be increased and costs can be saved due to the decreased need for sludge removal. The buildup of phosphorus, copper, and zinc will be reduced. In some instances where lagoons are undersized or are not effectively treating waste, solids removal may reduce the waste load to a level where proper anaerobic treatment can occur. The buildup of solids in transfer pipes and pumps will also be reduced. Solids and liquids from mechanical and gravity separators can be utilized in many different fashions, many of which allow the producer to develop a value-added by-product. Due to the relatively low moisture content, separated solids may easily be composted or fermented as a feed supplement. Composting of manure solids will create temperatures high enough to kill off bacteria while producing a stabilized soil amendment or bedding source for dairy free-stall barns. The liquid fraction from a separator contains most of the manure fertilizer value. With large fibers and solids removed, this liquid can either be treated in an aerobic or anaerobic lagoon or be pumped efficiently for proper land application. Dried manure solids can generally be stored and handled without offensive odors. In summary a solid/liquid separator may accomplish the following: reduce the volume of manure storage needed improve anaerobic digestion reduce concentrations of phosphorus, copper, and zinc in sludge and effluents reduce pipe clogging problems allow the use of irrigation or direct soil injection equipment reduce pumping horsepower needed and increase pumping distances allow a greater hauling distance for the solids versus liquid slurry produce value-added by-products