Submitted to: 1997 Southeast Sustainable Animal Waste Workshop
Publication Type: Proceedings
Publication Acceptance Date: 1/26/1997
Publication Date: N/A
Interpretive Summary: Animal waste treatment is a significant agricultural and environmental problem that is growing rapidly as a result of expanded, confined animal production. Large numbers of production facilities in watersheds and river basins necessitate functional and sustainable treatment of wastewaters. Wetlands have been used successfully for municipal wastewater treatment. New evidence shows that they have potential for the treatment of animal wastewater. Constructed wetlands can transform and assimilate large quantities of C, N, and P from wastewater. However, at the high loading rates necessary for substantive nutrient mass removal, constructed wetlands do not produce an effluent acceptable for discharge. Thus, subsequent land application is necessary. Croplands, vegetative strips, and woodlands are viable options for the final treatments. Terminal land application does not require discharge permits and monitoring of discharge water quality. Therefore, it is an approach that fits well with the capacities of constructed wetlands. The capacity of mass N removal by wetlands can likely be increased by pre-wetland treatment of wastewater such as overland flow, media filtration, or the use of encapsulated nitrifier technology.
Technical Abstract: Confined animal production generates enormous per-unit-area quantities of waste. Wastewater from dairy and swine operations has been successfully treated in constructed wetlands. Wetlands normally have sufficient denitrifying microbial population, C sources, and anaerobic conditions to promote denitrification processes. However, when very high mass removal of N and P is required, pre- or in-wetland procedures that promote oxidation and nitrification are needed to increase treatment efficiency. Such procedures offer the greatest potential for improved treatment capacity of constructed wetlands. An overland flow treatment removed 59% of N applied in swine wastewater at a 50-kg/ha/d rate. A media filter treatment transformed up to 32% of the inflow total N into nitrate when wastewater was recycled four times. Immobilization of nitrifying microorganisms in polymer pellets resulted in faster nitrification rates and smaller reactors. The rate of nitrification using these pellets was 600 g of ammonia-N/cubic m/d. Solids removal prior to wetlands treatment is also essential for long-term functionality. When wetlands were combined with grass filter strips, an application of swine wastewater containing 14 kg/ha/day of N was treated to over 95% N removal. Polyacrylamide is effective for separating nutrients before the waste enters typical lagoon treatment. Low rates (25-100 mg/L) removed 80% of suspended solids, organic N, and organic P from swine flushing effluents.