Submitted to: Wetlands in the Agricultural Landscape Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/10/1995
Publication Date: N/A
Interpretive Summary: In the past, land application of animal wastes in the U.S. Eastern Coastal Plain was an environmentally safe practice because a few animal producers were scattered across the landscape. Now, confinement of hogs in large- scale production units in this region generates enormous per-unit-area quantities of wastes. Application of liquid swine wastes to land has several problems, such as nuisance odor, high solid content, high nutrient concentrations, and limited pumping distances. Constructed wetlands are an acceptable method for mass removal of nitrogen from animal wastes. However, the anaerobic conditions of the wetland soil and low temperatures may limit the microbial processes to recycle nitrogen. Phosphorus removal is limited by the characteristics of the wetland soil, as well as the soil anaerobic conditions. Currently, we are investigating the aeration of swine wastewater by pre-treatment via overland flow and media filter to increase the nitrogen removal efficiency. Phosphorus still needs to be precipitated before the pre-treatment unit by adding alum or lime. Ultimately, the necessary treatments for swine wastewaters will depend upon the amount of land available for wastewater application. Where the sustainability of the terminal land treatment site is a concern, a total animal waste management system is required. This system may include a wetland and pre/post-wetland treatments arranged in a way that maximizes the total mass removal efficiency on an area basis.
Technical Abstract: Swine production is an important agricultural enterprise that requires significant attention to waste management. An investigation on swine wastewater treatment using constructed wetlands was initiated in Duplin Co., NC, in 1993. Three sets of two, 3.6- by 33.5-m constructed wetland cells were used. Sets of cells contained rush/bulrushes, bur- reed/cattails, or soybean in soil saturated culture and rice. Nitrogen loading rates of 3 and 10 kg/ha/day were used for the first and second year of treatment, respectively. Orthophosphate-P inflow ranged from 6 to 17 mg/L. Ammonia-N outflow ranged from 1 to 11 mg/L. Orthophosphate-P outflow ranged from 2 to 14 mg/L. Total mass removal for N and P was high (> 90%) with the low loading rate, but it decreased with the higher loading rate. Nitrate-N outflow levels increased up to 31 mg/L during the fall and winter periods with the high loading rate, probably due to more oxidative conditions and lower denitrification activity. Phosphorus removal decreased with the high rate, probably due to anaerobic conditions and limited capacity of the wetland soil. Dissolved organic carbon removal efficiency was low (< 58%) at low and high loading rates. Our data suggests that more oxygen during the warm months would be beneficial in our cells for improved removal of both N and P. Enhanced treatment efficiency and sustainability of the constructed wetland system may be obtained by sequencing with other methods such as overland flow or media filtration.