A.A. Szögi, P.G. Hunt, F.J. Humenik, K.C. Stone, J.M. Rice 2
Swine production is an important agricultural enterprise that requires significant attention to waste management. An investigation of the treatment of swine wastewater using constructed wetlands was initiated in Duplin Co., NC, in 1993. The investigation used three sets of two, 3.6- by 33.5-m constructed wetland cells that contained either natural wetland or water tolerant agronomic plants. Sets of cells contained rush/bulrushes, bur-reed/cattails, or soybean in soil saturated culture and rice. Nitrogen loading rates were obtained by mixing wastewater from an anaerobic lagoon with fresh water. Nitrogen loading rates of 3 and 10 kg ha-1 d-1 were used for the first and second year of treatment, respectively. Nutrient concentrations were reported on a quarterly mean basis, and nutrient removal efficiencies were estimated by mass balances. Ammonia-N inflow ranged from 22 to 90 mg L-1. Orthophosphate-P inflow ranged from 6 to 17 mg L-1. Ammonia-N outflow ranged from 1 to 11 mg L-1. Orthophosphate-P outflow ranged from 2 to 14 mg L-1. Total mass removal for N and P was very high (> 90%) with the low loading rate, but it substantially decreased (%) with the higher loading rate. Nitrate-N outflow levels increased up to 31 mg L-1 during the fall and winter periods, probably due to more oxidative conditions and lower denitrification activity. Phosphorus removal decreased substantially (%) with the high loading rate, probably due to anaerobic conditions and limited storage 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 would be beneficial in our cells for improved long-term removal of both N and P. Enhanced oxidation and treatment efficiency, and sustainability of the constructed wetland system may be obtained by sequencing with other land treatment methods such as overland flow or media.
