ARS | Publication request: Marsh-pond-marsh wetland treatment of nitrogen and phosphorus in swine anaerobic lagoon wastewater: A case study

Submitted to: International Conference on Wetland Systems for Water Pollution Control
Publication Type: Proceedings
Publication Acceptance Date: September 10, 2008
Publication Date: November 1, 2008
Citation: Reddy, G.B., Hunt, P.G., Poach, M.E., Forbes, D., Matheny, T.A., Stone, K.C., Szogi, A.A., Ducey, T.F. 2008. Marsh-pond-marsh wetland treatment of nitrogen and phosphorus in swine anaerobic lagoon wastewater: A case study. In: Proceedings of the International Conference on Wetland Systems Technology in Water Pollution Control, November 1-7, 2008, Indore, India. pp. 754-765.

Technical Abstract: Constructed wetlands have been used to treat animal waste and are able to remove considerable amount of nitrogen (N), phosphorus (P), chemical oxygen demand (COD), biological oxygen demand (BOD), and solids. The removal mechanisms of N in constructed wetlands are sedimentation, adsorption, plant and microbial assimilation, nitrification-denitrification, and volatilization, whereas P removal was based on adsorption, precipitation, and plant-microbial assimilation. Marsh-pond-marsh (M-P-M), marsh-floating bed-marsh (M-FB-M) and continuous marsh wetlands (40 m x 11 m) were established at North Carolina A&T State University swine farm. Swine wastewater from anaerobic lagoon was treated in these constructed wetland cells at varying loads (2 to 50 kg/h/day) of N, and the N and P removal rates and volatilization contribution in N removal were measured. Higher than 30 kg N/ha/day has lowered the N removal because of less residence time and high hydraulic load. Also, it was noted that N removal was higher in warmer months than in colder months. When wastewater was applied at alternate flooding and drying regimes, higher drying days showed improved N removal which was due to better nitrification in the wetlands. Two pond areas were used as covered floating wetlands (pond area) with the introduction of air. Air treatment did not show any improvement in N removal and non-covered and covered pond areas (floating wetland) also did not show any difference in N removal. But covered pond areas certainly reduced NH3 volatilization. Phosphorus removal rates over seven years ranged from 30 to 40%; however, in 2007 the P removal has been reduced. Examination of the soil accumulation of N and P were highest in the sludge layer of the M-P-M and M-FB-M wetlands. For N accumulation, the inflow and outflow marshes had the highest rates of accumulation, whereas for P accumulation the pond section displayed the highest rate of accumulation. Observations of ammonia volatilization reveal that marsh sections have lower volatilization rates than the pond section and that volatilization in the pond section, in contrast to the marsh sections, was effected by N load. Also, it was noted that these wetlands were limited in nitrification by studying the denitrification enzyme activity. The thought was that these wetlands may not be providing enough oxygen to have high nitrification rates and therefore air was introduced in pond areas of M-P-M wetlands. These studies demonstrate that biological processes play a critical and significant role in removing N. The diversity of microorganisms and their functionalities in wetlands need to be recognized and intensely investigated. Predictive studies of the M-P-M wetland system against the reported literature reveal that while the system is effective in removing N, P treatment is inadequate, requiring pre- or post-wetland treatment.