|Szogi, A - WASHINGTON STATE UNIV.|
|Humenik, F - NC STATE UNIV.|
|Reddy, G - NC A&T STATE UNIV.|
Submitted to: Recycling of Agricultural Municipal and Industrial Residues
Publication Type: Proceedings
Publication Acceptance Date: June 19, 2000
Publication Date: N/A
Interpretive Summary: In the USA there is enormous public sentiment against traditional animal waste management via anaerobic lagoons and land application of wastewater. Much of this concern is because the large number of swine in concentrated areas promotes heavy nutrient loading to available land. Resolution of the problem via traditional municipal wastewater treatment has not proven to be esatisfactory because of difference in the waste and economics. Farms are generally thought to be better suited for passive, natural treatment alternatives with very high loading potential. One of the few such alternatives is constructed wetland treatment. Constructed wetlands are located on upland sites, and they may contain either natural or agronomic plants. We used both continuous marsh and marsh-pond-marsh systems. The plant communities grown in the wetlands were rush-bulrush, bur-reed-cattail, soybean grown in saturated-soil culture, and flooded rice. The nitrogen removal rates were remarkably constant for all of the wetland - as much as ten-fold higher than standard agronomic applications of manures. Additionally, initial estimates indicate that problems with ammonia loss were minimal. Microbial transformations were likely the more dominate treatment factors. Our findings indicate that constructed wetlands are a viable alternative for improved animal waste treatment.
Technical Abstract: In the USA, we assessed constructed wetlands (surface flow) with both natural and agronomic plants for treatment of anaerobic-lagoon swine wastewater. We used both continuous marsh and marsh-pond-marsh systems. The plant communities grown in the wetlands were rush-bulrush, bur-reed-cattail, soybean grown in saturated-soil culture, and flooded rice. Nitrogen loading rates ranged from 2 to 35 kg/ha/day. The N removal rates were remarkably constant for all of the wetland types up to a loading of 25 kg/ha/day [y = 0.86 (N loading rate) - 0.3, R**2 = 0.98]. At the lower loading rates, plant and soil accumulation constituted a significant portion (~ 30%) of the total amount applied, but at the higher loading rates, microbial transformations were likely the more dominate treatment factors. Denitrification enzyme assays (DEA) indicated that nitrate was the limiting factor and that denitrification could be increased dby protocols to promote oxygen incorporation or pre-wetland nitrification of wastewater. However, the DEA values were not exceptionally high which indicates that ammonia volatilization might be significant. However, initial values of ammonia obtained via open chamber measurements indicate minimal losses.