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Crehan, Ryan

Natural Resources

2005

MS

Anaerobic digestion of agriculture waste is becoming increasing common due to its ability to reduce the amount of biological solids, limit nuisance odors and produce economically beneficial methane. While the process may improve farm viability, the digester effluent has the potential to become a non-point source pollutant unless properly contained. As anaerobic digesters become more common in the treatment of dairy manure, there will be a pressing need to determine appropriate systems to treat the waste generated from these systems. A pilot scale anaerobic digester coupled with duckweed pools and a subsurface flow constructed wetland was monitored to determine the effluent quality of the digester and to perform an analysis of the constructed wetland treatment system. Significant reductions in total phosphorus, ammonia, total suspended solids and CBOD were observed. Ammonia levels in the digester effluent were found to be extremely high (683 mg/l) and limited duckweed growth. Nitrification was promoted through the use of a trickling filter which reduced ammonia levels and improved duckweed growth. The largest mechanism for phosphorus removal was settling. Duckweed uptake followed by harvesting also accounted for a substantial percentage of the nitrogen and phosphorus removal. Uptake by emergent wetland species accounted for a low percentage of the phosphorus removal. Recommendations for a redesigned sizing are presented based on the performance of the system.