University of California Water Resources Center

Onsite wastewater treatment systems were operated at the UC Davis wastewater treatment facility for investigation of the fate of indigenous coliphage, nitrogen, and phosphorus in these systems. The treatment systems were selected because of their high efficiency and role in the future of onsite wastewater treatment. The treatment systems included (a) three high porosity, high surface area multi-pass biofilm reactors, (b) two submerged aerated biofilm reactors; one was inoculated with specific bacteria (i.e., bioaugmentation) for enhanced performance, and (c) a traditional septic tank followed by sand infiltration beds. In addition, soil basins were used to further evaluate the fate of contaminants after discharge from a treatment process to the environment. The septic tanks were found to remove less than 12.5 to 23.4 percent of nitrogen, 0 to 6.7 percent of phosphate, and 16.5 to 25.3 percent of virus, from the influent. The textile biofilters were found to remove 35.2 percent of nitrogen, no phosphorus, and 82 percent of virus from septic tank effluent. The sand beds were found to remove 12.8 percent of nitrogen, no phosphorus, and 96.4 percent of virus. After installation of the aeration systems, the sand bed performance improved for all parameters measured. In the soil infiltration system, all virus were removed and nitrogen and phosphorus were reduced to concentrations of 2 mg/L after passing through 30 in of Yolo loam soil.