Removal of COD and BOD5 in Sanitary Sewer Overflow with Fixed Media Bioreactors

Abstract

EPA estimates that 23,000-75,000 overflow events of sanitary sewer systems occur annually in the Unites States, discharging 1-3107 m3 of untreated wastewater. Treatment of sanitary sewer overflows (SSO) has not been widely used due to the cost and difficulty of remote management. Variable hydraulic and pollutant loading also limits the treatment. Fixed film bioreactors can be used as on-site wastewater treatment systems that have a relatively low cost and maintenance and can potentially provide high treatment efficiency. The purpose of this research was to test the removal of BOD5 and COD in SSO using sand, peat and textile (felt) as treatment media. The influent SSO was a mixture of primary sludge from a wastewater treatment plant diluted with tap water. To simulate a 25-year overflow event, the wastewater was loaded at 0.2 m/hr (5 gal/ft2/hr) for six hours once a month, followed by monitoring of the effluent BOD5 and COD. The filter media and influent BOD5 concentration were two major factors that impacted the removal of BOD5 (p<0.001). The effluent BOD5 concentration of sand columns was the lowest, 148 mg/L. The felt-based system had the highest effluent BOD5 concentration among the three media. Filter media type, influent concentration, and operation time each had a significant effect on the COD removal of bioreactors (p= 0.001). Sand bioreactors averaged about 90% COD removal. Peat had the lowest average removal of 75%. High influent COD concentration enhanced the relative removal of felt media. The results showed that sand medium performed well for the removal of BOD5 and COD in SSO.