PERFORMANCE ANALYSIS OF RECIRCULATING BIOLOGICAL FILTERS FOR SAMLL-SCALE APPLICATIONS: FILTER PROPERTIES AND OPERATION

Recirculating sand filters (RSFs) were studied as an option for treating decentralized or clusterbased wastewater. This study examined RSF performance using two filter media (Crushed glass and sand), two hydraulic loading rates (HLRs) (3-5 gpd/ft2 per day and 10-15 gpd/ft2 per day), two recycle ratios (1:3-1:5 with HLR of 3-5 gpd/ft2 per day, 1:1-1:2 with HLR of 10-15 gpd/ft2 per day), and two dosing frequencies (48 times per day, and 96 times per day). The domestic wastewater influent, from Mill Cove Wastewater Treatment Plant (Bedford, NS, Canada), served as the feed water in the bench-scale experiments described herein. In general, crushed glass demonstrated similar performance as conventional silica sand under a range of operational characteristic. In particular, at high dose frequencies the average effluent BOD from the sand filter was 4.8 mg/L, and the average BOD from the crushed glass filter was 8.5 mg/L. Similar performance data was obtained for TSS, NH4 +N, TN, and Fecal Coliform (F.C). The NH4 +-N values in the filter effluents were less than 1 mg.l−1 on average, which meant NH4 +-N supplication was a possible limiting factor for biomass growth. These results indicate that crushed glass has the potential to replace sand as a biofilter medium, which could be an important secondary market for recycled glass or for geographic regions where sand is not readily available.