INTERMITTENT PACKED BED FILTRATION: INVESTIGATION OF REMOVAL MECHANISMS FOR IMPROVED DESIGN

Twenty-five percent of the households in the United States use decentralized systems to treat residential wastewater. Septic tanks followed by soil absorption systems comprise ninety-five percent of these onsite wastewater treatment systems. Failure of septic systems is common and primarily caused by inadequate biological treatment in the soil absorption field. Failing septic systems can become a direct source of contaminants to nearby surface water and groundwater. The shift from disposal of onsite wastewater to reliable and adequate treatment of that water prior to disposal or reuse is now a recognized imperative (U.S. EPA, 1998). Alternatives to the conventional systems must be investigated systematically through controlled studies.Three intermittently dosed, packed bed filters were operated for 4 months. Each filter utilized a different medium: sand, nonwoven textile fabric (NWTF), and sintered glass. During that time, influent and effluent measurements of two conventional wastewater quality parameters, total suspended solids and BOD5, were made. It was concluded that the shallow (15 cm maximum depth) packed bed filters were able to produce high quality effluent despite the relatively high loading rate of 0.12 m/day. NWTF has an identified advantage over sand, the conventional filter medium, due to its very high porosity. The sand filter clogged regularly at the higher dosing frequency, likely due to higher bacterial concentrations in the surface layer. The NWTF was able to provide a more robust degree of treatment that was not affected by the increased dosing frequency. Ongoing research is now focused on the effect of dosing frequency on the type of bacteria comprising the microbial community.