LONG-TERM TREATMENT PERFORMANCE OF INNOVATIVE SYSTEMS

Abstract

Six full-scale innovative onsite wastewater treatment systems were installed in 1999 to replace failed septic systems. The systems installed consisted of two textile filters; one textile filter followed by a bottomless sand filter; one single pass sand filter; one modular peat filter followed by an ultraviolet (UV) light disinfection unit; and one fixed activated sludge treatment system followed by a UV disinfection unit. This paper reports results of long-term treatment performance monitored for BOD5, TSS, fecal coliform, TP, and TN collected for 33 sample events over a 48-month period. All packed bed filters operating in a single pass or recirculating mode produced mean BOD5 and TSS effluent concentrations between 2–9 mg/l, representing a 91–99% reduction. The fixed activated sludge treatment system produced BOD5 and TSS concentrations that averaged 15 and 10 mg/l, respectively. TN reductions averaged 15 and 21% for the single pass sand filter and single pass modular peat filter, respectively. TN reductions for the two recirculating textile filters averaged 44–47%. Mean TN concentrations for the one textile filter operating in a mixed effluent mode and the fixed activated sludge treatment system were 8 and 14 mg/l, respectively, and met the Rhode Island TN standard of <19 mg/l on 100% and 77% of the sampling events, respectively. TP removal in the single pass sand filter was 40%, and minimal in all other systems. The single pass sand filter consistently achieved the highest level of fecal coliform reduction (3.9 logs) followed by the two recirculating textile filters (3.1–3.4 logs), and then the peat filter (3.3 logs). The two UV light disinfection units produced effluent with a geometric mean fecal coliform concentration between 2 and 6 counts / 100ml. Operational procedures/problems encountered for the systems are also briefly discussed.