INTEGRATED RECIP® WATER TREATMENT SYSTEM WITH U.V. DISINFECTION FOR DECENTRALIZED WASTEWATER TREATMENT: PART I: MICROBIAL DYNAMICS

A novel wastewater treatment system (ReCip®), developed for on-site and decentralized treatment of domestic wastewater, was modified by installing either low pressure-low intensity 25 and/or 65 watt U.V. lights into the systems pumping operation. This modification enabled the wastewater to be exposed to low intensity U.V. light up to 24 times per day. In addition, two subsurface-flow constructed wetlands were installed down-gradient from the ReCip-U.V. treatment unit to facilitate removal of nitrate and to evaluate re-growth of indicator organisms (E.coli and Enterococcus). The integrated system treated from 200 to 400 gallons (0.87 m3 influent ± 0.266 m3/day) of wastewater each day. It was hypothesized that this new ReCip® U.V. configuration could be effective and less costly than conventional one-pass U.V. disinfection systems because of the long hydraulic retention time (2-3 days), and the recurrent exposure of pathogens to low intensity U.V. lights. Over the course of these studies, three different light-position configurations and two wattages were tested. During the final six months of monitoring, the reciprocating U.V. light configuration (65 watt lamps in each of cells C and D), resulted in 3-5 log reductions of E.coli and Enterococcus. In most instances, E.coli levels were reduced to less than 5 cells/100 mL of treated effluent. The use of U.V. did not impact wastewater treatment and the integrated ReCip-U.V. system provided excellent wastewater treatment with respect to removal of suspended solids, odor, turbidity, chemical oxygen demand (COD), TKN and ammonia-nitrogen. Treated wastewater was clear, odor free, with low concentrations of indicator bacteria, organic matter, and nitrogen. Based on results of the twenty two month study, it is recommended that the system have two 65 watt U.V. lights, one in each of the last two ReCip® treatment cells (C and D), and that the ReCip® system be operated such that the wastewater is exposed to U.V. lights from 12 to 24 times per day.