Use of leaching chambers for on-site sewage treatment

An innovative chamber system was installed for on-site sewage treatment beneath an active parking lot at a restaurant near Cornwall, Ontario. The configuration of this prototype system used polyethylene leaching chambers over which wastewater was allowed to trickle. The chambers were vented to the surface to provide direct, passive air transfer. This demonstration project was examined as a cost-effective wastewater treatment alternative for a very constrained site. The leaching chambers were installed over a geotextile-covered sand filter bed. Chamber sidewall contact contributed an additional 50% to the total soil contact area hence justification for a footprint reduction. A labile carbon source (sawdust) was added into one half of the bed to encourage dissimilatory denitrification. Average hydraulic loading was 50 l m(-1) day(-1) (5 cm day(-1)). Treatment rates exceeded more than 4 orders of magnitude removal for E. coli; 90% biochemical oxygen demand; ammonium; and 99% total phosphorus. Nitrate-N on the carbon-amended side averaged 0.6 mg l(-1) compared with 8.6 mg l(-1) on the (non-carbon) control side. This project has demonstrated that effective on-site treatment can be accomplished. Flow and load equalization, pulse dosing, chamber venting, phosphorus precipitation, and denitrification were keys to treatment success. Applications include domestic and commercial sites.