Effective Treatment of Domestic Effluent with a Peat Biofilter – A Case Study at Tingha

The discharge of septic tank effluent onto highly permeable soils may lead to nutrients entering the groundwater or flowing laterally from the site to pollute local streams. Seven domestic dwellings in a small village in northern New South Wales (NSW) were refurbished with new septic tank systems, and individual on-site land application systems were constructed to reduce the high risks of contamination of the groundwater and other off-site effects in this village. Peat biofilters were installed between the septic tank and the subsoil leach drains to reduce levels of phosphorus, nitrogen and faecal coliforms entering the soil. Wooden boxes, each 3 m x 3m x 0.9 m deep were built above ground, over prepared leach drains. Firstly, 100 mm of sand and 600 mm of a blend of humic and fibrous peat were placed into the box. Secondly, a pipe distribution system was placed on top of the peat and an additional 100 mm of peat covered the distribution system. Each 60 litres of effluent, pumped from a collection well into the distribution system, percolated through the biofilter before entering the leach drains underneath. Six septics and five of the seven peat biofilters were monitored between April 2001 to March 2002 for a range of chemical and biological indicators. Faecal coliform removal averaged 99.7%, ammonia reduction was 96% although most of this was converted to nitrate (increase of 275%), while nitrogen and phosphorus removal averaged 54% and 75% respectively. The peat biofilter was an economic long-term solution, utilising a low energy, low maintenance system to improve the quality of the effluent, removing problem nutrients and allowing the effluent to be more safely applied to the sandy soils.