The use of constructed wetlands as an alternative form of on-site wastewater treatment in a temperate climate

It is estimated that between 40% and 60% of on-site systems in Australia are not treating domestic wastewater to acceptable levels. This study investigates the viability of constructed wetlands as an alternative form of on-site treatment of domestic greywater in temperate climates. A case study wetland was constructed to treat domestic greywater from a single household, providing an insight into the design, construction, operational performance, hydraulic flow and reed growth of a small-scale wetland operating in Tasmania. A review of current literature provides an insight into constructed wetlands, emphasising their use as a form of on-site wastewater treatment. Interviews with officers from five local government councils indicates that knowledge of constructed wetlands is very limited, but a great deal of interest was shown by the interviewed environmental health officers, who suggested that they may be willing to trial wetlands within their municipalities. All the local governments interviewed were experiencing problems with the current and accepted forms of on-site wastewater treatment. Testing of the case study wetland over a nine-month period showed that pollutant removal processes were occurring across all testing parameters except ammonia and phosphorous. Significant findings from the case study that would improve the quality of the final effluent include the importance of healthy reeds with deep root systems, improving hydraulic flow within the Wetland to prevent short-circuiting, and the necessity of additional pre and post wetland treatment. Greywater alone does not have sufficient nutrients and trace elements to sustain vigorous growth for the common reed, Phragmites australis. A combined flow of black and greywater led to vigorous and healthy reed growth. The wetland produced an effluent with an average of 64 mg/L BOD5 (60% removal), 48.5 mg/L suspended solids (88% removal), 18,427 FCU/100mL faecal coliforms (99.2% removal), 0.008 mg/L nitrite (65% removal), 2.9 mg/L nitrate (6% removal), 2.2 mg/L ammonia, 6.7 mg/L phosphorous, 537 pS/cm conductivity, and a pH of 7.7. It is expected that treatment would improve as the reeds and root systems mature and the design improvements are implemented.