Surface wetlands for the treatment of pathogens in stormwater: three case studies at Lake Macquarie, NSW, Australia

The treatment of stormwater using surface constructed wetlands has become common in the last decades. However, the use of constructed wetlands for stormwater management has not been thoroughly evaluated in their capacity to treat microbial loads. The case studies presented in this paper are situated at Lake Macquarie, a large estuarine lagoon located approximately 150 km north of Sydney, Australia. To protect the lake ecosystem from the impact of increasing urban development, the local Council constructed numerous stormwater quality improvement devices (SQIDs) at selected locations. The SQIDs typically consisted of trash racks, gross pollutant traps and surface constructed wetlands. To evaluate the effectiveness of three of these devices in reducing faecal contamination, water samples were collected for faecal coliforms (FC) during and following rainfall at inlets and outlets of the structures. Results indicated one of the SQIDs as the most efficient for bacterial reduction, while the other two provided low or non reduction of FC. Results also illustrated dependence of bacteria reduction on flow conditions. Comparison of devices suggested that hydraulic residence times and other design parameters strongly influenced the capacity of each device to reduce FC counts during different weather conditions.