Subsurface wetlands as effective wastewater treatment and recycling options in urban villages: WA case studies

Around the world there is a paradigm shift occurring, one that is moving away from traditional centralised wastewater infrastructure towards decentralised wastewater system options. In Western Australia (WA) the development of decentralised systems has been slow. However significant steps have been made towards making decentralisation a reality, with several innovative technologies based on natural biological processes being trialed, such as constructed wetlands. The WA State Government is investing research in practical case studies that will assess the viability of decentralised wastewater schemes, within WA urban villages. The research is to be conducted over three years starting with two decentralised greywater systems, progressing in the final year (2008) with research into combined wastewater systems. The first case study site, Bridgewater Lifestyle Village (BWLV) located in Erskine south of Perth, will encompass 380 individual greywater systems that are centrally managed with the treated greywater used to irrigate the gardens of each home. The second site, Timbers Edge Residential Resort (TERV) located in Dawesville also south of Perth, will encompass 260 homes connected to one centrally managed greywater treatment system, with the treated greywater being used to irrigate the estates public open space. Both of these sites are located in a high population growth corridor adjacent to the Peel Harvey Estuary; are within close proximity to RAMSAR5 protected wetlands; and experience high water table levels. In order to meet environmental and public health concerns, innovative solutions would be required. Each site employs a wastewater treatment and recycling system that mimics natural processes. This paper will introduce two types of subsurface constructed wetlands that are either operating or will be operating in the near future at the two case study sites. The first system discussed is the evapotranspiration trenches at BWLV. These are a low maintenance biological system consisting of a plastic lined gravel-filled trench planted with various hardy aquatic plants and will be placed in home sites where the groundwater table is higher than 50cm. The second system at TERV is known as the Biofilter system and consists of a series of concrete chambers planted with wetland plants. This paper will then discuss how these systems recycle the water locally to reduce water demand; what the residents’ responsibilities are and how different management arrangements can effectively manage and operate these systems