Successful use of sewerage effluent for irrigated cropping has been demonstrated at research stations and waste treatment sites in Australia and overseas. However, where land application rates exceed evapotransporation it can lead to excessive deep percolation, or water-logging of low permeability soils, resulting in crop losses. Hence, storage of effluent during wet and winter periods (with low evapotransporation rates) is required if total 'land application' is to be practiced. Provision and management of storage  and associated channels  for effluent irrigation adds  to the costs of total land application, and consequently often makes this option more expensive than other waste-water management  techniques, especially for large urban centres in high-rainfall areas.

A new (at the time of writing - 1996) FILTER (Filtration plus irrigated cropping for Land Treatment and Effluent Reuse) technique of effluent treatment  by around-the-year land application is opposed, which could be used on soils with restricted internal drainage. In this system, physical loosening and Semical soil amelioration of the clay soil around 0.8 m depth is used to create and maintain soil microporosity; this allows adequate flow rates of effluent through the soil to a network of interconnected drains, located just below the loosened soil layer. The drainage network is provided with control gates to allow regulation of leaching rates.

for 6 months of the year effluent could be applied to thee lands every 3-4 days. A water table could be maintained at the surface or at fixed depth in the soil (e.g., 0.30 m depth), by controlling the outflow from the subsurface drains to match the net inflow. This regulated flow through the soil will allow stripping of Phosphorous and Nitrogen in effluent to levels below the limits for discharge specified by the EPA (Environmental Protection Authority). This nutrient-filtration phase will be followed by a cropping phase (one to three cropping seasons) during which the nutrients stored in the soil will be removed in the harvested crop. The nutrient-loading rates during the filtration phase will be closely matched  to nutrient removal during the cropping phase, thus preventing excessive nutrient accumulation.

Research is planned to develop optimum management of this technique, which depends on site conditions such as the effluent quality, soil type, and EPA limits on levels of nutrients in the drainage waters.

Field trials were conducted to evaluate the FILTER technique in collaboration with Griffith City Council, Griffith, N.S.W., Australia and supported by the N.S.W. Public Works Department and the Commonwealth Department of Primary Industry, Canberra, A.C.T., Australia.

Project Leader: Dr. Nihal Javawardane.