Current status of recycled water for agricultural irrigation in Australia, potential opportunities and areas of emerging concern

Abstract

Three per cent of Australian agricultural irrigation comes from recycled water. The 1990s establishment of states' Environment Protection Authorities and their regulatory standards and effluent disposal charges led to effluents from Wastewater Treatment Plants (WWTPs) being used for agricultural irrigation. Adelaide and Melbourne, with agricultural land close to plants, expanded intensive vegetable industries. Sydney has limited land available and discharges 90% of its sewage through deep ocean outfalls after primary treatment. Brisbane with more distant farms, found pumping effluent hard to justify economically. Some larger regional cities/towns purchased farms to manage discharges as commercial businesses. Others market recycled water to nearby growers. Uses depend on treatment standards. Water with secondary treatment and pathogen reduction is suitable for processed crops, grazed or cut pastures, sugar cane, cotton and wine grapes, and is widely used for amenity horticulture, but requires careful salinity management. Water with tertiary treatment meeting log reduction pathogen standards may be used on food crops eaten raw (e.g. lettuce). Commonwealth government subsidies during the millennium drought (2001-2009) supported WWTP upgrades and irrigation infrastructure expansion. However, seasonal water demand and unwillingness of growers to pay full cost recovery prices led to some recycled waters still being discharged to water bodies. Some schemes over-estimated likely irrigation demand. Currently, there is scope for further developing recycled water agricultural irrigation by submitting business cases for subsidies from the new National Water Grid Authority. But there is increasing interest in the potential use of recycled water for drinking water augmentation, for which Australia has had guidelines since 2008. Perth has capacity for 28 hm³/yr recycled water to replenish its groundwater drinking sources while Brisbane has three plants totalling 84 hm³/yr for indirect potable supply, but not yet operating. Recycled water for critical human needs could eventually out-compete agricultural irrigation.

Keywords: Effluent discharge; Farming; Reverse osmosis; Salinity; WWTP; Water reuse.