Phosphorus as a limiting factor on sustainable greywater irrigation

Water reuse through greywater irrigation has been adopted worldwide and has been proposed as a potentialsustainable solution to increasedwater demands. Despite widespread adoption, there is limited domestic knowledgeof greywater reuse. There is no pressure to produce low-level phosphorus products and current guidelinesand legislation, such as those in Australia,may be inadequate due to the lack of long-termdata to provide a soundscientific basis. Research has clearly identified phosphorus as a potential environmental risk to waterways frommany forms of irrigation. To assess the sustainability of greywater irrigation, this study compared four residentiallots that had been irrigated with greywater for four years and adjacent non-irrigated lots that acted as controls.Each lot was monitored for the volume of greywater applied and selected physic-chemicalwater quality parametersand soil chemistry profiles were analysed. The non-irrigated soil profiles showed low levels of phosphorusand were used as controls. The Mechlich3 Phosphorus ratio (M3PSR) and Phosphate Environmental Risk Index(PERI) were used to determine the environmental risk of phosphorus leaching from the irrigated soils. Soilphosphorus concentrations were compared to theoretical greywater irrigation loadings. The measured phosphorussoil concentrations and the estimated greywater loadings were of similar magnitude. Sustainable greywaterreuse is possible; however incorrect use and/or lack of understanding of howhousehold products affect greywatercan result in phosphorus posing a significant risk to the environment.