Greywater reuse for irrigation: A critical review of suitability, treatment, and risks

Greywater accounts for approximately 75 % of domestic wastewater and generally contains fewer contaminants than domestic wastewater. Therefore, its treatment and reuse represent a promising approach to supplement irrigation demand. This study comprehensively evaluates the quality characteristics of greywater based on its source, applied treatment methods, and its potential health, environmental, soil, and agricultural impacts. Various physical, chemical, and biological treatment processes have been analysed, with the most commonly employed technologies including membrane bioreactors (MBRs), constructed wetlands, media filtration (sand, activated carbon), disinfection methods (UV, chlorine, ozone), and advanced oxidation processes. The effectiveness of these methods has been assessed concerning the intended reuse application, emphasizing the critical role of disinfection in ensuring safe irrigation use. The health and environmental implications of greywater reuse have been examined, focusing on the risks associated with pathogen contamination, detergent residues, and micropollutants, while also evaluating the efficiency of treatment processes in mitigating these risks. From an environmental perspective, the accumulation of essential nutrients such as nitrogen and phosphorus, the potential for salinity buildup, and alterations in soil microbial balance have been investigated. Regarding soil and agricultural impacts, this study analyzes how greywater reuse influences soil structure (e.g., permeability, infiltration), plant growth responses, and the accumulation of heavy metals. These findings contribute to the development of scientifically grounded recommendations for the safe and sustainable reuse of greywater within water management strategies, promoting its role as an alternative water source for irrigation.