Parameters affecting greywater quality and its safety for reuse

Reusing greywater (GW) for onsite irrigation is becoming a common practice worldwide. However, alongside its benefits, GW reuse might pose health and environmental risks.

This Israeli study assesses the risks associated with onsite GW reuse, and the main factors affecting them.

Greywater from 34 households in Israel was analysed for physicochemical parameters, Escherichia coli (as an indicator for rotavirus), Pseudomonas aeruginosa, and Staphylococcus aureus. Each participating household filled out a questionnaire about their GW sources, treatment, and usages.

Quantitative microbial risk assessment (QMRA) was performed based on the measured microbial quality, and on exposure scenarios derived from the questionnaires and literature data. The type of treatment was found to have a significant effect on the quality of the treated GW.

The average E. coli counts in GW (which exclude kitchen effluent) treated by professionally designed systems resulted in acceptable risk under all exposure scenarios, while the risk from inadequately treated GW was above the accepted level as set by the World Health Organization (WHO). Barriers that reduce exposure (e.g. gloves, drip irrigation) would reduce the overall risk.

In conclusion, safe greywater reuse requires a suitable and well designed treatment system. A risk-assessment approach should be used to adjust the current regulations/guidelines, and to assess the performance of GW treatment and reuse systems.

Science of The Total Environment, Volume 487, 15 July 2014, Pages 20–25.