Water quality of gray water for reuse

Abstract

This study was designed to evaluate the safety of gray water for reuse purposes. The physical and chemical quality of treated gray water met water reuse standards set by the State of Arizona for surface irrigation purposes. The number of microorganisms in gray water significantly decreased after biological treatment and sand filtration. However, the number of fecal coliform bacteria in treated gray water was still higher than the standard for reuse as set by the State of Arizona for surface irrigation. This is also true for rain water which was stored in a tank. No indigenous Salmonella were isolated from gray water. It was found that both Salmonella typhimurium and Shigella dysenteriae, seeded into gray water, can persist for at least several days. This implied that there may be some risk associated with gray water reuse when the gray water contains these pathogenic bacteria.