Assessment of biologically active GAC and complementary technologies for gray water treatment

The reuse of gray water for applications ranging from irrigation to showering is a viable means to reduce net water demand when water supplies are stressed. The objective of this study was to investigate the treatment of gray water using biologically active granular-activated carbon (GAC) and complementary technologies. Technologies were challenged individually or in combination using a synthetic gray water formulation based on NSF/ANSI Standard 350. Specific technologies included: GAC; biologically active GAC (BAC); a newly developed intermittently operated BAC (IOBAC) process; ion exchange (IX); coagulation with a cationic polymer; microfiltration; ultrafiltration (UF); and multi-barrier combinations thereof. For control of organic contaminants such as surfactants, BAC and IOBAC performed well over test periods as long as 6 months. Combinations of IOBAC treatment with coagulation pretreatment and UF post-treatment resulted in sustained chemical oxidant demand and turbidity value reductions in excess of 90 and 99.5%, respectively. Such an approach would be useful for gray water treatment for low tier applications like irrigation or toilet flushing, or as a pretreatment system upstream of reverse osmosis (RO) membranes and/or advanced oxidation processes for high tier reuse applications such as showering.