Source separated graywater: Chemistry, unit operations, and criteria towards re-use

Abstract

Water scarcity due to increasing population, climate change, and natural resource depletion has led to exploring alternate sources of useable water through the treatment and reuse of wastewater. Additionally, increasing complexity of logistics and costs to transport water are driving the development and demonstration of decentralized wastewater treatment units. Graywater, or wastewater that does not include water from toilets, is a particularly promising source of water for reuse due to lower contaminant loading when compared to other wastewater streams. In this study, ultrafiltration (UF) and reverse osmosis (RO) membrane technologies with ultraviolet (UV) disinfection was evaluated for the treatment of low strength graywater from shower facilities over a six-month period. With >100,000-gallons of source separated graywater treated, this is one of the largest and most comprehensive graywater treatment events to date. Water reuse guidelines were established to reflect the most stringent reuse requirements in the United States. The combined treatment train of UF and RO met compliance metrics for all analytes of interest. This UF/RO system not only addresses issues with water quality, but water quantity as well. A water recovery rate of 85 % multiplies the effective volume of usable water by a factor of 6.5, creating a significant reduction in volume required. Both the quality of the treated water and the effective volume gains from the multiplier effect make decentralized treatment of source separated graywater by UF/RO a viable technology to address physical and economical water scarcity. This system can be used in austere environments to capture a currently untapped source of water for reuse.