Graywater research findings at the residential level

Abstract

As populations continue to grow and water supply sources become more stressed, innovative means for reducing our reliance on municipal water are becoming more prevalent. Graywater reuse is one water conservation practice which has the potential of reducing household water demands by 30% indoors and outdoors, depending upon irrigation demands. In areas where water scarcity is an ongoing challenge, implementation of graywater reuse practices is becoming more widely accepted. However, constituents commonly found in graywater may pose a threat to the environment or human health. The objective of this thesis is to present graywater research findings from 2003 to the present which have occurred as part of a graywater research program at Colorado State University. The research findings address issues and concerns raised regarding graywater and present the case for graywater reuse being a viable safe, simple and economical technology. In order for graywater reuse applications to continue to expand, the concerns regarding public health risks raised by regulating agencies and public health officials need to be fully addressed. Early research on a residential pilot graywater system for outdoor irrigation formed the foundation for more recent research targeting effects on soil quality (chemistry and microbiology), plant health, groundwater contamination, graywater quality and potential human health risks (Sharvelle, 2009, Shogbon, 2010, Neghaban-Azar, 2012). An optimal residential graywater system prototype for drip irrigation has been developed (Alkhatib, 2008) which includes two tanks, one for collection, coarse filtration and settling and the other for usable storage. The WERF study (Sharvelle et al., 2012) showed no need for disinfection of graywater being used for irrigation. The presence and levels of pathogens on field sites whether being irrigated with either municipal water or graywater were the same. The WERF research (Sharvelle et al., 2012) coupled with the prototype configuration supports no need for inclusion of disinfection as part of the treatment train when graywater is being applied for irrigation. The most recent research is a multi-residential graywater reuse demonstration project for toilet flushing completed on Colorado State University campus, Aspen Hall (Hodgson, 2012). Graywater used for toilet flushing will require a higher level of treatment due to the increased potential for exposure. Hodgson studied and selected Chlorine as the disinfectant for the residence hall. The resulting water quality with storage, filtration and disinfection determined by Hodgson achieves similar results as found in the 2003 residential pilot graywater system research which used UV rather than chlorine. The difficulty of navigating the varying graywater regulations between states drove Glenn's research (2012) into the graywater requirements for each state and who developed a tool for use by regulators to homeowners for finding an appropriate graywater technology to meet their local requirements. Also, a need was identified for providing a comprehensive guidance manual for separating graywater from blackwater for graywater reuse (Bergdolt, 2011). The manual provides design guidance and maintenance best management practices to ensure safe and appropriate graywater installation and operation.