An Overview of Graywater Collection and Treatment Systems

The use of graywater is becoming more and more common, especially in areas where water resources are scarce. A wide range of graywater systems exists; from simple collection to complex collection/treatment. Currently, the market recognized this trend and need for using graywater. So, some manufacturers made some effort regarding innovating engineered graywater collection/treatment systems. This paper examines some of the graywater collection and treatment systems available in the market for use in a household and in some other buildings along with their weaknesses and strengths. Several systems were selected to show the diversity of systems available and the big picture. Designers of the systems tried to comply with the guidelines set by authorities on the use of graywater such as underground irrigation, no cross connections with potable water system, vented and sealed tanks, no human contacts, etc. At the commercial level, toilet flushing did not receive as much attention as landscape irrigation in the US. However, several successful cases for using graywater in toilet flushing were found in other countries like Germany, Australia, and the UK. The more complex systems are utilized for toilet flushing. Treatment units such as sedimentation, filtration (coarse filters and sand filtration), aeration, and disinfection were encountered. Biological treatment existed where multi-house or multi-user collection systems exist (e.g. hotel and multi-storey residential building). Based on that overview, simplicity, flexibility, effectiveness, reliability, and cost are criteria that should be considered while designing a graywater system. These criteria were used in designing a graywater system in a single household in Fort Collins, CO. The system involved continuous recycling and aeration. Further system modifications included assessing the level of filtration and disinfection needed to maintain an effective system. Preliminary investigations showed acceptable levels of indicator organisms. Emphasis has been placed on microbial quality since local boards of health are concerned with human contact and exposure to enteric pathogens.