Grey Water Recycling for Reuse in Toilet Flushing: a Case Study in Thailand

Grey water from washbasins represents the least polluted source of waste water in households and buildings. This research study investigated three alternatives in recycling grey water from washbasins for reuse in toilet flushing systems. Grey water was collected from the washbasins of a nine-storey university building. The water was treated employing three distinct treatment systems in order to determine the most appropriate system when reusing such water in flushing systems. The grey water treatment systems under scrutiny were composed of a sedimentation tank, a 24-hour aeration tank and a sand and carbon filtering tank, functioning in conjunction with a final sedimentation tank. The water quality from the selected treatment system had TSS, BOD₅, and Turbidity measures of 1.67 mg/l, 3.33 mg/l, and 3.33 NTU, respectively. Fecal coliform bacteria and E. Coli were not found in the treated water. Efficiency measures in reducing TSS, BOD₅, and Turbidity were 93%, 75%, and 91%, respectively. Fifty-five toilet users were interviewed during the experiment, sixty nine percent of which reported that the recycled water was comparable to tap water. In conclusion, this research recommends treating grey water from washbasins and reusing it in flushing systems in order to deploy water more efficiently in buildings.