Physicochemical Treatment of Low Strength Greywater for Toilet Flushing Reuse

Abstract

Greywater is the wastewater that results from laundry, kitchen sinks, dishwashers, bathtubs, showers and hand basins. Greywater can be segregated from backwater and can be treated easily for reuse in irrigation, carwash, or toilet flushing. It provides an interesting alternate of fresh water especially in water scarce areas. Greywater having low strength of contaminants can be treated and reused effectively by using physicochemical treatment systems. The objective of this study was to design a greywater recycling and reuse system at IESE, NUST, and evaluate the system performance to produce a treated effluent quality that meets the greywater toilet flushing reuse standard. Two sources of greywater: Boys Washroom at IESE, NUST and Ghazali Boys Hostel, NUST were studied. The treatment system targeted the removal of suspended particles and organic content followed by disinfection by chlorine. Based on the results, average daily greywater production was equal to 85 gallons per day and the greywater quality was fairly low strength. Vertical Pressure Sand Filter contributed to the 80% removal of the suspended particles while the overall greywater treatment system efficiently removed up to 90% of the turbidity and TSS for both greywater sources. The organic content removal in the form of BOD and COD was 80% which was majorly achieved through Granular Activated Carbon Filter. The optimum disinfectant dosage was selected as 11 mg/L of chlorine at which the residual chlorine was >1 mg/L after 30-minute contact time and no Total Coliform growth were observed for the period of four days. The saved water is sufficient for up to 5,200 flushes in case of older toilets and 10,000 flushes in newer toilets in a year. Greywater reuse for toilet flushing can be considered a potential sustainable solution to water shortages experienced in a water-stressed country like Pakistan.