Assessment of greywater quality and performance of a pilot-scale decentralised hybrid rainwater-greywater system

• Published in: Journal of cleaner production 2018-01, Vol.172, p.81-91
• Main Authors: Leong, Janet Yip Cheng, Chong, Meng Nan, Poh, Phaik Eong
• Format: Article
• Language: English
• Subjects: Activated carbon; Alternative water; Filtration; Malaysia; Ozone; Principal component analysis
• ISSN: 0959-6526; 1879-1786
• DOI: 10.1016/j.jclepro.2017.10.172

Decentralised hybrid rainwater-greywater systems can switch between climate-independent greywater during dry seasons or climate-dependent rainwater during monsoon seasons, resulting in higher water savings than either rainwater harvesting or greywater recycling systems alone. However, hybrid systems are not widely adopted due to a lack of data on untreated rainwater and greywater quality and a paucity of case studies on pilot-scale systems. This study aimed to monitor untreated greywater quality from two full-scale greywater recycling systems and to assess the performance of a decentralised hybrid rainwater-greywater treatment system operating on a pilot-scale under controlled conditions. Both mixed greywaters sourced from washbasins and ablution activities, and from washbasins, showers, baths, and laundry discharges must be treated prior to reuse: untreated greywater was frequently contaminated with faeces (20/32 samples tested positive for Escherichia coli), and exceeded the allowable Malaysian limits for both recreational waters with body contact (Class IIB) and irrigation waters (Class IV) for total coliforms (27/32), biochemical oxygen demand (BOD5) (19/32), chemical oxygen demand (COD) (12/32), colour (8/32), turbidity (24/32), ammonia (NH3-N) (16/32), phosphates (PO4-P) (28/32), and manganese (Mn) (4/14). Principal component analysis yielded 4 principal components: organic matter from food and body residues; detergents; faecal contamination; and ammonium salts. The pilot-scale hybrid treatment system featured a multimedia filter (MMF), a granular activated carbon filter (GAC), and ozone disinfection. A hydraulic loading rate of 10 L/min produced the highest overall removal efficiencies as longer retention times allowed more pollutant adsorption. Overall, the pilot-scale system removed 52% COD, 53% BOD5, 14% NH3-N, 67% PO4-P, 81% colour, 81% turbidity, 50% total suspended solids (TSS), 53% of total coliforms, 63% copper (Cu), and 29% zinc (Zn) from greywater sourced from a mixture of showers/baths and laundry. The GAC was the most effective at removing COD, colour, turbidity, and Zn. Finally, a series of dilution experiments of greywater with rainwater and mains water was conducted to emulate real scenarios during the practical implementation of hybrid systems with mains water top-up. Greywater dilution had little impact on removal efficiency of colour, turbidity, TSS, and TDS, and dilution of greywater with either mains water or rainwater is recomme