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Greywater

Student: Dr R Tandlich
Supervisors: Dr WJ Muller
Degree: Postdoctorate


My research activities have focused mainly on the characterisation and treatment of greywater from different types of urban dwellings in South Africa. Greywater is domestic wastewater without any input from toilets. It is comparable in composition to domestic sewage, and has been used in several countries as a surrogate for drinking water in irrigation and toilet flushing. In everyday life, greywater accounts for 60 to 70 % of the drinking water consumption by civilian populations, and so reuse this resource could lead to huge cuts in the demand for drinking water. Problems with greywater reuse include the content of potential pathogens, nitrates, phosphates, boron and xenobiotic organic compounds. I tis also important to establish public perception of greywater, and find out potential obstacles in greywater reuse. For this purpose, I was involved in conducting a survey of the local households and businesses with respect to greywater reuse. Twelve households in total were surveyed in the suburb, the informal settlement, and the township of Grahamstown, with the age of the respondents ranging from 15 - 65. The businesses interviewed included three brick making companies, the Rhodes University ground-staff (the two main employers in the Makana Municipality), as well as maintenance staff of sports fields in the township. 88 % of the households interviewed pay for water provision into their houses. Out of these, 72 % indicated willingness to reuse partially treated greywater for gardening and sanitation, but 28 % were concerned about potential health implications. 2 out of 3 companies consulted and interviewed pay for water provision. 55 % of the interviewed persons said they would be willing to use alternatives to purified water, while 45 % were concerned about the health implications of using unpurified water.

In 2006, a simple treatment system for on-site greywater reuse was developed for the Buffalo municipality in East London. Using sorption, entrapment and biofilm development, the system provided removal efficiencies of up to 68 % for chemical oxygen demand (COD) and nitrates, while up to 86 % of particulate mater was removed for greywater. Based on the results of the survey about greywater reuse, chlorination experiments with greywater of mixed origin were conducted. The pathogenic load of greywater was quantified by the concentrations of faecal and total coliforms, and the disinfection was conduected using a mixture of sodium dichloroisocyanurate (SDCC) and trichloroisocyanuric acid (TCC). A simple and cheap continuous release-dosage form was used as delivery system. Faecal and total coliform concentrations dropped below 800 CFUs/100mL after 65 hours of chlorination, providing irrigation quality water according to the DWAF guidelines. Based on the measurements of COD and the biochemical oxygen demand (BOD5), organic matter in greywater became more refractory during 65 hours, as indicated by the increase in the COD:BOD5 from 1.03 at 0 hours of chlorination to 20.89 after 65 hours of chlorination. pH controls the type of disinfection by-products formed. Alkaline values lead to trihalomethanes, while acidic pH values lead to haloacetic acids. Both haloacetic acids and trihalomethanes are classified as probable human carcinogens, or actual human carcinogens. During the period, required for the elimination of pathogens, the pH values of the treated greywater dropped from 6.82 to 4.30, indicating the dominance of haloacetic acids among disinfection by-products. Before on-site applications of greywater for reuse, the toxicological risks, originating from the treated greywater will be characterized using Microtox and Daphnia pulex test.


Last Modified: Fri, 14 Aug 2015 11:14:43 SAST