Investigation of recycling perspectives of grey water for resource recovery in Witbank, South Africa

Abstract

South Africa is a water scarce country. The demand for water is exceeding the supply significantly in some of the cities of the country. Simultaneously, a significant amount of grey water is generated by the households in the cities. Consequently, an argument has emerged that if grey water is treated and re-used for domestic use purposes, then it can contribute to the alleviation of the challenges to meet the water demand. Besides, grey water also constitutes significant amount of resources such as Nitrogen, Phosphorous and Potassium. Therefore, a study was done by considering the city of Witbank of the Mpumalanga Province in South Africa in order to examine the quality (impurities and nutrient content) of grey water generated in the study area, explore the appropriate treatment processes to treat the grey water to and to quantify the availability of Nitrogen, Potassium and Phosphorus so that resources such as water and chemical resources (Nitrogen, Potassium and Phosphorus) can be recovered from grey water. The study was motivated by the need to reduce the high demand for scarce fresh water and the amounts of generated waste water, and a resource recovery through recycling process can ease the pressure on the environment. Grey water from bathrooms, showers, kitchens, laundry and sinks were collected from domestic water users of Witbank Mpumalanga Province, based on the location of the area such as central areas, upscale development and township of the city Witbank. Grey water samples were collected across the four seasons of the year and analysed in the laboratory for physical, chemical, operational, microbiological and resource content before and after treatment processes using various treatment combinations such as aerobic screening (AS), Multimedia Filtration (MMF), Ultraviolet radiation (UV) and Chlorination (CL). After treating grey water with a combination of MMF, AS and UV, the physical, chemical, operational and microbiological characteristics of grey water are compared with the standards recommended by the Department of Water Affairs and National Standards Specifications of South Africa. Also, a household survey targeting areas of Witbank as water users was carried out to collect household data relating to socio-economic characteristics and water demand, water supply scenarios. The data collected was statistically analysed. The results of the survey indicated that upscale development areas, had the highest income and household water usage followed by central areas, then townships and lastly the city. There was a significant (p < 0.05), correlation between income and water consumption. There was also a significant, positive (p < 0.05) correlation between income and grey water production. Household surveys indicated a significant, positive (p < 0.05) correlation between income, water consumption and grey water production. The results also confirmed that income, water consumption and grey water production across upscale development, city, the townships and central areas in Witbank were significantly (p < 0.05) different. Regression analysis of income as an independent variable and water demand as a dependent variable indicated a linear and significant causal correlation between income and household water demand exists. Results of the experimental study indicated that the physical, chemical, operational alert and microbiological characteristics of grey water improved significantly to fall within the standard stipulated by the Department of Water Affairs after subjecting untreated grey water to individual and a combination of aerobic screening (AS), Multimedia Filtration (MMF), Ultraviolet radiation (UV) and Chlorination (CL) treatment processes. The grey water also contains significant amount of Nitrogen, Potassium and Phosphorus. Therefore, if recycling of grey water is conducted appropriately then quality water for domestic use can be recovered and re-used. Also, there is a potential for recovery of significant amount of the chemical resources such as Nitrogen, Potassium and Phosphorus.