Impact of wastwater effluent disposal on surface water quality in Mahikeng, South Africa
The deterioration of surface water quality is of great global concern since water is a crucial resource for all aspects of life. In South Africa, water scarcity continues to plunge the country and this has led to the damming of major rivers in order to cater to the acute demand for water. The South African constitution stipulates that wastewater effluent from wastewater treatment plants (WWTP) could be discharged into surface water, as one of the alternatives to combat issues of water scarcity in the country. Such is the case in Mahikeng, the capital of the North West Province, South Africa. The town's main wastewater treatment works (Mmabatho WWTW) receives both domestic and commercial wastewater from Mahikeng, treats it using secondary wastewater treatment processes, and discharges its treated effluent into surface water (Setumo dam). Setumo dam serves as the town's main source of water, which is abstracted by the Mmabatho water treatment works (WTW), purified and supplied to the urban and peri-urban areas of Mahikeng. The communities surrounding the dam also utilise the raw water from the dam for domestic purposes. It is on this account that this study assessed the impact of wastewater effluent discharges onto the quality of water in Setumo dam. Two hypothesis were formulated in order to achieve the overall aim of the study, where the first hypothesis (HO) stated that the wastewater effluent discharged by Mmabatho WWTW has no significant impact on Setumo dam water quality whereas the second hypothesis (Hl) stated that the wastewater effluent discharged by Mmabatho WWTW has a significant impact on Setumo dam water quality. Wastewater effluent and dam water samples from Mmabatho WWTW effluent discharge pipe and Setumo dam respectively were collected during the wet and dry seasons. The collected samples were then analysed for physicochemical (temperature, pH, EC, TDS, nitrates and phosphates, and heavy metals - arsenic, cadmium, copper, iron, lead, manganese, nickel, and zinc) and bacteriological parameters (heterotrophic bacteria, total and faecal coliforms). Results from the wastewater effluent analysis were compared with the DWA (2013) wastewater effluent quality standards while results from the dam water analysis were compared with the SANS:241 (2015) and WHO (2011) drinking water quality standards. Polymerase chain reaction (PCR) analysis was used to detect the presence of Escherichia coli (E. coli) and Klebsiella. One-way ANOV A was used to examine the statistical seasonal and spatial differences in the analysed dam water parameters. The analysis of the health risks associated with the consumption of water from Setumo dam was done using the risk quotient equation and the water quality index (WQI) was computed to determine the overall quality of the dam water. Pearson correlation coefficient was used to determine the association between the pollutants in the wastewater effluent and the dam water. During the wet season, pH, EC, nitrates, phosphates, arsenic, copper, and lead were found to be above the DW A (2013) wastewater effluent quality standards while phosphates, lead, and zinc were above the permissible wastewater effluent limits during the dry season. In the dam water, all the physicochemical parameters were within the SANS:241 (2015) and WHO (2011) drinking water quality standards during the dry season except for nitrates, arsenic, lead during the wet season. The bacterial counts were significantly higher in both the wastewater effluent and the dam water during both sampling seasons except for heterotrophic bacteria in the dam water. As expected, the results from the PCR analysis confirmed the presence of E. coli in both the wastewater effluent and the dam water during both seasons. No Klebsiella was detected in the wastewater effluent and dam water during both sampling seasons. The detection of E. coli indicates that inadequately treated wastewater effluents may have the potential impact of disseminating pathogenic bacteria to the surface water intended for both human and animal use and this could, in tum, result in an outbreak of water-borne diseases. The one-way ANOVA results suggest that there exists a statistically significant seasonal variation in the dam water quality (0 ~ p :S 0.04) in all analysed parameters except for the EC, TDS, and phosphates, whereas EC, TDS, and total coliform bacteria yielded significant spatial variations (0 ~ p :S 0.09). The risk assessment analysis revealed that nitrates, arsenic, and lead presented significant health risks to Setumo dam water consumers during the wet season (RQ > 1) and the faecal coliform bacteria during both seasons. Water quality index results revealed that the dam water quality varied between the categories "bad" in the wet season to "medium" in the dry season which would be expected given the changes in season. The Pearson correlation coefficient demonstrated strong significant correlations (r = 0.05) between the pollutants in the wastewater effluent and in the dam, and across the dam sampling points. The study, therefore, recommended that there should be a continuous assessment of the wastewater effluent from the Mmabatho WWTW in order to establish whether it conforms to the DWA wastewater effluent quality standards, so as to protect the quality of the surface water resource that serves as a disposal basin and in tum, mitigates the health issues arising from poor surface water quality.