Water quality trend analysis and the impact of wastewater treatment effluent on water quality in the Klip River, RietKlip sub-catchment

Abstract: Water quality in South Africa is in a poor state and continues to deteriorate. The water quality problems pose a threat to the environment by affecting aquatic ecosystems as well as the wellbeing of humans. Rapid urbanization and industrialization are the major contributors to the degradation of water resources. Gauteng Province is the heartbeat of economic activity in South Africa and experiences inward migration of people seeking better opportunities. As a result, many wastewater treatment plants are overloaded and unable to handle the increased effluent loads produced. This study focused on the impact of the Waterval Wastewater Treatment Plant (WWTP) effluent discharge in the Klip River. This was done by examining the water quality trends and measuring any changes over a period of time. Existing accessible data from January 2006 up to March 2020 within four monitoring sites were extracted from the Department of Water and Sanitation’s (DWS) Water Management System (WMS) database. These four monitoring sites upstream of Waterval WWTP (U-WAT1), Waterval WWTP (WAT2), Rietspruit confluence with Klip River (C-RIET3) and downstream of Waterval WWTP (D-WAT4) are respectively situated upstream of the discharge point, the discharge point, downstream, and the Rietspruit which confluences with Klip River. Water quality variables monitored included electrical conductivity (EC), pH, chemical oxygen demand (COD), nitrate-nitrogen (NO3-N), phosphate (PO4-P), sulphates (SO4), Suspended Solids (SS), Escherichia. coli (E. coli) and faecal coliforms. The water quality trend analysis and regression analysis results for sites U-WAT1, D-WAT4 and C-RIET2 revealed that water quality was ideal in terms of EC and pH and showed a combined proportion of ideal, acceptable, tolerable and unacceptable in terms of SO4, COD, NO3-N and PO4-P, respectively. Faecal coliforms, E. coli and SS were unacceptable when compared with the Klip River in-stream water quality guidelines (KRIWQG). The water quality trend analysis results for WAT2 site for the study period January 2006 up to March 2020 revealed that the quality of water in terms of EC, PO4-P, pH and SO4 were ideal, acceptable and tolerable when compared with water quality guidelines; while COD, NO3-N, SS, E. coli and faecal coliforms were found frequently unacceptable. The pairwise comparison results agree with the trend analysis results for all the sites. When comparing the four sites it is clear that there are other sources of microbiological contamination in addition to effluent discharge from WWTP. It is therefore clear from the results that other variables were within the water quality guidelines, while COD, NO3-N, SS, E. coli and faecal coliforms were found to exceed the set KRIWQG. This study therefore recommends that Waterval WWTP should institute measures to manage and improve treatment of the identified variables exceeding the water quality guidelines. Wetlands can assist in the uptake and reduction of contaminants and should therefore be protected by authorities and water users. Bio-monitoring assessments and data verification should be incorporated in the data collection process. As the urban population grows, there is a need to expand wastewater treatment infrastructure and maintain the existing aging infrastructure.M.Sc. (Aquatic Health