The effect of treated wastewater effluent on the water quality of the Natalspruit river

Abstract

Lack of effective wastewater management strategies poses a serious threat to the environment and human health around the world. South Africa's freshwater resources are threatened by human influence and dwindling at an alarming rate. Global climate change is expected to exacerbate this stress unless sustainable measures are not implemented. The main objective of this study was to assess the effect of treated wastewater on the water quality of the Natalspruit river. For a closer examination of downstream effect on river water quality, this study focused on three wastewater treatment plants (herein referred to as Plant A, B, and C) that discharge effluent into the Natalspruit river. Historical data for a period of three years from 2016 to 2018 was used to determine the potential threat posed by effluent discharge to the river water quality. The three years data was adequate to see current trends, make projections about future trends, to respond to the study objectives and to meet the requirements for a mini-dissertation. The historical data set was derived from the database of the Ekurhuleni Water Care Company (ERWAT) monitoring programs. The extent of downstream water pollution was determined using the Single Factor Pollution Index (Pi), and the suitability of downstream water for reuse was determined using the Water Quality Index (WQI). The Water License Standard (WUL) was used to determine the downstream water quality index. Statistical analysis on water quality using the General Linear Model (GLM) showed significant (p) differences in mean concentrations of physicochemical water quality parameters. Electric conductivity, chemical oxygen demand, ammonia, and nitrate concentrations increased downstream of the effluent discharge point primarily due to relatively higher effluent concentrations, except for EC. The suspended solids (SS), pH, and phosphate levels, however, did not show any significant change. Water quality (WQI scale) of the Natalspruit river declined from excellent upstream of plant A to good downstream of plant C. Similarly, the river water quality, according to a single factor pollution index (Pi), also indicated the negative effects of the treated wastewater from three wastewater treatment plants in the river water system. This was despite the fact that the effluent quality from three wastewater treatment plants was within the Water and Sanitation Department's WUL and River Water Quality Objectives (RWQO) limits (DWS). Apparently, this study found a non-point source pollution between the upstream and downstream sampling points that needs to be quantified in order to determine the actual contribution of wastewater treatment effluent to the Natalspruit river. Therefore, future studies of the impact of treated wastewater on river systems in particular, and on other sources of pollution in general, should select downstream sampling points in a way that represents an almost homogeneous mixture of effluent in the river system, while minimizing any other source of non-point contribution that might affect the measurement.