The long-term impact of Northern Wastewater Treatment Works effluent on macroinvertebrates and water quality in the Jukskei River

Abstract

In South Africa, poor wastewater treatment plant operation and maintenance and neglect of sewage treatment infrastructure have become a source of concern. This problem also manifests itself in the increasing incidence of untreated wastewater, which is non-compliant with national water resources legislation, policies, norms, and standards to protect water resources. The Northern Wastewater Treatment Works is situated in the densely populated Gauteng Province. The study aim was to look at the long-term impacts of Northern Wastewater Treatment Works effluent on macroinvertebrates and water quality in the Jukskei River over ten years (2010-2020). The study primarily focused on historical data collected and analysed by Johannesburg Water SOC Ltd over ten years (2010-2020). Furthermore, some primary data was gathered and analysed using standard laboratory analysis methods. The study investigated how wastewater effluent affected macroinvertebrates and the water quality of the Jukskei River concerning the issued water use licence, DWS general wastewater, and resource quality objectives (RQOs) limits. Standard aquatic sampling methods were used to collect primary data for the low and high flow surveys, which took place between July and October 2020. This period was representative of the dry and the wet season. The water quality was measured in situ with a handheld calibrated HACH meter for primary data. pH, conductivity (S/cm), temperature (°C), and dissolved oxygen (DO) in mg/L were among the constituents measured. Chemical water quality was also examined using standard sampling protocols. The water quality analysis was completed at a SANS accredited laboratory. Macroinvertebrate sampling was conducted using a standard SASS net and dislodging macroinvertebrates from their habitat and MIRAI. The SASS5 survey was completed during primary data collection at different biotopes, i.e. stone biotopes, vegetation biotopes, and gravel, sand, and mud biotopes. The SASS5 data interpretation guideline was used to interpret the SASS5 information during the survey. Secondary data included Johannesburg Water SOC Ltd.'s monthly water quality and biomonitoring data. The data from three selected monitoring points were collected over ten years, from January 2010 to October 2020, and analysed to establish historical trends and seasonal variation in contaminants loads for each parameter. The long term impact of wastewater was assessed using the following parameters; electrical conductivity, pH, nitrate, chemical oxygen demand, ammonia, e coli, phosphate (as orthophosphate) and suspended solids.

The collected data were arranged into dry and wet seasons. The data was analysed in Microsoft Excel to assess the differences in water quality of selected monitoring points and create time-series graphs to examine the changes in water quality variables over time. Furthermore, biomonitoring data were analysed to determine the available macroinvertebrate community at the three selected monitoring points. The overall results indicated that the critical parameters in the Jukskei River for all three selected monitoring points exceeded both general, licence wastewater discharge and RQO limits. The results also showed partial effectiveness of the Northern Works in treating wastewater. The water quality of the Jukskei River was found to have exceeded some of the essential parameters (Ammonia, suspended solids and E. coli). These could be due to equipment malfunctioning or high inflow, which is above the capacity of the works and non-point source pollution within the Jukskei River catchment. The three sampling points were initially analysed separately, and then the data were merged to compare parameters from the three sampling sites. An ANOVA was used to determine any statistically significant difference between the three selected sampling sites. A p-value of 0.05 or less was considered statistically significant. The results showed that out of eight parameters, only five parameters were compliant with WUL limits (EC, nitrate, COD, Orthophosphate and pH), and the other three (ammonia, suspended solids, E Coli) were not compliant with WUL's wastewater discharge limit. The final results showed that most results came from the upstream and discharge points of Northern Works. The biomonitoring reports analysis of primary and secondary data collection has also shown a decrease in intolerant macroinvertebrates within the study area. The present ecological status has also deteriorated from category C to E/F, indicating that the Jukskei River has been significantly modified, probably due to different anthropogenic sources upstream and partially treatment of wastewater at the WwTW. The primary data also indicated that poor water quality has contributed to a poor community of macroinvertebrates. It was the dominant driver contributing to the modified state of the Jukskei River. The absence of intolerant taxa indicated changed Physico-chemical conditions within the Jukskei River.