An investigation of the impact of Darvill WWTW effluent on the Msunduzi River ecosystem

MSc (Ecological Water Requirements), North-West University, Potchefstroom Campus

In South Africa, there are 824 wastewater collector and treatment systems. However, it is estimated that only 60 of these systems are effective. The rest of the systems are releasing effluent that is not of good quality to the environment. The poor quality of effluent being discharged to the water resources and other pollution sources have led to a significant decline in water quality of South Africa’s water resources. The most affected rivers are those in the urban areas because of the many anthropogenic activities that are concentrated in these areas. The Msunduzi River is no exception as it emanates in the urban area of Pietermaritzburg. Various media platforms have reported on a number of pollution incidences that occur in the Msunduzi River. The Darvill Wastewater Treatment Works (WWTW) also discharges treated wastewater effluent into the Msunduzi River. This study assessed the impact of effluent discharges from the Darvill WWTW on the Msunduzi River water quality and aquatic life. Existing water quality and biomonitoring data was obtained from the Umgeni Water Board. The water quality samples were collected at three (3) sites upstream of the Darvill WWTW, two (2) sites at the Darvill WWTW final effluent discharge point and one (1) site downstream of the Darvill WWTW. For the purpose of this study data was extracted from Umgeni Water and analysed for the parameters including pH, electrical conductivity (EC), suspendend solids (SS), chemical oxygen demand (COD), ammonia (NH3), nitrate (NO3), Soluble Reactive Phosphate (SRP) as orthophosphate and Escherichia coli (E.col)i. The concentration of each parameter was measured against the Darvill WWTW Water Use Licence (WUL) Limits issued by Department of Water Affairs (DWA) in 2010, General Limits (issued in 2013 by the then Minister of Water and Environmental Affairs), and as well as the Target Water Quality Range (TWQR) from the South African Water Quality Guidelines for aquatic ecosystems. Data was extracted for 2010-2015 period and again for 2016-2020 period. The 2010-2015 period was used as historical data to be compared with the 2016-2020 water quality data. The biomonitoring data, available from 2010-2018, was assessed to identify changes to the organisms in the Msunduzi River in the study area. Biomonitoring results were analysed using the Integrated Habitat Assessment Scoring (IHAS), Biotic Index (BI) and Average Score Per Taxon (ASPT) scores. The available biomonitoring results were compared amongst the sample sites to identify changes from the points upstream of the Darvill WWTW and those downstream of the Darvill WWTW. The results revealed that the Msunduzi River is generally polluted in the study area. This is shown by the results of the parameters at the points upstream of the Darvill WWTW. The pollution of the river in this area emanates from various sources including residential areas, industries and livestock presence. The pH and electrical conductivity parameters were mostly in compliance with the WUL, General Limit and TWQR set for surface water at the upstream points. However, few non-compliance instances were recorded for EC at the discharge point and downstream. The concentration of assessed parameters at upstream points suggests input from several sources as the main cause of their presence in the water and suggests an urban river that is currently modified but deteriorating. The deterioration of the Msunduzi River is also evident through the comparison of the two time periods, 2010-2015 and 2016-2020. Whilst the parameters still show compliance of the water quality with the standards, a closer look at the data reveals that the concentration levels keep increasing in the water. The biomonitoring data showed that the aquatic life in the Msunduzi River is in a moderate condition. Even though the results were moderate for the biological data, the Darvill WWTW effluent discharges have little direct impact on the aquatic ecosystem of the Msunduzi River. This is because the results show significant improvement in the aquatic life and water quality condition at the downstream point. The downstream point scored higher in all three indices when compared to the upstream points. However, if the water quality of the Msunduzi River is not improved, by managing the activities and eliminating pollution from the surrounding areas, in a long term, it will not be conducive to support the aquatic life of the Msunduzi River.

Masters