Impact of wastewater treatment effluent on the water quality of the Crocodile river, Ehlanzeni district, Mpumalanga

Abstract

Rapid water resource depletion and pollution have led to the decline of available water for human consumption and the sustenance of ecological integrity. There is only 3% of freshwater on the planet, of which 77% is found in icecaps and glaciers and 22% found in groundwater, leaving 1 % of the fresh water, which is readily available in rivers, dams, and lakes which is not evenly distributed. Excessive discharge of poorly treated wastewater effluent has impacted global water resource systems intensely. Globally, around 80% of wastewater flows back into the environment either as untreated or partially treated, which poses risks to downstream ecosystems and people relying on the rivers and streams as a water source. The study aimed at assessing the impact of wastewater treatment effluent on the quality of Crocodile River within Ehlanzeni District in Mpumalanga Province. Sampling was conducted at six sampling Sites located within the study area in Mbombela Local Municipality and Nkomazi Local Municipality. These included three wastewater treatment plants discharging effluent into the Crocodile River, the sampling points were as follows: White river wastewater treatment works (WWTW) (Site 1), White river – Crocodile River (Site 2), Kanyamazane WWTW (Site 3), Kanyamazane N4 Bridge (Site 4), Matsulu WWTW (Site 5) and Downstream Komatipoort WWTW (Site 6). Parameters such as water temperature (Tem, °C), pH, electrical conductivity (EC, μs/cm), and dissolved oxygen (DO, mg/L) were analysed onsite using a portable meter Hach multi-probe meter Model HQ40d which was calibrated before use. Chemical Oxygen Demand (COD), phosphates, nitrates, ammonia, total suspended solids, and E. coli were analysed in a SANAS accredited laboratory and were conducted according to the SANAS accredited LP-ZAM Hach water analysis methods and SANS 5221 methods. The study revealed that Site 1 was not complying with the effluent standards set out in their Water Use Licence ( WUL). This was evidenced by the effluent’s Ammonia, Nitrate-Nitrite, E. coli, and COD concentration that were frequently above limit during the period of study. The effect of the pollution loading from the WWTW’s effluent was observed from a downstream sampling Site (Site 2) water quality whereby seasonal fluctuations in E. coli were observed which can be attributed to the discharged. However, assimilation of the discharged effluent was also noted since there is no other WWTW discharging effluent. Water Quality Index (WQI) undertaken downstream of the WWTW at Site 2 showed that there is a discharge of poorly treated effluent, although the water quality of the river is still acceptable, with an index of 31.27. The study further revealed that Site 3 and Site 5 were generally compliant with the effluent standards set out in their WULs, except for phosphate which was non-compliant during the duration of the study. Regression and bivariate statistical analysis of the historic effluent quality for both WWTWs (Site 3 and 5) show a steady increase in phosphate concentration in the discharged effluent as time progresses. The results of the WQI conducted at Site 4, which is located downstream of site 3 reflected that the quality of the river at this point was very poor, with an index of 101.18, which was mainly attributed to high E. coli (overall mean of 2x103 counts per ml). These water quality trends and spatial distribution of nutrients and E. coli specifically at site 4 gives information on non-point sources of pollution mainly during wet seasons, specifically from settlements around the Kanyamazane area situated next to the water resource. Downstream Komatipoort WWTW (Site 6) water quality also showed that there is a point source pollution specifically from poorly treated discharged effluent. Concentrations of constituents were frequently non-compliant to the resource quality objectives (RQO) . Regression and bivariate statistical analysis of historic water quality for this site indicated a steady increase of nitrite-Nitrate and phosphate over time. Water Quality Index (WQI) conducted at this site also illustrated that water quality is very poor, with an index value of 501.05, and based on the water quality trend analysis, poor water quality at this site is mainly attributed to high E. coli counts frequently recorded throughout the study. The results obtained in the present study indicated that there is pollution in the Crocodile River concerning WWTW effluent related constituents which were studied. Based on the results of the study, the pollution of the Crocodile River can be attributed to, amongst others non-point sources, poor quality effluent discharged unto the water resource. In addition, poorly treated effluent from wastewater treatment plants discharged into the water resources has a significant impact on the functioning, integrity, and quality of the water resource and associated ecosystem. Several studies also reported the impact of wastewater effluent on the receiving environment and they confirm that there is still a lot of work that needs to be undertaken with regards to improving effluent quality to protect water resources. Actions and measures must be taken by relevant governing authorities to mitigate the pollution of water bodies through the implementation and enforcement of laws and regulations relating to effluent discharge for the protection of South Africa’s water resources.