Assessment of the impact of wastewater treatment plant discharges and other anthropogenic variables on river water quality in the eThekwini Metropolitan area.
On a global scale the deterioration in riverine water quality is of great concern since water is one of the most valuable and essential resources that forms the basis of all life. For South Africa, the declining water quality is of even more importance since the country is located in a semi-arid part of the world with scarce water supplies. The quality of water in many rivers in South Africa continues to deteriorate at unprecedented rates, which affects its availability and use. This situation is quite the same for rivers in the eThekwini Metropolitan Area which is located in Kwazulu-Natal, a coastal province of South Africa. This study assesses the qualitative impact of wastewater plant discharges from the uMhlatuzana; Northern and KwaMashu Wastewater Treatment Works, on the uMhlatuzana River; uMgeni River and uMhlangane River, respectively. Samples were collected from identified points upstream and downstream of the wastewater discharges and the results were analysed in terms of the t-test statistical technique to identify any significant change in water quality between the upstream and downstream sites. In addition, the samples collected were analysed for physico-chemical and microbiological parameters as respects compliance with the Target Water Quality Guideline Range for aquatic ecosystems (DWAF, 1996); as well as in comparison with the general requirements for purification of wastewater (DWAF, 1984). The results from the t-test statistical analyses indicated that there was significant difference between the upstream and downstream water quality for the following parameters and sites: pH and permanganate value at the uMgeni River sampling sites; for dissolved oxygen at the uMhlatuzana and uMgeni River sampling sites ; for total dissolved solids, conductivity, chlorides, ammonia; nitrite and nitrates at all sampling sites. In 50% of the instances there was compliance with the Target Water Quality Guideline Range for aquatic ecosystems (DWAF, 1996). The majority of sites did not meet the general requirements for purification of wastewater (DWAF, 1984); and the results indicate that negative impacts from wastewater discharges occurred in 76% of the instances, while other anthropogenic influences adversely affected water quality in 23% of instances. This study has identified the extent; nature and source of water quality impacts on the rivers and it could serve as a useful tool for rehabilitation and monitoring since it identifies the major source of adverse water quality impacts.