Evaluation of the impacts of municipal wastewater treatment on the receiving environment: a case study of the Olifantsvlei wastewater treatment plant in the Gauteng Province, South Africa

摘要

South Africa is water scarce country with maximum rainfall received in the summer season which lasts for only three months (November, December and January); hence the water resources have to be protected. The municipal wastewater effluents are considered one of the environmental threats that impact the water quality of the streams. This study was conducted to assess the environmental impact that the wastewater effluent has on the Klip River system, the performance of the plant and also to assess the spatial and temporal variations of water quality along the Klip River system.The study focused mainly on historical data over a five period (2009 – 2013) years secondary data which was analysed by Johannesburg Water Ltd (Pty) and primary data were also collected and analysed using the standard methods of laboratory analysis. The standard methods used include Ion selective electrode, gravimetric techniques, iodemetric titration, membrane filtration method; colorimetric method, automated flow injection method and inductively coupled plasma atomic emission spectrometry (ICP – AES). The aim of collecting the primary data during the dry and wet seasons was to verify the secondary data. The data set was further analysed using multivariate techniques such as principal component analysis (PCA), factor analysis (FA) and discriminant analysis (DA) to determine the spatial and temporal variation of water quality. The data set using ten water quality parameters (ammonia, sulphates, Chlorine, Chemical Oxygen Demand, conductivity, Escherichia coli, sodium, nitrates, pH and suspended solids) was grouped into four sampling points (influent, effluent, downstream and upstream points) and four seasons.Discriminant analysis of water quality showed that out of ten water quality parameters analysed, only sulphates was a less significant parameter to discriminate between the sampling points. For the temporal variations, eight water quality parameters (ammonium, Chlorine, Conductivity, sodium, nitrates, pH, sulphates and suspended solids are the most significant parameters to discriminate between the four seasons. PCA/FA results highlighted similarities in terms of water quality loading between summer and winter seasons and between the winter and autumn seasons. Summer and winter seasons had strong positive loading in COD, ammonium, suspended solids and E. coli whereas the autumn and spring seasons had strong positive loading in sodium, chlorine and pH. The study further highlighted that the Olifantsvlei Wastewater Treatment Works (WWTW) is effectively treating the wastewater up to the required standards before discharging them into the Klip River system. This study concludes that the Olifantsvlei WWTW does not contribute significant loads of pollutants into the Klip river system.