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University of South Africa (2021)

Water quality and potential toxicity assessment of desalinated seawater for drinking purpose in the City of Cape Town, South Africa

Badiso, Bulelwa

Titre : Water quality and potential toxicity assessment of desalinated seawater for drinking purpose in the City of Cape Town, South Africa

Auteur : Badiso, Bulelwa

Université de soutenance : University of South Africa

Grade : M. Environmental Science 2021

Résumé partiel
The Western Cape is progressively becoming threatened by resultant water shortages caused by the frequent drought conditions, necessitating the need to explore alternative water supplies through seawater desalination to produce reliable drinking water to meet demand. Desalination involves the removal of dissolved salts from seawater to generate saline free drinking water to meet various human needs. The study investigated the water quality levels and potential toxicity of seawater desalination processes from intake water, to the final treated water intended for drinking, with the purpose of ascertaining its fitness for consumption. The discharge effluent from these plants was also assessed to determine its potential toxicity on the environment using aquatic test organisms. The microbiological and physico-chemical water quality of the raw and final treated water samples of the Strandfontein and Monwabisi desalination plants, Cape Town, South Africa, and their efficiency were investigated. The raw, final treated water and brine effluent of the Strandfontein and Monwabisi desalination plants were analysed for ecotoxicity using the test organisms, namely : marine algae (Phaeodactylum tricornutum), marine crustacean (Artemia franciscana) and marine bacterium (Vibrio fischeri). The monitoring studies were conducted over a 12 months period from December 2018 to November 2019. The raw and treated final water quality from seawater samples were determined and assessed against the South African National Standard (SANS) 241 : 2015 limits for drinking water pertaining to microbiological, physical, aesthetic and chemical determinants related to long-term consumption. The study findings showed trends of highest bacterial counts for Escherichia coli (E. coli) and enterococci in the raw water from these two desalination plants during the winter period, which may be associated with rainfall periods within the City of Cape Town that flushes faecal contaminants from wastewater effluents into the rivers and ultimately into the sea. Higher trends of E. coli in the raw water from Monwabisi were also observed during the summer period which may be associated with increased recreational use of this beach during the hot summer months and favourable temperatures for bacterial growth. Enterococcus and E. coli were determined in the raw water from both desalination plants and the t-test results for the bacteria showed a p value > 0.05, thus there was no significant difference for E. coli and enterococcus in the raw water samples. Increased heterotrophic plate counts (HPC) of 324 CFU/mL for Monwabisi and 175 CFU/mL for Strandfontein were observed during the summer period in the treated water

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