Application of biological assays to evaluate the aquatic toxicity of a WWTP effluent in Western Cape, South Africa

Abstract

Management of wastewater from diverse sources are important because effluents are discharged into the aquatic environment after treatment. In this study, the water quality of the Veldwachters River and associated ecotoxicity risks of the wastewater treatment plant’s (WWTP) effluent were evaluated. Physicochemical characterisation over four seasons and ecological risk assessment of WWTP’s effluent using aquatic organisms comprising of the producer Raphidocelis subcapitata, consumer Daphnia magna and decomposer Tetrahymena thermophila as experimental models were investigated. The crustaceans were subjected to 48 h exposure for mortality while both algae and the protozoan were exposed for growth inhibitions at 72 h and 24 h respectively. Physicochemical characteristics were within regulatory limits. Growth inhibition was observed in autumn and winter for R. subcapitata and in summer and spring for T. thermophila. Crustaceans D. magna (consumer) was classified as Class III (acute toxicity) for the effluent in all seasons. Meanwhile, the most sensitive organism in the applied battery of biotests was the protozoan T. thermophila (decomposer), demonstrating a toxic unit (TU) > 100, while R. subcapitata and D. magna demonstrated 1 TU < 10. These results showed that the effluent have potential toxicological effects on aquatic organisms and provided insights into the required intervention strategies for pollution reduction. Graphical abstract