Effects of municipal wastewater treatment plant effluent quality on aquatic ecosystem organisms

The management and quality monitoring of wastewater have an important role in sustainable development. A recent approach in environmental protection involves the ecotoxicological assessment of effluents to complement the usual chemical evaluations. This study assessed the impacts of wastewater treatment plant (WWTP) effluent quality in a location in Western Cape province, South Africa using organisms that bear different ecosystem-level function responsibilities like the Pseudokirchneriella subcapitata (microalgae), Daphnia magna (crustaceans), and Tetrahymena thermophila (protozoan) in addition to the physicochemical parameters. The effluent showed values of chemical oxygen demand (COD; 41-83 mg L^-1), dissolved oxygen (DO; 2.7-3.1 mg L^-1), Redox potential (189-265 mV), and total dissolved solids (TDS; 656-718 ppm). The protozoan Tetrahymena thermophila ecotoxicity test exhibited toxic effects of the effluents within 24-h with a mean lethal value (LC₅₀) of 1.12% for the winter season. The findings of this study revealed that analyzed physicochemical parameters are within the regulatory water quality acceptable standard thresholds with few exceptions, while the biotests were able to determine the toxicity levels and sensitivities of each test. The results showed that the WWTP whole effluent exerted toxicity to test organisms, but dilution can mitigate the effects considerably. The use of ecotoxicological assessment methods for municipal WWTP effluent may enhance existing water management strategies.