Comprehensive Evaluation on the Bio-Toxicity of Three Advanced Wastewater Treatment Processes

Abstract

Water quality and safety of tailwater is crucial to achieve sustainability of water resources. However, the traditional monitoring method based on chemical and physical indicators cannot reflect the actual biological effects. The objective of this study was to provide effective biological indicators in water quality monitoring and the safe discharge of sewage. The influent, secondary effluent, and tailwater were sampled from three sewage treatment plants with different advanced-treatment processes (wetland, ozone + ultraviolet, and filter + ultraviolet), and the removal efficiencies of the tail water on acute toxicity and genotoxicity were assessed by Vicia faba micronucleus test, acute comprehensive evaluation (TU), and genotoxicity test. The results showed that physical and chemical indicators could meet the national standards of pollutant discharge in urban sewage treatment plants, and the biological toxicity of the tail water after each treatment process significantly reduced. According to TU method, the biological acute toxicity of the treated effluent had obvious decrease by 25.49%, 30.43%, and 30.85% in the deep treatment process of wetland, ozone + ultraviolet, and filter + ultraviolet respectively, and Selenastrum capricornutum was not suitable for the comprehensive acute toxicity evaluation. The treated effluents by ozone + ultraviolet had the highest degree of genetic toxicity reduction (35.9%) compared to undercurrent wetland (33.63%), and filter + ultraviolet (11.19%). Correlation analysis demonstrated that TP concentration was significantly negative correlation with the toxicity of Selenastrum capricornutum and the growth inhibition of Selenastrum capricornutum, which can act as indicator species represented by TP concentrations.