Toxicity screening and evaluating in chlorination disinfection of wastewater reclamation processes

Reclamation and re-use of wastewater is one of the most effective ways to alleviate the shortage of water resources, while the safety of reclaimed water becomes one of the critical problems for protecting human health and the ecosystem. While a toxicity test can vividly reflect biological effects of chemicals as a whole, in this study, the Microtox test was used to screen toxicity changes of wastewater during conventional reclamation processes. The results showed that toxicities of water samples decreased continuously along reclamation processes except chlorination/dechlorination in which the toxicity increased significantly. Furthermore, as for different forms of residual chlorine, toxicity of wastewater was quite different with increasing chlorine dosage. NH₃-N had a trend to decrease toxicity of disinfected wastewater, while UV₂₅₄ had a trend to increase toxicity. It was found that there was a good linear relationship between toxicity formation and UV₂₅₄/NH₃-N ratio for wastewater after disinfection with combined chlorine form before peak-point.