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The effects of chlorine dioxide and chlorine disinfections on the genotoxicity of different biologically treated sewage wastewater samples were studied by umu-test. The experiment results showed that when chlorine dioxide dosage was increased from 0 to 30 mg/L, the genotoxicity of wastewater first decreased rapidly and then tended to be stable, while when the chlorine dosage was increased from 0 to 30 mg/L, the genotoxicity of wastewater changed diver sely for different samples. It was then found that ammonia nitrogen did not affect the change of genotoxicity during chlorine dioxide disinfection of wastewater, while it greatly affected the change of genotoxicity during chlorine disin fection of wastewater. When the concentration of ammonia nitrogen was low (< 10-20 mg/L), the genotoxicity of wastewater decreased after chlorine disinfection, and when the concentration of ammonia nitrogen was high (> 10-20 mg/L), the genotoxicity of wastewater increased after chlorine disinfection.

A Treatability Index is developed to allow comparison of different reservoir waters according to their effects on a water treatments works. For the water treatment works which employs rapid gravity filters, the index is the product of the algal concentration, the clarification coefficients of algae and the filtration rate. The index is applied to reservoir waters within Thames Water area. Algae observed in reservoirs are grouped according to their shapes. Among these groups, twenty frequently observed species were selected and their clarification coefficients were measured. The treatability index was then evaluated for different waters and at different times of the year. The results were correlated to the filter run lengths and the development of headloss across the filters.

Abstract-Disinfection is an important measure to ensure the water quality security. Chlorine dioxide -as a strong oxidizer is widely used for disinfection of drinking water and wastewater. This paper firstly introduces the basic properties of chlorine dioxide, then detailly analyses its disinfection -functionality and advantages, finally discuss the prospect of application