Strengthened Coagulation Efficiency Research And Safety Analysis Of Waste Streams Joint Recycle

Faced with the improvement of water quality standards and the problems of low turbidity and micropollution in recent years, modification of water treatment technology is imperative. Waste streams recycle can decrease the water consumption in water treatment plants(WTPs), meanwhile enhanced coagulation, providing a new feasible modification method for WTPs. However, waste streams contain relatively high quantity of pollutants, so the recycle ratio and security issues during recycle must become one of the research topics.The quality characteristics of wastewater was investigated firstly and its strengthen coagulation efficiency and the impact of waste streams direct recycle on water quality was forecasted. Based on the mixed water turbidity and considered the temperature effect, the best mixed water turbidity range was optimized and determined by pilot test in summer and winter respectively, followed by continuous waste streams direct recycle. The pollutant levels were monitored continuously and the water physical and chemical index of water treatment process of waste streams direct recycle and conventional treatment were then compared. But physical and chemical index can only reflect single instantaneous concentration of pollutants in the water and pollutants ususlly act in biology by synergistic action and additive effect. Therefore, a set of biological genetic toxicity test was established, which included Ames, SOS/umu, micronucleus test(vivo and vitro) and mice sperm abnormality test and was used to futher evaluate the water safety of waste streams direct recycle process.The test showed that the water quality of alum sludge supernatant was as basically good as that of raw water and related water quality parameters of filter backwash wastewater were lower than that of raw water. Organic matters in two wastewaters were mianly particulate or adsorbed on larger flocs. It infers that waste streams direct recycle in appropriate proportion will not have great influence on water quality. According to pilot test and related studies, it is suggested to WTPs that the best mixed water turbidity is within the range of 125~170 NTU in summer and within the range of 40~55 NTU in winter.The continuous waste streams direct recycle test within best mixed water turbidity indicates that the pollutants in waste streams has no enrichment phenomenon basically except the trace enrichment of Mn in sedimentation tank sludge, and in the context of saving coagulant, continuous waste streams direct recycle will not affect the water quality after coagulation and sedimentation processes in terms of traditional water quality index, organic matter and Mn content. Meanwhile, waste streams direct recycle can enhance the removal of Al and Fe in different seasons and improve soluble organic matter removal to some extent in summer. The filter effluent quality of waste streams direct recycle was as basically good as that of conventional treatment and various water quality indexes meet “ drinking water health standards ”(GB5749-2006).Genotoxic tests of water during end of waste streams continuous recycle in winter showed that, waste streams continuous recycle did not result in the enrichment of frameshift mutagens,and Ames test cannot be used to judge the mutagenicity of waste streams continuous recycle effluent water because of plentiful antibacterial substances in raw water. According to equivalent concentrations of positive results, the carcinogenic risk of waste streams continuous recycle effluent water was relative low within the safety level. Meanwhile, micronucleus test in vitro and vivo showed that, in the design of experiment doses, waste streams continuous recycle effluent water had no damage effect on chromosome and there is no significant difference with conventional treatment effluent water. In addition, the effluent after sedimentation and disinfected water of waste streams continuous recycle had no mutagenic effect on male germ cells in the design of experiment doses. In conclusion, from the perspective of biological genetic toxicity, continuous waste streams direct recycle effluent water shows a basically similar safety with conventional treatment effluent water in the design of experiment doses.