Study On The Control Of Dichloroacetonitrile Generation By Two-point Influent Activated Carbon-quartz Sand Biofilter

In recent years,the micro pollution of source water is serious,and the nitrogen containing disinfection by-products(N-DBPs)produced by disinfection are more toxic than conventional pollutants,and they have been gradually detected in water plants and attracted people’s attention.The source control of N-DBPs by biofilter is an effective method to control N-DBPs in drinking water.However,there is little research on the control of N-DBPs by activated carbon-quartz sand biofilter with potential application value.Therefore,it is of great significance to study the control of N-DBPs formation by activated carbon-quartz sand biofilter.In this study,the two-point influent activated carbon-quartz sand biofilter was used for experimental research,and the single point influent activated carbon-quartz sand biofilter and quartz sand biofilter were used as the control.Taking typical N-DBPs dichloroacetonitrile(DCAN)as the research object and tyrosine(Tyr),an important precursor of DCAN,as the model precursor,the experiment explored the control of activated carbon-quartz sand biofilter on DCAN formation from the two aspects of Tyr removal and DCAN formation potential,in order to provide better theoretical support for its control of DCAN formation.The analysis of the pollutant treatment effect of biofilter and the effect of controlling the formation of DCAN shows that the average Tyr removal rate of two-point influent activated carbon-quartz sand biofilter(73%)is significantly higher than that of other filters,and its organic matter removal(49%)is also significantly better than that of other filters.In the study of nitrogen removal effect,the two-point influent activated carbon-quartz sand biofilter shows the best total nitrogen(TN)removal rate(28%).The changes of three nitrogen(DIN)and Tyr in the biofilter are concentrated in the upper 0 ～ 30 cm of the filter material,at the same time,the changes of DO and p H are also concentrated in the upper half of the filter.The DCAN formation potential of the two-point influent activated carbon-quartz sand biofilter is the lowest,and the removal rate of the effluent DCAN formation potential is about 78%.And deeply explore the influencing factors of water temperature and backwashing,when the water temperature decreased,the biodiversity and biomass decreased,and the removal rate of DCAN formation potential of filter effluent decreased;during the backwash cycle(24 h),the formation potential of DCAN in the effluent of the three biofilters decreased.Beyond the backwash cycle,precursor accumulation occurred,and the formation potential of DCAN in the effluent was higher than that in the influent.The nitrogen transformation and microbial community of biofilter were deeply discussed,it was found that the removal of Tyr was related to the nitrogen transformation in the filter,and mainly concentrated in the upper part of the filter.There was a positive correlation between DIN loss and Tyr change,and the correlation of two-point influent activated carbon-quartz sand biofilter(0.73)was the highest.Samples were taken for high-throughput sequence in the stable stage in summer and winter respectively.In both summer and winter,the diversity and uniformity index of two-point influent activated carbon-quartz sand biofilter were better than that of activated carbon-quartz sand biofilter and quartz sand biofilter.The analysis at the phylum and genus levels found that the flora richness related to Tyr removal in the two-point influent activated carbon-quartz sand biofilter was relatively high,contributing to the removal of Tyr.The highest ratio of nitrite oxidizing bacteria / ammonia oxidizing bacteria(NOB/AOB =6.93)and the highest abundance of denitrifying bacteria in the two-point influent activated carbon-quartz sand biofilter led to the best denitrification and the lowest nitrite accumulation.Because the two-point influent changes the microbial growth environment,compared with the two-point influent activated carbon-quartz sand biofilter,the activated carbon-quartz sand biofilter has higher similarity with the quartz sand biofilter as a whole.