The Formation Of Halo Acetic Acid In The Process Of Wastewater Reclaimation Process And Disinfection

The regeneration and utilization of urban sewage is an effective way to alleviate the shortage of water resources.As a regenerated water source,two levels of effluent still contain a large number of organic substances and pathogenic microbes,and disinfection is a necessary link to ensure the safety of reclaimed water.Chlorination is the most widely used water disinfection method at present,but chlorine can react with some organic matter in the water to produce a"three"disinfection by-product in the process of disinfection.Among them,haloacetic acid?HAAs?is a substance with high biotoxicity in the known by-products of reclaimed water disinfection,and its content is second to three halogen methane.?THMs?.Therefore,the effective regulation of the disinfection by-products of reclaimed water is of great significance for the reuse of wastewater,especially for ecological reuse.In this study,the effluent of two sedimentation tank of a sewage treatment plant in Xi'an was taken as the object of coagulation sedimentation,filtration and chlorination test.The indexes of temperature?T?,pH,DOC,chlorine content?Cl₂?and bromine ion?Br-?and HAAs production were statistically analyzed.The key factors affecting the formation of HAAs were analyzed,and the HAAs preconditioning of regenerated water disinfection was established.Measure the model.On this basis,the HAAs prediction model is tested by model goodness of fit,significance test,internal validation,and correlation between predicted and measured values.At the same time,using tryptophan as a typical representative of the precursors of disinfection by-products in the regenerated water,simulated disinfection was carried out by the method of interval adding chlorine to study the generation law and toxicity of tryptophan in the process of disinfection.Through research,the purpose of this study was to provide some technical support for the prediction of disinfection by-products during the process of wastewater regeneration.Theoretical basis.The main conclusions are as follows:?1?The experiment of coagulation,sedimentation,filtration and disinfection was carried out on the two grade effluent of urban sewage.The results showed that three chloroacetic acid?TCAA?was the main HAAs in the process of wastewater regeneration and disinfection,and the other types of HAAs were lower or lower than the detection limit.Through the correlation analysis of the influence factors?temperature,pH,DOC,chlorination amount and bromine ion?on the HAAs production,it is found that the amount of chlorine and temperature are the key factors affecting the formation of HAAs during the disinfection process,and pH,DOC and bromine ion are the secondary factors affecting the formation of HAAs.?2?On the basis of the comprehensive consideration of the related factors,the HAAs multiple linear regression model and multiple nonlinear regression model are established,which are suitable for the process of reclaimed water disinfection.L-TCAA C_TCAA=-50.713+0.468T+7.320pH-0.175DOC+2.802Cl₂-45.826Br^-L-HAAsC_HAAs=-61.088+1.011T+9.460pH+0.685DOC+4.734Cl₂-80.515Br^-NL-TCAA C_TCAA=3.675·10^-13·T^1.064·pH^10.581·DOC^-0.514·Cl₂^3.153Br-^-0.080NL-HAAs C_HAAs=3.346·10^-5·T^0.788·pH^3.188·DOC^0.117·Cl₂^1.942Br-^-0.760?3?Using tryptophan as a typical representative of the precursors of the disinfection by-products,the formation potential of halo acetic acid was tested.The results showed that the main HAAs was TCAA and the other types of HAAs were generated but the proportion was less.When chloramine disinfection test was carried out in the way of interval adding chlorine,it was found that when the interval of adding chlorine was 0min?chlorine and ammonia was added simultaneously?,the amount of Cl-HAAs generated was the most;when the interval of interval adding chlorine was5min,the amount of the generated Cl-HAAs was the least,and the amount of Br-HAAs was the most;when the interval time was 1min,the amount of Br-HAAs generated was the least.It is indicated that when tryptophan is used as a precursor,the dosage of halo acetic acid can be reduced effectively,and the toxicity of HAAs is reduced with the shortening of the interval.