Study On The Method Of Chlorine Supplement And Disinfection By-products During Storage Of Reclaimed Water

With the improvement of wastewater reuse technology,reclaimed water has become a stable water source,which can effectively solve the problem of water shortage.However,the current facilities of the reclaimed water supply pipeline network are backward,and the amount of reclaimed water resources is large.The reclaimed water will be stored for a longer or shorter time.At present,there are few related studies on the changes of water quality during the storage of reclaimed water and the measures for replenishing chlorine after chlorine depletion.In order to ensure the water quality and end-use water safety during the storage of reclaimed water,this paper conducted a chlorine supplement disinfection test study on the problem of chlorine exhaustion during the storage of reclaimed water,using sodium hypochlorite as the chlorine disinfectant.First,the water quality changes after chlorine supplementation were analyzed,the main chlorine-consuming pollutants were determined,a chlorine attenuation model and a method for calculating the amount of chlorine input were established,and then the conditions of chlorine attenuation were analyzed.Finally,the main influencing factors of typical disinfection by-products in the process of chlorine disinfection were studied,and the characteristics of the precursors of disinfection byproducts were analyzed,and the formation of disinfection by-products was controlled by using enhanced coagulation.The experimental results show that NH₄⁺-N and humic acid are the two most pollutants that consume the most chlorine after regenerating water.After the chlorine supplement,the pH continued to increase,and the higher the sodium hypochlorite dosage,the higher the pH.As the pH increased,the relative proportion of HClO and ClO^-changed.When the pH exceeded 7.5,the relative proportion of HClO starts to be lower than ClO^-,which greatly reduces the disinfection effect.With the increase of residence time,the turbidity shows an upward trend.When the water temperature is low in autumn and winter,in order to meet the water requirement of the turbidity limit of 5 NTU and the residence time is within 24 h,the amount of chlorine injected should not exceed 6 mg/L.The higher the amount of chlorine input,the higher the turbidity of the water,resulting in white flocs in the water and faucets.It is detected that the substance contains a large amount of aluminum.This is because the hydrolysis of sodium hypochlorite increases the pH,resulting in the coagulant polyaluminum chloride precipitate.In this paper,a model for predicting the amount of chlorine replenishment in regenerated water is established.First,the improved first-order kinetic model C = C₀+A ×exp?-?k?× t?is found to be the most suitable for the reclaimed water through the residual chlorine decay attenuation model,which can fit the actual attenuation change of chlorine well,and the fitting degree is above 0.99.In order to determine the calculation method of the chlorine attenuation coefficient k in the residual chlorine attenuation model and the chlorine concentration A participating in the reaction,a chlorine attenuation coefficient model and a chlorine-consuming substance model were established,which are?k?= 0.953-0.093 × A and A = 6.38-6.39?0.18 ^ x₁?-0.63?0.98 ^ x₂?,where the chlorine attenuation coefficient k is negatively correlated with the chlorine concentration A participating in the reaction.The calculation of the chlorine concentration A participating in the reaction is mainly related to ammonia nitrogen and humic acid.Therefore,when the ammonia nitrogen concentration x1 and humic acid x2 are known,the value of chlorine concentration A involved in the reaction can be calculated,and then substituted into the calculation equation of the chlorine attenuation coefficient k,the chlorine attenuation coefficient k can be obtained,and finally the two substitute the chlorine attenuation model.According to this calculation method,the residual chlorine concentration corresponding to the disinfection contact time t and the time required when the residual chlorine is below the prescribed standard can be calculated.In addition,through the above formula and the required storage residence time,the residual chlorine requirements of the water terminal to guess the amount of chlorine supplement that meets the requirements.After experiments,it was found that the amount of chlorine injected,the initial ammonia nitrogen concentration,and the concentration of humic acid had a greater influence on the generation of typical disinfection by-products.After chlorine supplementation,the amount of chloroform generated first increased and then decreased,and it was generated at 48 h.The amount reached the highest level,and the amount of chloroform production began to decrease with the decay of residual chlorine after 48 h.The higher the amount of chlorine input,the higher the amount of chloroform generated,and the higher the initial ammonia nitrogen concentration,but the lower the amount of chloroform and carbon tetrachloride generated.Therefore,keeping a certain concentration of ammonia nitrogen can greatly reduce the generation of typical disinfection by-products.Humic acid is a precursor of chloroform.Before disinfection of regenerated water,the content of humic acid in the water should be reduced as much as possible.Humic acid mainly contains C,H,O,N,and S elements,and contains a large number of hydroxyl,carboxyl,alcohol,phenol,and benzene rings,and other active groups containing a large number of unsaturated bonds,which easily generate chlorinated disinfection by-products.Enhanced coagulation is currently the best process for controlling the precursors of disinfection by-products.In this experiment,five kinds of coagulants,such as ferrous sulfate,ferric chloride,polyferric sulfate,polyaluminum chloride,and aluminum sulfate,were selected to analyze the amount of disinfection by-products produced after the chlorine treatment of water treated with different coagulants.After analysis,it was found that ferric chloride has better control effect on chloroform in chlorination and disinfection than other coagulants,followed by ferrous sulfate,and polyaluminum chloride has the best control effect on carbon tetrachloride.When the dosage of coagulant is 10 mg/L,the production of carbon tetrachloride reaches the lowest level.After that,even if the dosage of coagulant is increased,the production of carbon tetrachloride will not be reduced.