Research On Enhanced Coagulation Process Based On Cellar Water And Application Of Integrated Purification Device

At present,some arid regions and remote mountainous areas in China are still facing the problems of water scarcity,high cost of water supply pipe network laying,and difficulty in construction of the pipe network facilities.A large number of residents still use rainwater cellar water as domestic and drinking water.In the first five-year plan to march towards the second centenary goal,,the party and the country attach great importance to solving people’s livelihood problems,and solving the problem of drinking water safety is the top priority.Based on the characteristics of cellar water supply system and water quality in arid areas and remote mountainous areas,an integrated water purification device with coagulation,activated carbon adsorption,ultrafiltration,and ultraviolet disinfection was designed and processed according to our preliminary study.The main research contents include the optimization of coagulant and coagulant aids;the the optimum operation condition of disinfection and pre-oxidation and the integrated water purification device.The coagulation effects of five coagulants,polyaluminum chloride,polyferric sulfate,polyaluminum ferric chloride,aluminum trichloride,and ferric trichloride,were compared in cellar water.Optimizing 3 kinds of coagulants suitable for cellar water and their dosage range for compounding experiment research,adopting compound ratio（concentration ratio）of 2:1,1:1,1:2 to study the flocculation effect of coagulant compound.Comparing the above five kinds of coagulants alone and nine different combination of coagulation compound agents,polyaluminum chloride PAC owned the best purification effect,and the optimum dosage was 20mg/L.The experiment was carried out to study the addition of coagulant aid on the basis of the optimal coagulant PAC and the optimal dosage of 20mg/L.The dosage of coagulant aid PAM had greatly improved the coagulation effect with an optimal dosage of 2.5mg/L,and dosing point of 30s after the start of mixing.On the basis of the optimal coagulant and dosage,experiments were carried out to study the disinfection and pre-oxidation coagulation process.With sodium hypochlorite as the disinfectant,the optimum condition for disinfection and pre-oxidation was that the disinfectant dosage was 3 mg/L and pre-oxidation time was 20min.After the pre-oxidized coagulation,it was detected that the generation of five kinds of disinfection by-product（DBPs）in cellar water showed an upward trend with the increasing dosage of disinfectant.Trichloromethane and dichloroacetic acid were relatively high in DBPs.In addition,the amount of five kinds of DBPs within 0-25min rose slowly as the pre-oxidation progressed.Comparing the results of the coagulation experiment group and the non-coagulation control group,it showed that flocculation can effectively remove the precursors of DBPs and inhibit the formation of DBPs.Orthogonal experiments on the coagulation process of the device were carried out to study the best operating conditions,the purification effect on different water sources,and the long-term operating conditions in continuous operation.The best coagulation condition of the device:the flocculant dosage was 20mg/L with polyaluminum chloride（PAC）,and,the coagulant dosage was 2.5mg/L with polyacrylamide（PAM）,the mixing stage time t₁ was 2min with rotation speed of 500r/min,the time t₂ of the fast stirring phase was 12min with speed of 300 r/min,the time t₃of the slow stirring phase was 10minwith speed of 100 r/min,and the precipitation time was30min.After the pilot test of continuous operation of the device,the integrated purification device studied in this paper can meet the limit requirements of the"Drinking Water Hygiene Standard GB5749-2006".Although,the purification effect got worse in both effluents as the number of operations increased,the removal rate for pollutants recovered after backwashing.Furthermore,on the basis of the preliminary device design and operation problems,suggestions for device optimization were put forward,including simplification and adjustment of the,size of the stirring blade,replacement of the filter element,and addition of miscellaneous water outlets.