The Experimental Study On Slightly Polluted Cellar Water Treatment By Combined Process Of Ultrafiltration

Due to geographical location and climatic factors,the shortage of drinking water is very serious in Northwest China,especially in Northwest villages,and towns and water collecting cellar is used as a drinking water source.Due to the large-scale development of heavy industry in northwest China,the pollution of atmospheric precipitation is becoming more and more serious,and the economic conditions are lagging behind.The rainwater is not well protected in the process of slope convergence and storage.It often causes manure and manure,Scattered leaves,sand and other secondary pollution,a serious impact on the residents of water safety.In this study,the slightly polluted cellar water in villages and towns in Northwest China was taken as the research object,and the effects of ozone and enhanced coagulation ultrafiltration integrated process on the removal of main pollutants and membrane flux in water were studied,the aim is to provide reliable experimental and technical support for cellar water treatment.Firstly,used the ultrafiltration to treat the slightly polluted cellar water,and explored its influence on the effluent quality and membrane performance.In order to remove contaminants in water and delay membrane fouling,intensified coagulation pretreatment experiments were carried out.In the experiment,the effects of coagulants?PAC,PAS,PFS,PAFC?,coagulants?NPAM,APAM?and powdered activated carbon?wood,coal,shell,coconut shell?on cellar water were studied by three kinds of enhanced coagulation methods,which increased the dosage of coagulant,adding coagulant and compound powder activated carbon,and the optimum coagulation combination and hydraulic conditions were determined.The response surface is applied to establish the regression model between each index and dosage,and the optimal dosage and the optimal removal rate can be optimized.The removal efficiency of pollutants and the recovery of membrane flux by enhanced coagulation ultrafiltrationcombinedwithdifferentfiltrationandcombinationmodeswere analyzed.Finally,in order to further strengthen the treatment effect of the process and more effectively alleviate the membrane fouling,the enhanced coagulation/ultrafiltration combined with ozone was used,the removal effect of pollutants and the recovery of membrane flux under different filtration and coagulation methods were analyzed,to determine the best combination of ultrafiltration integrated process,influence study on water quality and membrane flux combination,removal of various aspects of the inquiry.In the experiment of treating the slightly polluted cellar water by separate ultrafiltration,the content of loess and sediment in the cellar water is higher,the turbidity exceeds 30NTU,the content of ammonia nitrogen and organic matter is higher than the sanitary standard for drinking water.In addition,the molecular weight distribution of organic matter is two grade,and the distribution of COD_Mn(UV₂₅₄)is concentrated in two intervals of greater than100KDal and less than 3KDal,which accounts for 67.83%?72.37%?of the total organic matter.When using separate ultrafiltration to treat cellar water,turbidity removal effect is more than 96%,organic matter removal rate is about 20%,ammonia nitrogen removal effect is very small.The water quality of the dead end filtration and the wrong flow filtration is similar,but the attenuation of the dead end filtration flux is slightly better than that of the wrong flow.Both of them make the irreversible pollution aggravate,and the membrane loss is serious.In the experiment of enhanced coagulation treatment of micro polluted pit water,the most suitable combination of enhanced coagulation is wood powder activated carbon/PAC/NPAM.The best dosage is:PAC 34.13mg/L,NPAM 0.20 mg/L,activated carbon dosage 32.11mg/L;the optimum hydraulic conditions:rapid stirring speed of 200 r/min,stirring time 2 min,the flocculation speed 20r/min,flocculation time 30min,adding NPAM after adding PAC1.5min,the adding point of activated carbon is located before the flocculant.Under this condition,the removal rate of turbidity can reach 98.33%,the removal rate of ammonia nitrogen can reach 42.09%,the removal rate of COD_Mnn can reach 50.47%,and the removal rate of UV₂₅₄54 can reach 78.56%.Through analysis,it is concluded that PAC mostly relies on enmeshment.NPAM mainly relies on hydrogen bonds and protonation of its own groups,and wood powder activated carbon can remove pollutants by its own surface adsorption capacity.The response surface method was used to establish four models,with turbidity,ammonia nitrogen,COD_Mnn and UV₂₅₄54 as response values.The model was significant and accurate and reliable.In the experiments on treatment of cellar water by enhanced coagulation combined with ultrafiltration,dead end flow and on-line coagulation are the best combinations.On line coagulation,alum flower will be deposited on the surface of ultrafiltration membrane to form cake layer,which can intercept pollutants,help to increase membrane flux,and effectively reduce membrane fouling.It eliminates the precipitation link,reduces time and saves energy.After combined use,the effluent quality was significantly improved,ammonia nitrogen removal rate increased by 30%,COD_Mnn removal rate increased by 38%,and UV₂₅₄removal rate increased by 67%,and the removal rates of pollutants can be as follows:turbidity99%,ammonia nitrogen 51%,COD_Mn64%and UV₂₅₄85%.Enhanced coagulation combined with ultrafiltration obviously slowed down the attenuation of membrane flux and prolonged the service life of ultrafiltration membrane.In the experiments on treatment of slightly polluted cellar water by ozonation,enhanced coagulation and ultrafiltration integration,ozone pre oxidation enhanced coagulation and ultrafiltration is the best integrated process,effectively alleviating membrane fouling,and the target pollutant removal rate can reach 99.45%turbidity,57.84%ammonia nitrogen,COD_Mn76.31%and UV₂₅₄94.49%,all of which reach the hygienic standard of drinking water.When the cellar water is directly ozonation,the index of organic matter in water has no obvious improvement,and the turbidity and ammonia nitrogen have negative effect.The best contact time is 3min.However,ozone can change the composition of organic matter and molecular weight in cellar water,destroy the unsaturated structure of humic substances,and oxidize some organic matter to small molecules,which is conducive to the enhancement of coagulation.Ozone pre oxidation promotes coagulation process in integrated process,and enhanced coagulation is the main part of pollutant removal.Ultrafiltration can remove pathogenic microorganisms and ensure the stability of the whole integrated process.