| As the third generation of urban drinking water production technology,ultrafiltration technology has been gradually promoted and applied in China.Ultrafiltration membrane can effectively remove colloids and particles in water sources to guarantee drinking water safety.However,during the production process of drinking water by ultrafiltration water plant in China,the operation and management problems caused by ultrafiltration membrane fouling accumulation and the water quality issue with low removal efficiency of dissolved organic matter have become the bottleneck for further application of ultrafiltration process.One effective way to solve the above problems was combining pretreatment unit with ultrafiltration membrane.By changing the influent water quality through pretreatment,the membrane fouling can be efiiciently alleviated and the water quality of permeate could be promoted.In this paper,the novel UV/chlorine advanced oxidation process was applied as the core of the pretreatment process.UV/chlorine preoxidation,UV/chlorine/PAC pretreatment and UV/chlorine/Fe(II)pretreatment are used as the pretreatment methods,respectively.The influence of UV/chlorine based pretreatments prior to ultrafiltration process for membrane fouling mitigation and corresponding mechanisms are systematically investigated.Firstly,the typical micro-polluted surface water source was adopted as ultrafiltration raw water,and the mitigation of membrane fouling by UV/chlorine pre-oxidation was studied.The feasibility of UV/chlorine combined ultrafiltration process as drinking water production process was explored.The results show that UV/chlorine preoxidation can significantly alleviate the increase of membrane fouling at a low dosage.Through the enhanced removal of dissolved organic matter,UV/chlorine oxidation reduced the source of membrane pollutants.At the same time,preoxidation transforms part of macromolecular organics in natural water into micromolecular organics,which could reduce the adhesion of pollutants on the membrane surface.The micro morphology of the membrane surface shows that the cake layer formed by direct ultrafiltration of raw water is rough and irregular,while the cake layer on the membrane surface is more uniform and smoother after UV/chlorine pretreatment.The results showed that UV/chlorine pretreatment affects the interface contact between the pollutants and membrane,which could form better hydraulic back-wash and filtration conditions.The removal of atrazine(ATZ)by UV/chlorine pretreatment was also discussed.Because the molecular weight of micro pollutants is far smaller than the pore diameter of ultrafiltration membrane,the removal rate of such substances by ultrafiltration membrane is usually lower than 10%.The removal rate of ATZ by the combined UV/chlorine ultrafiltration process can reach 87% when the UV dose is extended.The preliminary economic comparison shows that the cost of UV/chlorine is far lower than that of UV/hydrogen peroxide.More over,as chlorine is widely used as disinfectant in water purification plant,by adding UV irradiation and pre-chlorine dosing unit,low-cost transformation of the process can be realized.The results show a good prospect of engineering application of UV/chlorine combining with ultrafiltration process.Then,the surface water source polluted by algae was used as the target water for drinking water purification.The effect of UV/chlorine/PAC pretreatment on membrane fouling was investigated.As the UV/chlorine alone could hardly achieve satisfying efficiency in membrane fouling caused by eutrophia water.The UV/chlorine/PAC pretreatment was applied for fouling control and organic matter removal.The results show that UV/chlorine/PAC processes can greatly promote the membrane fouling control ability and reduce the loadings for ultrafiltration membrane unit.For highly eutrophia water,this process can effectively remove the organic matter contaning C=C bonds in algal organics(EOM)and natural organics(NOM).The rising of trans-membrane pressure was very slow with UV/chlorine/PAC pretreatment.For example,the total and irreversible membrane fouling resistance caused by slightly eutrophia water could at most reduced by 63% and 92%,respectively.At the same time,the removal efficiency of micropollutants like microcystins(MC-LR),ATZ and p-CNB were also improved to 42-76%.For the purification of eutrophia water,the UV/chlorine/PAC pretreatment could obviously reduce membrane fouling and improve the effluent quality.On the basis of the above research,the pretreatment of UV/chlorine/Fe(II)was adopted to improve the water purification efficiency for complex water sources.Humic acid,bovine serum protein,sodium alginate and their mixture were selected as typical organic pollutants,respectively.The influence of typical organics during the process of UV/chlorine/Fe(II)with membrane filtration was revealed through varying mixing proportion of different organics.The reaction pathways,water matrix,molecular weight distribution and the content of fluorescent organic matter have been investigated to explore the performance and mechanisms of UV/chlorine/Fe(II)pretreatment.The results suggested wide-range molecular weight substances could be removed by UV/chlorine/Fe(II)pretreatment,which induced the great mitigation of both reversible and irreversible membrane fouling.As for the BSA feed solutions,the reduction rate of total and irreversible membrane fouling resistance reached 83-84% and 76-79%,respectively.And the reversible fouling resistance of SA could even be reduced by 96% at most.For the feed wate mainly containing HA and BSA,the fouling indeices could be evaluated and predicted through Fmax.The experiments of complex mixed feed water and analysis of model fitting established the mathematic relationship between fouling and pretreatment method.Based on this,the application of UV/chlorine/Fe(II)pretreatment for various conditions could adjusted according to the variation of feed water to change the interface between pollutants and membrane.Better performance of membrane fouling alleviation could be achieved.Started with the ultrafiltration treatment of micro-polluted surface water,the membrane pollution caused by natural organic matter in surface water can be effectively controlled by UV/chlorine pretreatment.Then,the UV/chlorine was adopted as the core of ultrafiltration pretreatment unit,and UV/chlorine/PAC adsorption pretreatment was used to alleviate the membrane pollution caused by eutrophia water.Through the identification of algae source and natural organic matter and model fitting,the removal of membrane pollutants by the combined effects of oxidation and adsorption in UV/chlorine/PAC adsorption pretreatment was revealed.On this basis,the pretreatment of UV/chlorine/Fe(II)inhibited the rapid growth of membrane resistance in the filtration of complex organic feed water.Through the analysis of raw water composition and membrane fouling mechanism,the general rules and methods of membrane fouling control by UV/chlorine/Fe(II)pretreatment were clarified. |
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