Study On The Fouling Behavior Of Dongjiang Water By Ultrafiltration And The Effect Of Pretreatment On Pollution Control

With the intensification of water pollution,the conventional treatment process of existing water plants has been difficult to cope with the demand for high quality water.Due to the advantages of good water quality,simple operation and management,and small footprint,ultrafiltration is now widely used as a deep treatment technology for drinking water.However,organic matter in natural water bodies can cause serious membrane contamination,resulting in reduced water production,increased operational energy consumption and shortened membrane life,which is a bottleneck limiting the large-scale promotion and application of ultrafiltration in the field of water treatment.In this study,the membrane contamination problem in the ultrafiltration process of Dongjiang water is addressed by identifying the contaminant components,and systematically studying the removal of contaminants and the control of membrane contamination by different pretreatment process combinations,and then proposing suitable contamination control strategies.The specific research work and conclusions are as follows.1.By studying the water quality characteristics of Dongjiang water,the fouling behavior of ultrafiltration membranes,the components of membrane surface pollution and the composition of the washing liquid,it can be seen that the chemically reversible pollutants in Dongjiang water are mainly proteins and most humic pollutants.The chemical irreversible pollutants are polysaccharides and a small number of humic substances.The hydrophilic and hydrophobic separation of raw water shows that the proportion of hydrophobic components of NOM in raw water（strong sparse 37.76%+weak sparse 28.82%）is greater than that of hydrophilic components（33.42%）.The pollution degree of the ultrafiltration membrane caused by different hydrophilic and hydrophobic components is:hydrophilic component>raw water>strong hydrophobic component≈weak hydrophobic component.2.Analysis of the characteristics of raw water quality components in different seasons shows that the pollutant content in winter and spring（December-May）is relatively low（humus is about 1.2 mg/L,protein is about 1 mg/L,and polysaccharide is about 2 mg/L）.The pollutant content is relatively high in summer and autumn（June-November）,and reaches the highest value in the flood season in August.Humus was 2.624 mg/L,protein was 2.2 mg/L,and polysaccharide was 6.3 mg/L.3.In the control of Dongjiang water by a single pretreatment,the optimum dosage of powdered activated carbon（PAC）for adsorption pretreatment was 30 mg/L.The optimum dosage of polyaluminum chloride（PACl）for coagulation pretreatment was 20 mg/L.The optimum dosage of potassium permanganate（KMn O₄）for oxidation pretreatment was 0.1mg/L.For humic-based raw water,the use of oxidation or coagulation pretreatment to alleviate the pollution of ultrafiltration membranes is better than adsorption pretreatment.For protein-based raw water,coagulation or oxidation pretreatment is more advantageous.For the raw water mainly composed of polysaccharides,the effect of adsorption pretreatment is better.4.In the control of Dongjiang water by combined pretreatment,the combined adsorption-coagulation pretreatment process has the best effect.The optimal dosage is 20 mg/L PAC+30mg/L PACl.The removal rates of total organic carbon,humic acid,protein and polysaccharide were 88.83%,83.53%,75.22%and 86.12%,respectively.Considering that the existing coagulation dosage of the water plant is low（20-35mg/L）,the economic dosage of combined pretreatment is determined by experiments to be 10 mg/L PAC+10 mg/L PACl.The removal rates of total organic carbon,humic acid,protein and polysaccharide were 68.15%,72.52%,73.15%and 77.15%.Compared with the existing coagulation and sedimentation process in the water plant,the combined pretreatment（optimal dosage and economic dosage）can control membrane fouling more effectively.5.It has been verified by the ultrafiltration pilot test that after the ultrafiltration process is connected to the sedimentation tank,it can not only maintain a low transmembrane pressure differential operation,improve the effluent quality,but also reduce the investment and operating energy consumption of the sand filtration process.The optimal combination of pretreatment and optimal dosage has a good effect on aleviating the fouling of the ultrafiltration membrane,which can reduce the operating energy consumption,slow down the membrane fouling,and prolong the service life of the membrane.Internal pressure PES membrane（Inge）and external pressure PVDF membrane（Memstar）are more suitable for ultrafiltration process water plants using Dongjiang water as raw water.6.Effects of water chemical conditions（p H,IS,calcium ions）on membrane fouling of humic acid（HA）,bovine serum albumin（BSA）and sodium alginate（SA）were studied.For BSA,severe contamination occurs at p H values close to the isoelectric point.However,the fouling of HA and SA on the ultrafiltration membrane slowed down with the increase of p H.With the increase of IS and Ca²⁺concentration,the three pollutants fouled the ultrafiltration membrane more seriously.7.Using the XDLVO theory to analyze the interaction energy barriers of different pollutant-membrane and pollutant-fouling membrane interfaces are BSA>HA>SA,which is consistent with the flux behavior of the three pollutants.The reduced interfacial energy barrier reduces the resistance of the membrane surface to contaminants and increases the deposition of contaminants to the membrane surface.In addition,the steady-state flux value in the late stage of membrane filtration strongly depends on the interaction of pollutant-fouling membrane interface.Under different p H conditions,the steady-state flux values of the three pollutants in the late stage of filtration were positively correlated with the energy barrier values of the pollutant-fouling membrane interface.The higher the energy barrier,the greater the flux.