Improvement Of Ultrafiltration Membrane Performance By Powdered Activated Carbon

The significance of Ultrafiltration(UF) technology applied in water treatment has been widely recognized in recent years,and there are also obvious deficiencies in membrane fouling and poor removal of dissolved organic matter.Therefore, How to improve water quality under the premise of effectively reducing membrane pollution becomes both an emphasis and a nodus in membrane technology field. The activated carbon powder(PAC) can remove effectively natural organic matter, algal toxin, pesticide residue owing to the special pore structure.As a consequence,UF membrane and PAC can construct the combined PAC-UF process,and the process can both remove organic matter performed by PAC and guarantee the UF membrane for particulate matter to be trapped completely.However,it’s controversial for the properties of PAC varied with different sizes and aperture structures have the effect on the absorption efficiency and slowing down the membrane fouling.In this study,the polyvinyl chloride(PVC) hollow fiber ultrafiltration membrane was employed.Three diffreent particle sizes of PAC(50μm,3μm and 0.2μm)were selected to build the PAC-UF combined process,the influence of particle size of PAC on the removal of HA and the membrane fouling were evaluated at different operation conditions for two kinds of combined processes:the conventional PAC-UF(PAC dosage is not more than 60mg/L) and the high concentration PAC-UF(PAC concentration is 50g/L).The conclusion is as follows:1.The surface functional groups and physical structural properties of the PAC were characterized by Boehm titration and BET method. Moreover, the adsorption properties of HA were investigated through the static adsorption experiments. The results indicated that the PAC particle size significantly affects the pore structure, but not change the surface functional groups. Reducing PAC size significantly improve its adsorption capacity and adsorption rate of HA. PAC can effective adsorb the HA of small molecular mass fractions which is difficult to intercept by UF membrane. Three kinds of PAC adsorption of HA differences lies in the adsorption of relative molecular mass between 30 KDa and 100 KDa.2.The effect of particle size of PAC on the removal efficiency and the membrane fouling were investigated by building the conventional PAC-UF process using different parameters. Dosing PAC can effectively reduce membrane fouling.With the increase of adsorption capacity, which improved the removal efficiency for organic matter of the PAC-UF process and slowed the membrane fouling further. Centralized dosing could easily lead to the activated carbon pore blockage, difficult to maintain effective adsorption of organic matter in the water to follow, the most effective way for the PAC-UF process is continuous dosing system.Increased aeration and continuous aeration can improve PAC adsorption environment and inhibit the formation of cake layer, thereby improving the organic removal efficiency and mitigating fouling.With the decreases of PAC size,the effect of improving fouling weakened at continuous aeration and excessive aeration(≥0.5L/min). When turbidity coexist with humic acid, membrane surface formed a dense filter cake layer,and the removal rate increased.but the membrane fouling exacerbated.With the reduction of particle size of the PAC,the degree of flux decline slowed down.. the organic matter which was adsorbed by PAC as one of most the major factors which relieved membrane fouling,the saturated PAC will aggravate membrane fouling.3.The treatment efficiency of PAC-UF process was investigated by different pretreatment method(PACl as coagulant and O3 as oxidant). The results showed that coagulant was cooperated with PAC on removal of organic components of different molecular weight, but also PAC had the coagulation-supporting effect. The mechanism of alleviating membrane fouling is that pre-coagulation can effectively reduce the flux decline, reduce pollution load and improve the structure of the cake layer. However, in ozone pretreatment process, O3 led to a shift in HA morphology, increase small molecular weight organic compounds and hydrophilic organic compounds, which can alleviate membrane fouling.4.The effect of particle size of PAC on removal efficiency(UV254,DOC,NH4+-N and NO2--N) and transmembrane pressure TMP was investigated by building the HCPAC-UF process during startup and different parameters.The results show that the PAC(0.2μm) can inhibit the growth of microorganisms at startup. There was a little difference between UV254 and DOC under different particle of the PAC,and the particle size reduction can significantly improve the transmembrane pressure.The removal efficiency at different aeration(0.15m3/h, 0.3m3/h and 0.5m3/h) was no significant difference,but increased aeration can enhance the destructive effects of water agitation for the concentration polarization layer and cake layer andslow the membrane fouling.Increased flux(14.5L/m2 h, 27.4L/m2 h and 38.2L/m2h)will result in reduction of HRT and increased radial flow drag force,causeing the organic removal rate decreased and TMP doubled,but no significant change to the ammonia.Decreasing particle size has a great influence on the adsorption performance for PAC, the membrane antifouling can be significantly improved.However,the PAC particle size properties and the change of operating conditions has no obvious effects on biological degradation ability.