Study On The Coagulation Mechanism And Membrane Fouling Control Of Effluent Organic Matters Obtained From Wastewater Treatment Plant

With the shortage of water becoming more serious,wastewater reuse is currently considered globally as the most critical element of sustainable water management.Irreversible membrane fouling of effluent organic matter?EfOM?during advanced treatment of secondary effluent reclaim through ultrafiltration has become the technical bottleneck of restricting its large-scale application.Identifying the main contaminants of membrane fouling in EfOM,revealing membrane fouling mechanism and controlling membrane fouling effectively have become important issues in advanced treatment of secondary effluent.Coagulation-ultrafiltration process was employed in advanced treatment of secorndary effluent from a wastewater plant in Wuhan.Resin fractionation and analysis techniques were introduced for characterization of the main fouling components.XDLVO theory was introduced to investigate the effect of the interaction between model pollutant humic aicd?HA?and bovine serum albumin?BSA?on membrane fouling mechanism.Further,the coagulation mechanism of HA,BSA,sodium alginate?SA?and Ca²⁺,and the correlation between floc morphological characteristics and membrane fouling indexes were explored as well.Finally,on the basis of the research,the membrane fouling mechanism of EfOM and its fractionations from a wastewater plant in Wuhan was analysised and high performance of advanced treatment with coagulation-ultrafiltration process was carried out.The conclusion of this research could provide theoretical guidance and technical parameters for practical engineering application.Main conclusions in this study are as follows:?1?The results of composition characterization of EfOM from a wastewater treatment plant in Wuhan showed that there were four fluorescent components in EfOM,including terrestrial humic acid,tryptophan-like substance,tyrosine-like substances and humic substance related to the internal oxidation.The characteristics ultraviolet adsorption of aromatic functional groups was low,fluorescence intensity of protein and soluble microbial products were higher and molecular weight distribution was mainly in 1k¹0k Da,which were much different from that in the Northwest of China,North China,and East China.?2?During the investigation on membrane fouling of directly ultrafiltration,it was indicated that the intermolecular interaction between BSA and HA had increased the removal effiency of UV₂₅₄ from 45.2%to 67.2%and enhanced the distribution of hydraulic reversible membrane fouling into 80%when HA and BSA mixed as 1:1.In the meantime,the calculation of surface interaction energy indicated that the intermolecular interaction between BSA and HA enhanced the the van der waals interaction and polar attraction between contaminant and polyvinyl chloride membrane.With SA concenteation of 0.2 mg/L,the gel-like structure of sodium alginate could lead to cake layer with better hydraulic reversible ability.However,SA had enhanced the polar attraction between contaminant and membrane with high concerntration?0.5 mg/L?,which causing serious chemical reverible membrane fouling with increasement of proportion from 7.5%to 60.4%.As common inorganic pollutants in secordary effluent,Ca²⁺could enhance the polar attraction between HA and membrane surface,which led to significantly increase in chemical reversible membrane fouling from 7.5%to 47.7%.?3?The results showed that intermolecular interaction between BSA and HA had affected the interaction of HA and Al₁₃,and led to decline of floc strength factor from 67.1%to 45.2%,increasing hydraulic reversible membrane fouling of cake layer from 40.5%to66.1%.The research found out that SA not only decomposed high surface structure of Al₁₃through complexation,crippling charge neutralization mechanism,but also promoted the AlCl₃ floc growth and increased floc strength from 49.2%to 62.9%through crosslinking ability.The adsorption,complexation and bridging between Ca²⁺and contaminants could improve coagulation performance and modify floc morphological characteristics,which led to porous cake layer with better compressive ability.However,the interaction between Ca²⁺and contaminants could also lead to enhancement in irreversible membrane fouling of Al₁₃floc about 4.1 times.The correlation of floc morphology and membrane fouling showed that bigger the floc size,more serious the membrane fouling.The floc growth rate of AlCl₃?1.2?m/s?was higher than Al₁₃(AlO₄Al₁₂?OH?₂₄?H₂O?₁₂⁷⁺)?0.5?m/s?,therefore Al₁₃ exhibited better effect on membrane fouling control.?4?Coagulation-ultrafiltration process was applied to control membrane fouling of secorndary effluent from a wastewater treatment plant in Wuhan.The results indicated that organic colloid was the main contaminant causing irreversible membrane fouling and cake layer formation was the main membrane fouling mode.According to the bench scale experiments in this study,higher performance of membrane fouling control could be achived by using polyaluminum chloride(contained 93.9%Al₁₃)with basification=2.2,under dose of 0.12 mmol/L(Al³⁺)and floc size suggested in the range of 150²00?m with in-line coagulation-ultrafiltration process.