Study On Removal Mechanism And Technology Of Emerging Organic Matters

Efficient removal of emerging organic pollutants（EOPs）is a technical problem in water treatment processes.The removal of EOPs by conventional water treatment process is ineffective,pretreatment or advanced treatment combined with conventional process is necessary to improve their removal efficiencies.Consequently,research and construction of technique and combined processes for efficient removal of EOPs is an important development direction in water treatment field.Recently,techniques of advanced oxidation and membrane separation,as advanced treatment techniques for upgrading and modification of conventional water treatment process,have been deeply studied and widely used.In this paper,the removal efficiency and degradation mechanism of intracellular organic matter（IOM）and bisphenol A（BPA）of typical EOPs were studied and analyzed by coagulation,titanium dioxide（TiO₂）photocatalytic oxidation,membrane filtration and their combination techniques,respectively.Meanwhile,the removal characteristics of IOM,BPA and IOM/BPA composites were investigated,and the control of membrane fouling was studied.The main results can be achieved as following:Aluminum sulfate（AS）and polyaluminum chloride（PACl）both played a positive effect on the removal of IOM.The removal of aromatic IOM was higher by PACl;AS and PACl preferred to remove high molecular weight IOM,whereas the removal of PACl for low molecular weight IOM was higher than that of AS.The aromatic substance of IOM was completely degraded by TiO₂ photocatalytic oxidation,and the adsorption and degradation of IOM were mainly concentrated in the fractionations of 1-3kDa and less than 1kDa.The content of protein-like organic matter was higher than that of humic-and fulvic-like substances regardless of their molecular weight.The humic-like substance was mainly concentrated in 10-30 and3-10kDa,and fulvic-like substances was mainly concentrated in 10-30 and30-100kDa.The combined processes of membrane with AS coagulation,PACl coagulation and TiO₂ advanced oxidation exerted better removal performance of IOM than that of single techniques.The BPA removal by AS coagulation was efficient,with the maximum removal efficiency of 25.4%,and the coagulation mechanism was dominant by charge neutralization.The BPA removal by PACl was higher than that of AS,reaching up to37.7%,and the removal was depended on the content of Al_b.The solution pH and the concentration of humic acid had a great influence on the removal of BPA by AS and PACl coagulation.The optimum pH was 6.5⁷.5.The removal of the low concentration of BPA（0.01mg/L）in natural water by AS was poor,and the highest removal rate was only 16.8%.The highest removal of BPA by TiO₂ photocatalytic oxidation was 82.5%under the conditions of catalyst loading of 1g/L and the initial concentration of BPA of 1mg/L.Under such condition,the removal of the low concentration of BPA（0.01mg/L）in natural water was 53.5%.The degradation of BPA by TiO₂ photocatalytic oxidation was easier to proceeded under low pH,and the degradation rate of BPA decreased under high pH.Hydroxyl radical was the main oxidation mechanism.During the process of membrane filtration for the BPA,the removal of BPA rate was less by the membrane of 100kDa,however,that of BPA was higher by the membrane of 1kDa,and the membrane pollution resistance of BPA for less than 1kDa accounted for the largest proportion of total pollution resistance,which was the main component of membrane fouling.To the removal of BPA,The combined processes of membrane with AS coagulation,PACl coagulation and TiO₂ advanced oxidation exerted also better removal performance of IOM than that of single techniques.The effect of aluminum sulfate and polyaluminum chloride on the coagulation removal of IOM/BPA composite pollution was obvious.When the total concentration of IOM/BPA increased,the removal rates of UV₂₅₄,DOC and BPA showed a downward trend,but the removal rate of UV₂₅₄54 was significantly higher.In the term of DOC and BPA,when the concentration ratio of IOM/BPA was 10/5mg/L,BPA was removed efficiently with the maximum removal rate（31.6%）.IOM/BPA combined pollution was degradated efficiently by the photocatalytic degradation with titanium dioxide.IOM with different molecular weights had a great influence on the removal efficiency of BPA.The smaller molecular weight of IOM had a positive effect on the degradation of BPA.The IOM of less than 1kDa was contributed to the maximum removal rate for 95.6%;when the total concentration of IOM/BPA composite pollutants increased,the removal rates of UV₂₅₄ and DOC decreased.For BPA/IOM combined pollution,the BPA removal effect was less affected by IOM when the BPA concentration was lower,conversely,When the concentration of BPA was higher,the removal effect of BPA was greatly affected by the concentration of IOM.The maximum removal rate of UV₂₅₄54 and BPA were 49.1%and 99.5%by photocatalytic oxidation of titanium dioxide for IOM/BPA composite pollution.During the process of membrane filtration for the IOM/BPA composite pollution,the removal rate of BPA and IOM was significantly higher than that of other pore size ranges by membrane filtration of less than 1kDa pore size.The concentration of IOM had less effect on BPA removal rate by membrane filtration.The removal rate of IOM and BPA for IOM/BPA composite pollution were 98.0%and 98.3%by titanium dioxide photocatalytic oxidation/membrane filtration technology,respectively,which was obviously better than aluminum sulfate coagulation/membrane filtration and polyaluminum chloride coagulation/membrane filtration.Combined technology effectively alleviated the degree of membrane fouling.The research results can provide technical support for the upgrade of the conventional treatment process and the removal mechanism and combined treatment process of composite pollution for typical emerging organic pollutants.