Research On The Performance And The Mechanism Of Humic Acid Removal By The Photocatalysis-Membrane Integrated Process

Membrane technology is widely used in the field of drinking water treatment. However, the Humic Acid (HA) existing in the surface water is a typical membrane fouling matter, which can lead to serious membrane fouling phenomenon during the membrane filtration process and can generate the harmful disinfection by-products during the disinfection process. Therefore, the photocatalysis-membrane integrated process is introduced to remove the HA, in which, the photocatalysis process as the pretreatment technology for the membrane filtration can degrade the HA and alleviate the membrane fouling phenomenon.The photocatalysis process is the primary part of the integrated process, so deeply understanding the basic rules of the photocatalysis degradation of HA is the foundation of correctly applying the photocatalysis process to degrade HA. As a new water treatment process, it's significant to study the pollution removal performance and the membrane fouling characters of the practical applying of the photocatalysis-membrane integrated process. In order to prevent the membrane fouling and the loss of the nano-sized TiO2, the silica-gel supported TiO2 is prepared by the sol-gel method as the photocatalyst. Moreover, the photocatalysis reaction is carried out continuously by the photocatalysis -membrane integrated process, which provides the conditions for the study of the performance of continuous use of photocatalyst TiO2, the deactivation reasons of the photocatalysts and lays a foundation for the practical use of the photocatalysis process.This thesis mainly studies on the HA removal performance, the influencing factors, the membrane fouling characters of the photocatalysis-membrane integrated process. Moreover, this thesis also studies on the mechanism of photocatalysis degradation of HA, the deactivation mechanism and the reactivation methods of the photocatalysts TiO2.The performance of HA removal by the photocatalysis-membrane integrated process is studied. The static experimental results indicate that the HA-like matters with large Molecular Weight (MW) can be degraded completely by the photocatalysis reaction. However, the protein-like matters with small MW as the by-products generate, which are hard to be degraded. The concentration of organic matters in the outlet water is low during the running of the integrated process, which are mainly the protein-like matters. The HA can be degraded effectively in the first 32h of system running in the membrane reactor. The organic matters are mainly the protein-like matters as the by-products of HA. The degradation performance is deteriorating with the decreasing of the degradation ability of TiO2. The HA-like matters with large MW in the mixture of the membrane reactor increase after 32h running. The fouling layer on the membrane surface forms during the running period of the integrated process, which plays an important role to remove the organic matters.The influencing factors of HA removal by the photocatalysis-membrane integrated process are studied. The static experimental results indicate that the photocatalysis degradation of HA is in accordance with the pseudo first order reaction kinetics. The reaction rate constant is increasing with the decreasing of the initial concentration of HA, the pH value and the increasing of the dosing quantity of TiO2, the reaction temperature. The inlet of Ca2+, Mg2+, HCO3? , H 2 PO?4 can inhibit the degradation of HA. But the inlet of Cl? , SO 42? is benefit for the adsorption of HA on the surface of TiO2, which can promote the degradation of HA. The increasing of the initial concentration of HA and the membrane flux can alleviate the continuous degradation performance by the photocatalysis-membrane integrated process. However, the intermittent running method can enhance the degradation performance.The membrane fouling phenomenon of the photocatalysis-membrane integrated process is studied. The static experimental results indicate that the HA cannot foul the membrane after 60min degradation. The by-products with small MW cannot foul the membrane, either. The running results of the photocatalysis-membrane integrated process illustrate that the photocatalysis technology as the pretreatment for the membrane filtration can control the membrane fouling effectively. The structure of the fouling layer on the membrane surface in the integrated process is relative loose and rough, which is benefit for the decreasing of membrane resistance. Low initial concentration of HA, low membrane flux and the intermittent running method is helpful for membrane fouling control.The mechanisms of photocatalysis degradation and the deactivation of photocatalyst TiO2 in the photocatalysis-membrane integrated process are studied. The mechanism of HA adsorbed on the TiO2 surface and the mechanism of the photocatalysis degradation process is studied. The experimental results indicate that the adsorption of HA on the TiO2 surface is weakening, when increasing the pH value. And the hydroxyl radicals play important roles on the photocatalysis degradation of HA. Moreover, the oxidation of the hydroxyl radicals works on the surface of the TiO2 under the acid condition, but works in the solution under the alkaline condition. The photocatalysis degradation process almost stops without dissolved oxygen. Moreover, the deactivation of TiO2 may due to that the competitive reaction between the organic matters with small MW adsorbed steadily on the TiO2 surface and the HA-like matters with large MW not adsorbed steadily happens on the surface of TiO2. The on-line reactivation method by ultraviolet irradiation is carried out in the photocatalysis-membrane integrated process, which can recover the photocatalytic ability of TiO2 well.