| Recent years, due to the development of membrane technology and membrane process, the combined processes of membrane separation and other technologies have attracted great attention in the field of wastewater treatment and reuse. Although membrane filtration offers many advantages over conventional separation processes, some drawbacks, such as membrane fouling, high cost and scarcity of membrane reactor formations, limited it's broadly application in wastewater treatment. This paper focuses on the extension of the potential application and field of membrane process. Polyethersulfone, a kind of excellent membrane material, was chosen to prepare flat homogeneous PES microporous membrane and flat composite PES membrane by solution phase inversion method. The influences of various technical conditions on membrane structures and properties were studies. The flat homogeneous PES microporous membrane and flat composite PES membrane with good performances and controllable structures were prepared. The performances of the PES flat composite membrane were investigated during the process of applications in membrane bioreactor (MBR). The performances of anti-foul and pollutants removal efficiencies of submerged hollow-fiber membrane bioreactor (SH-MBR),submerged flat membrane bioreactor (SF-MBR) and submerged rotating membrane bioreactor (SR-MBR) were investigated. A hybrid membrane bioreactor (H-MBR) was developed to enhance the nitrogen and phosphorus removal, and its performance was investigated too. Photocatalytic membrane reactor, which combines both the advantages of classical photoreactor in which the catalyst is in suspension and membrane processes where separation at molecular level takes place, was designed to degrade organic pollutants in wastewater. Its feasibility was evaluated too. A pilot scale car washing wastewater was treated and reused by the combined process of membrane filtration and catalytic ozonation. The main conclusion of this thesis are as follows:(1) The structures and properties of membrane were affected by the polymer concentration and the type and content of the additive. With the increase of the polymer content, the fingerlike macrovoid structures converted to spongy pore gradually, and porosity of the membrane decreased. With the increase of the proportions of PVP from 0% to 10%, fingerlike pore developed sufficiently. When the contents of PVP exceeded 10%, fingerlike pore began to fade away and pore size became smaller. The hydrophilic performance of the membrane was improved by the addition of PVP. Water, used as a kind of nonsolvent additive, made the thickness and porosity of membrane decreased. Pore size and water flux increased with the increase of water content in casting solution. The addition of TiO2 improved the mechanical properties, water flux and anti-foul property of membrane. Based on the above studies, the preparation conditions of membrane with excellent performance were optimized as follows: PES concentrations varied from 11wt% to 15wt%, the content of PVP was 3-8wt%, the content range of water additive was 3-5wt%, the content of nano-TiO2 was from 0.3wt% to 0.5wt%, coagulation baths was water, the temperatures of casting solutions and coagulation baths were about 30oC, respectively. Under the optimal conditions, the homogeneous mricroporous PES membranes were prepared. The pore diameter on the top layer and porosity were 0.5-2μm and approximate 80%, respectively. The range of the water flux was 400-600 L/h.m2.(2) Polymer concentrations, the type and content of additive, the proportion of polyethersulfone to sulfonated polyethersulfone (PES/SPES) and the sulfonic rate of SPES had more obvious effect on the PES flat composite membrane structures and properties. Suitable addition of SPES could improve water flux and hydrophilic performance of the membrane. Increasing SPES sulfonic rate was propitious to hydrophilic performance of the membrane, but it was made against to the water flux. The preparation conditions of membrane with excellent performance were optimized as follows: PES/SPES=80/20(wt), the sulfonic rate of SPES was 5.2%, polymer concentrations varied from 10wt% to 13wt%, the content of PVP was 5-8wt%, the content of water additive was about 6wt%, the content of nano-TiO2 was from 0.3wt% to 0.5wt%, coagulation baths was water, the temperatures of casting solutions and coagulation baths were about 30oC, respectively. Under the optimal conditions, PES flat composite membranes were prepared. The pore diameter on the top layer and porosity were 0.5-2μm and approximate 80%, respectively. The range of water flux and contact angel were 250-1400 L/h.m2 and 65o-75o, respectively.(3) SH-MBR using PP hollow-fiber membrane and SF-MBR using PES flat composite membrane were used to treat sewage. The qualities of effluent of these two MBRs were excellent, the removal efficiencies of COD were higher than 90%. The optimal operation parameters of SH-MBR and SF-MBR were same: TMP=20kPa, 8min/2min.(4) A novel type of submerged rotating membrane bioreactor (SR-MBR), in which a rotatable rounded flat sheet membrane module fixed on the axes and moved by an electromotor, was used to treat synthetic sewage. Thus, an innovative membrane module, which is fixed on the axes and rotated by an electric motor was developed instead of the traditionally immobile membrane module to enhance filtration capacity and fouling prevention ability. The results indicated that the cross-flow velocity produced by the rotation of the membrane module, could help to prevent reversible fouling in the operation. The fouling prevention ability increased proportionately with increasing the rotation speed of the membrane module, ratio of aeration intensity to permeate flux (A/F) and stoppage time in an intermittent permeation cycle until their critical values were reached after which further increases would have little effects. The critical values for rotation speed, A/F and stoppage time were 60 r.min-1, 15 and 1 min for every 10 min cycle, respectively. Under this optimal condition, SR-MBR remained stable for a long time continuously running, and its equilibrium flux reached 61 L/h.m2, which was about 6 times of that of SH-MBR and SF-MBR.(5) Microorganism in H-MBR was more active than that in SMBR. The removal efficiencies of COD, NH3-N and TN reached to 92%, 80% and 70% respectively. The TP removal efficiency of H-MBR was not enough, only about 60%, when the TP concentration of the influent ranged from 5-6 mg/L. Declined the influent TP concentration to 3 mg/L, the TP concentration of the effluent became less than 1 mg/L, and the removal efficiency of TP reached 70% above.(6) The membrane which prepared by polyvinylidenefluoride (PVDF) was stable to UV irradiation. It was suitable to be used in the photocatalytic membrane reactor. The photocatalytic activity of TiO2-mounte activated carbon (TiO2/AC) catalyst was better than that of TiO2 and TiO2-AC photocatalysts. The selected membrane had the capability to retain the catalyst and to reject the partially degraded organic species. The removal efficiencies of phenol and COD were increased 19.3% and 18.7% due to the membrane separation. The photocatalytic membrane reactor combines both the advantages of classical photoreactor in which the catalyst is in suspension and membrane processes where separation at molecular level takes place seems very attractive.(7) The removal efficiencies of phenol solution were studied by TiO2/AC, activated carbon catalytic ozonation and ozonation alone. Results shows, TiO2/AC can well improve the efficiency of catalytic ozonation, and enhance the utilization of ozone. The pilot scale car washing wastewater was treated by the combined process of membrane filtration and catalytic ozonation. The results indicated that the qualities of effluent were better than the standards of reuse water, and the costs of this combined process and run fee were low. The cost of the engineer for 30t/d car washing wastewater treatment and reuse was 2315RMB per 1m3 wastewater. And the operation cost was as low as 0.97 RMB per 1m3 water. This membrane separation– catalytic ozonation combined process holds broadly applied potential in car washing wastewater treatment and reuse. |
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