| In recent years, membrane separation technology is rather popular in wastewater treatment research and researchers at home and abroad has carried out a great number of researches about it. However, problems such as severe membrane fouling and high cost of membrane preparation restrict its development. The modification of membrane surface is a critical way to reduce membrane fouling. Dynamic membrane (DM) technology was put forward initially as a modification method and draws the attention of researchers with advantages of low cost, big flux, high rejection efficiency, simple preparation and easy cleaning etc.Inorganic dynamic membranes (DM) were prepared on the inner surface of porous ceramic tubes with kaolin as coating materials, and applied to separation of oil-in-water emulsion in the present work. The grey relational analysis (GRA) method was used to study various operation parameters which can affect separation characteristics of the DM. Affecting extent of operation parameters on steady permeate fluxes during DM formation and separation was concluded to be cross-flow velocity>trans-membrane pressure difference of separation>coating time>pressure difference of preparation>concentration of coating suspension>temperature of coating suspension>oil concentration. On the basis of the above conclusion, a single-factor experiment was conducted in an effort to investigate the effects of operating conditions of DM formation on separation properties. Results show that the steady fluxes of oil-in-water emulsion separation first increase, and then decrease with increase in cross-flow velocity, coating time, pressure difference of preparation and concentration of coating suspension. The optimal coating conditions were determined to be801/h of cross-flow velocity,25min of coating time,0.14MPa of pressure difference of preparation and0.5g/l of coating suspension concentration. The DMs prepared under the optimal conditions have advantages of anti-fouling and increased steady flux in separation of oil-in-water emulsion compared with ceramic membranes without coating. In order to examine the influence of operating conditions on the steady flux, the separation factor, R was defined in this study, with which the reliability of the GRA was further verified.Secondly, on the basis of monolayer kaolin coating research, the two-layer composite DM is prepared on the inner surface of porous ceramic tube with better coating materials (Al2O3,ZrO2and kaolin). The combination of DM and support is assessed by comparing the related SEM images. The actual separation capability of DM is investigated by measuring flux and rejection rate etc. during separation of oil-in-water emulsion. The experiments show that the prepared Al2O3/ZrO2DM has a good performance and is available for separation of oil-in-water emulsion.Finally, on the basis of critical particle size model early built by our laboratory, flux model and DM formation model are built during formation of the cake, and then thickness and flux of DM under certain operating conditions can be predicted by simulation study. Through the simulation, the effects of various operating conditions on thickness and homogeneity of DM are studied and the result shows that changing the flow and pressure difference can influence the thickness and changing the flow can influence the homogeneity. In addition, the model calculation shows a good correspondence to the experimental results. |
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