In this study, two types of chemical mechanical polishing wastewaters (designated Cu-CMP wastewater and mixed-CMP wastewater, respectively) from a wafer fabrication plant was treated by a simultaneous electrocoagulation/electrofiltration (EC/EF) process using laboratory-prepared TiO2/Al2O3 composite membranes. First, tubular membrane supports of Al2O3 were prepared by the extrusion method. Then the slip composed of nanoscale TiO2 (prepared by sol-gel process) and 1 wt% of corn starch was applied on the aforementioned tubular membrane supports by the dip-coating method, followed by sintering to obtain tubular TiO2/Al2O3 composite membranes. These tubular inorganic composite membranes then were incorporated into an EC/EF treatment module for the treatment of CMP wastewaters. The permeate qualities were evaluated. In addition, the effects of different operating modes (i.e., the flow-through mode and recirculation mode) on membrane flux and permeate quality were conducted. Finally, the effects of changing the backwash time and backwash cycle on the membrane flux were also investigated. Experimental results have shown that the slip containing 75 v/v% of TiO2 sol and 25 v/v% of corn starch solution would yield a membrane layer with a thickness of 13 £gm and a pore size of 15 nm. On the CMP wastewater treatment, the removal efficiencies of copper ion and total organic carbon (TOC) were found to increase with the increasing electric field strength. This relationship, however, did not apply to other water quality items. Under the optimal operating conditions of using the recirculation mode, the removal efficiencies for turbidity and TOC for Cu-CMP wastewater were determined to be 98% and 90%, respectively. Similarly, a turbidity of < 1 NTU (a removal efficiency of 99%) was obtained for mixed-CMP wastewater. By using the same optimal operating conditions for the recirculation mode to treat Cu-CMP wastewater, initial fluxes of 300 L/h¡Em2 and 280 L/h¡Em2 were obtained for the flow-through mode and recirculation mode, respectively. The corresponding initial fluxes for mixed-CMP wastewater were 370 L/h¡Em2 and 360 L/h¡Em2, respectively. For the case of the recirculation mode, the removal efficiencies of total solids content, silicon, copper ion, TOC, and turbidity for Cu-CMP wastewater were 71%, 85%, 72%, 90% and 99%, respectively. The corresponding removal efficiencies of 68%, 88%, 78%, 90% and 99%, respectively were determined for the case of the flow-through mode. On the other hand, the removal efficiencies of total solids content, silicon, TOC, and turbidity for mixed-CMP wastewater using the recirculation mode were 76%, 84%, 78% and 99%, respectively; whereas 78%, 86%, 72% and 99%, respectively for the flow-through mode. Based on the above findings, the operating mode is not a significant parameter in influencing the membrane flux and quality. Permeate obtained in this work was found to be recyclable for the use in irrigation and make-up water for cooling towers. Backwashing was found to be important to the membrane flux in this study.

Water is essential for life as well as industrial growth. Therefore, this research is mainly to explore the treatment capacity of LCD (Liguid Crystal Display) industrial wastewater recycling by a simultaneous electrocoagulation/electrofiltration (EC/EF) process using laboratory-prepared multi-tubular TiO2/Al2O3 composite membranes. First, tubular membrane supports of Al2O3 were prepared by the extrusion method. Then the slip composed of nanoscale TiO2 (prepared by sol-gel process) was applied on the aforementioned tubular membrane supports by the dip-coating method, followed by sintering to obtain tubular TiO2/Al2O3 composite membranes. Then, two types of LCD industrial wastewaters (designated TFT-LCD wastewater and STN-LCD wastewater, respectively) from different LCD fabrication plants were treated by EC/EF process using TiO2/Al2O3 composite membranes. Moreover, the permeate qualities were evaluated under the recirculation-mode operation. In addition, the effects of different operating parameters (i.e., electric field strength, trans-membrane pressure, and crossflow velocity) on membrane flux and permeate quality were evaluated. Relations of the water quality and the different operation modes (i.e., the recirculation mode, flow-through mode, and secondary treatment mode) were also discussed. Finally, the effects of changing the backwash time and backwash cycle on membrane flux were investigated. In the recirculation mode, both kinds of wastewater achieved a satisfactory organics and anion removal. An average of about 90¢H of COD (Chemical Oxygen Demand) and TKN (Total Kjeldahl Nitrogen) could be removed. For anions (i.e., NO3¡Ð, NO2¡Ð, Cl¡Ð and SO42¡Ð), their removal efficiencies were all over 90%. Furthermore, TOC (Total Organic Carbon) and turbidity also had removal efficiencies of over 98%. When the operation mode was changed from the recirculation mode to flow-through mode, the changes of permeate quality were not obvious. But the cumulative quantity of permeate of the flow-through mode was greater than that of the recirculation mode. As for the experimental result of the secondary treatment mode, the permeate qualities were found to be improved. In this case, an average removal of over 95% of NO3¡Ð, NO2¡Ð, Cl¡Ð, and SO42¡Ð could be obtained. According to experimental results shown above, the treated water could be recycled and reused as the cooling tower make-up water if its pH and conductivity values were reduced. However, these problems could be easily resolved by proper adjustments of pH. Overall speaking, the tubular TiO2/Al2O3 composite membranes and simultaneous EC/EF treatment module employed in this work are capable of treating LCD industrial wastewater for the purpose of reclamation.