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.

In this study, the wastewater from oxide chemical mechanical polishing (oxide-CMP) process of semiconductor wafer fabrication was treated by crossflow electro-ultrafiltration with self-prepared tubular inorganic membranes. First of all, a recipe of alumina (72 wt%), bentonite (8 wt%) and water (20 wt%) was determined for the extrusion of green tubes. The porous ceramic green tubes of 200 mm in length thus obtained were subjected to further curing, drying, and sintering processes. The inner and outer radii of the porous ceramic supports were 6.0 mm and 10.0 mm, respectively. Then, nanoscale TiO2 (i.e., the slip) was prepared by sol-gel method. On the tops of porous ceramic supports thin layers of nanoscale TiO2 were applied by the dip-coating method. To analyze the microstructures of tubular inorganic membranes and confirm the nanoscale TiO2 films, a scanning electron microscope equipped with energy-dispersive X-ray analyzer (SEM-EDS) and X-ray diffractometer (XRD) were employed. The self-prepared tubular inorganic composite membranes (TICMs) were futher characterized by permporometry and Kelvin equation to determine their pore size distributions and nominal pore sizes. In addition, through the employment of polyethylene glycol (PEG) of different molecular weights and total organic carbon analysis method, the molecular weight cut-off (MWCO) and tightness coefficient of each TICM was determined. It was found that the self-prepared TICMs were suitable for ultrafiltration applications. In this work, wastewater from the oxide-CMP process of semiconductor wafer fabrication was treated by crossflow electro-ultrafiltration with self- prepared TICMs. The permeate qualities were evaluated. Experimental results have shown that permeate of a higher filtration rate, a turbidity of below 1 NTU, 90% removal of total suspended solids, and a removal efficiency of greater than 80% for soluable silica could be obtained under the conditions of an electric filed strength of 30 V/cm and transmembrane pressure of 5 kgf/cm2. For permeate to meet the feed water requirements for the ultrapure water system, it has to be further treated to lower its silica content to ¡Ø 6 mg/L. Overall speaking, by incorporation of the tubular inorganic composite membranes prepared in this work into the novel electrofiltration treatment module for the treatment of oxide-CMP wastewater would yield permeate suitable for the purpose of reclamation.

This study addresses three major parts: (1) to establish the technology for the preparation of tubular ceramic membrane substrates; (2) to establish the technology for the preparation of tubular carbon/ceramic membranes; and (3) to reclaim water from chemical mechanical polishing (CMP) wastewaters by a combined treatment system of a novel simultaneous electrocoagulation/electrofiltration (EC/EF) process coupled with laboratory-prepared tubular composite membranes (TCMs) and evaluate its feasibility of water recycling and operating cost. First, in this work the green substrates of tubular porous ceramic membranes consisting of corn starch were prepared using the extrusion method, followed by curing, drying, and sintering processes. Experimental results have demonstrated that an addition of starch granules to the raw materials would increase the porosity, pore size, and permeability of the sintered matrices but accompanied by a decrease of the compressive strength. It revealed that the membrane substrates with desired pore sizes and permeability could be obtained by adding a proper amount of corn starch. The nominal pore sizes of the prepared membrane substrates were ranging from 1 to 2 £gm. The membrane substrates thus obtained are suitable for crossflow microfiltration applications. Second, the carbon/alumina TCMs and carbon fibers/carbon/alumina TCMs were obtained by the chemical vapor deposition (CVD) method resulting in a pore size distribution of 2 to 20 nm and a nominal pore size ranging from 3 to 4 nm. Besides, during the CVD process the reaction temperature was found to be the main factor for influencing the pore size of carbon fibers/carbon/alumina TCMs and the type of carbon fibers. When the reaction temperature was above or equal to 1000 ¢J, the pore size of TCMs increased due to the pyrolysis of thin carbon layers. The ¡§Tip-Growth¡¨ mechanism was found for tubular carbon fibers formation under such conditions. On the other hand, ¡§Base-Growth¡¨ (also known as ¡§Root-Growth¡¨) mechanism was found for curved and irregular carbon fibers formation when reaction temperature was under or equal to 950 ¢J. Third, for reclaiming water from CMP wastewaters, experimental results of laboratory-prepared carbon/alumina TCMs incorporated into the custom-made EC/EF treatment module used was found to be capable of treating oxide-CMP wastewater in a proper manner. Permeate thus obtained had a turbidity of below 0.5 NTU and the removal efficiencies of TS (total solids content) and Si were 80% and 93 %, respectively. Further, for understanding the applicability of fractional factorial design and Taguchi experimental design, two laboratory-prepared carbon fibers/carbon/alumina TCMs (i.e., Tube B and Tube E obtained from two different preparation conditions) incorporated into the EC/EF treatment module were chosen for evaluating the performance of CMP wastewaters treatment. Permeate obtained based on the fractional factorial design of experiments had a turbidity of below 1.0 NTU and the removal efficiencies of TOC (total organic carbon), Cu and Si were all above 80 % except for the TS (i.e., ranging from 72 to 74%). Permeate obtained based on the Taguchi experimental design had a turbidity of below 0.3 NTU and the removal efficiencies of TS, TOC, Cu and Si were ranging from 82 to 91%. Apparently, similar optimum operating conditions were obtained from the fractional factorial design and Taguchi experimental design. Permeate thus obtained could be reused as the make-up water of cooling towers. The operating cost of Cu-CMP wastewater treatment based on a total water reclaim of 600 m3 per day was determined to be NT$ 98 (i.e., US$ 3.22) and NT$ 35 (i.e., US$ 1.05) per m3 of permeate for Case 1 (i.e., the filtration area of 0.0189 m2 in one EC/EF module) and Case 2 (i.e., the filtration area of 0.0801 m2 in one EC/EF module), respectively.