Investigating the fouling potential of the metal-silicate complex on membrane by response surface method (RSM)

BACKGROUND: To optimize the filtration efficiency of membrane systems for chemical mechanical polishing (CMP) wastewater, the fouling potential of silica, aluminum-silicate complex, and copper-silicate complex was investigated by the response surface method. RESULTS: The mathematical models for three kinds of fouling were successfully developed based on the SDI_0.1μm-1atm and MFI_0.1μm-1atm to describe the fouling potential. These models indicate that the metal-silicate complex fouling was severe at a neutral pH. Moreover, the models reveal that the effect of metal ions on fouling potential is significant. Compared with the feed solution conditions of 500 mg SiO₂ /L and pH 7.5, when 1 and 5 mg Al³⁺/L are added, the MFI_0.1μm-1atm values increase by 109% and 156%, respectively. In addition, when 1 and 5 mg Cu²⁺/L are added, the MFI_0.1μm-1atm values increase by 210% and 313%, respectively. CONCLUSION: The decrease in filtration efficiency was in the order of copper-silicate complex > aluminum-silicate complex > silica. Therefore, the fouling potential increased significantly when the influent contained trace metal ions (Al³⁺ or Cu²⁺) at a near-neutral pH, demonstrating the importance of managing pH and metal ions in CMP wastewater for membrane systems. In addition, the MFI_0.1μm-1atm is more suitable than the SDI_0.1μm-1atm for evaluating fouling potential. The SDI_0.1μm-1atm has limited value and a narrow range for fouling potential measurement. In contrast, the MFI_0.1μm-1atm is more sensitive and has a more comprehensive detection range.