Efficient integration of electro-coagulation and ceramic membranes for the treatment of real chemical mechanical polishing (CMP) slurry wastewater from the semiconductor industry

Chemical mechanical polishing (CMP) slurry wastewater from the semiconductor industry contains dissolved silica, organic compounds, and nitrate contaminants that require more rapid and effective treatment than that offered by biological treatment processes. In this study, we conducted a comparative investigation of electro-coagulation (EC) alone and together with ceramic microfiltration (MF) and nanofiltration (NF) membranes to determine their removal efficiency for these contaminants and to understand their retention mechanisms. In the EC process, we tested four charge loadings (50, 100, 200, and 400 C/L) in the removal of the contaminants via adsorption onto coagulated flocs. The effluent from the EC process was then subjected to cross-flow ceramic membrane filtration. The integration of EC and the ceramic MF membrane was effective only in removing dissolved silica, with the addition of a ceramic NF membrane to the system essential for removing the organic and nitrate compounds. An examination of the physicochemical properties of the ceramic membranes revealed that the pore size of the ceramic NF membrane was considerably smaller than the molecular weight of the contaminants remaining in the effluent after either treatment with EC alone or treatment with the integrated EC and ceramic MF membrane system. The ceramic NF membrane also had a negative surface charge at pH 4–5, which was similar to the pH of real CMP slurry wastewater, resulting in improved contaminant removal due to electrostatic repulsion. Our engineered systems provide important insights into the management of semiconductor wastewater and the development of sustainable solutions to each treatment.