Preparation of carbon fibers/carbon/alumina tubular composite membranes and their applications in treating Cu-CMP wastewater by a novel electrochemical process: Part 2

This work (designated Part 2 of this study) aims to further discuss the present authors’ research findings relevant to that of reported earlier (designated Part 1 of this study). In Parts 1 and 2 of this study, carbon fibers/carbon/alumina tubular composite membranes (CCA-TCMs) were first prepared through substrate formation, polyvinylidene chloride (PVDC) film wrapping, PVDC carbonization, catalyst precursor coating, and the chemical vapor deposition (CVD) process. The finished CCA-TCMs, with a pore size distribution ranging from 2 to 20 nm and a nominal pore size of ca. 3.5 nm, were further characterized by environmental scanning electron microscopy (ESEM), high-resolution transmission electron microscopy (HR-TEM), and permporometry. The so prepared CCA-TCMs were incorporated into a crossflow simultaneous electrocoagulation and electrocoagulation (EC/EF) treatment module to evaluate their capabilities in treating Cu-CMP (chemical mechanical polishing of the copper layer) wastewater obtained from a wafer fab. Crossflow EC/EF performance tests were carried out based on the Taguchi experimental design using the electric field strength, crossflow velocity, transmembrane pressure, and filtration area as the experimental factors. Under the optimal operating conditions, the EC/EF treatment module coupled with CCA-TCMs are capable of treating Cu-CMP wastewater to yield permeate with a turbidity of below 0.3 NTU. In the meantime, the removal efficiencies ranging from 82 to 91% for total solids (TS), total organic carbon (TOC), Cu, and Si could be obtained. By comparing the results of Part 1 and Part 2 of this study, the optimal operating conditions determined from the experimental designs based on the fractional factorial and Taguchi method yielded similar good qualities of permeate. A further evaluation of the technical significance of this study shows promising fundamental and practical results.