Integrating entrapped mixed microbial cell (EMMC) technology for treatment of wastewater containing dimethyl sulfoxide (DMSO) for reuse in semiconductor industries

Abstract

Solvents containing dimethyl sulfoxide (DMSO) are widely used in the rinse process of stripping photoresistors in semiconductor manufacturing industries. The disposal/reuse of wastewater containing DMSO is a serious problem because of its high concentration of organic carbon and the need to suppress the odor from its sulfur contents. An entrapped mixed microbial cell (EMMC) process was used to investigate the effectiveness of removing DMSO from a synthetic wastewater in a once-through up-flow fixed-bed bioreactor. Both cellulose triacetate and cellulose acetate were used to prepare the EMMC carriers. Various hydraulic retention times (HRTs) (based on the void volume) of 3, 4, 5, 6, and 12 h were investigated when the concentration of DMSO was 500 mg/l and 1,000 mg/l. It was found that the addition of 50 mg/l of sucrose was needed to serve as the carbon source for possible co-metabolism of DMSO. Based on the result of the impact of various dilution rates (1/HRT) on the TOC (total organic carbon) removal efficiency and TOC remaining, a dilute curve for this relationship was plotted. Thus, an optimal operational criterion was developed, i.e., it must be operated at a dilution rate of less than 0.15 h⁻¹ or at an HRT of higher than 6.66 h, in order to achieve more than 95% of TOC (or more than 99% of DMSO) removal efficiency when using the cellulose triacetate as the EMMC carriers. This process performance was compared to the bio-contact filter (BCF) process conducted in Japan. It was found that the present study is capable of producing much less effluent nitrogen (including NH₄-N and NO₃-N) content than the BCF process under similar loading conditions. It is possible that integrating the unit process of EMMC as pretreatment with microfiltration (MF) and reversed osmosis (RO) processes is promising for the reuse and recycling of semiconductor wastewater. Thus, higher quality (less organic carbon and inorganic nitrogen content) pretreated water can be further treated by another physical chemical process, such as MF and RO, for the production of superpurity water for reuse in the semiconductor manufacturing industry.