An industrial-scale biodegradation system for volatile organics contaminated wastewater from semiconductor manufacturing process

Abstract

Among all organic solvents, 2-propanol (isopropyl alcohol, IPA) and 2-propanone (acetone) are extensively used for wafer cleaning in semiconductor industries due to their relative high volatilities. However, the excess organic solvents always enter the wastewater treatment system along with impurities and result in a much higher chemical oxygen demand (COD) loading. Therefore, wastewater and gas phase contaminated by 2-propanol and 2-propanone has to be treated properly prior to discharge not only to meet the stipulated regulations, but also keep the health impact away. In this study, an integrated biodegradation system was constructed to remove 2-propanol and 2-propanone in the wastewater from the semiconductor manufacturing process. Special microorganisms were screened and inoculated onto granular-type activated carbon and packed carrier to give the biological activated carbon (BAC) reactors and biofilter, which were adopted to deal with wastewater and emitting gas, respectively. During the operation, with a well manipulation of the concentration of dissolved oxygen (DO) and necessary nutrients in BAC reactors and biofilter, the residual 2-propanol and 2-propanone in wastewater and flue gas can be eliminated successfully. The operating results show that when the total hydraulic retention time (HRT) is controlled as 24 h, the removal efficiency of COD in wastewater can reach 97% higher and the residual COD in emitting gas can be reduced to less than 0.1% even with a COD loading as high as 1440 mg/L. Under this condition, the COD value of the final effluent can meet the regulated limit, i.e. 100 mg/L. After a long-term operation, the running cost needed for this integrated system is estimated to be 2.5 NTD/m 3 wastewater. It can be concluded that the problem of 2-propanol and 2-propanone treatment pertaining to the semiconductor industries can be solved effectively with high economical and practical feasibilities.