Regenerating Absorbent Water from Semiconductor VOCs Absorber by Using Nonwoven Biofilm Carriers

Iso-propanol and acetone are two most common volatile organic compounds (VOCs) in the organic exhaust from semiconductor factories. Both of the chemicals are high in water solubility and easy to biodegrade. Bioscrubber is the suitable air pollution control (APC) technology for this kind of exhaust. In bioscrubbers, VOCs-laden water is usually regenerated by the activated sludge bioreator followed by a clarifier for water/suspended sludge separation before it is returned to VOCs absorber. In Taiwan, smaller footprint APC devices are favored because of limited space. This study used non-woven biofilm carriers (NBCs) bioreactor to replace activated sludge process for the absorbent water regeneration. No clarifier was applied in NBCs bioreactor system because most microorganisms were hold in carriers and the effluent SS concentrations were kept within acceptable ranges. A two months on-site pilot test was employed to evaluate the performance of this NBCs bioreactor to reclaim the absorbent water from a semiconductor plant exhaust absorber. The flow rate of VOCs exhaust to the absorber ranged from 1.5 to 1.8 CMM with total hydrocarbon concentration from 150 to 440 ppmv. About 80 to 90 % of VOCs were absorbed in water, then the VOCs-laden water was introduced to the two-stage NBC reactor system for VOCs biodegradation. Effluent of the two-stage NBC reactor system was directly reused in absorber for VOCs absorption. During the test period, city water was only used for evaporation loss make-up, no absorbent water was wasted. The influent COD of NBCs bioreactor ranged from 200 to 560 mg/L whereas iso-propanol concentration ranged from 3 to 33 mg/L and acetone concentration ranged from 55 to 305 mg/L. The effluent COD of NBCs bioreactor ranged from 80 to 290 mg/L where both iso-propanol and acetone concentrations were below 0.5 mg/L. Effluent SS concentration of NBCs bioreactor was maintained between 3 to 140 mg/L which is acceptable for absorber operation. On-site pilot test showed that NBCs bioreactor system can remove iso-propanol and acetone effectively and can regenerate the absorbent water for reuse in the bioscrubber system.