Treatment of Gas-borne Volatile Organic Compounds (VOCs) by an Activated Sludge

by Chang, Hsiao-Yu

Biological processes have been proven to be economical and effective for control of volatile organic compounds (VOCs) with concentration of <1,000 mg C/m3 and VOCs such as toluene, xylenes, and dichloromethane(DCM) have been shown to be biodegradable. An activated sludge tank can be used as a bioscrubber for the purpose. Into the tank, an air stream is introduced through the spargers originally for aeration. Water-soluble contaminants in the air stream are absorbed into the mixed liquid and, subsequently, degraded by the microorganisms in the aeration tank. In this study, a pilot-scale activated-sludge tank (0.4 m¡Ñ0.4 m in cross-sectional area and 3 m in water depth) was used as a bioscrubber to study the treatability of gas-borne toluene, xylenes, and DCM. Synthetic gases with the three VOCs with concentrations in the rang of 250-1000 ppm (measured as methane) were used as the test gases. Effects of volumetric aeration rate (Q/V), influent VOC concentration, and submerged liquid depth on the removal efficiency of the influent VOCs were tested. Results show that with Q/V = 3.75-11.25 m3/m2.h, pH = 6-8, MLSS (mixed liquor suspended soilds concentration) = 1600-2800 mg/L, and submerged liquid depth D = 1.1 m, removal efficiencies were 93.1, 93.9, and 98.8%, respectively, for toluene, xylenes, and DCM. The removal efficiencies were nearly independent of the operating conditions.