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Volume 9, No. 2, June 2009, Pages 198-208 PDF(324 KB)  
doi: 10.4209/aaqr.2008.10.0049   

Bio-Oxidation of Air-Borne Hydrophobic VOCs in Activated Sludge Aeration Tanks-Effects of Activated Sludge Concentration and Gas Diffuser

Ming-Shean Chou, Yu-Feng Chang, Hsiao-Yu Chang

Institute of Environmental Engineering National Sun Yat-Sen University Kaohsiung 80424, Taiwan, Republic of China




An activated sludge aeration basin (20 cm i.d., 140 cm height) equipped with either a coarse air diffuser (a plastic pipe perforated with 56 orifices of 2 mm in diameter) or a fine diffuser (porous plastic type with 100-micrometer pores) was utilized to treat an air-borne hydrophobic VOC (toluene, 700-800 mg/m3). The purposes of this study were to test the influences of both MLSS and diffuser type on the VOC removal efficiency. Results show that higher MLSS (mixed liquor suspended solids) such as 10,000-40,000 mg/L in the mixed liquor did not enhance greatly the transfer and removal of the introduced toluene. Instead, activated sludge basins with a normal MLSS (e.g., 2000-4000 mg/L) in the mixed liquor and an efficient gas diffusion system with volumetric VOC transfer coefficient of around 10-15 1/h can be used for the removal of hydrophobic VOCs from the introduced gas. For achieving a removal of over 95% of the introduced toluene or similar hydrophobic VOCs, commercial air diffusers for aerobic biological wastewater treatment basins can be used with a submerged liquid depth of over 0.40 m over the diffusers and an aeration intensity (air flow rate/basin cross-sectional area) of lower than 5.0 m3/m2.h.



Keywords: Hydrophobic VOCs; Activated sludge aeration; Bio-oxidation; Diffuser.



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