Kinetics of toluene and sulfur compounds removal by means of an integrated process involving the coupling of absorption and biodegradation

BACKGROUND: Scrubbing using an organic solution instead of an aqueous solution could be a useful way to improve the removal of hydrophobic compounds. Absorption of toluene, dimethyldisulfide (DMDS) and dimethylsulfide (DMS) in an organic solution (di-2-ethylhexyladipate - DEHA), followed by biodegradation by activated sludge was considered, with particular attention to kinetic aspects. DEHA was selected for its relevance in terms of absorption capacity and absorption velocity of the selected volatile organic compounds (VOCs). After the biodegradation step and owing to its cost, recycling of the VOC-free solvent should be considered. RESULTS: Enhancement of VOC mass transfer from the organic to the aqueous phase due to bacterial activity was highlighted and the main driving force was found to be biosurfactant production rather than biodegradation reaction. However, the mass transfer rate between the two phases was shown to be lower than VOC biodegradation rate; hence, significant biodegradation of DMDS and toluene was recorded in a few days during batch experiments, 0.10 and 0.09 mmol respectively. Toluene showed higher biodegradation rates (about 0.05 and 0.10 mg h(-1) for DMDS and toluene), leading to higher growth rates. Contrarily, owing to its high volatility, important DMS losses were observed. CONCLUSION: The relevance of the proposed integrated process was shown for hydrophobic VOC removal, at least for toluene and DMDS. Unfortunately, the absorbent phase was also degraded, proved by detection of by-products during analyses of the aqueous phase headspace. The comparison of DEHA with other solvents or solid polymers available for multiphase bioreactor applications may be a reliable option to continue this work. (C) 2010 Society of Chemical Industry