Anaerobic and microaerobic biodegradation of benzene: Effect of important intermediates

Abstract

The effect of important intermediates on the anaerobic and microaerobic benzene biodegradation was investigated. An up-flow anaerobic/microaerobic sludge blanket reactor was operated at a hydraulic retention time (HRT) of 24 h and fed with water contaminated with benzene (∼4.2 mg L−1) and ethanol (1 g COD L−1). Initially, reactor operating parameters such as variation of applied flow rates, microaeration application points, and effluent recirculation were studied to optimize microaeration. Secondly, the interference of benzene degradation intermediates (phenol, benzoate, and toluene) was investigated. The addition of low concentrations of oxygen (0.5–2 mL air min−1) ensured high benzene removals (∼76–86 %), with the best obtained for a flow rate of 1 mL of air min−1, for which there was a d% removal increase compared to the anaerobic stage. Although the contact time between the air bubbles was short, the best application point was close to the feed. Effluent recirculation was necessary to maintain good mass transfer and high benzene removal efficiencies. The loss by stripping was considered negligible, even at the microaerobic stages, proving the biological removal of this compound. Finally, the intermediates added to the contaminated water reduced benzene removal, with benzoate being the compound that most negatively influenced the benzene removal process, even under microaerobic conditions. Therefore, it is a key intermediate in the benzene anaerobic and microaerobic biodegradation process.