Anoxic biodegradation of BTEX in a biotrickling filter

Abstract

Emissions of BTEX (benzene, toluene, ethylbenzene and xylene) from the petrochemical industry are characterized by a low pollutants concentration and the absence of oxygen. Biodegradation of these pollutants using nitrate as the electron acceptor is of key interest to reuse the residual gas for inertization purposes. However, the biological mineralization of BTEX is often limited by their recalcitrant nature and the toxicity of the secondary metabolites produced. The potential of an anoxic biotrickling filter for the treatment of a model O₂-free BTEX-laden emission at inlet individual concentrations of ~700mgm^-3 was here evaluated. A UV oxidation step was also tested both in the recycling liquid and in the inlet gas emission prior to biofiltration. Removal efficiencies >90% were achieved for both toluene and ethylbenzene, corresponding to elimination capacities (ECs) of 1.4±0.2gm^-3h^-1 and 1.5±0.3gm^-3h^-1, respectively, while ~45% of xylene (EC=0.6±0.1g m^-3h^-1) was removed at a liquid recycling rate of 2mh^-1. Benzene biodegradation was however limited by the accumulation of toxic metabolites in the liquid phase. The oxidation of these intermediates in the recycling liquid by UV photolysis boosted benzene abatement, achieving an average EC of 0.5±0.2gm^-3h^-1 and removals of ~40%. However, the implementation of UV oxidation as a pretreatment step in the inlet gas emission resulted in the deterioration of the BTEX biodegradation capacity of the biotrickling filter. Finally, a high bacterial diversity was observed throughout the entire experiment, the predominant phyla being Proteobacteria and Deinococcus-thermus.

Keywords: Anoxic BTEX removal; Benzene; Biotrickling filtration; Ethylbenzene; Toluene; Xylene.