Enhanced biodegradation of styrene vapors in the biotrickling filter inoculated with biosurfactant-generating bacteria under H₂O₂ stimulation

Biotrickling filters (BTFs) applied to hydrophobic volatile organic compounds (VOCs) suffer from limited mass transfer. Phase transfer kinetic and equilibrium effects limit the biodegradation of hydrophobic VOCs especially at high concentrations. This study evaluates two strategies for overcoming the problem. First, a natural process was used to enhance the aqueous availability of styrene, a hydrophobic VOC model, by inoculating the BTF with a mixture of biosurfactant-generating bacteria. This method achieved a maximum elimination capacity (ECmax) of 139 g m^-3h^-1 in the BTF at an empty bed residence time (EBRT) of 60s. The highest concentrations of the biosurfactants surfactin and rhamnolipid were 205 and 86 mg L^-1, respectively, in this step. Sequencing 16S rRNA confirmed the presence of biosurfactant-producing bacteria capable of biodegrading styrene in the BTF including Bacillus sonorensis, Bacillus subtilis, Lysinibacillus sphaericus, Lysinibacillus fusiformis, Alcaligenes feacalis, Arthrobacter creatinolyticus, and Kocuria rosea. Second, the effect of adding H₂O₂ to the recycle liquid on the BTF performance was determined. The biodegradation and mineralization of styrene in the BTF operated at a loading rate of 266 g m^-3h^-1 and H₂O₂/styrene molar ratio of 0.05 with EBRT as short as 15 s were 94% and 53%, respectively, with the EC of 250 g m^-3h^-1. High concentrations of antioxidant enzymes (peroxidase and catalase: 56 and 7 U g_biomass^-1, respectively) were produced and biosurfactant generation was increased in this step, contributing to enhanced styrene biodegradation and mineralization. The styrene biodegradation and mineralization values in the BTF in the last day operated under similar conditions but without H₂O₂ were 11.4% and 5.3%, respectively. The bacterial population had no considerable change in the BTF after adding H₂O₂. Accordingly, stimulating the BTF inoculated with biosurfactant-generating bacteria with H₂O₂ is a promising strategy for improving the biodegradation of hydrophobic VOCs.