Enhancing removal performance of ortho xylene by adding polydimethylsiloxane into two-stage biofilter

[Display omitted] •The 0.5 % polydimethylsiloxane addition enhanced removal efficiency to 85 %.•Fungal biofilter had higher degradation ability compared to bacterial biofilter.•The biofilters evolved into a co-degradation system.•Sphingomonas and Sphingobium were the dominant bacterial species.•Fusarium and Cladosporium became the primary fungal components. A two-stage biofilter was built, augmented with polydimethylsiloxane (PDMS), to enhance the degradation of ortho xylene (o-xylene), and evaluate the feasibility of different PDMS concentrations for improving the removal effect. The results showed that PDMS concentration of 0.50 % significantly enhanced the purification efficiency and mineralization rate of o-xylene to 85(±1)% and 81 %, respectively. Simultaneously, the surface tension of the circulating liquid was reduced by 31.91 mN/m. Furthermore, the polysaccharide concentration of biofilters were increased by 6.90 mg/g and 7.38 mg/g, respectively, while the protein concentration was enhanced by 7.98 mg/g and 9.29 mg/g, respectively. It is worth noting that Sphingomonas and Sphingobium emerged as the dominant bacterial genera after intensification. Fusarium and Cladosporium became the predominant fungal genera in BTF1 and BTF2, respectively. Therefore, the two-stage biofilter containing bacteria and fungi combined with the addition of PDMS can effectively improve the degradation effect.