Enhanced elimination of gaseous toluene and methanol emissions in a two-liquid phase trickling bioreactor: Performance evaluation, dynamic modeling, and microbial community shift

Abstract

Negative interactions of the components usually restrict the application of trickling bioreactors (TBRs) for the simultaneous biodegradation of multi volatile organic compounds (VOCs). Modifications like the addition of non-aqueous phase (NAP) to TBRs can lead to design higher performance biological air cleaner systems for industries with mixed VOCs emissions. In this study, removal of toluene and methanol as hydrophobic and hydrophilic VOCs, respectively, was assessed in an up-flow two-liquid phase TBR (TLP-TBR) in the presence of silicone oil (5% v/v) as the NAP. The toluene and methanol inlet loading rates (ILRT and ILRM) were 18–36 and 0–187.2 g m−3 h−1, respectively, at a constant empty bed residence time of 60 s. The system could withstand against increasing ILRs so that removal efficiency (RE) of toluene >80% was obtained at various ILRs, while RE of methanol was almost stable at >90%. After optimization of a developed dynamic mathematical model, including mass transfer and kinetic mechanisms, the overall mass transfer coefficients of toluene and methanol were obtained as 1.9 × 10−4 and 2.1 × 10−4 m s−1, respectively. About 50% of biofilm depth was active for toluene biodegradation, indicating the prevalence of diffusion-limited regime for toluene removal. The microbial diversity shifted from the original inoculum to dominant toluene-degrading Gordonia and Burkholderia close to the gas inlet with relative abundance of 30% and 20%, respectively. While, methanol-degrading Hyphomicrobium sp. had higher contribution (19%) at top of the column. Therefore, the presence of NAP could facilitate the sustainable application of TBR through a suitable microbial composition shift.