Use saponins to enhance the removal of benzene vapors in a foam bioscrubber system

Abstract

Surfactants are often used to enhance the efficacy of bioreactors in treating waste air streams containing hydrophobic volatile organic compounds (VOCs). In this study, biosurfactant - saponins was innovatively applied in a self-designed reflux foam bioscrubber (RFB) to remove benzene vapor from waste gas stream. The optimal operating parameters and long-term performance of this saponins enhanced RFB were investigated. The important optimal operational conditions are as follows: saponins concentrations of 40–50 mg/L, defoam liquid reflux rate of 60% and pH range of 6.5–7. A 90-day experiment was conducted to evaluate the stability of this system, and benzene removal rates stabilized at around 99.52 ± 0.03% after day 7. Microbial characteristics in this bioreactor were also investigated using 16 S rRNA gene sequencing technologies. The relative abundance of benzene-degrading microbial species, such as Actinobacteria and Saccharibacteria, increased significantly after 90 days of the experiment. Furthermore, the analysis of metabolic pathways revealed the presence of abundant degradation enzymes and diverse degradation pathways in the RFB system. This study is believed to be the first to investigate such metabolic pathways in the context of biotechnological treatment of VOCs. Together, the lessons learned from this study suggest that the application of saponin is a viable enhancement for the reflux foam bioscrubber system in removing hydrophobic VOCs gases.