Efficient prediction of gaseous n-hexane removal in two-phase partitioning bioreactors with silicone oil based on the mechanism and kinetic models

Two-phase partitioning bioreactors (TPPBs) have been widely used because they overcome the mass-transfer limitation of hydrophobic volatile organic compounds (VOCs) in waste gas biological treatments. Understanding the mechanisms of mass-transfer enhancement in TPPBs would enable efficient predictions for further industrial applications. In this study, influences of gradually increasing silicone oil ratio on the TPPB was explored, and a 94.35 % reduction of the n-hexane partition coefficient was observed with 0.1 vol.% silicone, which increased to 80.7 % along with a 40-fold removal efficiency enhancement in the stabilised removal period. The elimination capacity increased from 1.47 to 148.35 g/(m3·h), i.e. a 101-fold increase compared with that of the single-phase reactors, when 10 vol.% (3 Critical Micelle Concentration) silicone oil was added. The significantly promoted partition coefficient was the main reason for the mass transfer enhancement, which covered the negative influences of the decreased total mass-transfer coefficient with increasing silicone oil volume ratio. The gradually rising stirring rate was benefit to the n-hexane removal, which became negative when the dominant resistance shifted from mass transfer to biodegradation. Moreover, a mass-transfer-reaction kinetic model of the TPPB was constructed based on the balance of n-hexane concentration, dissolved oxygen and biomass. Similar to the mechanism, the partition factor was predicted sensitive to the removal performance, and another five sensitive parameters were found simultaneously. This forecasting method enables the optimisation of TPPB performance and provides theoretical support for hydrophobic VOCs degradation.