A mathematical model for VOCs removal in a treatment process coupling absorption and biodegradation

Abstract

Abstract Biological treatments are used in gas treatment when containing Volatile Organic Compounds (VOC). Key factor to enhance treatment efficiency is to maximize mass transfer from gas to liquid. VOCs can be removed from the gas flow by absorption in a separate gas–liquid contactor before entering a Two-Phase Partitioning Bioreactor (TPPB) (Two-stage unit). The Non-Aqueous Phase Liquid (NAPL), a silicone oil in this study, is able to solubilize large amounts of hydrophobic VOCs while avoiding toxicity effects on the microorganisms. The aim of this study is to provide a designing tool for the degradation process occurring in the TPPB. Simulations considering mass transfer coupled with biodegradation kinetics were considered when investigating the TPPB mechanisms. A single VOC (toluene) was first taken as a reference to assess the accuracy of the model in comparison with experimental results. A mixture of seven VOCs (toluene, m-xylene, 1,3,5 trimethylbenzene, n-heptane, ethyl acetate, methyisobutylketone and isopropyl alcohol) presenting a wide range of hydrophobicity was then implemented in the model considering no interaction regarding their biodegradation. Degradation kinetics of the mixture (representing an actual exhaust gas from an industrial plant) were compared with experimental results. The developed model tends to highlight that modeling results are closed to experimental results. The results delivered by the model shows that mass transfer, through the “kLa” value, is a key parameter to enhance efficiency of NAPL renewal by biological regeneration.