Key role of microbial characteristics on the performance of VOC biodegradation in two-liquid phase bioreactors.

Despite being studied for over 20 years, little is known about the mechanisms underlying the treatment of volatile organic compounds (VOCs) from industrial off-gases in two-liquid phase bioreactors (TLPBs). Recent reports have highlighted a significant mismatch between the high abiotic mass transfer capacity of TLPBs and the low VOC biodegradation rates sometimes recorded, which suggests that a process limitation might also be found in the microbiology of the process. Therefore, this study was conducted to assess the key role of microbial characteristics on the performance of VOC biodegradation in a TLPB using three different hexane degrading consortia. When silicone oil 200 cSt (SO200) was added to the systems, the steady state hexane elimination capacities (ECs) increased by a factor of 8.7 and 16.3 for Consortium A (hydrophilic microorganisms) and B (100% hydrophobic microorganisms), respectively. In the presence of SO200, Consortium C supported a first steady state with a 2-fold increase in ECs followed by a 16-fold EC increase after a hydrophobicity shift (to 100% hydrophobic microorganisms), compared to the system deprived of SO200. This work revealed that cell hydrophobicity can play a key role in the successful performance of TLPBs, and to the best of our knowledge, this is the first report on hydrophobic VOC treatment with exclusive VOC uptake within a nonbioavailable non aqueous phase. Finally, an independent set of experiments showed that metabolite accumulation can also severely inhibit TLPB performance despite the presence of SO200.