Effect of oil concentration and residence time on the biodegradation of α-pinene vapours in two-liquid phase suspended-growth bioreactors

Recently, research on the use of binary aqueous–organic liquid phase systems for the treatment of polluted air has significantly increased. This paper reports the removal of α-pinene from a waste air stream in a continuous stirred tank bioreactor (CSTB), using either a single-liquid aqueous phase or a mixed aqueous–organic liquid phase. The influence of gas flow rate, load and pollutant concentration was evaluated as well as the effect of the organic to aqueous phase ratio. Continuous experiments were carried out at different inlet α-pinene concentrations, ranging between 0.03 and 25.1 g m−3 and at four different flow rates, corresponding to residence times (RTs) of 120 s, 60 s, 36 s and 26 s. The maximum elimination capacities (ECs) reached in the CSTB were 382 g m−3 h−1 (without silicone oil) and 608 g m−3 h−1 (with 5% v/v silicone oil), corresponding to a 1.6-fold improvement using an aqueous–organic liquid phase. During shock-loads experiments, the performance and stability of the CSTB were enhanced with 5% silicone oil, quickly recovering almost 100% removal efficiency (RE), when pre-shock conditions were restored. The addition of silicone oil acted as a buffer for high α-pinene loads, showing a more stable behaviour in the case of two-liquid-phase systems.

► α-Pinene removal was optimized in a CSTB inoculated with a bacterial co-culture containing Rhodococcus erythropolis.
► Adding silicone oil (2 or 5%, v/v) resulted in an enhancement of α-pinene transfer from the gas to the liquid-phase.
► The highest elimination capacities were 382 g m−3 h−1 (without silicone oil) and 608 g m−3 h−1 (with 5%, v/v, silicone oil).
► Two-liquid-phase systems showed a more stable behaviour either during or after overload conditions.