A two‐phase partitioning airlift bioreactor for the treatment of BTEX contaminated gases

Abstract

This investigation characterizes a novel 11 L airlift two-phase partitioning bioreactor (TPPB) for the treatment of gases contaminated with a mixture of benzene, toluene, ethylbenzene, and o-xylene (BTEX). The application of the TPPB technology in an airlift bioreactor configuration provides a novel technology that reduces energy intensity relative to traditional stirred tank TPPB configurations. The addition of a solid second phase of silicone rubber beads (10%, v/v) or of a liquid second phase of silicone oil (10%, v/v) resulted in enhanced performance of the airlift bioreactor relative to the single phase case, with 20% more BTEX being removed from the gas phase during an imposed transient loading. During a 4 h loading step change of three times the nominal loading (60 g m(-3) h(-1)), overall removal efficiencies for the airlift TPPBs containing a liquid or solid phase remained above 75%, whereas the single phase airlift had an overall removal efficiency of 47.1%. The airlift TPPB containing a silicone rubber second phase was further characterized by testing performance during steady-state operation over a range of loadings and inlet gas flow rates in the form of a 3(2) factorial experimental design. Optimal operating conditions that avoid oxygen limitations and that still have a slow enough gas flow rate for sufficient BTEX transfer from the gas phase to the working volume are identified. The novel solid-liquid airlift TPPB reduces energy inputs relative to stirred tank designs while being able to eliminate large amounts of BTEX during both steady-state and fluctuating loading conditions.

Estimating the cellular maintenance coefficient and its use in the design of two-phase partitioning bioscrubbers

“…The cell mass was maintained in the range of 9-11 g/L for 10 days and the fluctuation of cell mass may be due to intermittent loading of the compound for 10 h a day and 5 days a week to simulate an actual industry operating schedule. Interestingly, other research using polymers as a second phase instead of an organic solvent in a TPPB fed with a mixture of benzene, toluene, ethylbenzene and o-xylene to a microbial consortium showed biological steady state from 300 to 400 h of operation with a collective maintenance coefficient of 0.0103 h -1 at biological steady state [9]. We could prolong the biological steady state to about 1 month without medium change by refining medium formulation with the same microorganism, A. xylosoxidans Y234, for benzene degradation in a TPPB [32].…”

“…These difficulties led to the design of a two-phase partitioning bioscrubber (TPPB) in which aqueous and organic phases were completely mixed as a single homogenous phase [7,8]. We have recently shown the potential of replacing the liquid organic phase of TPPBs with inexpensive polymers as a second phase, which has the advantage of allowing the use of microbial consortia, while also eliminating operational challenges (e.g., emulsions) which sometimes arise in two-liquid phase TPPBs [9].…”

Model for a solid‐liquid airlift two‐phase partitioning bioscrubber for the treatment of BTEX

“…A schematic of the airlift SL-TPPB used by Littlejohns and Daugulis,3 which is modeled in the current study, can be seen in Fig. 1.…”

“…3 Performance indicators (removal efficiency and elimination capacity) were predicted over various loadings and inlet gas flow rates. An estimability analysis of model parameters was completed in order to identify the parameters to which output is most sensitive.…”

The effect of starvation periods on the performance of a two-liquid-phase mixed tank bioreactor for removal of n-hexane from air streams

“…Silicone oil has been found to be the best second phase for two-phase partitioning bioreactors [1]. Littlejohns and Daugulis [4] reported a 30% increase in removal efficiency of BETX from air after inclusion of silicone oil (10%, v/v). Arriaga et al [5] reported large improvement in the elimination capacity of a biofilter after use of silicone oil.…”