Transient performance of two‐phase partitioning bioreactors treating a toluene contaminated gas stream

Abstract

Two-phase partitioning bioreactors (TPPBs) consist of a cell-containing aqueous phase and an immiscible organic phase that sequesters and delivers toxic substrates to cells based on equilibrium partitioning. The immiscible organic phase, which acts as a buffer for inhibitory substrate loadings, makes it possible for TPPBs to handle high volatile organic compound (VOC) loadings, and in this study the performance of liquid n-hexadecane and solid styrene butadiene (SB) polymer beads used as partitioning phases were compared to a single aqueous phase system while treating transient loadings of a toluene contaminated air stream by Achromobacter xylosoxidans Y234. The TPPBs operated as well-mixed stirred tanks, with total working volumes of 3 L (3 L aqueous for the single-phase system, 2 L aqueous and 1 L n-hexadecane for the solvent system, and 2.518 L aqueous volume and 500 g of SB beads for the polymer system). Two 60-min step changes (7 and 17 times the nominal loading rates, termed "small" and "large" steps, respectively) were imposed on the systems and the performance was characterized by the overall removal efficiencies, instantaneous removal efficiency recovery times (above 95% removal), and dissolved oxygen recovery times. For the small steps, with a nominal loading of 343 g/m3/h increasing to 2,400 g/m3/h, the TPPB system using n-hexadecane as the second phase performed best, removing 97% of the toluene fed to the system compared with 90% for the polymer beads system and only 69% for the single-phase system. The imposed large transient gave similar results, although the impact of the presence of a second sequestering phase was more pronounced, with the n-hexadecane system maintaining much reduced aqueous toluene concentrations leading to significantly improved performance. This investigation also showed that the presence of both n-hexadecane and SB beads improved the oxygen transfer within the systems.

Performance evaluation of a water/silicone oil two‐phase partitioning bioreactor using Rhodococcus erythropolis T902.1 to remove volatile organic compounds from gaseous effluents

“…Similar observations on biomass have been made by Nielsen et al, 11 who reported an adaptation in biomass steady state when a benzene loading step change was imposed, suggesting evidence of a characteristic value of maintenance energy requirements. Boudreau and Daugulis 35 also found a constant cell concentration between 6.4 and 8.7 g L −1 in a TPPB with a solvent or polymer beads as the second phase.…”

Effect of surfactants and biomass on the gas/liquid mass transfer in an aqueous‐silicone oil two‐phase partitioning bioreactor using Rhodococcus erythropolis T902.1 to remove VOCs from gaseous effluents

“…1 These reactors involve the use of a second non-aqueous phase ('oil') to improve the solubility and transfer of hydrophobic compounds. Some authors have proposed this technology as a way of removing hydrophobic compounds such as benzene, 2 hexane 3 and toluene, 4,5 and have demonstrated an improvement of elimination capacity in comparison with classical biofilters treating the same or similar compounds 6 -8 in terms of hydrophobicity. 9 In particular, the effectiveness of an aqueous-silicone oil (10% V/V) TPPB using Rhodococcus erythropolis T902.1 in removing volatile organic compounds (VOCs) from gaseous effluents has been established.…”

Novel Bioreactors for Waste Gas Treatment

“…For shock-loads tested in the presence of the second organicphase by different researchers, an enhancement in the performance arising from the presence of a second-phase was observed. Anew, the instantaneous removal effi ciency recovery times, after re-instating pre-shock conditions, also show a clear trend with the one-liquid-phase system recovering more rapidly, as a result of little pollutant absorption (Boudreau and Daugulis 2006 ) .…”