ARTICLE A Two-Phase Partitioning Airlift Bioreactor for the Treatment of BTEX Contaminated Gases Jennifer V. Littlejohns, Andrew J. Daugulis Department of Chemical Engineering, Queen’s University, Kingston, Ontario, Canada K7L 3N6; telephone: 613-533-2784; fax: 613-533-6637; e-mail: andrew.daugulis@chee.queensu.ca Received 29 January 2008; revision received 24 March 2009; accepted 26 March 2009 Published online 3 April 2009 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/bit.22343 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 applica- tion of the TPPB technology in an airlift bioreactor config- uration provides a novel technology that reduces energy intensity relative to traditional stirred tank TPPB config- urations. 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 experi- mental 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. Biotechnol. Bioeng. 2009;103: 1077–1086. ß 2009 Wiley Periodicals, Inc. KEYWORDS: airlift; biodegradation; BTEX; microbial con- sortium; partitioning bioreactor Introduction Printing facilities (Thanacharoenchanaphas et al., 2007), petroleum refineries (Stewart et al., 2001) and contaminated sites undergoing remediation (Liang et al., 2009) are all sources of gaseous emissions of benzene, toluene, ethyl- benzene, and o-xylene (BTEX). Due to the toxicity of BTEX components, treatment of these waste gas streams is needed in order to meet regulatory emission standards. Biological treatment methods, such as biofilters, can provide a low-cost, energy efficient, and effective solution for the degradation of BTEX. However, biofilters can have limitations such as bed drying, biomass clogging, and the inability to effectively handle fluctuations in loading (Khan and Ghoshal, 2000). Therefore, there has been recent interest in the design and improvement of novel biological BTEX treatment systems that have the ability to operate beyond the current abilities of biofilters (Kan and Deshusses, 2005; Studer and von Rohr, 2008). However, design of novel biological treatment systems can often involve stirred tank reactors, which are energy intensive and compromise the energy benefits that are typically associated with biological treatment methods. A solution to this is the implementation of airlift bioreactors, which can provide a low energy alternative to traditional stirred tanks. An example of such a novel biological treatment method that has been researched to date primarily in stirred tank vessels is the two-phase partitioning bioreactor (TPPB), which is gaining popularity for the destruction of toxic compounds in waste gases (Aldric and Thonart, 2008; Arriaga et al., 2006; Bailon et al. 2009; Mun ˜oz et al., 2008). TPPBs consist of a cell containing aqueous phase and a non- toxic, non-bioavailable second phase that can sequester high and fluctuating concentrations of toxic substrates and release them to the aqueous phase for subsequent degradation based on microbial metabolic demand. This provides the ability to treat fluctuating concentrations of toxic compounds with low water solubility by alleviating toxic levels in the aqueous phase and improving mass transfer out of the gas phase. Silicone oil has been traditionally used as the immiscible phase in a TPPB and is non-bioavailable to microbial consortia, however, because of its fixed chemical structure, silicone oil cannot be modified for optimal uptake and release of target molecules. Correspondence to: A.J. Daugulis ß 2009 Wiley Periodicals, Inc. Biotechnology and Bioengineering, Vol. 103, No. 6, August 15, 2009 1077