Please cite this article in press as: A. Kumar, et al., Membrane-based biological waste gas treatment, Chem. Eng. J. (2007), doi:10.1016/j.cej.2007.06.006 ARTICLE IN PRESS +Model CEJ-5327; No. of Pages 10 Chemical Engineering Journal xxx (2007) xxx–xxx Review Membrane-based biological waste gas treatment Amit Kumar, Jo Dewulf, Herman Van Langenhove ∗ Research Group of Environmental Organic Chemistry and Technology (EnVOC), Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium Received 8 March 2007; received in revised form 29 May 2007; accepted 6 June 2007 Abstract This article presents a literature review on developments of membrane reactors for biological waste gas treatment as well as examples of applications to different compounds. The use of membranes combines selective separation of compounds from a waste gas stream followed by biological removal. Gas transport phenomena and different types of membranes used in biological waste gas treatment are discussed. So far, membrane-based biological waste gas treatment has only been tested on laboratory scale. If the long-term stability of these reactors can be demonstrated, membrane bioreactor technology can be useful in the treatment of gas streams containing poorly water-soluble pollutants and highly chlorinated hydrocarbons, which are difficult to treat with conventional methods for biological waste gas treatment. © 2007 Elsevier B.V. All rights reserved. Keywords: Waste gases; Membrane bioreactors; Biological treatment; Biofilm 1. Introduction Membrane bioreactor (MBR) technology is advancing rapidly, and different MBR configurations have evolved dur- ing last 30 years [1]. MBR systems have mostly been used to treat industrial, domestic, and specific wastewaters, where a small footprint, water reuse, or stringent discharge standards are required. In this review, we will focus on transport and biodegradation of pollutants in membrane bioreactors for waste gas (MBRWG) treatment. In a MBRWG, gaseous pollutants dif- fuse through the membrane and are subsequently degraded by the microorganisms in the biofilm attached to the membrane sur- face [2–4]. Biomass may also be suspended in the liquid phase. MBRWG are especially favorable for poorly water-soluble com- pounds. Membrane materials can be dense, microporous, porous or composite. Dense materials are more selective, while microp- orous materials are more permeable but susceptible to plugging by biomass [5]. Passage of the pollutants contaminated air across the membrane allows passive diffusion of contaminants through the membrane into the liquid biofilm phase on the other side, driven by the concentration gradient [5]. The mass transfer coef- ficient through a dense membrane depends on the solubility and diffusivity of the contaminant. By careful selection of membrane ∗ Corresponding author. Tel.: +32 92645953; fax: +32 92646243. E-mail address: herman.vanlangenhove@ugent.be (Herman. Van Langenhove). material, pollutants can therefore be extracted selectively from the gas phase [5,6]. While membrane bioreactors for volatile organic compounds (VOCs) treatment have yet to be tested at full scale, a number of features have emerged from the lab and pilot- scale work carried out to date. Compared with the traditional biological waste gas treatment techniques such as biofiltration, MBRWG have several advantages: presence of a discrete water phase allows optimal moistening of the biomass and removal of degradation products, avoiding inactivation of the biomass. Moreover, in MBRWG the gas and liquid flow can be varied independently without problems of flooding, loading or foaming [7]. A MBR also have the high construction cost disadvantage. Furthermore, their long-term operational stability still has to be demonstrated. In this review we summarize the state-of-the-art of membrane based biological waste gas treatment. In addition, transport phe- nomena through membranes and development of MBRWG for biological waste gas treatment are summarized. 2. Membrane bioreactor configurations for waste gas treatment Different membrane bioreactor configurations have been used, all on lab-scale: hollow fibre (i.d. < 0.5 mm), capil- lary (0.5 mm < i.d. < 10 mm), tubular (i.d. > 10 mm), flat sheet and spiral-wounded membrane type reactors [8]. A schematic 1385-8947/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2007.06.006