Electroactive mixed culture derived bioﬁlms in microbial bioelectrochemical systems: The role of pH on bioﬁlm formation, performance and composition Sunil A. Patil a , Falk Harnisch a,⇑ , Christin Koch b , Thomas Hübschmann c , Ingo Fetzer c , Alessandro A. Carmona-Martínez a , Susann Müller c,⇑ , Uwe Schröder a a Institute of Environmental and Sustainable Chemistry, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig, Germany b Department of Bioenergy, UFZ-Helmholtz Centre for Environmental Research, Torgauer Strasse 116, 04347 Leipzig, Germany c Department of Environmental Microbiology, UFZ-Helmholtz Centre for Environmental Research, Permoserstrasse 15, 04318 Leipzig, Germany article info Article history: Received 3 June 2011 Received in revised form 21 July 2011 Accepted 22 July 2011 Available online 28 July 2011 Keywords: Microbial bioelectrochemical systems Microbial fuel cells Flow-cytometry Microbial community analysis Multivariate statistics abstract The pH-value played a crucial role for the development and current production of anodic microbial elec- troactive bioﬁlms. It was demonstrated that only a narrow pH-window, ranging from pH 6 to 9, was suit- able for growth and operation of bioﬁlms derived from pH-neutral wastewater. Any stronger deviation from pH neutral conditions led to a substantial decrease in the bioﬁlm performance. Thus, average cur- rent densities of 151, 821 and 730 lA cm 2 were measured for anode bioﬁlms grown and operated at pH 6, 7 and 9 respectively. The microbial diversity of the anode chamber community during the bioﬁlm selection process was studied using the low cost method ﬂow-cytometry. Thereby, it was demonstrated that the pH value as well as the microbial inocula had an impact on the resulting anode community struc- ture. As shown by cyclic voltammetry the electron transfer thermodynamics of the bioﬁlms was strongly depending on the solution’s pH-value. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Electrochemically active microbial bioﬁlms not only play a key role in environmental oxidation reduction cycles, e.g. (Nielsen et al., 2010), but also in microbial bioelectrochemical systems (BES) (Rabaey et al., 2010). Within this seminal technology micro- bial bioﬁlms are exploited for anodic oxidation reactions (Logan, 2009; Lovley, 2008; Schröder, 2007) as well as for cathodic reduc- tion reactions, e.g. (Harnisch and Schröder, 2010). These latter reactions may range from the oxygen reduction in microbial fuel cells (MFC) to the reductive production and/or upgrading of chem- icals, e.g. H 2 , in microbial electrolysers. Common to the majority of these BES applications is the bioﬁlm at the anode that is responsible for the microbially assisted oxida- tion of the substrate (i.e. wastewater constituents). Except for pure culture studies, which are highly relevant concerning the investi- gation of fundamentals, the anodic bioﬁlms in BES are generally formed from natural bacterial sources, i.e. inoculums, like waste- water. The wastewater derived bioﬁlms exploited in the initial phase of BES research often possessed an only minor bioelectrocat- alytic activity (Kim et al., 2001) and consequently different enrich- ment procedures were presented leading to an increased anodic bioﬁlm performance, see e.g. (Kim et al., 2005; Liu et al., 2008; Rabaey et al., 2004). Up to now, the majority of BES studies using mixed culture bio- ﬁlms were performed using laboratory conditions tailored towards highest activity, i.e. metabolic turnover, and thus maximum cur- rent production. However, as BES technology has to be integrated into wastewater treatment technology lines (Rozendal et al., 2008) it has to be taken into account that the bioﬁlms may face dif- ferent, often suboptimal and quickly varying abiotic conditions during their formation and operation. This is especially a challenge when wastewater is used as feed, since its quality changes quickly due to the amount and kind of the various inﬂow sources. Recently, we have demonstrated on the example of the operation tempera- ture (Patil et al., 2010) that the inﬂuence of external environmental conditions can be severe. Concerning the inﬂuence of the pH-value in the anodic com- partment in BES, all recent studies were restricted to a comparably narrow pH-window around pH neutral, e.g. (Bifﬁnger et al., 2008; He et al., 2008; Hong et al., 2009; Jadhav and Ghangrekar, 2009; Liu et al., 2005; Puig et al., 2010). Furthermore, acidophilic (Borole et al., 2008) or alkalophilic (Liu et al., 2010) microorganisms were exemplarily studied for a potential application of BES under ex- treme pH conditions. Yet, as all these studies were performed in entire MFC devices, in which not only a potential pH dependent 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.07.087 ⇑ Corresponding authors. E-mail addresses: f.harnisch@tu-braunschweig.de, f.harnisch@tu-bs.de (F. Harnisch), Susann.mueller@ufz.de (S. Müller). Bioresource Technology 102 (2011) 9683–9690 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech