Abstract
Surface chemistry is known to influence the formation, composition, and electroactivity of electron-conducting biofilms. However, understanding of the evolution of microbial composition during biofilm development and its impact on the electrochemical response is limited. Here we present voltammetric, microscopic and microbial community analysis of biofilms formed under fixed applied potential for modified graphite electrodes during early (90 h) and mature (340 h) growth phases. Electrodes modified to introduce hydrophilic groups (-NH2, -COOH and -OH) enhance early-stage biofilm formation compared to unmodified or electrodes modified with hydrophobic groups (-C2H5). In addition, early-stage films formed on hydrophilic electrodes are dominated by the gram-negative sulfur-reducing bacterium Desulfuromonas acetexigens while Geobacter sp. dominates on -C2H5 and unmodified electrodes. As biofilms mature, current generation becomes similar, and D. acetexigens dominates in all biofilms irrespective of surface chemistry. Electrochemistry of pure culture D. acetexigens biofilms reveal that this microbe is capable of forming electroactive biofilms producing considerable current density of > 9 A/m2 in a short period of potential-induced growth (~19 h following inoculation) using acetate as an electron donor. The inability of D. acetexigens biofilms to use H2 as a sole source electron donor for current generation shows promise for maximizing H2 recovery in single-chambered microbial electrolysis cell systems treating wastewaters.
Highlights
Microbial electrochemical technologies (METs) are electrochemical devices which utilize microbial biofilms formed at a polarized electrode to drive electrochemical reaction(s) (Rittmann, 2018)
A higher relative abundance of G. psychrophilus to G. sulfurreducens was found in all biofilms, revealing that surface chemistry supported the dominance of electroactive bacteria other than G. sulfurreducens
The sigmoidal shaped cyclic voltammetric (CV) obtained at 250 h after inoculation (Fig. 2B), when fit to a simple model for steady-state voltammetry (Jana et al, 2014), indicates that electron transfer is dominated by a redox species with an estimated half-wave potential of -0.45 V vs Ag/AgCl, once the approximately 60 Ω uncompensated resistance is accounted for by correcting at each applied potential to achieve the best fit between model and recorded CV
Summary
Microbial electrochemical technologies (METs) are electrochemical devices which utilize microbial biofilms formed at a polarized electrode (anode and/or cathode) to drive electrochemical reaction(s) (Rittmann, 2018). Several approaches have been developed to establish and improve electrochemical communication between the electroactive bacteria and the anode These include chemical treatment of anodes (Dumitru and Scott, 2016), and modification of anode surfaces with mediators (Dumitru and Scott, 2016; Park et al, 2000) and with chemical/functional groups (Artyushkova et al, 2015; Cornejo et al, 2015; Dumitru and Scott, 2016; Guo et al, 2013; Kumar et al, 2013; Lapinsonnière et al, 2013; Picot et al, 2011; Saito et al, 2011; Santoro et al, 2015; Scott et al, 2007). Santoro et al, reported development of a more diverse consortia consisting of various classes of Clostridia and Proteobacteria species on functionalized gold electrodes after 45 days (Santoro et al, 2015)
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