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    High current densities enable exoelectrogens to outcompete aerobic heterotrophs for substrate

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    Type
    Article
    Authors
    Ren, Lijiao
    Zhang, Xiaoyuan cc
    He, Weihua cc
    Logan, Bruce E.
    KAUST Grant Number
    KUS-I1-003-13
    Date
    2014-08-05
    Online Publication Date
    2014-08-05
    Print Publication Date
    2014-11
    Permanent link to this record
    http://hdl.handle.net/10754/598464
    
    Metadata
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    Abstract
    © 2014 Wiley Periodicals, Inc. Chemical oxygen demand (COD) removal rates could be described by first-order kinetics with respect to COD concentration at different current densities, even under open circuit conditions with no current generation. The COD concentration was reduced more quickly with current generation due to the greater consumption of substrate by exoelectrogens, and less substrate was lost to aerobic heterotrophs. Higher current densities enabled exoelectrogens to outcompete aerobic heterotrophs for substrate, allowing for increased coulombic efficiencies with current densities. © 2014 Wiley Periodicals, Inc. In mixed-culture microbial fuel cells (MFCs), exoelectrogens and other microorganisms compete for substrate. It has previously been assumed that substrate losses to other terminal electron acceptors over a fed-batch cycle, such as dissolved oxygen, are constant. However, a constant rate of substrate loss would only explain small increases in coulombic efficiencies (CEs, the fraction of substrate recovered as electrical current) with shorter cycle times, but not the large increases in CE that are usually observed with higher current densities and reduced cycle times. To better understand changes in CEs, COD concentrations were measured over time in fed-batch, single-chamber, air-cathode MFCs at different current densities (external resistances). COD degradation rates were all found to be first-order with respect to COD concentration, even under open circuit conditions with no current generation (first-order rate constant of 0.14±0.01h-1). The rate of COD removal increased when there was current generation, with the highest rate constant (0.33±0.02h-1) obtained at the lowest external resistance (100Ω). Therefore, as the substrate concentration was reduced more quickly due to current generation, the rate of loss of substrate to non-exoelectrogens decreased due to this first-order substrate-concentration dependence. As a result, coulombic efficiencies rapidly increased due to decreased, and not constant, removal rates of substrate by non-exoelectrogens. These results show that higher current densities (lower resistances) redirect a greater percentage of substrate into current generation, enabling large increase in CEs with increased current densities. Biotechnol. Bioeng. 2014;111: 2163-2169.
    Citation
    Ren L, Zhang X, He W, Logan BE (2014) High current densities enable exoelectrogens to outcompete aerobic heterotrophs for substrate. Biotechnology and Bioengineering 111: 2163–2169. Available: http://dx.doi.org/10.1002/bit.25290.
    Sponsors
    Contract grant sponsor: King Abdullah University of Science and Technology (KAUST)Contract grant number: KUS-I1-003-13
    Publisher
    Wiley
    Journal
    Biotechnology and Bioengineering
    DOI
    10.1002/bit.25290
    PubMed ID
    24889278
    ae974a485f413a2113503eed53cd6c53
    10.1002/bit.25290
    Scopus Count
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