Electrochemical and Microbiological Characterization of Bioanode Communities Exhibiting Variable Levels of Startup Activity

Abstract

Microbial electrochemical technologies (METs) require the establishment of anode biofilms to generate electrical current. The factors driving bioanode formation and their variability during startup remain unclear, leading to a lack of effective strategies to initiate larger-scale systems. Accordingly, our objective was to characterize the electrochemical properties and microbial community structure of a large set of replicate bioanodes during their first cycle of current generation. To do this, we operated eight bioanode replicates at each of two fixed electrode potentials [−0.15 V and +0.15 V vs. standard hydrogen electrode (SHE)] for one fed-batch cycle. We found that startup time decreased and maximum current generation increased at +0.15 V compared to −0.15 V, but at both potentials the bioanode replicates clustered into three distinct activity levels based on when they initiated current. Despite a large variation in current generation across the eight +0.15 V bioanodes, bioanode resistance and abundance of Geobacter species remained quite similar, differing by only 10 and 12%, respectively. At −0.15 V, current production strongly followed Geobacter species abundance and bioanode resistance, wherein the largest abundance of Geobacter was associated with the lowest charge transfer resistance. Our findings show that startup variability occurs at both applied potentials, but the underlying electrochemical and microbial factors driving variability are dependent on the applied potential.

Determining incremental coulombic efficiency and physiological parameters of early stage Geobacter spp. enrichment biofilms

“…enrichment biofilms differ from mature biofilms. Consequently, investigations on the physiological development of electroactive biofilms should be intensified for, e.g., optimizing organic load during start-up phase of MET [48,49]. Furthermore, microbial community analysis of the bulk liquid [73] as well as headspace gas analysis will be helpful for assessing and quantifying competitive microbial processes, especially in Geobacter spp.…”

“…avoiding the current erratic behavior thereof [48][49][50]. Therefore, a study combining timeresolved substrate analysis during batch cultivation with electrochemical measurements of Geobacter spp.…”

First settlers persist

“…This handicap was already identified in 2009 by Larrosa et al, proposing a minimum of four replicates for MFC experiments for leveling off variation in performance. In the last decade, this experimental variability was demonstrated in various single studies of different labs, e.g., Koch et al and Ortiz-Medina et al 3,4 Recently, the unreliability of biofilm anodes was confirmed in a global ring test. 5 In essence, stochasticity in the formation of biofilm anodes, especially for complex substrates and inoculums, results in an almost unpredictable performance thereof.…”