Abstract
The electrogenic biofilm and the bio-electrode interface are the key biocatalytic components in bioelectrochemical systems (BES) and can have a large impact on cell performance. This study used four different anodic carbons to investigate electrogenic biofilm development to determine the influence of charge accumulation and biofilm growth on system performance and how biofilm structure may mitigate against pH perturbations. Power production was highest (1.40 W/m3) using carbon felt, but significant power was also produced when felt carbon was open-circuit acclimated in a control reactor (0.95 W/m3). The influence of carbon material on electrogenic biofilm development was determined by measuring the level of biofilm growth, using sequencing to identify the microbial populations and confocal microscopy to understand the spatial locations of key microbial groups. Geobacter spp. were found to be enriched in closed-circuit operation and these were in close association with the carbon anode, but these were not observed in the open-circuit controls. Electrochemical analysis also demonstrated that the highest mid-point anode potentials were close to values reported for cytochromes from Geobacter sulfurreductans. Biofilm development was greatest in felt anodes (closed-circuit acclimated 1209 ng/μL DNA), and this facilitated the highest pseudo-capacitive values due to the presence of redox-active species, and this was associated with higher levels of power production and also served to mitigate against the effects of low-pH operation. Supporting carbon anode structures are key to electrogenic biofilm development and associated system performance and are also capable of protecting electrochemically active bacteria from the effects of environmental perturbations.
Highlights
IntroductionBioelectrochemical systems are able to convert organic matter to electrical energy by using inherent metabolic processes associated with a district group of electrogenic microorganisms that are able to facilitate extracellular electron transfer to the anode
Microbial fuel cells (MFCs) are comprised of anodic and cathodic chambers, each typically containing carbon-based electrodes and separated by an ion exchange membrane; these electrodes can be electrically connected to an external electrical circuit to generate a cell voltage.Bioelectrochemical systems are able to convert organic matter to electrical energy by using inherent metabolic processes associated with a district group of electrogenic microorganisms that are able to facilitate extracellular electron transfer to the anode
Confocal and scanning electron microscopy (SEM) microscopy showed that cells and extracellular polymeric substances (EPS) were spread across the electrode surfaces of all the material types, and this was apparent in the carbon felt, where large levels of biomass were associated with high levels of capacitance. These results suggest that it is the acclimation of the biofilm and the amount of active biomass that may facilitate power production; previous work has shown that microbial electrochemical biofilms can both alternate between storing energy and generating power, potentially enhancing the capacity of bioelectrochemical systems [48]
Summary
Bioelectrochemical systems are able to convert organic matter to electrical energy by using inherent metabolic processes associated with a district group of electrogenic microorganisms that are able to facilitate extracellular electron transfer to the anode. MFC systems have been applied to a number of environmental treatment and sensing processes, notably, in wastewater treatment, in energy conservation for remote sensor systems and as on-line biosensors [1]. It is known that the performance of MFC biofilms is affected by a number of different factors, including temperature, substrate, material type, construction, flow rate and pH [2]. Carbon is considered to be a good support material for electrogenic biofilms due to its inherent biocompatibility, high surface area and relatively low cost [3]; whilst electrical conductivity is good, it presents significantly higher resistances than typical metals. A number of strategies have been employed to improve the biocatalytic/electrochemical properties of carbon in reactor systems
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