Peter Aelterman

Minimizing losses in bio-electrochemical systems: the road to applications

Bio-electrochemical systems (BESs) enable microbial catalysis of electrochemical reactions. Plain electrical power production combined with wastewater treatment by microbial fuel cells (MFCs) has been the primary application purpose for BESs. However, large-scale power production and a high chemical oxygen demand conversion rates must be achieved at a benchmark cost to make MFCs economical competitive in this context. Recently, a number of valuable oxidation or reduction reactions demonstrating the versatility of BESs have been described. Indeed, BESs can produce hydrogen, bring about denitrification, or reductive dehalogenation. Moreover, BESs also appear to be promising in the field of online biosensors. To effectively apply BESs in practice, both biological and electrochemical losses need to be further minimized. At present, the costs of reactor materials have to be decreased, and the volumetric biocatalyst activity in the systems has to be increased substantially. Furthermore, both the ohmic cell resistance and the pH gradients need to be minimized. In this review, these losses and constraints are discussed from an electrochemical viewpoint. Finally, an overview of potential applications and innovative research lines is given for BESs.

Loading rate and external resistance control the electricity generation of microbial fuel cells with different three-dimensional anodes

The electricity generation, electrochemical and microbial characteristics of five microbial fuel cells (MFCs) with different three-dimensional electrodes (graphite and carbon felt, 2mm and 5mm graphite granules and graphite wool) was examined in relation to the applied loading rate and the external resistance. The graphite felt electrode yielded the highest maximum power output amounting up to 386Wm(-3) total anode compartment (TAC). However, based on the continuous current generation, limited differences between the materials were registered. Doubling the loading rate to 3.3gCODL(-1)TACd(-1) resulted only in an increased current generation when the external resistance was low (10.5-25 Omega) or during polarization. Conversely, lowering the external resistance resulted in a steady increase of both the kinetic capacities of the biocatalyst and the continuous current generation from 77 (50 Omega) up to 253 (10.5 Omega)Am(-3)TAC. Operating a MFC at an external resistance close to its internal resistance, allows to increase the current generation from enhanced loading rates while maximizing the power generation.

Bioanode performance in bioelectrochemical systems: recent improvements and prospects

In a bioelectrochemical system (BES) operated with a bioanode, the anode performance plays an important part in the overall performance. Fundamental aspects of bioanodes have been intensively investigated, enabling us to better understand the growth, kinetics functioning and interactions of anodophilic microorganisms. Recently, various technological advances have improved the properties and operation of anodes and have increased bioanode performance by up to tenfold. To further boost the performance of bioanodes by several orders of magnitude, practical microbiological approaches deserve more investigation. This article reviews the factors affecting bioanode performance, the recent advances and the prospective strategies for improving it. Future application perspectives of bioanodes are also proposed.

High shear enrichment improves the performance of the anodophilic microbial consortium in a microbial fuel cell.

In many microbial bioreactors, high shear rates result in strong attachment of microbes and dense biofilms. In this study, high shear rates were applied to enrich an anodophilic microbial consortium in a microbial fuel cell (MFC). Enrichment at a shear rate of about 120 s−1 resulted in the production of a current and power output two to three times higher than those in the case of low shear rates (around 0.3 s−1). Biomass and biofilm analyses showed that the anodic biofilm from the MFC enriched under high shear rate conditions, in comparison with that under low shear rate conditions, had a doubled average thickness and the biomass density increased with a factor 5. The microbial community of the former, as analysed by DGGE, was significantly different from that of the latter. The results showed that enrichment by applying high shear rates in an MFC can result in a specific electrochemically active biofilm that is thicker and denser and attaches better, and hence has a better performance.