Hitesh C. Boghani

Control of power sourced from a microbial fuel cell reduces its start-up time and increases bioelectrochemical activity.

Microbial fuel cell (MFC) performance depends on the selective development of an electrogenic biofilm at an electrode. Controlled biofilm enrichment may reduce start-up time and improve subsequent power performance. The anode potential is known to affect start-up and subsequent performance in electrogenic bio-catalytic consortia. Control strategies varying electrical load through gradient based maximum power point tracking (MPPT) and transient poised anode potential followed by MPPT are compared to static ohmic loading. Three replicate H-type MFCs were used to investigate start-up strategies: (1) application of an MPPT algorithm preceded by poised-potential at the anode (+0.645 V vs Ag/AgCl); (2) MFC connected to MPPT-only; (3) static external load of 1 kΩ and 500 Ω. Active control showed a significant reduction in start-up time from 42 to 22 days, along with 3.5-fold increase in biocatalytic activity after start-up. Such active control may improve applicability by accelerating start-up and enhancing MFC power and bio-catalytic performance.

Inhibition of methane production in microbial fuel cells: Operating strategies which select electrogens over methanogens

Methanogenesis may diminish coulombic efficiency of microbial fuel cells (MFCs), although its importance is application dependent; e.g., suppression of methanogenesis may improve MFC sensing accuracy, but may be tolerable in COD removal from wastewaters. Suppression of methanogenesis was investigated in three H-type MFCs, enriched and acclimated with acetate, propionate and butyrate substrates and subsequently operated under open and closed circuit (OC/CC) regimes. Altering the polarisation state of the electrode displaces microorganisms from the anodic biofilm and leads to observable methane inhibition. The planktonic archeal community was compared to the electrode biofilm whilst under the OC/CC regimes. Semi-quantitative DNA analyses indicate a shift in some dominant species, from the electrode to the solution, during OC operation. The effect of prolonged starvation on anodic species was also studied. The results indicate progressive inhibition of methanogenesis from OC/CC operations; and virtual cessation of methanogenesis when an MFC was starved for a significant period.

Scaling Up of MFCs: Challenges and Case Studies

Rapid commercialization and expansion of biological and biotechnological platforms can contribute significantly towards realizing the concept of global bio-based economy. Bioelectrochemical systems (BESs) is one such emerging bio-based technology developed over the last few decades with multi-faceted utility. They assist in active valorization of resources in the form of bioelectricity (microbial fuel cell, MFC), biohydrogen (microbial electrolysis cell, MEC), value-added bioproducts (microbial electrosynthesis, MES) with concomitant waste management (bioelectro-treatment, BET) (Lovley 2006; Rosenbaum and Franks 2014; Venkata Mohan et al. 2014a, b). Of these, MFCs are heavily studied BES units and scalability is an important indicator in realizing their potential for practical application and global utility (Logan 2010). Scientific investigations and scale-up studies suggested that MFC operation at high reactor volumes (>5 L) are complex and are often challenged by several limitations. In this chapter, the problems associated with critical governing factors have been enlisted into operational, electrochemical and economic limitations. A brief overview of representative pilot-scale case studies like Bioelectro MET, Value from Urine, EcoBots and Peepower is presented in subsequent sections. Furthermore, possible technical and technological solutions, and future perspective to overcome the mentioned limitations are also included.

Reactor design and scale-up

This chapter discusses microbial fuel cell (MFC) reactor design and the important area of scale-up, the mechanism by which laboratory experimentation can be brought to industrially relevant and cost-effective use, while being able to accept and process appropriate feedstocks. Performance indicators are needed to establish design and operational criteria; in particular, the importance of their measurement, applicability, and the factors that affect system efficacy. Several cell architectures have been proposed for improved functionality, control mechanisms, connectivity, and the integration of MFCs with other systems. The prospects for MFC technology may lie in using the energy derived from oxidizing wastes at the anode, driving useful reactions at the cathode, in scaled-up systems to maximize potential economic benefits.