Microbial fuel cells (MFCs) convert organic waste directly into electricity, which is a competitive advantage over other energy generating systems. It is a technology that offers an environmentally friendly service at high-energy conversion efficiency. Full commercialization has yet to be achieved in areas such as wastewater treatment and remote power applications, due to challenges with the level of power output from individual units, cost of materials and scale-up. Unlike some conventional chemical fuel cells that are now fully commercial, MFCs are still at pilot scale testing [1-4]. However, several smaller-scale MFC-based applications have been implemented including, biochemical oxygen demand (BOD) measuring sensors (HABS2000, KORBI), benthic MFCs as on-site power sources for conventional sensors [5-7] and power sources for small electronic gadgets, mobile phones and robots, as well as Pee Power urinals [3, 8, 9].

Single MFCs can generate on average <0.5V at maximum power transfer, which is lower than what electronic circuits and peripheral devices require. Scaling up is therefore critical for the technology to be implemented in practice and find a route to market, and for this purpose several approaches have been proposed. One approach is to enlarge individual units to scale [2], and the second is to miniaturise individual units [10] and stack collectives of these small units together [11, 12]. Independent of size or volume, more than one unit will need to be connected together to increase the voltage and current up to operational levels. This can be in series (voltage boost), parallel (current boost) or a combination of series and parallel (voltage + current boost).

As an alternative to these common connections, a novel method of MFC configuration is suggested in this work, with the introduction of added electrodes – so-called “pins”. The purpose of this type of connection is to enable control and monitoring of the MFC by modulating the physicochemical environment and the idea is derived from electronic transistors and control theory.

This long-term study has been focusing on the development of MFCs for practical applications and scale-up. Through this approach, a novel transistor analogy is proposed with potential for improving power, controlling biochemical reactions, sensing and unconventional computation.

Acknowledgements

This work has been supported by the UK EPSRC, grant numbers EP/I004653/1 and EP/L002132/1 and

Bill & Melinda Gates Foundation, grant no. OPP1094890.

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