Electron Storage in Electroactive Biofilms

Abstract

Microbial electrochemical technologies (METs) are promising for sustainable applications. Recently, electron storage during intermittent operation of electroactive biofilms (EABs) has been shown to play an important role in power output and electron efficiencies. Insights into electron storage mechanisms, and the conditions under which these occur, are essential to improve microbial electrochemical conversions and to optimize biotechnological processes. Here, we discuss the two main mechanisms for electron storage in EABs: storage in the form of reduced redox active components in the electron transport chain and in the form of polymers. We review electron storage in EABs and in other microorganisms and will discuss how the mechanisms of electron storage can be influenced. Controlling Electron Flows in EABs for High Electron EfficiencyTo safeguard the Earth's resources for future generations, it is of utmost importance to reduce our CO 2 footprint and to recover valuable components from waste streams for reuse. To address this huge challenge, it is essential to develop and mature sustainable technologies. Microbial electrochemical technologies (METs) have promising applications in resource and energy recovery and bioremediation [1][2][3][4]. METs collectively refer to systems that use a combination of electrodes and electroactive biofilms (EABs) (see Glossary) for different biological conversions. The key property of these EABs is that they can transfer electrons between chemical bonds and electrodes, which can serve many different applications [5,6] (Box 1).

New fragmented electro-active biofilm (FAB) reactor to increase anode surface area and performance of microbial fuel cell

“…Several biofilm substances such as EPS and bacterial nanowire are reported as electron conductors (Angelaalincy et al 2018;Ucar et al 2017) and contribute to electrode electron transfer reactions (Kumar et al 2017). On the other hand, besides the endoelectrogens (Borole et al 2011;Patil et al 2012) and electron storage compounds (Ter Heijne et al 2020), there might be non-conductor materials in the biofilm that block the long-range electron transfer to the electrode. Depending on the surrounding materials, the biofilms might contain mineral crystals, corrosion particles, clay, or silt particles (Donlan 2002); this might influence the biofilm matrix's electron conductivity nature, which may affects the FAB performance.…”

“…However, Strycharz and Tender (2012) argue that there was no evidence to support metallic conductivity. According to Ter Heijne et al (2020), the electro-active biofilms (EABs) study is at an earlier stage. Meanwhile, most studies focus on how electron transfer, but there is an urgent research gap: (1) how to steer biofilm formation in MFC to increase energy generation and (2) lack of clear understanding on different EABs phenomenon.…”

Microfluidic Microbial Bioelectrochemical Systems: An Integrated Investigation Platform for a More Fundamental Understanding of Electroactive Bacterial Biofilms

“…The formation of the biofilm is then greatly impacted by the electric communication thus generated. This phenomenon is especially interesting in electroactive species, which have high polarizability since they are able to perform EET [ 111 , 112 ].…”

Moving bed capacitive bioanodes

“…The likely mechanism is the use of the cytochromes and other redoxactive proteins [66]. The charge storage is essential for the planktonic EAB to function when no electron acceptor is readily available, but also useful for biofilms which can remain active even if the electrical circuit is not accepting electrons (open circuit) [67].…”

“…The first capacitive bioanode used an external capacitor [101], and Deeke and colleagues developed an integrated capacitive bioanode using a graphite plate coated with activated carbon. The capacitive bioanode produced 1.2 A/m 2 or 81 A/m 3 reactor [67,85]. Though the experiments comparing non-capacitive and capacitive bioanodes show the benefits of intermittent use of charge storage, application of capacitive bioanodes has not resulted in high current densities.…”