## 1 Introducing Microbial Electrochemical Systems for Bioremediation, Energy and Biofuel Production  
Microbial electrochemical systems (MESs), also commonly referred to as bioelectrochemical systems (BESs), are technologies that harness the metabolic functions of living microorganisms to convert chemical energy stored in organic material to bioelectrical current production or biofuel production [1]. These technologies span the collective fields of microbial electrochemistry, engineering, materials science and environmental science among others. Two major types of MESs are microbial fuel cells (MFCs), which utilise microorganisms to convert organic compounds into electrical power, and microbial electrolysis cells (MECs), which require a net power input for the microbially driven synthesis of biofuels and other commodity chemicals through microbial electrosynthesis (ME) [2; 3; 4; 5]. MESs are generally comprised of the same basic components: a working electrode and a counter electrode, contained in separate compartments, which may be separated by a proton exchange membrane (PEM). The anolyte medium of the MES contains organic or inorganic substrates that provide a source of electron donors to the microbes in the anode chamber. In pure culture MESs, anode-respiring bacteria (ARB) oxidise electron donors present in the anolyte medium and pass the electrons to the anode as the final electron acceptor; whereas, in mixed microbial community MESs, the electron donors present as complex organics are often first oxidised by fermentative bacteria. The ARBs may then oxidise the simple organic acid by-products of the fermentation. Electrons donated to the anode by the ARBs then travel to the cathode via a conductive wire connecting the two electrodes. These electrons combine with the protons that have physically relocated from the anode to the cathode via the PEM to form resultant products such as water or biofuels such as methane or ethanol [1; 5]. MFCs came to prominence with the discovery of electrochemically active microorganisms (EAMs), microbes with the ability to interact with electrodes [6]. [PERSON] and [PERSON] [7] demonstrated that some microorganisms could respire by coupling organic carbon oxidation with dissimilatory Fe(III) reduction, using the iron as the final electron acceptor. The work of [PERSON] and [PERSON] [8] found that MFCs produced electricity using various carbohydrate carbon sources and chemical mediators to transfer electrons. Some EAMs were also discovered that were able to generate electricity in MFCs without the need for chemical mediators. One of the earliest examples was _Shewanella putrefaciens_, an Fe(III)-reducing bacteria, using an electrode as its electron acceptor [9]. EAMs can be classified as electricigens, microbes which are capable of completely oxidising organic compounds to carbon dioxide and donating electrons directly to an electrode [10; 11], and electrotrophs, microbes that can accept electrons from electrodes for the reduction of terminal electron acceptors [12]. Marine and aqueous sediments have also been used as a substrate in benthic microbial fuel cells (BMFC) [13; 14]. Also known as sediment MFCs (SMFC), they generate a small but constant current from microbial processes occurring in the sediment of aqueous environments. BMFCs can be utilised in marine and aqueous environments to power equipment that requires a constant low level power [2; 13; 14]. MFCs can vary in architecture from single and double-chambered fuel cells to stacked MFCs. Stacked MFCs are a parallel configuration of MFCs which are higher in efficiency than standard two-chamber MFCs [15]. Benthic or sedimentary microbial fuel cells (SMFCs) are another form of MFC where the anode is placed into the aquatic sediments, and the cathode into the overlying water column to generate power [10].