Bioelectrochemical reactors are a type of bioreactor where bioelectrochemical processes can take place. They are used in bioelectrochemical syntheses, environmental remediation and electrochemical energy conversion. Examples of bioelectrochemical reactors include microbial electrolysis cells, microbial fuel cells and enzymatic biofuel cells and electrolysis cells, microbial electrosynthesis cells, and biobatteries. This bioreactor is divided in two parts: The anode, where the oxidation reaction takes place; And the cathode, where the reduction occurs.
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History
In 1911 M. Potter described how microbial conversions could create reducing power,and thus electric current. Twenty years later Cohen (1931) investigate the capacity of bacteria to produce an electrical flow and he noted that the main limitation is the small capacity of microorganism to current generation. It tooks until the 60's since Berg and Canfield (1964) build the first Microbial Fuel Cell (MFC). Nowadays the investigation on bioelectrochemical reactors is increasing exponentially. These devices have real application on fields like water treatment, energy production and storage, resources production recycling and recovery.
Principles
Electron current is inherent to the microbial metabolism. Microorganism transfer electrons from an electron donor (lower potential species)to an electron acceptor (higher potential species) If the electron acceptor is an external ion or molecule, the process is called respiration. If the process is internal, electron transfer is called fermentation. The microorganism attempt to maximize their energy gain by selecting the electron acceptor with the highest potential available. In nature mainly mineral containing iron or manganese oxides are being reduced. Often soluble electron acceptors are depleted in the microbial environment. The microorganism can also maximize their energy selecting a good electron donor which can be easily metabolized. These processes are done by extracellular electron transfer (EET). The theoretical energy gain ΔG for microorganism relates directly the potential difference between the electron acceptor and the donor. But the inefficiencies like internal resistances will decrease this energy gain. The advantage of these devices is their high selectivity and in high speed processes limited by kinetic factors. The most common studied species are Shewanella oneidensis and Geobacter sulfurreducens. However, more species have been studied in recent years.
In March 25, 2013, Scientists at the University of East Anglia were able to transfer electrical charge by letting the bacteria touch on a metal or mineral surface. The research shows that it is possible to 'tether' bacteria directly to electrodes.