High Exoelectrogenic Biofilms Formation in Microbial Fuel Cells

Abstract

Background. Microbial fuel cells are devices in which electricity is generated by microorganisms called exoelectrogens. During the process of anaerobic respiration exoelectrogens emit electrons outside the cell. These electrons can be transferred to the anode of biofuel cell via several different mechanisms. Electricity generation in microbial fuel cells depends primarily on the electrochemical activity of the exoelectrogens present in the anode space. Nowadays, the usage of microorganisms, immobilized as biofilms on the anode, is constantly increasing. Natural sources for exoelectrogens selection such as activated sludge, biofilter biofilms, sediments of seas and rivers have a very diverse microbial composition. Therefore, it is important to immobilize relatively deficient in natural sources exoelectrogens on the anode during the biofilm formation process. The main research areas are the development of a technique for obtaining of electroactive biofilms enriched with exoelectrogens along with reduction of the period of biofilm formation process. Objective. We set a goal to study the process of high exoelectrogenic biofilm formation basing on the combination of different methods of exoelectrogens isolation and immobilization at the anode of a microbial fuel cell. Methods. A three-stage technique was used to obtain a highly exoelectrogenic biofilm which, due to the combination of typical isolation and immobilization techniques of exoelectrogens, allows obtaining the biofilm in which the vast majority of microorganisms are exoelectrogens. In the first stage, a biofilter biofilm was used as a source of exoelectrogens. The biofilm formed in the first stage was used as an inoculum for the second stage of biofilm formation. During the second stage an additional selective factor (applied additional potential in the electrical circuit of the microbial fuel cell) was used. The third stage of biofilm formation was the isolation of exoelectrogens capable of reducing ferum (III) compounds from secondary biofilm with subsequent application of these cells as inoculum.Results. The usage of the proposed method allows obtaining of a biofilm enriched with exoelectrogenic bacteria. The maximum current density generated by the biofilm, obtained during the first stage, reaches 140 μA/cm 2 , during the second -400 μA/cm 2 , during the third -615 μA/cm 2 . The duration of biofilm formation at each stage was 110 h, 40 h, and 60 h, respectively. Conclusions. It has been proven that the duration of biofilm formation is reduced almost twice as a result of a combination of typical methods of isolation and immobilization of exoelectrogens; obtained biofilm has high electrochemical activity and properties similar to biofilm, formed by pure cultures of exoelectrogens.

Anode Biofilm Formation With Applied External Voltage

“…In the anode chamber, either exoelectrogenic an-ode bacteria represented by a pure culture or a microbial consortium can be used as bioagents that decompose organic compounds with the release of electrons. The microbial consortium is more resistant to changes in the qualitative and quantitative composition of the medium due to a wide range of compounds, which is able to transform [4]. The main role in the production of electricity is played by exoelectrogenic bacteria, which are directly attached to the anode [2].…”