Microbial strategies for the conversion of photosynthetically derived compounds

The activities of mankind have seriously perturbed the worldwide carbon cycle. They resulted in an exponential increase of the atmospheric CO2 concentration and an excessive organic load of aquatic systems, both with adverse consequences. To mitigate these effects microbial strategies could be adapted, in which the microbial fuel cell (MFC) could play a role. A sediment MFC for example links the microbial oxidation of sediment organic matter at an anode with direct electricity production. In a first strategy in this work the cultivation of microalgae was coupled to the production of renewable energy by means of anaerobic digestion of the microalgal biomass. The effluent of the digester was polished in a standard MFC and nutrients and water were recuperated. The resulting cycle delivered a gross power of 9 kW ha-1. Secondly, through the stimulation and exploitation of natural processes in sediments, the oxidation of organic compounds could be enhanced. This could for instance be achieved with a manganese cycle, but could also be obtained through the installation of a sediment MFC, as practically demonstrated. In order for a sediment MFC to work efficiently, a sustainable cathode reaction is required. Therefore a biocathode was developed that uses oxygen as final electron acceptor. The startup and operational performance with respect to different cathode base materials and different salinities was further investigated. In a next research topic the technology of the sediment MFC was combined with living rice plants, hence forming a plant MFC. Electricity could be generated in situ from rhizodeposits, organic compounds set free by plant roots. The power a sediment MFC was a factor 7 higher in the presence of living plants. A stable power of up to 330 W ha-1 could be assigned to the oxidation of rhizodeposits. Finally the microbial communities on the anodes of these plant MFCs were investigated through molecular analyses. The electrical circuit resulted in remarkable changes in the composition of the bacterial as well as the archaeal community

Evaluation of biocathodes in freshwater and brackish sediment microbial fuel cells

Biofilms on biocathodes can catalyze the cathodic oxygen reduction and accordingly guarantee high cathode redox potentials. The present research assessed the use of biocathodes in full-sediment microbial fuel cells. Carbon felt-based biocathodes were evaluated in freshwater systems, and an extension of their application to brackish systems and/or stainless steel webs as base material was considered. Efficient biocathodes could be developed within days through inoculation with active microorganisms. Carbon felt was found most suited for the biocathodes in freshwater with increased performance at salinities around 80-250 mM. Maximum long-term performance reached 12.3 A mu W cm(-2) cathode. The relative benefit of stainless steel seemed to increase with increasing salinity. A combination of stainless steel cathodes with biofilms could, however, also result in decreased electrical performance. In an efficiently catalyzing cathodic biofilm, an enrichment with an uncultured Proteobacterium-previously correlated with steel waste-was observed

Minireview: The potential of enhanced manganese redox cycling for sediment oxidation

Both natural and anthropogenic processes are responsible for excessive organic loading of submerged soils, with detrimental environmental consequences. The often insufficient natural attenuation can be enhanced by exploiting microbial manganese cycles. This review describes how an anoxic oxidation of organic matter with concomitant reduction of MnO2 can link up with a reoxidation of the resulting, soluble Mn(II) in oxic layers. The potentially attainable oxidation rates through these natural cycles are of the same order as the organic carbon accumulation rates. The microbiology and physiology of the responsible organisms are discussed, as well as examples of naturally occurring manganese cycles and the possibility to engineer his natural phenomenon

Microbial Community Analysis of Anodes from Sediment Microbial Fuel Cells Powered by Rhizodeposits of Living Rice Plants ▿ †

By placing the anode of a sediment microbial fuel cell (SMFC) in the rhizosphere of a rice plant, root-excreted rhizodeposits can be microbially oxidized with concomitant current generation. Here, various molecular techniques were used to characterize the composition of bacterial and archaeal communities on such anodes, as influenced by electrical circuitry, sediment matrix, and the presence of plants. Closed-circuit anodes in potting soil were enriched with Desulfobulbus-like species, members of the family Geobacteraceae, and as yet uncultured representatives of the domain Archaea

Minimizing losses in bio-electrochemical systems: the road to applications

Bio-electrochemical systems (BESs) enable microbial catalysis of electrochemical reactions. Plain electrical power production combined with wastewater treatment by microbial fuel cells (MFCs) has been the primary application purpose for BESs. However, large-scale power production and a high chemical oxygen demand conversion rates must be achieved at a benchmark cost to make MFCs economical competitive in this context. Recently, a number of valuable oxidation or reduction reactions demonstrating the versatility of BESs have been described. Indeed, BESs can produce hydrogen, bring about denitrification, or reductive dehalogenation. Moreover, BESs also appear to be promising in the field of online biosensors. To effectively apply BESs in practice, both biological and electrochemical losses need to be further minimized. At present, the costs of reactor materials have to be decreased, and the volumetric biocatalyst activity in the systems has to be increased substantially. Furthermore, both the ohmic cell resistance and the pH gradients need to be minimized. In this review, these losses and constraints are discussed from an electrochemical viewpoint. Finally, an overview of potential applications and innovative research lines is given for BESs

Microbial fuel cells generating electricity from rhizodeposits of rice plants

Living plants transport substantial amounts of organic material into the soil. This process, called rhizodeposition, provides the substrate for the rhizospheric microbial community. In this study, a laboratory-scale sediment microbial fuel cell, of which the anode is positioned in the rhizosphere of the rice plants, is used to microbially oxidize the plant-derived organics. An electrical current was generated through the in situ oxidation of rhizodeposits from living rice plants. The electrical power output of a sediment microbial fuel cell was found to be a factor 7 higher in the presence of actively growing plants. This process offers the potential of light-driven power generation from living plants in a nondestructive way. Sustainable power productions up to 330 W ha could be attributed to the oxidation of the plant-derived compounds