In bioelectrochemical systems (BESs), the anode potential can be set to a fixed voltage using a potentiostat, but there is no accepted method for defining an optimal potential. Microbes can theoretically gain more energy by reducing a terminal electron acceptor with a more positive potential, for example oxygen compared to nitrate. Therefore, more positive anode potentials should allow microbes to gain more energy per electron transferred than a lower potential, but this can only occur if the microbe has metabolic pathways capable of capturing the available energy. Our review of the literature shows that there is a general trend of improved performance using more positive potentials, but there are several notable cases where biofilm growth and current generation improved or only occurred at more negative potentials. This suggests that even with diverse microbial communities, it is primarily the potential of the terminal respiratory proteins used by certain exoelectrogenic bacteria, and to a lesser extent the anode potential, that determines the optimal growth conditions in the reactor. Our analysis suggests that additional bioelectrochemical investigations of both pure and mixed cultures, over a wide range of potentials, are needed to better understand how to set and evaluate optimal anode potentials for improving BES performance.

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Electricity can be directly generated by bacteria in microbial fuel cells (MFCs) from many different biodegradable substrates. When cellulose is used as the substrate, electricity generation requires a microbial community with both cellulolytic and exoelectrogenic activities. Cellulose degradation with electricity production by a pure culture has not been previously demonstrated without addition of an exogenous mediator. Using a specially designed U-tube MFC, we enriched a consortium of exoelectrogenic bacteria capable of using cellulose as the sole electron donor. After 19 dilution-to-extinction serial transfers of the consortium, 16S rRNA gene-based community analysis using denaturing gradient gel electrophoresis and band sequencing revealed that the dominant bacterium was Enterobacter cloacae. An isolate designated E. cloacae FR from the enrichment was found to be 100% identical to E. cloacae ATCC 13047 T based on a partial 16S rRNA sequence. In polarization tests using the U-tube MFC and cellulose as a substrate, strain FR produced 4.9 ؎ 0.01 mW/m 2 , compared to 5.4 ؎ 0.3 mW/m 2 for strain ATCC 13047 T . These results demonstrate for the first time that it is possible to generate electricity from cellulose using a single bacterial strain without exogenous mediators.

A hydrogen utilizing exoelectrogenic bacterium (Geobacter sulfurreducens) was compared to both a nonhydrogen oxidizer (Geobacter metallireducens) and a mixed consortium in order to compare the hydrogen production rates and hydrogen recoveries of pure and mixed cultures in microbial electrolysis cells (MECs). At an applied voltage of 0.7 V, both G. sulfurreducens and the mixed culture generated similar current densities (ca. 160 A/m 3 ), resulting in hydrogen production rates of ca. 1.9 m 3 H 2 /m 3 /day, whereas G. metallireducens exhibited lower current densities and production rates of 110 ؎ 7 A/m 3 and 1.3 ؎ 0.1 m 3 H 2 /m 3 /day, respectively. Before methane was detected in the mixed-culture MEC, the mixed consortium achieved the highest overall energy recovery (relative to both electricity and substrate energy inputs) of 82% ؎ 8% compared to G. sulfurreducens (77% ؎ 2%) and G. metallireducens (78% ؎ 5%), due to the higher coulombic efficiency of the mixed consortium. At an applied voltage of 0.4 V, methane production increased in the mixed-culture MEC and, as a result, the hydrogen recovery decreased and the overall energy recovery dropped to 38% ؎ 16% compared to 80% ؎ 5% for G. sulfurreducens and 76% ؎ 0% for G. metallireducens. Internal hydrogen recycling was confirmed since the mixed culture generated a stable current density of 31 ؎ 0 A/m 3 when fed hydrogen gas, whereas G. sulfurreducens exhibited a steady decrease in current production. Community analysis suggested that G. sulfurreducens was predominant in the mixed-culture MEC (72% of clones) despite its relative absence in the mixed-culture inoculum obtained from a microbial fuel cell reactor (2% of clones). These results demonstrate that Geobacter species are capable of obtaining similar hydrogen production rates and energy recoveries as mixed cultures in an MEC and that high coulombic efficiencies in mixed culture MECs can be attributed in part to the recycling of hydrogen into current.Electrohydrogenesis is an efficient method for generating hydrogen gas from organic matter in reactors known as microbial electrolysis cells (MECs) (17,18,26). MECs differ from air-cathode microbial fuel cells (MFCs) in that the cathode remains anaerobic, and voltage is added in order to generate hydrogen at the cathode. Under the biological conditions in MECs, hydrogen evolution is not a thermodynamically favorable reaction. However, combining the hydrogen formation reaction potential of Ϫ0.41 V at the cathode (E CAT ) with the anode potential (E AN ) typically obtained in MFCs with an E AN of Ϫ0.30 V (1 g of acetate/liter) results in a minimum required voltage of only 0.14 V. Applied voltages (E AP ) of 0.2 V (0.45 kWh/m 3 H 2 ) or larger are needed in practice to produce measurable quantities of hydrogen, but this input is substantially less than the average of 2.3 V (5.1 kWh/m 3 H 2 ) required for water electrolysis (13).Recent improvements in designs and materials have substantially improved hydrogen yields, production rates, and energy recoveries (3,18,(27)(2...

BACKGROUND: UV-curable coatings are promising candidates for environmentally friendly marine foulingrelease coatings. Cationic UV-curable epoxy-siloxane release coatings show good release performance but suffer from poor coating mechanical properties. A difunctional oxetane monomer, DOX, was co-photopolymerized with an epoxy-siloxane oligomer at loading levels from 10 to 40 wt% to obtain toughened fouling-release coatings. RESULTS:The DOX-toughened coatings showed enhanced cationic photopolymerization activity, solvent resistance and modulus. DOX-toughened coatings (10 and 20 wt%) exhibited higher impact resistance. The DOX-toughened coatings showed no leachate toxicity and the coatings were hydrophobic and non-toxic to biofilm growth when analyzed with marine bacteria and algae. In general, 10 and 20 wt% DOX-toughened coatings exhibited better marine bacteria and algae fouling-release performance among the DOX-toughened coatings. Pseudo-barnacle shear release stress for the DOX-toughened coatings increased with increasing DOX content. Live barnacle reattachment assay showed that 10 and 20 wt% DOX-toughened coatings had comparable barnacle removal stress to commercial silicone reference coatings. CONCLUSIONS: DOX-toughened (10 and 20 wt%) UV-curable epoxy-siloxane coatings exhibited enhanced mechanical properties and better overall marine fouling-release performance among the toughened UV-curable release coatings studied.