Proton exchange membranes (PEMs) are one of the most important components in microbial fuel cells (MFCs), since PEMs physically separate the anode and cathode compartments while allowing protons to transport to the cathode in order to sustain an electrical current. The Nafion 117 membrane used in this study is generally regarded as having excellent proton conductivity, though many problems for its application in MFCs remain. We investigated problems associated with Nafion including: oxygen leakage from cathode to anode, substrate loss, cation transport and accumulation rather than protons, and biofouling. It was found that Nafion was quite permeable to oxygen. The oxygen mass transfer coefficient (K O) and the oxygen diffusion coefficient (D O) for Nafion was estimated as K O = 2.80 × 10−4 cm/s and D O = 5.35 × 10−6 cm2/s, respectively when a 50 mM phosphate buffer was used as the catholyte. The MFC with distilled water instead of phosphate buffer showed similar values (K O = 2.77 × 10−4 cm/s, D O = 5.27 × 10−6 cm2/s), indicating that the catholyte shows no significant effects on oxygen diffusion. Nafion was also found to be permeable to acetate, but this seems to be negligible. Cations in the anolyte, presenting in high concentration due to their supply to optimize the anodic bacterial growth condition, were rapidly transported through the Nafion membrane. They occupied negatively charged sulfonate groups of Nafion, which consequently reduced contact chance of protons due to their competition. According to energy dispersive X-ray (EDX) analysis, the relative atomic percentage of carbon (30.9%) and fluoride (59.7%), the basic backbone materials of Nafion, in used Nafion was lowered, compared to that obtained with new Nafion (C = 32.8%, F = 60.1%); whereas sodium and iron, which do not exist in new Nafion, increased by up to 1.16% and 0.24% of the atoms, respectively. This indicates that these two cation species already occupied an important fraction of the negatively charged sulfonate groups, which can cause the hindrance of proton migration. Nafion operated over a period of 50 days was contaminated with biofilm causing adverse effects on mass transport through the membrane. Bacteria growing on Nafion were much more heterogeneous compared to those observed on the anode carbon felt surface. The densest biofilm was observed in the outermost few millimeters of anode carbon felt, and the biofilm density gradually decreased with inward depth.

For biological hydrogen production by fermentation to be a useful method of hydrogen generation, molar yields of hydrogen must be increased. While heat treatment of a soil inoculum increases hydrogen yields by preventing loss of hydrogen to methanogenesis, hydrogen is still lost to acetic acid generation from hydrogen and CO2. To reduce hydrogen losses via acetogenesis, CO2 concentrations in the headspace were substantially reduced during hydrogen production using a chemical scavenger (KOH). CO2 in the headspace was decreased from 24.5% (control) to a maximum of 5.2% during the highest gas production phase, resulting in a hydrogen partial pressure of 87.4%. This reduction in CO2 increased the hydrogen yield by 43% (from 1.4 to 2.0 mol of H2/mol of glucose). The soluble byproducts in all tests consisted primarily of acetate and ethanol. Higher concentrations of ethanol (10.9 mM) remained in solution from bottles with CO2 removal than in the control (1.2 mM), likely as a result of hydrogen inhibition of biological ethanol conversion to acetic acid. These results show that hydrogen production can be increased by removing CO2 in the reactor vessel, likely as a result of suppression of acetogenesis.

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Silvimonas terrae gen. nov., sp. nov., a novel chitindegrading facultative anaerobe belonging to the 'Betaproteobacteria' During the course of a study on the culturable aerobic and facultatively anaerobic bacterial community of forest soil and rice fields near Daejeon, South Korea, a large number of novel bacterial strains were isolated. One of these isolates, strain KM-45 T , was identified as belonging to the family Neisseriaceae in the 'Betaproteobacteria' lineage and was the subject of further taxonomic investigation. We report on its taxonomic position, including genotypic, chemotaxonomic and classical phenotypic characteristics, in order to establish its phylogenetic affiliation, and propose that strain KM-45 T should be placed in a novel genus and species, for which the name Silvimonas terrae gen. nov., sp. nov. is proposed. Strain KM-45T was isolated from forest soil collected near the Korea Advanced Institute of Science and Technology (KAIST) in Daejeon, South Korea. The soil was homogenized by using an Ace Homogenizer (Nihonseiki Kaisha Ltd). The suspension was spread on R2A agar plates (Difco) after being diluted serially with 50 mM phosphate buffer (pH 7?0). The plates were incubated at 30 u C for 2 weeks. Single colonies on the plates were purified by transferring them onto new plates and incubating again under the same conditions. The isolate was cultured routinely on R2A agar at 30 uC and maintained as a glycerol suspension (20 %, w/v) at 270 u C.Extraction of genomic DNA was performed by using a commercial genomic DNA extraction kit (Core Biosystem), and PCR-mediated amplification of the 16S rRNA gene and sequencing of the purified PCR product were carried out according to the methods given by Kim et al. (2005). The full-length 16S rRNA gene sequences were compiled by using SeqMan software (DNASTAR). 16S rRNA gene sequences of related taxa were obtained from GenBank. Multiple alignments were performed by using the CLUSTAL_X program (Thompson et al., 1997). Gaps were edited in the BIOEDIT program (Hall, 1999). Evolutionary distances were calculated by using the Kimura twoparameter model (Kimura, 1983). Phylogenetic trees were constructed by using the neighbour-joining (Saitou & Nei, 1987) and maximum-parsimony (Fitch, 1971) methods, using the MEGA3 program (Kumar et al., 2004) with bootstrap values based on 1000 replications (Felsenstein, 1985).A nearly complete 16S rRNA gene sequence of strain T was obtained (1491 bp). Preliminary comparison against the 16S rRNA gene sequences in GenBank indicated that strain T belonged to the order 'Neisseriales' of the 'Betaproteobacteria'. On the basis of 16S rRNA geneThe GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain T is AB194302.