Highly conductive textile electrodes for microbial fuel cells

High performance microbial fuel cells (MFCs) require effective mech. and elec. interaction between electrode surfaces and attached microbial biofilms. Three-dimensional porous electrodes with large-surface area offer an attractive means of achieving this objective. Here we report a novel porous electrode in which a conductive carbon nanotube (CNT) coating is applied to a com. textile. The CNT-textile composite was evaluated as an anode in a MFC. The macroporous structure of textile allowed growth of biofilm inside the anode, increasing the active surface area for electron transfer. The CNT-textile composite outperformed a normal carbon cloth electrode, and appears promising for MFC applications

Application of high-density oligonucleotide microarrays to the study of Crenarchaeota community structure and dynamics in an aerated activated sludge wastewater treatment plant

Despite the fact that biological wastewater treatment is practiced widely to remove organics, nutrients, toxics, and pathogens from polluted water, little is known about the ecology of microbial communities in bioreactors. In particular, the prevalence, diversity, functional inlpo11ance, and population dynamics of nonthermophilic Crenarchaeota in aerated activated sludge wastewater treatment systems remain virtually unknown. The aim of this study was to elucidate the diversity and dynamics of nonthermophilic Crenarchaeota in aerated activated sludge systems and to link these dynamics to operational or environmental parameters. To this end, we used high-density 16S rDNA phylogenetic microarrays containing 500,000 probes to monitor bacterial and archaeal population dynamics in monthly samples from the aeration basin of a local municipal activated sludge wastewater treatnlent plant (WWTP) for a period of one year. Operational data were collected concurrently. Our results revealed a highly diverse prokaryotic community in the WWTP, with an average of 1606 bacterial and archaeal phylotypes detected at each sampling point. Eleven distinct and highly dynamic nonthermophilic Crenarchaeota phylotypes from groups l.la and l.lb were detected in 11 of the 12 months examined. Within each Crenarchaeal phylotype, 16S rRNA gene copy number varied by nearly an order of magnitude dUling the study period. Seven main covarying archaeal response groups in this time period were identified based on hierarchical clustering. The majority of the identified nonthermophilic Crenarchaeota phylotypes fell within the same response group, indicating significant covariation in population size among these phylotypes during the year of sampling. Our results suggest that nonthermophilic Crenarchaeota may play a previously unrecognized role in aerated activated sludge bioreactors. To our knowledge, this is the first application of high-density phylogenetic DNA microarray methods to the analysis of microbial community structure in activated sludge bioreactors

Microarray-Based Analysis of Microbial Community Composition and Dynamics in Uranium Bioremediation

A field-scale system is being used for evaluating in situ biological reduction and immobilization of U(VI) in the DOE ERSP Field Research Center, Oak Ridge, TN. Above-ground treatment of groundwater, including nitrate removal pre-conditions the groundwater for subsurface uranium immobilization. Treated water was then injected into the subsurface with ethanol to stimulate microbial reduction of U(VI) to insoluble U(IV). The microbial community dynamics from one of the 4 frequently sampled monitoring wells (FW 102-3) was intensively analyzed with a functional gene array containing >24,000 probes and covering 10,000 genes in 150 gene categories. The results indicated that during the uranium reduction period, both FeRB and SRB populations reached their highest levels at Day 212, followed by a gradual decrease over 500 days. The uranium concentrations in the groundwater were significantly correlated with the total abundance of c-type cytochrome genes (r=0.73, p<0.05) from Geobacter-type FeRB and Desulfovibrio-type SRB, and with the total abundance of dsrAB (dissimilatory sulfite reductase) genes (r=0.88, p<0.05). The Mantel test of microarray and chemical data also indicated that there was significant correlation between the differences of uranium concentrations and those of total c-cytochrome gene abundance (r=0.75, p <0.001) or dsrAB gene abundance (r=0.72, p<0.01). The changes of more than dozen of individual c-type cytochrome genes from Geobacter sulfurreducens and Desulfovibrio desulfuricans showed significant correlations to the changes of uranium concentrations among different time points. Also the changes of more than 10 dsrAB-containing populations, including both cultured (e.g. D. desulfuricans, D. termitidis, Desulfotomaculum kuznetsovii,) and non-cultured SRB were significantly related to the changes in uranium concentrations, indicating their importance in uranium reduction. Interestingly, as expected, the changes of several dsrAB-containing sulfate-reducing populations previously recovered from this site showed significant correlations to the differences of uranium concentrations

Changes in microbial community structure during biostimulation for uranium reduction at different levels of resolution

Fonner radionuclide waste ponds at the ERSP-Field Research Center in Oak Ridge, TN pose several challenges for uranium bioremediation. The site is marked by acidic conditions, high concentrations of nitrate, chlorinated solvents, and heavy metals. A series of re-circulating wells serve to create a subsurface bioreactor to stimulate microbial growth for in situ U(VI) immobilization. Well FW-104 is the injection well for the electron donor (i.e., ethanol); well FW-026 is the extraction well for the recirculation loop; well FW-101 and FW-102 are the inner zones of biostimulation; and FW-024 and FW-103 are upstream and downstream wells, respectively, which are the outer protective zones. Microbial community composition and structure of groundwater from the wells were analyzed via clonal libraries of partial SSU rRNA gene sequences, a phylogenetic chip array (Bacteria and Archaea), and a functional gene chip array over time. LIBSHUFF analysis for the clonal libraries of the re-circulating wells showed that over each phase of manipulation for uranium immobilzation, the bacterial communities of the inner zones of biostimulation were more similar to each other than those of the outer protective zones. The outer protective zones were more similar to the injection well. LIBSHUFF analyses for the clonal libraries from FW-104 (injection), FW-101 and FW-I02 (biostimulation) showed that bacterial communities of the three wells were initially similar but developed changes through time. FW-101 and FW-I02 bacterial communities developed changes in parallel, while those of FW-I04 showed gradual changes. Diversity indices showed that bacterial diversity tended to increase during the initial phase of uranium bioreduction and decreased toward the end of uranium bioreduction (i.e., low U(VI) levels). As uranium levels declined, increasing Desulfovibrio-and Geobacter-like sequences were detected from the clonal libraries; moreover, Desulfovibrio-like sequences predominated over time. The results were further confinned via RT-PCR, and RT-PCR results correlated with OTU and PhyloChip distributions for Desulfovibrio. PhyloChip analyses also demonstrated the presence and dynamics of both acetoclastic and hydrogenotrophic methanogens. The results indicated that the microbial community composition and structure changed upon stimulating for uranium bioreduction conditions, and that sequences representative of the sulfate-reducers Desulfovibrio spp. and metal-reducers Geobacter spp. were detected in wells that displayed a decline in U(VI). In addition, when electron donor was added to the subsurface, community diversity increased with a subsequent decline in U(VI) levels. However, when levels of potential electron acceptors decreased, community diversity also decreased. The microbial community dynamics from one of the 4 frequently sampled monitoring wells (FW 102-3) was intensively analyzed with a functional gene array containing 27,000 probes covering 10,000 genes and >100 gene categories. The microarray data indicated that during the uranium reduction period, both FeRB and SRB populations reached their highest levels at Day 212, followed by a gradual decrease over 500 days. The uranium concentrations in the groundwater were significantly correlated with total abundance of c-type cytochrome genes (r=0.73, p<0.05) from Geobacter-type FeRB and Desulfovibrio-type SRB, and with the total abundance of dsrAB (dissimilatory sulfite reductase) genes (r=0.88, p<0.05). Mantel test of microarray data and chemical data also indicated that there was significant correlation between the differences of uranium concentrations and those of total c-cytochrome gene abundance (r=0.75, p <0.001) or dsrAB gene abundance (r=0.72, p<0.01). The changes of more than a dozen individual c-type cytochrome genes from Geobacter sulfurreducens and Desulfovibrio desulfuricans showed significant correlations to the changes of uranium concentrations among different time points. Also the cha