Biomethanation of Syngas Using Anaerobic Sludge: Shift in the Catabolic Routes with the CO Partial Pressure Increase.

Syngas generated by thermal gasification of biomass or coal can be steam reformed and purified into methane, which could be used locally for energy needs, or re-injected in the natural gas grid. As an alternative to chemical catalysis, the main components of the syngas (CO, CO2, and H2) can be used as substrates by a wide range of microorganisms, to be converted into gas biofuels, including methane. This study evaluates the carboxydotrophic (CO-consuming) methanogenic potential present in an anaerobic sludge from an upflow anaerobic sludge bed (UASB) reactor treating waste water, and elucidates the CO conversion routes to methane at 35 ± 3°C.

Specific inhibitors for identifying pathways for methane production from carbon monoxide by a nonadapted anaerobic mixed culture.

Specific inhibitors such as 2-bromoethanesulfonate (BES) and vancomycin were employed in activity batch tests to decipher metabolic pathways that are preferentially used by a mixed anaerobic consortium (sludge from an anaerobic digester) to transform carbon monoxide (CO) into methane (CH4). We first evaluated the inhibitory effect of both BES and vancomycin on the microbial community, as well as the efficiency and stability of vancomycin at 35 °C, over time. The activity tests with CO2-H2, CO, glucose, acetate, formate, propionate, butyrate, methanol, and ethanol showed that vancomycin does not inhibit some Gram-negative bacteria, and 50 mmol/L BES effectively blocks CH4 production in the sludge.

Growth profile of Carboxydothermus hydrogenoformans on pyruvate.

Carboxydothermus hydrogenoformans is a thermophilic anaerobic strain most widely known for its ability to produce hydrogen (H2) when grown on carbon monoxide (CO). Although relatively well studied, growth characterization on pyruvate has never been assessed. The present work fully characterizes growth of the bacterium on pyruvate as a sole carbon source.

Kinetics of CO conversion into H2 by Carboxydothermus hydrogenoformans.

The objective of this study was to improve the biological water-gas shift reaction for producing hydrogen (H(2)) by conversion of carbon monoxide (CO) using an anaerobic thermophilic pure strain, Carboxydothermus hydrogenoformans. Specific hydrogen production rates and yields were investigated at initial biomass densities varying from 5 to 20 mg volatile suspended solid (VSS) L(-1). Results showed that the gas-liquid mass transfer limits the CO conversion rate at high biomass concentrations.

Potential of wastewater-treating anaerobic granules for biomethanation of synthesis gas.

Gasification of biomass produces a mixture of gas (mainly carbon monoxide (CO), carbon dioxide (CO(2)), and hydrogen (H(2))) called synthesis gas, or syngas, by thermal degradation without combustion. Syngas can be used for heat or electricity production by thermochemical processes. This project aims at developing an alternative way to bioupgrade syngas into biogas (mainly methane), via anaerobic fermentation.

Electrolytic methanogenic-methanotrophic coupling for tetrachloroethylene bioremediation: proof of concept.

Coupling of methanogenic and methanotrophic catabolisms was performed in a single-stage technology equipped with a water electrolysis cell placed in the effluent recirculation loop. The electrolysis-generated hydrogen served as an electron donor for both bicarbonate reduction into CH4 and reductive dechlorination, while the O2 and CH4, supported the cometabolic oxidation of chlorinated intermediates left over by the tetrachloroethylene (PCE) transformation. The electrolytical methanogenic/methanotrophic coupled (eMaMoC) process was tested in a laboratory-scale setup at PCE loads ranging from 5 to 50 micromol/L(rx) x d (inlet concentrations from 4 to 11 mg/L), and at various hydraulic residence times (HRT).