Biological CO2 conversion to acetate in subsurface coal-sand formation using a high-pressure reactor system

Abstract

Geological CO2 sequestration in unmineable subsurface oil/gas fields and coal formations has been proposed as a means of reducing anthropogenic greenhouse gasses in the atmosphere. However, the feasibility of injecting CO2 into subsurface depends upon a variety of geological and economic conditions, and the ecological consequences are largely unpredictable. In this study, we developed a new flow-through-type reactor system to examine potential geophysical, geochemical and microbiological impacts associated with CO2 injection by simulating in-situ pressure (0–100 MPa) and temperature (0–70°C) conditions. Using the reactor system, anaerobic artificial fluid and CO2 (flow rate: 0.002 and 0.00001 ml/min, respectively) were continuously supplemented into a column comprised of bituminous coal and sand under a pore pressure of 40 MPa (confined pressure: 41 MPa) at 40°C for 56 days. 16S rRNA gene analysis of the bacterial components showed distinct spatial separation of the predominant taxa in the coal and sand over the course of the experiment. Cultivation experiments using sub-sampled fluids revealed that some microbes survived, or were metabolically active, under CO2-rich conditions. However, no methanogens were activated during the experiment, even though hydrogenotrophic and methylotrophic methanogens were obtained from conventional batch-type cultivation at 20°C. During the reactor experiment, the acetate and methanol concentration in the fluids increased while the δ13Cacetate, H2 and CO2 concentrations decreased, indicating the occurrence of homo-acetogenesis. 16S rRNA genes of homo-acetogenic spore-forming bacteria related to the genus Sporomusa were consistently detected from the sandstone after the reactor experiment. Our results suggest that the injection of CO2 into a natural coal-sand formation preferentially stimulates homo-acetogenesis rather than methanogenesis, and that this process is accompanied by biogenic CO2 conversion to acetate.

Microbial Communities Involved in Methane Production from Coal Treated by Potassium Permanganate

“…Although methanogens were detected after cultivation, no methane was produced or methane yield was below the detection limit. The similar phenomenon was also reported by Ohtomo et al [25], where methanogens were obtained from batch-type cultivation, no methanogens, however, were activated during experiment in the reactor system. For bacterial communities, Proteobacteria was observed to be the predominant phylum with 51.48% of the sequence reads, which consistent with some previous findings related to methanogenic communities for coal biodegradation [22] (Figure 2B).…”

Data report: permeability of ~1.9 km-deep coal-bearing formation samples off the Shimokita Peninsula, Japan

“…Each specimen was placed in impermeable, flexible heat-shrink tubing and then loaded into a pressure vessel. The pressure vessel is connected to three pumps ( Figure F1; Ohtomo et al, 2013). One pump controlled the pressure at the top of the specimen, one pump controlled the pressure at the bottom of the specimen, and one pump controlled the isostatic confining pressure around the specimen.…”

Microbial Growth under Supercritical CO 2

“…Biogeochemical models also suggest that diverse forms of microbial metabolism are thermodynamically favorable under reservoir conditions post-CO 2 injection (3,18), where an aqueous phase in direct contact with scCO 2 may have dissolved CO 2 concentrations exceeding 2.5 M (3). Furthermore, high-pressure incubations to simulate reservoir conditions with elevated (but not supercritical) CO 2 have demonstrated activity of acetoclastic methanogens (under 49.3-atm pressure with 86.4 mM CO 2 ) (19) and homoacetogens (under 395-atm total pressure with 126 mM CO 2 ) (20). Recently, field studies at the Ketzin CO 2 sequestration site in Germany and the Otway Basin site in Australia provided evidence that changes in microbial community composition occur following CO 2 injection, suggesting that a combination of processes, including differential survival and possibly growth, occurs in the subsurface after exposure to near-and supercritical levels of CO 2 (21,22).…”