Coal methanogenesis: energy production and water management
Planning for the future energy requirements requires innovative, multi-faceted, short-term and long-term approaches. Clearly, the long-term goal is to move away from fossil fuels and carbon-based energy, however mid-term or short-term alternatives are required to bridge current energy needs and environmentally conscious approaches to available fuels. One solution already in use is coalbed natural gas production, which is comprised of at least 90% methane (CH4).
CH4 is recognized as the cleanest fossil fuel since for the same energy output as other C-based fuels, such as oil and coal, it produces less carbon dioxide (CO2), nitrous oxides, sulfur oxides, particulates, and mercury.
Coalbed methane (CBM) capture involves collecting the gas already present in mature coals; release of the methane into wells is accomplished by depressurizing the formations by pumping out water. CBM sites are abandoned once all the already present natural gas is collected, but much of the infrastructure remains in place and can be resources for enhanced production of biogenic CBM by microorganisms. The US Energy Information Administration reported that the proven reserve of methane in coalbeds worldwide is over 6,000 tillion cubic feet (tcf). However, the amount that is viable to produce in terms of economic and environmental sustainability remains unknown, requiring advances in research and technology
Our group seeks to gain an applied understanding of CBM processes in two fronts: (i) solve bottlenecks microbial activity for more methane release, (ii) evaluate the effects on water quality and reuse from CBM technologies.
I. Microbial CBM:
Microbes from the domain Archaea, known as methanogens, naturally degrade C-based compounds to produce CH4; this is accomplished in cooperation with Bacteria. Production of methane from coal involves syntrophic relationships between multiple groups of microorganisms that have complementary metabolisms, starting with those able to metabolize complex molecules to the microorganisms that produce the narrow range of substrates that can be used by methanogens. Since many microorganisms can carry out these processes, the exact microorganisms involved vary based on the site, although some similarities in the microbial communities are apparent in all coal studies to date. Nevertheless, we propose that what is more important for biogenic CBM are the primary functions of the microbial community required for the process rather than taxonomic composition.
In this research, we hypothesize that the metabolism of the indigenous microbial community, elucidated through its genetic material, can provide a quantitative approach to optimize biostimulation and bioaugmentation processes for CBM. Two common strategies for enhancing bioremediation include 1) addition of nutrients through a process termed biostimulation and 2) addition of microorganisms, and possibly also nutrients, in a process termed bioaugmentation. Our research approach proposes that the affectivity of these two well-known bioremediation techniques is dependent on identifying, and then managing, the metabolic network and functional bottlenecks exerted over the native microbiota. State of the arte techniques including Stable Isotope Probing (SIP) and “omics” approaches are included in this work.
II. Water quality and toxicity from hydrocarbon-based technologies
Development of enhanced biogenic CBM technologies should consider the unintended consequences to the environment, including water use and water quality. Water is the needed vehicle to modify conditions or seed formations, and to displace methane out for harvesting. Much can be learned about what to expect for biogenic CBM contamination to the ground and surface water by investigating the legacy contamination from other hydrocarbon technologies. These include fracking of shale and coalbeds to increase capture of natural gas, petroleum mining, and tar runoff. For example, the US Environmental Protection Agency (EPA) and the USGS have found that a major source of contamination to the water is due to the fracking fluid, which introduces potentially carcinogenic compounds into the water and generally contains acidic chemicals that decrease the pH and can increase the mobility of additional human and ecotoxic compounds.
In this research we propose to evaluate whether the major contamination sources from biogenic CBM are originated from (i) the solubilized coal and transformed organic molecules within several chemical classes, and (ii) the nutrients added for biostimulation. We seek to develop biogeochemical and ecotoxicity models to test the potential hydrocarbon toxicity to the water from biogenic CBM.