Zaixing Huang

Low carbon renewable natural gas production from coalbeds and implications for carbon capture and storage

Isotopic studies have shown that many of the world’s coalbed natural gas plays are secondary biogenic in origin, suggesting a potential for gas regeneration through enhanced microbial activities. The generation of biogas through biostimulation and bioaugmentation is limited to the bioavailability of coal-derived compounds and is considered carbon positive. Here we show that plant-derived carbohydrates can be used as alternative substrates for gas generation by the indigenous coal seam microorganisms. The results suggest that coalbeds can act as natural geobioreactors to produce low carbon renewable natural gas, which can be considered carbon neutral, or perhaps even carbon negative depending on the amount of carbon sequestered within the coal. In addition, coal bioavailability is no longer a limiting factor. This approach has the potential of bridging the gap between fossil fuels and renewable energy by utilizing existing coalbed natural gas infrastructure to produce low carbon renewable natural gas and reducing global warming.Coalbeds produce natural gas, which has been observed to be enhanced by in situ microbes. Here, the authors add plant-derived carbohydrates (monosaccharides) to coal seams to be converted by indigenous microbes into natural gas, thus demonstrating a potential low carbon renewable natural gas resource.

Speciation, Fate and Transport, and Ecological Risks of Cu, Pb, and Zn in Tailings from Huogeqi Copper Mine, Inner Mongolia, China

Tailings collected from the tailing reservoir at Huogeqi Copper Mine, located in Inner Mongolia, China, were used in a leachate study to evaluate the acid potential, neutralization potential, and possibility for producing acid mine drainage (AMD) from the site. The speciation of Cu, Pb, and Zn contained in the tailings was also determined during the leachate study to further access the potential migration abilities of these metals. The results showed that the tailings did not produce significant AMD as the pH of the leachate ranged from 7 to 9 and decreased with time. The Cu, Pb, and Zn concentrations were high, ranging from 439.1 to 4527 mg/kg in the tailings and from 0.162 to 7.964 mg/L in the leachate, respectively. Concentrations of metals in the leachate and tailings were positively correlated. Over 60% of the Cu in the tailing samples existed in an oxidizable form. Most of the Pb also existed in its oxidized form, as did the silicate and Zn. Metals usually have higher mobility in their exchangeable and oxidizable forms and as such represent a higher potential risk to the environment. Results of risk assessment code also revealed that metals in tailings exerted medium to high risks to the environment.

Coal-derived compounds and their potential impact on groundwater quality during coalbed methane production

Coalbed methane (CBM) is an important unconventional energy source and accounts for a substantial portion of the overall natural gas production in the USA. The extraction of CBM generates significant amounts of produced water, where the withdrawal of groundwater may disturb the subsurface environment and aquifers. The release of toxic recalcitrant compounds from the coal seam is of great concern for those who use groundwater for irrigation and potable water sources. Experiments were conducted that determined a small fraction of coal carbon can be extracted and solubilized in water during the CBM formation and production. These soluble components included long-chain alkanes, aromatic hydrocarbons, and humic compounds. Biometer flask assays demonstrated that these compounds are bioamenable and can be potentially degraded by microorganisms to produce methane and carbon dioxide, where these biodegradation processes may further impact groundwater quality in the coal seam.