Stimulation of biogenic methane generation from lignite through supplying an external substrate

Biogenic methane generation from lignite is investigated using biochemical methane potential (BMP) tests. It is found that 8.4% w/v of lignite as a sole substrate does not produce a significant amount of methane. It is considered that the bioavailability of lignite is low and the inhibition of methane generation occurs when there is a high concentration of lignite. In order to initiate and stimulate biogenic methane generation in high concentrations of lignite, an external substrate such as rice straw, which is easily obtainable and a cheap material in East and Southeast Asia, is added to the lignite. For a low rice straw addition to lignite (6.25% w/w), the inhibition of methane generation is found, but as the amount of rice straw increases, methane is produced from the lignite. At the end of the incubation period, the calorific value of the incubated lignite decreases as the amount of rice straw increases, which agrees with the trend of increasing methane generation as the amount of rice straw increases. •High lignite concentration of more than 0.6% w/v inhibited biogenic methane generation.•Addition of rice straw to lignite induced biogenic methane generation from the lignite.•More than 33.3% of rice straw to lignite ratio(w/w), and 2,000 mg/L COD concentration of medium was required.•Biodegradability of lignite was evaluated through BMP tests and calorific value measurements.•The external substrate is beneficial at the initial stage of in situ coal bed biogenic methane production.