Injection of hydrogen peroxide into a coal seam for the in-situ production of organic acids and biogenic methane: A case study in Tempoku Coal Field, Japan

Although hydrogen peroxide (H 2 O 2 ) has been proposed as an effective agent to produce biogenic coalbed methane (CBM) through the generation of bioavailable organic acids from coal, in situ validation of this approach has yet to be performed. In this study, 1 m 3 of 0.3 wt% H 2 O 2 solution was injected into a seam of low-rank coal (lignite) in the Tempoku Coal Field, Japan, to confirm the in situ formation of organic acids and their transformation to biogenic methane. Based on the δ 13 C CO2 , δ 13 C CH4 , and δD CH4 values, the background methane in this coal field is biogenic and derived from the hydrogenotrophic pathway. The injected H 2 O 2 immediately reacted with the lignite seam, and the concentrations of organic acids in the well waters increased to maximum values of 27.2 mg/L (formic acid), 6.8 mg/L (oxalic acid), 5.7 mg/L (acetic acid), 1.3 mg/L (malonic acid), and 1.2 mg/L (succinic acid), within 4 d of injection. These concentrations decreased more rapidly than the rate of replacement by pristine groundwater, indicating microbial consumption. The concurrent decrease in δD CH4 values indicates a temporal change in the methanogenic pathway from hydrogenotrophic to acetoclastic during consumption of the produced acetic acid, because acetoclastic methanogenesis typically generates CH 4 with relatively low δD CH4 values.