Influencing mechanism of Fe2+ on biomethane production from coal

Abstract

The conversion of coal to biomethane is gaining considerable attention and can play a significant role in the field of energy research. To study the underlying influencing mechanism of adding exogenous Fe2+ on the process of the conversion of coal to biomethane, the biomethane production experiments were conducted using lignite and bituminous coal A as the substrate, and supplemented by different concentrations of ferrous ions. It is found that the optimum concentration of Fe2+ in the process of producing biomethane from coal is 10 mg/L. At this time, the cumulative methane production of lignite increased from 192 mL to 246 mL, and that of bituminous coal A increased from 165 mL to 197 mL, which increased by 13.5% and 10.8%. The added Fe2+ increased the content of iron in the humic acid state, which was easily absorbed and effectively utilized by microorganisms. This increase promoted the synthesis of hydrogenase and advanced the activity. Iron in the humic acid state also participated in the enzymatic reaction and promoted the activity of sulfate reducing bacteria and methanogens. Fe2+ in the free state formed FeS precipitates with the sulfur ion, which reduced the toxicity of soluble sulfides to bacteria. In both treated and untreated samples, the dominant methanogenic archaea changed from Methanobacterium before anaerobic fermentation to Methanosarcina after the reaction, indicating that Methanosarcina was favored under iron-abundant conditions. The experimental results improve understanding of the mechanism through which the addition of Fe2+ promotes the conversion of coal to biomethane.