Investigating the performance of different applied voltages on lignite biomethanation in microbial electrolytic cell coupled anaerobic digestion.

The performance of different applied voltages on the biomethanation of lignite is investigated in microbial electrolytic cells coupled with anaerobic digestion (MEC-AD). The cumulative methane production is only 35.1 mL/g lignite in the control reactor. However, the cumulative methane production is increased to 44.3 mL/g lignite in the MEC-AD reactor at the applied voltage of 1 V, and followed by 62.6 mL/g lignite (2 V), 102.8 mL/g lignite (4 V), and 123.8 mL/g lignite (8 V). The 3D fluorescence spectra further clarified that the applied voltage favored the hydrolysis of macromolecular organic matter such as humic acid in lignite. The microbial community abundance in the bulk solution shows that some specific microorganisms such as electroactive bacteria (Chloroflexi) and hydrogenotrophic methanogenic archaea (Methanobacterium) were well enriched in the MEC-AD reactors. These results indicate that MEC-AD facilitates direct interspecies electron transfer (DIET) between electroactive bacteria and archaea, and significantly increases methane production. However, the economic analysis concludes that the methane production at the applied voltage of 8 V could not compensate for the cost incurred by electricity. The MEC-AD reactor with an applied voltage of 4 V showed excellent biomethanation characteristics of lignite, which provides a basis for the resource utilization of lignite. • MEC-AD system promotes the production and biodegradation of humic acid from lignite. • Hydrogenotrophic methanogenic archaea in MEC-AD are well enriched in bulk solution. • MEC-AD system significantly enhance the DIET for methane production from lignite. • The applied voltage of 4V performs better lignite biomethanation and economic benefit. [ABSTRACT FROM AUTHOR]