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Electron-regulated flux towards biogas upgradation – triggering catabolism for an augmented methanogenic activity

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Abstract

Electromethanogenesis (EM) process was specifically designed to increase the conversion efficiency of organic substrates towards methane production and was further evaluated towards biogas upgradation applications. Four single-chambered EM systems were operated using designed synthetic wastewater (carbon source: 10 g L−1) to comparatively analyze the effect of applied voltage (AV −0.8 V; CC 100 Ω) and electrode placement on methanogenesis. The experiments were performed in three phases: the biomethanation phase (BM) (without electrodes assembly), electrode phase (MESOC; with electrodes assembly in an open circuit operation) and EM phase (MESCC/AV; electrodes assembly in a closed circuit or applied voltage operation). Electrode placement with a submerged anode and variations in the position of the cathode [partially air-exposed cathode; AV (R1/MESAV) and CC (R2/MESCC)] and completely submerged cathode [AV (R3/IE-MESAV) and CC (R4/IE-MESCC)] were evaluated. The results for the EM phase showed higher total biogas formation in R3/IE-MESAV (1.12 L), followed by R1/MESAV (0.91 L), R4/IE-MESCC (0.88 L) and R2/MESCC (0.59 L). Higher methane content was observed in R3/IE-MESAV (0.88 L) with a conversion efficiency of 76%, followed by R1/MESAV (0.66 L; 60%), R4/IE-MESCC (0.60 L; 56%) and R2/MESCC (0.37 L; 34%). EM operation depicted higher CH4 fraction with the co-generation of lower fractions of H2 and CO2 [R3/IE-MESAV (CH4-78%; H2-5%; CO2-17%), R1/MESAV (CH4-73%; H2-3%; CO2-22%), R4/IE-MESCC (CH4-68%; H2-5%; CO2-28%), R2/MESCC (CH4-63%; H2-4%; CO2-34%)] compared to control operation (CH4-61%; H2-4%; CO2-33%). The polarized microenvironment provided during EM (CC/AV) significantly contributed to biogas upgradation with a simultaneous CO2 reduction as compared to the BM and MESOC phases. Electrochemical characterization showed a high regulatory influence of the electron flux in R3/IE-MESAV, which helped to increase CO2 conversion/utilization compared to other conditions. EM influenced direct interspecies electron transfer (DIET), creating a microbe–electrode synergy leading to neutralize the disruptors influence (from side reactions) on final product formation. This study provides a specific strategy for increasing the overall methane yields with the influence of in situ/ex situ potential, while overcoming the limitations of methanogenesis.

Graphical abstract: Electron-regulated flux towards biogas upgradation – triggering catabolism for an augmented methanogenic activity

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Publication details

The article was received on 05 Aug 2019, accepted on 26 Oct 2019 and first published on 20 Nov 2019


Article type: Paper
DOI: 10.1039/C9SE00604D
Sustainable Energy Fuels, 2020, Advance Article

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    Electron-regulated flux towards biogas upgradation – triggering catabolism for an augmented methanogenic activity

    J. S. Sravan, O. Sarkar and S. V. Mohan, Sustainable Energy Fuels, 2020, Advance Article , DOI: 10.1039/C9SE00604D

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