Facilitated CO biomethanation by exogenous materials via inducing specific methanogenic pathways

Abstract

Syngas biomethanation is a promising route for syngas (mainly CO, CO2, H2 and CH4) upgrading from pyrolysis/gasification of recalcitrant waste. However, its great difficulty stems from the toxic inhibition and low conversion efficiency of CO. This study aimed to enhance the CO biomethanation efficiency by supplying different conductive materials (including braunite, magnetite, biochar-A, biochar-B, and granular activated carbon). The results showed that the reactors supplied with magnetite had the best promotion on methane production, followed by braunite addition, with an increase of 96.7% and 88.0% compared to the Control respectively. With added carbon-based materials, the methane production in the Biochar-A reactors were increased by only 56%, which in the Biochar-B and GAC reactors were reduced by 17% and 30%. Magnetite presented strong redox property and electronic shuttle function, electrons can be shuttled rapidly between Fe (II) and Fe (III), which was found promoted methanogenesis by facilitating direct interspecies electron transfer between Brooklawnia spp. and Methanosarcina spp. Additionally, lots of oxygen cavities on the magnetite surfaces were capable of CO adsorption, facilitated the exposure of CO to microorganisms and thereby utilization of CO increased. On the other side, braunite was an iron-based mineral, may promote the microbial CO metabolic and thus facilitate the carboxydotrophic hydrogenogenesis process, and thus facilitating interspecies hydrogen transfer during hydrogenotrophic methanogenesis. Correspondingly, obligate hydrogenotrophic methanogen Methanobacterium spp., Methanoculleus spp., Methanospirillum spp. were all found increased in Braunite reactors. Among which, the dominant Methanobacterium spp. (accounted for 30%) performed strong methanogenic activity with braunite even in hydrogen-deficient situations.