Tuning biochar surface area for optimal chain elongation: a strategy for high-efficiency medium-chain fatty acids production

Abstract

This study used ethanol and acetate as substrates, anaerobic digestion sludge as inoculum, and selected bamboo charcoal with three particle size conditions (< 25, 45–75, 100–250 μm) as the mediating material. While maintaining consistent electrical conductivity levels of bamboo charcoal, we investigated the effect of specific surface area on the chain elongation reactions. Experimental results demonstrated that when bamboo charcoal served as the mediating material, larger specific surface area significantly enhanced the chain elongation for the production of medium-chain fatty acids. Microbial community composition analysis via 16S rRNA sequencing demonstrated that bamboo charcoal intervention promoted the enrichment of Clostridium_sensu_stricto_12, a keystone functional microbe exhibiting statistically significant positive correlations with the yield, electron transfer efficiency, and selectivity of MCFAs. Metagenomic analysis identified the simultaneous presence of reverse β-oxidation and fatty acid biosynthesis pathways, with reverse β-oxidation pathway serving as the dominant route. Notably, the Candidatus_Microthrix genus exhibited dual functionality by engaging in both pathways for MCFAs production.

Graphical abstract

Keywords

Chain elongation / Bamboo biochar / Specific surface area / Medium-chain fatty acids / Reverse β-oxidation pathway

Highlight

	● Larger specific surface area markedly boosts the chain elongation (CE) effect.
	● Bamboo charcoal may preferentially promote the synthesis of caproate.
	● Carbon materials provide microbial attachment sites and facilitate DIET.
	● Clostridium_sensu_stricto_ 12 is a key functional microorganism.
	● Bamboo charcoal enhances the activity of the reverse β -oxidation (RBO) pathway.

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