Functional divergence of biochar and nano-Fe(3)O(4) in microbial chain elongation: Adsorptive regulation as an overlooked equilibrium driver.

Biochar sustains microbial chain elongation by adsorption-mediated regulation, retaining 2146.7 mg COD/L caproate and 756.9 mg COD/L butyrate to keep MCFA production going near steady state.

• Why it matters: Chain elongation toward medium-chain carboxylic acids is often constrained by product buildup that inhibits further conversion, leaving a gap in how to maintain activity after steady state.
• What they did: In steady-state fermentation, secondary biochar addition reinitiated substrate consumption and increased butyrate, while nano-Fe3O4 boosted initial caproate to 14.35 ± 0.86 g COD/L (1.82-fold) but did not extend CE after steady state.
• The result: In situ adsorption lowers dissolved product concentrations and reduces product activity, increasing the thermodynamic driving force for chain elongation and prolonging MCFA formation under near-steady-state conditions.

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