Mechanism of powdered activated carbon enhancing caproate production

Caproate, produced by microbial chain elongation process, is potential to replace the diversified fossil-based products, contributing to carbon neutrality. However, its production performance is far from indus-trial application, so the cost-effective enhancement measures are highly needed. This study confirmed powdered activated carbon (PAC) has a significant effect on enhancing caproate production performance. The production, yield, and selectivity of caproate were improved by more than 1-fold by the optimized PAC dosage of 15 g/L, comparing with control. Mechanism investigation from a new visual angle showed that PAC accelerated ethanol oxidation to generate acetyl-CoA, and simultaneously boosted the efficiency of reverse beta oxidation (RBO) by promoting the timely reaction of butyrate and acetyl-CoA to synthe-sis caproate. The addition of PAC also shifted the microbial community by enriching more caproate-producing bacteria but eliminating irrelevant ones. Furthermore, metagenomic analysis revealed that PAC effectively up-regulated the functional genes encoding key enzymes responsible for ethanol oxidation and RBO pathway, which was the root cause for the improved caproate production. This study presented the intrinsic insights into the mechanism of PAC promoting caproate generation, laying a foundation to the scale production of caproate.(c) 2023 Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.