Performances and mechanisms of granular activated carbon enhancing n-caproate production via chain elongation

Abstract

Conversion of organic waste to medium chain fatty acids, such as n-caproate, has aroused wide attention. However, n-caproate production faces problems of low substrate conversion efficiency and low electron transfer efficiency. In this work, the influence of granular activated carbon (GAC) on n-caproate production through chain elongation using ethanol as electron donor and acetate as electron acceptor was explored for the first time. With a GAC dosage of 10 g/L, the maximum n-caproate production of 11.34 g COD/L was obtained in 15 d chain elongation, which was about 38.15% higher than that of control. It is revealed that the induced GAC of 10 g/L increased the utilization efficiency of ethanol and acetate, and improved electron transfer efficiency during chain elongation. Microbial community analysis demonstrated that the GAC addition enriched chain elongation microorganisms Clostridium_sensu_strict_12, Caproiciproduccens and Sporanaerobacter, which were responsible for the enhancement of n-caproate production. Furthermore, the GAC addition enhanced ethanol oxidation and reverse-β oxidation pathways associated with n-caproate production. This work provides a theoretical reference for n-caproate production regulation with carbon-based conductive materials.