Improving medium chain carboxylic acid production by controlling microbial competition with 2-bromoethanesulfonate.

Suppressing the growth of unwanted microorganisms that potentially compete with chain elongation (CE) cultures is essential for enhanced medium chain carboxylic acid (MCCA) production. This study examines the effects of 2-bromoethanesulfonate (BES) supplementation in a defined media containing ethanol and volatile fatty acids (VFAs) and complex media containing green waste on CE performance. Two types of inoculums were employed: an anaerobic digestate (AD) derived from manure fiber and a mixed chain-elongating (MC) culture dominated with Clostridium sensu stricto 12. Results show that ethanol alone failed to suppress methanogenesis and instead promoted excessive ethanol oxidation (EEO), leading to acetate accumulation without further conversion to MCCA. In contrast, BES effectively inhibited methanogenesis, EEO, and other potential VFA oxidations, enabling MCCA production without adversely affecting CE microorganisms. This finding also confirmed that an inoculum from AD of manure fibers promoted MCCA production. Despite BES addition, homoacetogens could still grow when CE microorganisms were inhibited due to product accumulation. When BES was applied in the first stage of arrested anaerobic digestion (AAD) of green waste, it successfully suppressed the growth of undesired microbes in the following CE step, creating a more favorable environment for the subsequent MCCA production, which increased from 4.7 to 5.7 g/L. This finding highlighted that a suppression of undesired microbes using BES prior to the CE step was an effective strategy for improving caproic acid production.