pH as a key driver of green chemicals production in agroindustrial waste fermentation

Anaerobic fermentation (AF) has been demonstrated as a promising approach for the valorization of agroindustrial waste into value-added metabolites, such as short-chain fatty acids (SCFAs). However, the achieved yields and product spectrum are greatly influenced by operating parameters, out of which pH plays a crucial role in microbial activity. In this investigation, process pH was studied as a driving force to manipulate metabolite profile and yields by shaping the microbiome. Firstly, AF was conducted at pH 6.2 resulting in a metabolite production of 27.9 g L −1 fully composed of SCFAs with high bioconversion efficiency (61.3 %) since a key synergy between Firmicutes and Actinobacteria was enabled. Thereafter, the pH decrease to 5.5 boosted a lactic acid bacteria growth and throve the metabolisms towards carbohydrate consumption, resulting in the production of SCFAs (22.1 g L −1 ), but also ethanol (10.7 %) and hydrogen (136.2 mL·gCOD in −1 ). These findings underscore the potential of using pH as a strategy to tailor metabolite production. Moreover, the results revealed the presence of ethanologenic microorganisms in open mixed-culture, highlighting AF as promising technology to be explored with the aim of producing green chemicals (ethanol) beyond SCFAs, thereby opening a new research niche.