Evaluation of Semi-Continuous Anaerobic Fermentation of Alperujo by Methanogenesis Inhibition

Two methanogenesis inhibition strategies for enhancing volatile fatty acid (VFA) production through the anaerobic fermentation of alperujo, a byproduct of olive oil production, were evaluated. Methanogenesis inhibition was implemented via two different approaches, one by pH adjustment to 5.0 and another one by chemical inhibition using 2-bromoethanesulfonate (BES) at pH 7. The VFA accumulation at the end of the experiment was 67% higher under the BES condition than under the pH 5 condition. Interestingly, the VFA profiles were similar under both conditions, with acetic acid as the dominant product, followed by propionic and butyric acids. The results demonstrated a 25% increase in alperujo solubilization under the BES condition, compared to under the pH 5 condition. This latest finding, together with the similar VFA profiles on both strategies, suggests that the hydrolysis step in alperujo solubilization was impacted by the pH difference. These findings highlight the effectiveness of chemical inhibition in enhancing solubilization, hydrolysis, and VFA accumulation during anaerobic fermentation of alperujo and, most importantly, the negative effect of pH 5 on the solubilization step.