Valorization of olive mill wastewater for acetic acid production by <i>Bacillus </i>strains isolated from bovine rumen

The valorization of olive mill wastewater (OMW) through microbial fermentation presents an innovative approach to addressing environmental challenges associated with olive oil production. This study aimed to investigate the potential of Bacillus strains isolated from bovine rumen for acetic acid production using olive oil mill wastewater as the primary substrate. Physicochemical analyses revealed high organic load (chemical oxygen demand of 183 g O₂ L–1, biological oxygen demand of 7 g O₂ L–1) and acidic pH (4.5) in olive oil mill wastewater, making it suitable for microbial growth. A total of 25 bacterial strains were isolated, and preliminary screening based on biogas production identified five efficient acid-producing Bacillus strains. Species-level identification using the bacterial identification system confirmed the presence of Bacillus licheniformis and Bacillus circulans. Batch fermentations conducted over 120 h produced up to 14 mL of biogas per 100 mL of culture and acetic acid concentrations of 28 g L–1, highlighting the strains’ strong acidification capacity. This study demonstrates the feasibility of bioconverting agricultural waste into valuable bioproducts, contributing to sustainable waste management, bioenergy generation, and promoting circular economy practices.