Nutrient-free biorefinery of corn steep water into lactic acid by Bacillus licheniformis OP16-2 under thermo-alkaline conditions with a pilot-scale assessment

Abstract

Lactic acid (LA) is utilized across multiple industries, including polymers, chemicals, cosmetics, and food. Its production from lignocellulosic biomass offers a promising solution to overcome challenges in the production process, such as reducing costs and enhancing environmental sustainability, while also increasing the value of biomass. However, the required pretreatment of lignocellulosic materials to release fermentable sugars generates inhibitory compounds that affect microbial fermentation, alongside the potential risk of contamination by mesophilic and neutrophilic microorganisms. In this study, a strain of B. licheniformis was isolated, selected, and identified as a lactic acid producer utilizing corn steep water (CSW) as the sole source of carbon and nitrogen for LA production. This selection was based on the strain’s tolerance to high temperatures and inhibitory compounds, including sodium metabisulfite, sodium chloride, sodium acetate, and formic acid. Sequential optimization of substrate, culture medium, and fermentation parameters was performed using both classical and advanced statistical techniques, without the need for additional nutrient supplementation. Thermo-Alkaline lactic acid production with a pilot-scale assessment was evaluated. Using multi-pulse fed-batch fermentation in a 50 L bioreactor, the system was operated at 45 °C with pH controlled at 8.49 ± 0.30, achieved LA concentration at 152.6 ± 1.15 g/L with a high yield of 0.93 ± 0.02 g/g, and a total productivity of 0.940 ± 0.005 g/L/h after 162 h., starting with an initial CSW concentration of 80 g/L. To our knowledge, this represents the first report of B. licheniformis being utilized for LA production from untreated CSW as a low-cost substrate, without any additional treatments or supplements.