Sustainable biorefining of barley malt rootlets and pot-ale for recovery of biohydrogen and organic acids

Barley malt rootlets (BMRs) and pot ale are two underutilised biomass streams generated during the industrial processing of barley, a major industrial crop central to the malting and distilling sectors. This study applied a Taguchi experimental design to evaluate various parameters and maximise glucose extraction with both pot-ale and water-based extraction media, using BMRs as the sole feedstock. Using sulfuric acid as the acidulant, a BMRs load of 15 wt%, a hydrolysis time of 10 min, and an acid concentration of 0.3 M, a maximum glucose concentration of 39.6 ± 1.54 g/L in the pot-ale-based medium and 37.83 ± 1.75 g/L in the water-based medium was achieved. These findings demonstrate that pot-ale can effectively replace fresh water without compromising the recovery of sugars or proteins. Dark fermentation performance was strongly dependent on glucose concentration. Biohydrogen production was favoured at low initial glucose concentrations. As glucose concentration increased, there was a progressive shift in metabolism towards acidogenesis. Kinetic modelling indicated that the modified Han-Levenspiel model provided a good fit (R 2 = 0.99). The downstream processing focused on the efficient separation and purification of organic acids. Adsorption using activated carbon and liquid-liquid extraction using ethyl acetate resulted in over 95% decolourisation efficiency and higher lactic acid titres up to 5.69 ± 0.01 g/L, respectively. Overall, this study demonstrates a pathway for converting processing streams derived from industrial crops into sustainable feedstocks for the production of bio-based chemicals and biofuels within a circular biorefinery framework.