Techno-economic assessment of subcritical water hydrolysis of brewer’s spent grains to recover xylo-oligosaccharides

This study evaluated the techno-economic assessment of xylo-oligosaccharides (XOs) production from brewer’s spent grains (BSG) in a single and two sequential flow-through subcritical water hydrolysis (SWH) reactors at different temperatures (80–180 °C). The process with a single reactor produced the highest yield (72.83 mg XOs g⁻¹ BSG) at 180 °C. The SWH in two sequential reactors produced up to 52.47 mg XOs g⁻¹ BSG for the process operated at 80 °C followed by 130 °C. The lowest cost of manufacturing (18.36 USD kg⁻¹ XOs) was obtained for the process with two sequential reactors. Although the fixed capital investment was 0.82-fold lower for the process with a single reactor, the gross profit of the process with two sequential reactors was 30% higher, which resulted in a return on investment of 54.26% and a payback of 1.84 years. In conclusion, SWH is a potential eco-friendly process to produce XOs from BSG.