Ethanol and biogas production from waste fibre and fibre sludge: The FibreEtOH concept

The FibreEtOH concept was developed to tackle major challenges in the production of ethanol from lignocellulosics. The two feedstocks, waste fibre fractionated from solid recovered fuel, and pulp and paper mill fibre sludge, provide all-year-round supply of biomass with high hexose content (44–56%) and acceptable ash content (13–14%). They can be liquefied and hydrolysed by enzymes rapidly without a thermal or acidic pre-treatment, although they contain some recalcitrant mannose- and galactose-containing polysaccharides that require additional helper enzymes for complete hydrolysis to monosaccharides. Fractionation of solid recovered fuel, continuous liquefaction, and simultaneous saccharification and fermentation to ethanol, as well as biogas production from the fermented residue were demonstrated in pilot-scale with good results. Total yield consisting of C6 sugar hydrolysis yield (57%) and fermentation yield (84%) was 48% after only 6 h continuous liquefaction and 21 h fermentation. Average biogas production rate was 655 dm³ kg⁻¹ for fermentation residue from waste fibre and 400 dm³ kg⁻¹ from fibre sludge with methane content of 69–75%. Based on other results a hydrolysis yield of 75% is reachable within the process concept if the residence time in fermentation is extended. In this scenario 1000 kg of dry feedstock would produce 170 kg ethanol, 310 kg biogas, 360 kg waste sludge and 170 kg CO₂.