Comparative study of three optimized acid-based pretreatments for sugar recovery from sugarcane leaf waste: A sustainable feedstock for biohydrogen production

This paper reports the development and comparison of three optimized pretreatment models for xylose and glucose recovery from sugarcane leaf waste (SLW) using HCl, H2SO4 and HNO3. The input variables for each model consisted of acid concentration, temperature, solid to liquid ratio and heating time in the range of 0.5-5.0% (v/v), 60-100 °C, 30-50% (w/v) and 60-240 min respectively. All models showed high coefficients of determination (R2) above 0.78. Process optimization gave xylose and glucose yields of 78 and 11.48 g/L, 50.75 and 7.15 g/L, 30.82 and 3.99 g/L for HCl, H2SO4 and HNO3 pretreatments respectively. The HCl-based model gave up to 160% more sugar while simultaneously requiring a 2.5-fold lower heating time compared to H2SO4 and HNO3. The highest hemicellulose removal (93.15%) was also observed with the HCl model. Preliminary assessment of sugars from the optimized HCl pretreatment on dark fermentation gave a peak hydrogen fraction of 40.11% and a yield of 18.6 ml H2 g−1 fermentable sugar. The optimized pretreatments showed high efficiency at releasing xylose and glucose from SLW. In addition, the recovered sugars are excellent substrates for various fermentation bioprocesses and biofuel generation.