Optimization of reactor parameters for amplifying synergy in enzymatic co-hydrolysis and microbial co-fermentation of lignocellulosic agro-residues

This study provides an experimental framework for optimizing reactor parameters to amplify synergy in the co-hydrolysis of holocellulose from delignified agro-residue (Miscanthus giganteus), followed by co-fermentation of sugars to bioethanol in a Separate Co-hydrolysis and Co-fermentation (SCHCF) system. The optimal reactor conditions that result in 83% yield of reducing sugars from holocellulose are obtained as: holocellulose loading is 10 mg/ml, enzyme: substrate loading (mg/mg) of cellulase: cellulose is 1:15, of hemicellulase: hemicellulose is 1:12, reaction temperature is 46 °C, and the mixing regime is 8 h initial continuous mixing followed by no mixing, with a total hydrolysis time of 72 h. Co-fermentation of soluble sugars using a yeast cocktail of Saccharomyces cerevisiae MTCC 170 and Pachysolen tannophilus MTCC 1077 at an optimal mixing speed of 40 rpm for 18 h produces 5.7 mg/ml of bioethanol. These optimized reaction conditions promote synergy between enzymes and microorganisms by minimizing mass transfer resistance, substrate inhibition, cross-inhibition effects of enzymes, and the competition between the yeasts. This synergy results in a 77% ethanol yield in SCHCF, compared to 62% using cellulase-Saccharomyces cerevisiae and 18% using hemicellulase-Pachysolen tannophilus in SHF. This synergistic increase in ethanol yield could be further enhanced by substituting SCHCF with SCSCF.