Combined water extraction and sodium chlorite pretreated spent mushroom compost for protease production by separate hydrolysis and fermentation and simultaneous saccharification and co-fermentation

A process of simultaneous saccharification and protease production was successfully established from spent mushroom compost (SMC) created through edible fungi cultivation. The combined water extraction and sodium chlorite pretreatment significantly (p < 0.05) improved enzymatic digestibility of SMC, which led to a reducing sugar yield of 0.759 g/g that was 12 times higher than raw SMC. The water extract from SMC was recycled for simultaneous saccharification and protease production from pretreated SMC by Bacillus subtilis DES-59, which promoted the protein concentration and neutral protease activity by 21.9% and 11.6%, respectively. The simultaneous saccharification and co-fermentation (SScF) of pretreated SMC by Bacillus subtilis DES-59 produced 5518 U/mL protease, which was superior to the separate hydrolysis and fermentation (SHF) process. Fermentation residues containing Bacillus subtilis cells could be further converted into fertilizer. The closed-loop utilization of SMC was achieved using established processes, which indicates potential for application in future biorefineries.