Combined alkali and acid pretreatment of spent mushroom substrate for reducing sugar and biofertilizer production

Spent mushroom substrate (SMS) was pretreated with alkaline reagents including potassium hydroxide, lime and ammonia to enhance enzymatic saccharification. Under the best pretreatment conditions (1 M KOH, 80 °C, 90 min; 1 M lime, 80 °C, 120 min; 10 M ammonia, 70 °C, 120 min), the total reducing sugar (TRS) yield reached 258.6, 204.2 and 251.2 mg/g raw SMS, which were respectively 6.15, 4.86, and 5.98 times of untreated SMS. The effects of pretreatment by above alkaline reagents and sulfuric acid on the composition and structure of SMS were evaluated to provide comparative performance data. A new process, combined alkali and acid (CAA) pretreatment followed by enzymatic hydrolysis, was innovatively proposed to improve the cost-effectiveness and avoid environmental problems. The SMS residue after CAA pretreatment–enzymatic hydrolysis process was converted to biofertilizer with Pichia farinose FL7 and a cell density of 3.0 × 108 cfu/g in biomass was attained.