Sulphite addition during steam pretreatment enhanced both enzyme-mediated cellulose hydrolysis and ethanol production

Bioresources and Bioprocessing

Table 1 The acid group content, final pH and the enzymatic hydrolysis yield of the two-stage alkaline sulphite steam-pretreated substrates

Chemical loading	Condition	Acid group (µ mol/g substrates)	pH	Cellulose hydrolysis to glucose (%)
4% SO₂	One stage—200 °C 5 min	–	1.7	81
16% Na₂SO₃	Stage 1—160 °C 10 min Stage 2—210 °C 10 min	96	4.9	30
16% Na₂SO₃	Stage 1—160 °C 20 min Stage 2—210 °C 10 min	110	4.6	36
16% Na₂SO₃	Stage 1—160 °C 20 min Stage 2—220 °C 10 min	105	4.1	35
16% Na₂SO₃	Stage 1—160 °C 20 min Stage 2—230 °C 10 min	101	3.8	38

Each steam pretreatment used a sulphite loading of 16% (based on dry biomass) at the indicated temperature and residence time. Enzymatic hydrolysis was conducted at a solids loading of 5% for 48 h using a cellulase loading of 35 mg protein per g cellulose