Integrated process for bioconversion of paddy straw, cheese whey and molasses into ethanol

The present study on co-fermentation of paddy straw and cheese whey was carried out to assess the efficacy of whey as nutritional supplement for bioethanol production. Also, co-fermentation of paddy straw and molasses was carried out for enhanced ethanol production to make downstream processing and purification process easier. For agro-residues like paddy straw, breaking of recalcitrant lignin sheath is the first and success determining step in bioethanol production. To achieve this efficiently, five factors optimized were temperature, pressure, pH, residence time and particle size of paddy straw. Paddy straw (particle size: 0.5 mm) immersed in 2% sodium hydroxide solution (pH 10.0) in 1:10 was subjected to delignification using steam collected under pressure (temperature 121°C; pressure 15 psi) for 1 h. This resulted in 83.3% lignin removal with 86.4% cellulose and 11.1% hemicellulose recovery. Polysaccharide rich substrate was saccharified using commercial enzyme loaded at 7.5 FPU g^-1 substrate at 50°C for 2 h. Hydrolyzed substrate was fermented with yeast strain Candida utilis. The combined fermentation of paddy straw with cheese whey increased ethanol production from 29.0 mL L^-1 to 31.0 mL L^-1 without yeast nutrient supplementation and with molasses increased to 51.0 mL L^-1 ethanol with yeast nutrient supplementation.