Integration of acid pre-treated paddy straw hydrolysate to molasses as a diluent enhances ethanol production using a robust Saccharomyces cerevisiae NGY10 strain

Molasses is one of the most common feedstocks for ethanol production, which requires a large amount of water for dilution during fermentation. In present study, paddy straw hydrolysate (PSH) was integrated to molasses as diluent and fermentation bioprocesses were developed using a robust Saccharomyces cerevisiae NGY10 strain. Batch fermentation in serum bottle using 40% v/v molasses diluted with PSH under optimized conditions at 35 °C produced 97.11 ± 2.36 g/L (12.31% v/v) ethanol with 0.46 g/g yield and 2.2 g/L.h productivity in 30 h. During batch fermentation in a bioreactor at 35 °C and pH 5.5 with aeration (0.3 vvm for initial 6 h) maximum 104.63 ± 2.97 g/L (13.26% v/v) ethanol was produced with 0.47 g/g yield and 4.35 g/L.h productivity in 24 h. In fed-batch fermentation, ∼6.06% higher ethanol titre was achieved than batch fermentation, but productivity was decreased. Remarkably, simultaneous saccharification and fermentation at 40 °C with high solid loading (22.5% w/v) and pre-saccharification produced 104.21 ± 3.23 g/L (13.21% v/v) ethanol in 72 h when 1:1 mixture of molasses and acid-pretreated paddy straw was used. Taken together, the integration of PSH as diluent to molasses not only increases the ethanol yield and productivities but also saves water consumption and operational costs, and can be accommodated in existing sugar mill infrastructures.