Bioethanol has attracted interest as the major biofuel for transport. First generation bioethanol derived from sugarcane juice and grains such as corn is currently used to blend with petrol. But, the first-generation ethanol has the major disadvantage of food-fuel conflict. Hence, the non-edible lignocellulosic plant biomass is considered as potential feedstock for ethanol production.Production of ethanol from lignocellulose involves three major steps viz. pretreatment, enzymatic hydrolysis and fermentation. Low temperature aqueous ammonia soaking (AAS) is a potential pretreatment to minimize energy and recover high levels of both cellulose and hemicellulose. Hence, SCB was pretreated by AAS at low temperature by response surface method. Enzymatic hydrolysis of SCB pretreated by AAS under the optimized conditions resulted in 57.30% total sugars in the raw SCB. Addition of laccase to cellulase enzyme mixture enhanced the total sugar yield to 68.2%. When the laccase mediator 1-hydroxybenzotriazole (HBT) was added to the cellulase-laccase cocktail, the total sugar yield was further improved to 78.4%.The effect of laccase - mediator on enzymatic hydrolysis of AAS pretreated SCB was compared with SCB pretreated with NaOH and dilute H2SO4.
As ethanol distillation operation is economically sustainable when ethanol concentration is >5%, in order to produce high ethanol, high solids loading enzymatic hydrolysis (HSLEH) of SCB pretreated by low temperature AAS was optimized.The present glucan conversion of 74% in HSLEH was higher when compared with the reported values for biomass pretreated by high temperature steam explosion, acid and alkali pretreatments. The present ethanol titer (72.4 g/l) was also higher than the reported levels of ethanol in the second-generation bioethanol production.However, the utilization of xylose during fermentation was inhibited by high ethanol concentration in the broth.Therefore to utilize xylose efficiently and produce xylitol as a co-product along with ethanol for improving the production process economics, two-stage high solids enzymatic hydrolysis with xylanase followed by cellulase and separate fermentation of glucose and xylose using Candida tropicalis was performed. The separate fermentation of the xylose with C. tropicalis in two-stage aeration resulted in 34.5 g/l of xylitol.

Publications

1. Raj, K., Krishnan, C., 2018. High sugar yields from sugarcane bagasse using lowtemperatureaqueous ammonia pretreatment and laccase-mediator assisted enzymatic
hydrolysis. Ind. Crops Prod. 111, 673–683.
2. Raj, K., Krishnan, C., 2019. Improved high solid loading enzymatic hydrolysis of lowtemperatureaqueous ammonia soaked sugarcane bagasse using laccase-mediator
system and high concentration ethanol production. Ind. Crops Prod. 131, 32-40.

3. Raj, K., Krishnan, C., 2020. Improved co-production of ethanol and xylitol from lowtemperatureaqueous ammonia pretreated sugarcane bagasse using two-stage high solids
enzymatic hydrolysis and Candida tropicalis.Renew. Energy. 153,392-403