An Effective Conversion of Cotton Waste Biomass to Ethanol: A Critical Review on Pretreatment Processes

Cotton based textile industries are one of the major source of revenue to the Indian economy. India contributes around 30 % of world's total cotton cultivation every year. Cotton accounts for more than 70 % of total textile production in the country. Cotton is subjected to various processes to produce cotton based textile apparels. During the processing of cotton, more amount of cotton-based wastes are generated and they are landfilled or incinerated, in general. Cotton textile industries are facing critical problems on solid-waste management, which results in environmental pollution and health hazards. These wastes comprise lignin, hemicellulose and cellulose, which can be utilized as sustainable feedstock for the production of bioethanol. Cotton based lignocellulosic biomass requires specific pretreatment strategy to efficiently remove lignin and to solubilize hemicellulose, which increases the accessibility of hydrolytic enzymes during saccharification. Till date, various pretreatment technologies such as physical, physico-chemical, acid/alkali-, ionic liquids (ILs) and biological treatment methods are widely evaluated for lignin removal, hemicellulose solubilization and cellulose crystallinity reduction in cotton wastes to enhance the enzymatic hydrolysis and fermentation process. This paper reviews about different pretreatment methods implemented and its significance for the conversion of cotton wastes to bioethanol.