Due to population growth and improving living standards in the past few decades, fiber consumption and consequently waste textile production was greatly increased. Main strategies for waste textile management are landfill and incineration that caused many environmental problems while main part of these wastes can be turned into biological products such as biogas. Biogas is one of the leading biofuels that is produced by fermentation using anaerobic bacteria. In the present study, pretreatment of jean (as a waste textile) with sodium carbonate solution was performed to increase the efficiency of biogas production, reduce the crystallinity of cellulosic part, and separate cotton fibers from the synthetic part of textile, i.e., polyester. This alkaline pretreatment was performed on natural cotton and waste textile samples using various concentration of sodium carbonate (0, 0.5, and 1 M) at different temperatures (50, 100 and 150 ° C) for 120 min. Then the treated and untreated materials were anaerobically digested to biogas. The best improvement in the yield of methane production was achieved by pretreatment using 0.5 M sodium carbonate at 150 ° C for 120 min, giving a methane yield of 328.9 and 361.1 ml/g.VS after 40 days digestion. Under these conditions, polyester fibers were hydrolyzed and separated from the fabric structure so that the percentage of cellulose in the solid remained after the pretreatment was about 91%. The analysis showed that the alkali treatment can significantly increase water absorption ability, remove impurities of cellulosic part, reduce cellulose crystallinity, and hydrolyses polyester fiber, resulting in enhancement of biogas production. The pretreated samples were also subjected to enzymatic hydrolysis using cellulase and ? -glucosidase. The best glucose yield by enzymatic hydrolysis was obtained as 88.0% for cotton and 79.6 and 81.7 for textile, whereas the best results for untreated cotton and textile samples were 36.9% and 28.0%, respectively. Then the best results of enzymatic hydrolysis were fermented by Saccharomyces cerevisiae . The highest ethanol yield was 69.4% and 59.5% for cotton and textile, respectively. Keywords: Biogas, cotton, enzymatic hydrolysis, sodium carbonateو textile
