ORIGINAL ARTICLE Ethanol production from rice straw using thermotolerant Kluyveromyces sp. IIPE453 Rakesh Kumar Jain & Debashish Ghosh & Deepti Agrawal & Sunil Kumar Suman & Diwakar Pandey & Vasantha Thakur Vadde & Ashwini Kumar Dixit & Dilip K Adhikari & Diptarka Dasgupta Received: 27 June 2014 /Revised: 26 July 2014 /Accepted: 11 August 2014 # Springer-Verlag Berlin Heidelberg 2014 Abstract Present paper describes a process development for fractionation of holocellulose in rice straw into its monomeric sugars employing acid hydrolysis followed by enzymatic saccharification. Rice straw has been hydrolyzed at 140 °C and 0.6 % v/v dilute sulfuric acid with 90 min holding time for maximum recovery of pentose monomer (12.52 g xylose/ 100 g biomass). Pentose stream was used for yeast cell bio- mass generation. Commercial cellulase resulted in 79±0.05 % saccharification efficiency with acid-hydrolyzed biomass. Fermentation of saccharified broth using thermophilic yeast Kluyveromyces sp. IIPE453 (MTCC 5314) with cell recycle produced ethanol with an overall yield and productivity of 93.5±0.05 % and 0.90±0.2 g/L/h, respectively, and with negligible residual sugar in fermentation broth. Lignin-rich residual biomass had a high gross calorific value and could be used as a source of clean gaseous fuel. Keywords Rice straw . Dilute acid hydrolysis . Enzymatic saccharification . Ethanol fermentation . Thermotolerant yeast . Kluyveromyces sp. IIPE453 1 Introduction Biomass is envisaged as potential and most abundant renew- able source of raw material to produce alternative fuels in context of the current environmental scenario [1, 2]. The greatest challenge lies on technological front which includes efficient conversion and utilization of energy in deriving value-added products from lignocellulosic waste at an afford- able cost [3]. Amongst many new generation biofuels, ligno- cellulosic ethanol is one of the most widely accepted [4]. In addition to its use as fuel supplement, ethanol also finds its application as precursor material for various chemical as well as petrochemical industries [5]. Indian distilleries produce ethanol by molasses fermenta- tion. Recent increase in molasses pricing and its limited avail- ability has affected its production [6]. A nonmolasses feed- stock is required to meet ethanol demand (other than potable alcohol) for its use as fuel substitute with 5 % blending in gasoline as per Government of India directives. India produces 100 million metric tonne (MMT) rice per annum against world production of 727 MMT [7]. Rice straw finds limited application due to low bulk density and high mineral and silica contents. Small amount is used as cattle fodder, and the rest is disposed of as rural practice by open field burning which causes pollution [8, 9]. Hence, amongst various agricultural residues, it can be used as an attractive lignocellulosic feedstock to derive value-added products. A projected potential of 200 billion liters bioethanol from this single biomass feedstock can meet 5 % of country’ s total requirement [10]. Average lignocellulosic agricultural residues contain 32– 47 % cellulose, 19–27 % hemicellulose, 10–24 % lignin, and 10–24 % ash [11, 12]. High polysaccharide and low lignin content make rice straw a suitable feedstock for bioalcohol production (Table 1). However, high silicon dioxide (SiO 2 ) and ash content renders difficulty in hydrolysis and sacchari- fication. Ash content on a dry weight basis ranges from 13 to 20 %, varying according to the state of conservation of the straw after harvest, location to location. Silica plays signifi- cant role in rice starting from carbohydrate synthesis to grain R. K. Jain : D. Pandey : V. T. Vadde : A. K. Dixit Division of Chemical Recovery, Biotechnology & Lignin By-products, Central Pulp and Paper Research Institute, Saharanpur, Uttar Pradesh 247001, India D. Ghosh : D. Agrawal : S. K. Suman : D. K. Adhikari : D. Dasgupta (*) Biotechnology Conversion Area, Biofuels Division, CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun, Uttarakhand 248 005, India e-mail: ddgupta@iip.res.in Biomass Conv. Bioref. DOI 10.1007/s13399-014-0143-5