ORIGINAL ARTICLE Pilot-scale pretreatments of sugarcane bagasse with steam explosion and mineral acid, organic acid, and mixed acids: synergies, enzymatic hydrolysis efficiencies, and structure-morphology correlations Siddhartha Pal 1,2 & Shereena Joy 1 & Pramod Kumbhar 1 & Kalpana D. Trimukhe 3 & Rishi Gupta 4 & Ramesh C. Kuhad 4,5 & Anjani J. Varma 3,5 & Sasisanker Padmanabhan 1 Received: 31 May 2016 /Revised: 24 August 2016 /Accepted: 26 August 2016 # Springer-Verlag Berlin Heidelberg 2016 Abstract In lignocellulosic (LC) ethanol processes, to facili- tate enzymatic hydrolysis of cellulose, a physical chemical pretreatment is vital. In this study, we explored a single as well as a two-step physical-chemical pretreatment involving steam and mixed acid on unwashed sugarcane bagasse at pilot-scale level in a continuous horizontal reactor. To serve as a large- scale model, pretreatments were carried out at high solid levels of 18–20 % w/w . For the pretreatment, partial replacement of corrosive sulfuric acid with a milder acid-like oxalic acid was explored to derive possible advantages and synergies accruing by using a mixture of mineral acid and organic acid. The results of this work showed that first-step pretreatment carried out by the mixing of sulfuric acid (1.5 % w/w) and oxalic acid (1.5 % w/w) at 150 °C followed by a second-step steam ex- plosion pretreatment at 180 °C gave significant synergies and advantages over other variants of pretreatments investigated, such as lower inhibitor levels and lower reaction severity. On post-pretreated bagasse, this study conducted comparative en- zymatic hydrolysis study using a simple lab enzyme and a robust commercial enzyme. It was found that the addition of Tween 80 to the lab enzyme improved its performance to match the performance of the commercial enzyme. Scanning electron microscopy (SEM) studies were further carried out to correlate the morphology of pretreated samples with efficien- cy of enzyme hydrolysis. Besides morphological study, Fourier transform infrared (FTIR) studies of pretreated sam- ples showed higher syringyl/guaiacyl ratio for all pretreat- ments, indicating lower levels of pseudo-lignins, which is beneficial for improved enzyme hydrolysis. Keywords Bagasse . Pretreatment . Steam explosion . Mixed acid . Morphology . Bioethanol 1 Introduction The gradual transition from petroleum refinery to biomass refinery (Bbiorefinery^) mainly based on industrially signifi- cant agricultural residues has attracted a great deal of social and technological interests, resulting in utilization of renew- able and sustainable feedstocks for the production of biofuels and biochemicals. This renewed interest is expected to con- tribute toward substantial reduction in GHG emissions and our dependence on fossil fuels [1–3]. Sugarcane bagasse (SB) represents a large and sustain- able source of renewable biomass for the production of many value-added chemicals, bio-based polymers, and biofuels [ 1, 4–6]. In tropical countries like India and Brazil, sugarcane is mainly used for the production of cane juice, table sugar, and ethanol. The residual fibrous bagasse Electronic supplementary material The online version of this article (doi:10.1007/s13399-016-0220-z) contains supplementary material, which is available to authorized users. * Anjani J. Varma aj.varma@ncl.res.in * Sasisanker Padmanabhan sasisankerpadmanabhan@praj.net 1 Praj Matrix—The Innovation Center, Urawade, Pune 412115, India 2 Department of Technology, Savitribai Phule Pune University, Pune 411007, India 3 Polymer Science & Engineering Division, CSIR-National Chemical Laboratory, Pune 411008, India 4 Microbiology Department, Delhi University South Campus, New Delhi, India 5 Central University of Haryana, Jant-Pali, Mahendragarh, Haryana 12309, India Biomass Conv. Bioref. DOI 10.1007/s13399-016-0220-z