Ethanol Production from High-Solid SSCF of Alkaline-Pretreated Corncob Using Recombinant Zymomonas mobilis CP4 Rongxin Su & Yuanyuan Ma & Wei Qi & Mingjia Zhang & Fang Wang & Ruoyu Du & Jifeng Yang & Minhua Zhang & Zhimin He Published online: 25 September 2012 # Springer Science+Business Media, LLC 2012 Abstract In this work, Zymomonas mobilis was genetically improved for pentose utilization to increase the final ethanol concentration. It showed good fermentation ability on both soluble sugar mixture and lignocellulose. Nearly all the glu- cose and xylose in sugar mixture can be consumed, corresponding to 86 % of theoretic ethanol yield. Simulta- neous saccharification and co-fermentation (SSCF) of NaOH- pretreated corncob was then carried out in a high dry matter (DM) loading of 15–25 w/v%. At the DM loading of 15 %, the suitable operating conditions were determined, i.e., Z. mobilis loading of 0.30 g dry weight/L at 30 °C (pH5.5), under which the ethanol concentration reached 49.2 g/L. Higher final eth- anol concentrations were obtained when SSCF was operated at the fed-batch mode. Several amounts of substrate (1 % to 10 %) were added, and the highest final ethanol concentration (60.5 g/L) was obtained at 10 % DM addition. Keywords Simultaneous saccharification and co-fermentation . Recombinant Zymomonas mobilis . Corncob . Bioethanol . Xylose fermentation . Lignocellulose . Cellulose . High solids Introduction Increased concerns over the depletion of fossil fuel reserves and the negative impact of fossil fuels on the environment pressure society to find renewable energy alternatives [1]. Bioethanol is a highly promising alternative source of re- newable energy, and for large-scale usage, lignocellulosic materials are a promising choice in the production of second-generation bioethanol fuel. Corncob is an abundant agricultural residue, and because of its higher bulk density compared to other corn stalk parts, it is also easier to transport from fields to facilities. Therefore, corncob is considered as a highly potential raw material for bioethanol production. Cur- rently, several large energy companies, such as Poet (http:// www.poet.com/inspiration/company/biomass.asp) and DuPont (http://www.ddce.com/technology/feedstock.html), use corncob as one of the major feedstocks for cellulosic ethanol production. In China, 20 million tons of corncob can be obtained after an annual harvest of nearly 120 million tons of corn (Zea mays L.). Simultaneous saccharification and fermentation (SSF) is a potential step to convert lignocellulosic materials to ethanol. Compared with separate hydrolysis and fermentation (SHF), SSF is advantageous in avoiding the end-product inhibition of cellulase; the fermenting microorganism, such as Saccharo- myces cerevisiae, immediately consumes the produced glucose [2]. In addition, SSF integrates hydrolysis and fer- mentation in one reactor, thereby reducing equipment costs and decreasing the probability of contamination [3, 4]. For industry-scale lignocellulose-based ethanol production to be- come economically viable, the produced ethanol must be above 4 % (v/v) in the fermentation broth [5]. This can be achieved by operating SSF at a high dry matter (DM) concen- tration (higher than 10 %) [6]. In our previous work, we have obtained an ethanol concentration of up to 84.7 g/L at a high DM concentration of 25 % using fed-batch SSF [7]. Electronic supplementary material The online version of this article (doi:10.1007/s12155-012-9256-5) contains supplementary material, which is available to authorized users. R. Su and Y. Ma contributed equally to this work. R. Su : W. Qi : M. Zhang : F. Wang : R. Du : J. Yang : Z. He (*) State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, PR China e-mail: enzyme@tju.edu.cn Y. Ma : M. Zhang (*) Biomass Conversion Laboratory of Tianjin University R&D Center for Petrochemical Technology, Tianjin University, Tianjin 300072, PR China e-mail: mhzhangtju@gmail.com Bioenerg. Res. (2013) 6:292–299 DOI 10.1007/s12155-012-9256-5