Enrichment and optimization of anaerobic bacterial mixed culture for conversion of syngas to ethanol Ashish Singla a,b , Dipti Verma b , Banwari Lal a,b , Priyangshu M. Sarma a,b,⇑ a TERI University, 10 Institutional Area, Vasant Kunj, New Delhi 110 070, India b TERI, Darbari Seth Block, India Habitat Centre, New Delhi 110 003, India highlights  Anaerobic bacterial mixed culture enriched for conversion of syngas to ethanol.  Operational parameters optimized for enhancing ethanol production from syngas.  Semi-continuous fermentation study done for getting increased ethanol production.  Up-scaling studies done for further enhancing ethanol production from syngas. article info Article history: Received 13 June 2014 Received in revised form 18 August 2014 Accepted 19 August 2014 Available online 27 August 2014 Keywords: Syngas Mixed culture Optimization Ethanol Up-scaling abstract The main aim of the present study was to enrich anaerobic mixed bacterial culture capable of producing ethanol from synthesis gas fermentation. Screening of thirteen anaerobic strains together with enrich- ment protocol helped to develop an efficient mixed culture capable of utilizing syngas for ethanol pro- duction. Physiological and operational parameters were optimized for enhanced ethanol production. The optimized value of operational parameters i.e. initial media pH, incubation temperature, initial syn- gas pressure, and agitation speed were 6.0 ± 0.1, 37 °C, 2 kg cm 2 and 100 rpm respectively. Under these conditions ethanol and acetic acid production by the selected mixed culture were 1.54 g L 1 and 0.8 g L 1 respectively. Furthermore, up-scaling studies in semi-continuous fermentation mode further enhanced ethanol and acetic acid production up to 2.2 g L 1 and 0.9 g L 1 respectively. Mixed culture TERI SA1 was efficient for ethanol production by syngas fermentation. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Synthesis (syngas) gas, primarily a mixture of CO, CO 2 and H 2 is a major feedstock in production of many fuels and chemicals. It can be produced from gasification of several materials such as coal, wood, municipal solid waste and lignocellulosic biomass (Phillips et al., 1993). The essential syngas components CO, CO 2 and H 2 can be biologically converted into ethanol and other value added compounds such as acetic acid, 2-butanol, n-propanol and polyhy- droxyalkanoate (PHA) (Kundiyana et al., 2010). Catalytic processes are also used to convert syngas components into a variety of fuels and chemicals such as hydrogen, methane, methanol, ethanol, and acetic acid (Klasson et al., 1992). Biological processes, although rel- atively slower than chemical reaction have several advantages over catalytic process such as elimination of expensive metal catalyst, higher specificity of biocatalyst, lower energy costs, greater resis- tance to catalyst poisoning and independence of H 2 /CO ratio (Wolfrum and Watt, 2002). The biological reaction occurs under ambient condition of pH, temperature and pressure with the for- mation of specific products. However, direct production of fuels and chemicals from gasification technology is economically unfa- vorable and requires very large infrastructure as about 60% of the total investment cost in modern methanol plants is accounted for syngas generation (Vannby and Winter Madsen, 1992). Therefore, the economical advantage of biological processes through develop- ment of suitable biocatalyst to ferment gaseous substrate to valu- able products can be considered. Previous study indicates that FT process has a relative overall energy efficiency of 45%, while gas http://dx.doi.org/10.1016/j.biortech.2014.08.083 0960-8524/Ó 2014 Elsevier Ltd. All rights reserved. Abbreviations: PHA, polyhydroxyalkanoate; PBM, Pfennig’s basal media; TCD, thermal conductivity detector; FID, flame ionization detector; OD, optical density; CO, carbon monoxide; H 2 , hydrogen; rs, resparged; AA, acetic acid; EtOH, ethanol; SD, Sludge; CD, cow dung; CF, chicken faeces; VFA, volatile fatty acids. ⇑ Corresponding author at: TERI University, 10 Institutional Area, Vasant Kunj, New Delhi 110 070, India. Tel.: +91 11 24682100; fax: +91 11 24682144. E-mail address: priyanms@teri.res.in (P.M. Sarma). Bioresource Technology 172 (2014) 41–49 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech