Continuous mode of carbon dioxide sequestration by C. sorokiniana and subsequent use of its biomass for hydrogen production by E. cloacae IIT-BT 08 Kanhaiya Kumar, Shantonu Roy, Debabrata Das ⇑ Department of Biotechnology, Indian Institute of Technology Kharagpur, Kharagpur 721302, West Bengal, India highlights " Operating continuous mode of operation for CO 2 sequestration using C. sorokiniana. " Modeling and simulation of continuous culture of algae. " Utilizing algal biomass as substrate for H 2 production using E. cloacae IIT-BT 08. " Better H 2 energy using algal biomass as substrate over its use in biophotolysis. article info Article history: Received 1 December 2012 Received in revised form 24 January 2013 Accepted 25 January 2013 Available online 5 February 2013 Keywords: Chlorella sorokiniana CO 2 sequestration Algal biomass E. cloacae IIT-BT 08 Biohydrogen abstract The present study investigated to find out the suitability of the CO 2 sequestered algal biomass of Chlorella sorokiniana as substrate for the hydrogen production by Enterobacter cloacae IIT-BT 08. The maximum biomass productivity in continuous mode of operation in autotrophic condition was enhanced from 0.05 g L 1 h 1 in air to 0.11 g L 1 h 1 in 5% air–CO 2 (v/v) gas mixture at an optimum dilution rate of 0.05 h 1 . Decrease in steady state biomass and productivity was less sensitive at higher dilution and found fitting with the model proposed by Eppley and Dyer (1965). Pretreated algal biomass of 10 g L 1 with 2% (v/v) HCl–heat was found most suitable for hydrogen production yielding 9 ± 2 mol H 2 (kg COD reduced) 1 and was found fitting with modified Gompertz equation. Further, hydrogen energy recovery in dark fermentation was significantly enhanced compared to earlier report of hydrogen produc- tion by biophotolysis of algae. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The renewable energy sources have important role for decreas- ing not only the greenhouse effect but also to provide alternative option in the current exponential increase in worldwide energy de- mand resulting into depletion of energy reserves at greater pace. Moreover, it is the responsibility of civilized society to explore the possibility of using clean, efficient, sustainable and renewable sources of energy. Hydrogen is widely recognized as suitable and potential candidate as it has highest energy density among any known fuels (143 GJ tonne 1 ) and is the only common fuel that is not chemically bound to carbon. In addition, it produces only water on combustion (Levin et al., 2004). On the other hand, green algae have the ability to sequester CO 2 from flue gas and alleviate the im- pact of global warming due to increasing concentration of CO 2 in the atmosphere (Kumar et al., 2011). Though some of the green al- gae such as Chlamydomonas reinhardtii, Chlorella sorokiniana can be used for hydrogen production because of the presence of hydroge- nase enzymes. But its H 2 producing potential is always under scan- ner as the rate of hydrogen production is not encouraging. However, their biomass as such can be utilized as substrate for hydrogen producing bacteria. Enterobacter cloacae IIT-BT 08, a meshophilic facultative anaer- obic, gram-negative, rod shaped bacteria is widely known for its potential in H 2 production (Kumar and Das, 2001; Khanna et al., 2011a,b). Wild type E. cloacae has been reported to produce a prac- tical yield of 2.2 mol H 2 mol 1 glucose as against the theoretically limit of 4 mol H 2 mol 1 glucose (Kumar and Das, 1999). Previously, various studies on this potential strain have been conducted by many researchers based on process design, media optimization, ef- fect of pH, temperature, different substrates, reduced partial pres- sure, use of different configuration of reactors and different modes of operation such as batch, continuous, immobilization to improve the yield (Kumar and Das, 2001; Das, 2009; Khanna et al., 2011a). In addition, various carbonaceous substrates such as sewage 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.01.137 ⇑ Corresponding author. Tel.: +91 3222 278053; fax: +91 3222 255303. E-mail address: ddas.iitkgp@gmail.com (D. Das). Bioresource Technology 145 (2013) 116–122 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech