Continuous biohydrogen production in immobilized bioﬁlm system versus suspended cell culture Tu  gba Keskin a , Laura Giusti b , Nuri Azbar a, * a Bioengineering Department, Faculty of Engineering, Ege University, 35100 Bornova, Izmir, Turkey b Applied Chemistry and Materials Science Department, Faculty of Chemical and Process Engineering, Bologna University, Via Terracini 28, 40131 Bologna, Italy article info Article history: Received 13 July 2011 Received in revised form 26 September 2011 Accepted 4 October 2011 Available online 3 November 2011 Keywords: Biohydrogen Immobilized bioreactors CSTR Ceramic ball abstract In this study, the performance of a new cell immobilization material, namely ceramic ball, was examined for continuous biohydrogen production in comparison to suspended cell culture system (CSTR). Production of biohydrogen in both systems was assessed under thermophilic conditions. Both systems were operated at varying hydraulic retention times (HRT) by shortening HRT values from 24 to 1.5 h at an inﬂuent sucrose concentration of 10 g/l. The immobilized bioreactor conﬁguration outcompeted the CSTR bioreactor in terms of both volumetric hydrogen production (2.7 l H 2 /l/day for immobilized system @ HRT ¼ 3h and 0.5 l H 2 /l/day for CSTR @ HRT ¼ 24 h) and resistance to cell-washout (CSTR reactor lost signiﬁcant amount of biomass at short HRT values). It was concluded that immobilized bioreactor conﬁguration is much more robust than CSTR against high organic loading rates and 5 fold more volumetric hydrogen production was achieved in 8 fold smaller immobi- lized bioreactor. Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Recently energy need has increased exponentially all over the world due to the shortage ofthe fossil fuel reserves. There is also an urgent need to ﬁnd CO 2 neutral energy sources which do not have negative effects on environment.Hydrogen is known to be a viable alternative that could substitute fossil fuels. Besides hydrogen is accepted as the energy carrier of the future since it has no CO 2 emissions when burned and is 2.75 fold more energetic (122 kJ/g) than any conventional hydro- carbon based fuels [1]. The conventional hydrogen production methods such as thermochemical and physicochemical ones still negatively affect global warming since they are highly energy and pres- sure intensive. Therefore, it is crucial to maximize the use of renewable sources and environment friendly technologies in hydrogen production.Some of the renewable technologies namely; wind turbines; photovoltaic cells can be used during the production of hydrogen through electrolysis from water. But some drawbacks such as inefﬁcient energy conversion, high capital and operational costs are still an important issue for these systems. On the other hand, biological hydrogen production approach seems to be promising because wide variety of organic waste material could be used and the system could be operated under very low temperature and pressure conditions [2e4]. From this point of view, sustainable hydrogen production could be achieved by dark fermentation process in which anaerobic bacteria convert carbohydrate rich substrates into H 2 . The main advantage of this technology is that non-sterile organic waste materials can be used for dark * Corresponding author. Tel.: þ90 232 3884955-31; fax: þ90 232 3884955. E-mail addresses: keskin.tugba@gmail.com (T. Keskin), laura.giusti3@gmail.com (L. Giusti), nuriazbar@gmail.com (N. Azbar). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 1418 e1424 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.10.013