The effect of dilution and L-malic acid addition on bio-hydrogen production with Rhodopseudomonas palustris from effluent of an acidogenic anaerobic reactor Nuri Azbar*, F.Tuba Cetinkaya Dokgoz Ege University, Faculty of Engineering, Bioengineering Department, 35100 Izmir, Turkey article info Article history: Received 19 June 2009 Received in revised form 9 October 2009 Accepted 14 October 2009 Available online 7 November 2009 Keywords: Rhodopseudomonas palustris Cheese whey Photo fermentation Two stage hydrogen production Photosynthetic bacteria abstract In this study, H 2 was produced from cheese whey wastewater in a two-stage biological process: i) first stage; thermophilic dark fermentation ii) second stage; the photo fermen- tation using Rhodopseudomonas palustris strain DSM 127 (R. palustris). The effect of both dilution and addition of L-malic acid on the hydrogen production was investigated. Among the dilution rates used, 1/5 dilution ratio was found to produce the best hydrogen production (349 ml H 2 /g COD fed ). On the other hand, It was seen that the mixing the effluent with L-malic acid at increasing ratios had further positive effect and improved the hydrogen production significantly. It was concluded that dilution of the feeding helps to reduce the nitrogen content and the volatile fatty acid content that might be otherwise harmful to the photo-heterotrophic organisms. Overall hydrogen production yield (for dark þ photo fermentation) was found to vary 2 and 10 mol H 2 /mol lactose. Second conclusion is that cheese whey effluent should be mixed with a co-substrate containing L-malic acid such as apple juice processing effluents before fed into the photo fermentation reactor. ª 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. 1. Introduction CO 2 emissions due to extensive use of fossil fuels result in global warming and search for alternative fuels is in the priority list of most nations’ agenda [1]. The hydrogen is considered as one of the best alternative to fossil fuels. It has high energy content per unit weight of 122 kJ/g which is almost three times that of hydrocarbon and its combustion product contains only water and no CO 2 . It is preferred to biogas or methane because hydrogen is not chemically bound to carbon, and therefore, burning does not contribute to greenhouse gases or acid rain [2]. However, hydrogen is currently produced mainly from natural gas, a finite resource, through steam reforming, a process that generates large quantities of carbon dioxide (CO 2 ), which is a principal cause of global warming. Biological hydrogen production processes are environment friendly and less energy intensive compared to chemical processes and it is more attractive if carbohydrate rich organic wastes and wastewater are used as cheap substrate. Among the various bio-hydrogen production methods such as direct biophotolysis and indirect bio- photolysis, use of dark fermentation and photo fermentation sequentially (so called two-stage biological hydrogen production) seems to be promising method to improve H 2 yield. In the first step of two-stage process, complex carbo- hydrates are converted to organic acids, alcohols, H 2 and CO 2 by anaerobic fermentative bacteria (Clostridium sp, mix consortium taken from soil, anaerobic waste treatment sludge and compost). In the second stage, the organic acids are further fermented by the photo-heterotrophic bacteria (e.g. * Corresponding author. Tel.: þ90 2323880378; fax: þ90 2323884955. E-mail address: nuri.azbar@ege.edu.tr (N. Azbar). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he 0360-3199/$ – see front matter ª 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2009.10.044 international journal of hydrogen energy 35 (2010) 5028–5033