Global NEST Journal, Vol 14 No 2, pp 149-156, 2012 Copyright© 2012 Global NEST Printed in Greece. All rights reserved ANAEROBIC TREATMENT OF GLYCEROL FOR METHANE AND HYDROGEN PRODUCTION T. VLASSIS 1,2 1 Department of Chemical Engineering, University of Patra, G. ANTONOPOULOU 1,2 Karatheodori 1 st., 26500 Patras, Greece Κ. STAMATELATOU 3 2 Institute of Chemical Engineering and High Temperature Chemical G. LYBERATOS 2,4,* Processes, 26504 Patras, Greece 3 Department of Environmental Engineering Democritus University of Thrace, 67100 Xanthi, Greece 4 School of Chemical Engineering National Technical University of Athens 15780, Athens, Greece Received: 05/12/11 *to whom all correspondence should be addressed: Accepted: 09/03/12 e-mail: lyberatos@chemeng.ntua.gr ABSTRACT This work focused on glycerol exploitation for biogas and hydrogen production. Anaerobic digestion of pure glycerol was studied in a continuous stirred tank reactor (CSTR), operated under mesophilic conditions (35 o C) at various organic loading rates. The overall operation of the reactor showed that it could not withstand organic loading rates above 0.25 g COD L -1 d -1 , where the maximum biogas (0.42 ± 0.05 L (g COD) -1 ) and methane (0.30 ± 0.04 L (g COD) -1 ) production were achieved. Fermentative hydrogen production was carried out in batch reactors under mesophilic conditions (35 o C), using heat-pretreated anaerobic microbial culture as inoculum. The effects of initial concentration of glycerol and initial pH value on hydrogen production were studied. The highest yield obtained was 22.14 ± 0.46 mL H 2 (g COD added ) -1 for an initial pH of 6.5 and an initial glycerol concentration of 8.3 g COD L -1 . The main metabolic product was 1.3 propanediol (PDO), while butyric and acetic acids as well as ethanol, at lower concentrations, were also determined. KEYWORDS: Glycerol, anaerobic digestion, methane, biogas, fermentative hydrogen production, biohydrogen, initial pH, initial glycerol concentration. 1. INTRODUCTION In the last decades, much attention has been given to the production of biofuels, in order to reduce the dependence on fossil fuels. Biodiesel is one of the most common biofuels, which may be used directly in internal combustion engines (Rashid et al., 2008). Its production has increased rapidly in the last decade. In Europe, 3,184,000 tons were produced in 2005, 5,713,000 tons in 2007 and 9,570,000 tons in 2010 (http://www.ebb-eu.org/stats.php ). Biodiesel is formed via the transesterification reaction, where glycerol is the main by-product, corresponding to 10 % of the produced mass of biodiesel. The disposal of the huge surplus of glycerol caused a decrease in biodiesel price and a financial crisis in many industries associated with glycerol production (Torrijos et al., 2008). The conventional use of glycerol is in cosmetic, paint, food, tobacco and pharmaceutical industries. It is also used as a feedstock for the production of various chemicals (Johnson et al., 2007). Thermochemical processes, such as catalytic steam reforming, partial oxidation and pyrolysis, convert glycerol to hydrogen, methane and other derivatives (Fan et al., 2010). Specifically, steam reforming of glycerol leads to the production of H 2 , CH 4 , CO 2 and CO. The relative amounts of these compounds depends on the nature of the catalyst used and the operational conditions such as temperature and pressure (Nichele et al., 2012; Chen and Zhao, 2012). On the other hand, biochemical processes, such as anaerobic digestion and fermentation could potentially transform