Optimizing the production of hydrogen and 1,3- propanediol in anaerobic fermentation of biodiesel glycerol Bingchuan Liu a , Kyle Christiansen b , Richard Parnas b , Zhiheng Xu a , Baikun Li a, * a Department of Civil and Environmental Engineering, University of Connecticut, Storrs, CT 06269, USA b Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, CT 06269, USA article info Article history: Received 2 July 2012 Received in revised form 28 December 2012 Accepted 29 December 2012 Available online 30 January 2013 Keywords: Anaerobic fermentation Biodiesel glycerol Hydrogen 1,3-propanediol (1,3-PD) Metabolic pathway Hydrogen retention time (HyRT) abstract The conversion of glycerol in biodiesel waste streams to valuable products (e.g. hydrogen and 1,3-propanediol (1,3-PD)) was studied through batch-mode anaerobic fermentation with organic soil as inoculum. The production of hydrogen in headspace and 1,3-PD in liquid phase was examined at different hydrogen retention times (HyRTs), which were controlled by gas-collection intervals (GCIs) and initial gas-collection time points (IGCTs). Two purification stages of biodiesel glycerol (P2 and P3) were tested at three concentrations (3, 5 and 7 g/L). Longer HyRT (longer GCI and longer IGCT) led to lower hydrogen yield but higher 1,3-PD yield. The P3 glycerol at the concentration of 7 g/L had the highest 1,3-PD yield (0.65 mol/mol glycerol consumed ) at the GCI/IGCT of 20 h/65 h and the highest hydro- gen yield (0.75 mol/mol glycerol consumed ) at the GCI/IGCT of 2.5 h/20 h), respectively. A mixed-order kinetic model was developed to simulate the effects of GCI/IGCT on the production of hydrogen and 1,3-PD. The results showed that the production of hydrogen and 1,3-PD can be optimized by adjusting HyRT in anaerobic fermentation of glycerol. Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction The production of biodiesel has increased substantially over the past decade as the alternative energy resource to solve the shortage of fossil fuels and the release of greenhouse gases. According to national biodiesel board, the production capacity of biodiesel has reached 700 million gallons/year in 2008 [1]. For every gallon biodiesel produced, 1 pound glycerol is pro- duced as one of the major by-products in biodiesel waste streams [2]. This overproduction of glycerol lowered the price of purified glycerol from $1.00/lb in 1995 to $0.38/lb in 2005 [3]. In addition, short-chain aliphatic alcohols (e.g. methanol) and catalysts (e.g. NaOH or KOH) used in the biodiesel production process also exist in biodiesel waste stream [4], which make the glycerol in biodiesel waste streams difficult to use. Although most of the impurities can be removed by vacuum distillation and carbon treatment (a method for removing organic contaminants using carbon as absorbent), these pro- cesses are energy intensive [5] and pose the obstacles for the real-world application of the crude glycerol generated from biodiesel waste streams. Several energy efficient processes (e.g. combustion, com- posting, anaerobic digestion, and thermo-chemical or bio- logical conversions to value-added products) for utilizing glycerol have been investigated [6e10], among which anae- robic fermentation has gained most intention, since it * Corresponding author. E-mail address: baikun@engr.uconn.edu (B. Li). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 38 (2013) 3196 e3205 0360-3199/$ e see front matter Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijhydene.2012.12.135