Use of coffee mucilage as a new substrate for hydrogen production in anaerobic co-digestion with swine manure Mario Andrés Hernández a,b,⇑ , Manuel Rodríguez Susa a , Yves Andres b a Environmental Engineering Research Center, Universidad de los Andes, Bogotá, Colombia b Ecole des Mines de Nantes, GEPEA UMR CNRS 6144, Nantes, France highlights  Biohydrogen production using coffee mucilage and swine manure was achieved.  C/N ratio around 50 could support the increase in organic load keeping stability.  Repetitive batch cultivation is useful to detect changes in the pathway.  Butyric and acetic pathways are the main routes in biohydrogen production. article info Article history: Received 20 December 2013 Received in revised form 15 February 2014 Accepted 17 February 2014 Available online xxxx Keywords: Biohydrogen Co-digestion C/N ratio Coffee mucilage Repetitive batch cultivation abstract Coffee mucilage (CM), a novel substrate produced as waste from agricultural activity in Colombia, the largest fourth coffee producer in the world, was used for hydrogen production. The study evaluated three ratios (C1–3) for co-digestion of CM and swine manure (SM), and an increase in organic load to improve hydrogen production (C4). The hydrogen production was improved by a C/N ratio of 53.4 used in C2 and C4. The average hydrogen production rate in C4 was 7.6 NL H 2 /L CM d, which indicates a high hydrogen potential compare to substrates such as POME and wheat starch. In this condition, the biogas composition was 0.1%, 50.6% and 39.0% of methane, carbon dioxide and hydrogen, respectively. The butyric and acetic fermentation pathways were the main routes identified during hydrogen production which kept a Bu/Ac ratio at around 1.0. A direct relationship between coffee mucilage, biogas and cumulative hydrogen vol- ume was established. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Biohydrogen production from renewable resources such as wastes is a second-generation renewable energy. Their production can be accomplished through several biological methods as dark fermentation. Anaerobic digestion has been considered able to con- vert the complex carbon sources of wastes into hydrogen (Saratale et al., 2013). This substrate kind has several rewards and chal- lenges related to heterogeneous compositions, microorganisms, in- ert material and nutrients (Kapdan and Kargi, 2006; Ntaikou et al., 2010). In general, raw materials contain three types of macromol- ecule; carbohydrates, proteins and lipids. In lignocellulosic materials, lignin should be considered in addition with carbohy- drates as cellulose and hemicellulose. The dark fermentation involves hydrolysis and acetogenic steps where carbohydrates have been reported as a main substrate for hydrogen production (Kapdan and Kargi, 2006; Lin and Lay, 2004; O-Thong et al., 2008; Sreela-or et al., 2011). According to operating conditions and microorganisms, the metabolic route can be addressed to several products as hydrogen, carbon dioxide, VFAs, ethanol, succi- nate, lactate and other metabolites (Liu et al., 2008; Saint-Amans et al., 2001; Temudo et al., 2007). These products, except hydrogen and carbon dioxide, remain in liquid phase limiting high COD removal efficiencies (Lee et al., 2010). In fact, biohydrogen through dark fermentation of complex substrates has been reported as a useful first stage for a subsequent methane production process (Lee et al., 2010; Wang et al., 2013). In order to specify the kind of feedstock, it could be related to energy crops which showed a main constrain as demand of arable land. In contrast, the residues from the processing of agricultural products do not suppose additional technical equipment or infra- structure (Eisentraut, 2010). Due to the ability of dark fermenta- tion to use complex substrates as livestock, crop residues, wastes http://dx.doi.org/10.1016/j.biortech.2014.02.101 0960-8524/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Environmental Engineering Research Center, Universidad de los Andes, Bogotá, Colombia. Tel.: +57 1 3324312; fax: +57 1 3324313. E-mail address: mario-h1@uniandes.edu.co (M.A. Hernández). Bioresource Technology xxx (2014) xxx–xxx Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech Please cite this article in press as: Hernández, M.A., et al. Use of coffee mucilage as a new substrate for hydrogen production in anaerobic co-digestion with swine manure. Bioresour. Technol. (2014), http://dx.doi.org/10.1016/j.biortech.2014.02.101