Chemical Engineering Journal 160 (2010) 488–496 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Estimating anaerobic biodegradability indicators for waste activated sludge Alexis Mottet a,b , Emilie Franc ¸ ois a,b , Eric Latrille a , Jean Philippe Steyer a , Stéphane Déléris b , Fabien Vedrenne b , Hélène Carrère a,∗ a INRA, UR50, Laboratoire de Biotechnologie de l’Environnement, Avenue des Etangs, F-11100 Narbonne, France b Veolia Environnement R&D, Centre de Recherche sur l’Eau, F-78603 Maisons-Laffitte, France article info Article history: Received 22 September 2009 Received in revised form 25 March 2010 Accepted 26 March 2010 Keywords: Anaerobic digestion Biodegradability indicators Characterisation Waste activated sludge Methane abstract The aim of this study was to show the link between the initial characteristics of waste activated sludge (WAS) samples and their thermophilic anaerobic biodegradabilities, as determined by biochemical methane potential (BMP) tests, in order to develop relevant prediction indicators. Macroscopic parame- ters, biochemical composition and a fractionation of total solids by the Van Soest method were carried out on WAS samples which were taken from the inlet and outlet of full-scale sludge anaerobic digesters. Biodegradability was expressed as a function of WAS characteristics by the partial least square (PLS) regression technique. Among several PLS models, the most appropriated model was based on biochemical characterisation (carbohydrates, lipids and proteins) and two macroscopic parameters (soluble organic carbon and the ratio of chemical oxygen demand to total organic carbon). The biodegradability indicators developed in this study permitted the prediction of the methane production from WAS samples. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The European Union seeks to increase the share of energy from renewable sources in the Union total energy consumption from the 2005 level of 8.5% to 20% in 2020 [1]. This ambitious objective will contribute both to the worldwide efforts to deal with climate change and towards better control by the EU of its dependency on energy from outside. In this context, the anaerobic digestion of sewage sludge will therefore contribute to achieving the aim of the European directive. Indeed, the amount of sewage sludge is growing with the increase in the volume of the treated wastewater and the management of sewage sludge has thus become an environmental and economic issue. Thanks to anaerobic digestion, sewage sludge can be prof- itably used as a renewable energy resource because the organic matter it contains is converted into biogas made up of 60–70% of methane (CH 4 ) [2], which can be transformed into heat and/or electricity or biofuel. In 2006, the annual biogas production from sewage sludge in Europe was 949.5 kt of oil equivalent [3]. This potential is very significant since it represents 18% of the Europe’s total biogas production. Thus, the anaerobic conversion of sewage sludge should become an essential process in the modern wastew- ater treatment plant. Research on the optimisation of anaerobic digestion operat- ing conditions has shown that several parameters clearly impact ∗ Corresponding author. Tel.: +33 468 425 168; fax: +33 468 425 160. E-mail address: carrere@supagro.inra.fr (H. Carrère). on the biological conversion rates. The anaerobic biomass is very sensitive to pH and each population has an optimal range of pH [4]. The temperature has a big effect on both the microbial growth rates [5] and diversity [6]. Mixing strategy and inten- sity significantly affect performances and thus the production of methane [7]. The retention time also impacts on the process per- formance and biomass growth [8]. Consequently, several strategies can be applied to improve anaerobic conversion: thermophilic digestion (55 ◦ C) to increase degradation rates and methane pro- duction [9]; increasing sludge retention time [2]; introducing a pretreatment step such as thermal pretreatment [10], sonication [11], enzymatic hydrolysis [12] or chemical pretreatment [13] to make the organic matter more readily available by the anaerobic biomass. However, the mechanisms of anaerobic digestion are not well understood. In the case of sewage sludge, the process performances are limited with a mean conversion of organic matter from 30% to 50% [14]. Moreover, methane production depends on the sludge type. Indeed, the biodegradability of waste activated sludge (WAS) is lower than that of primary sludge [15]. The WAS matrix is more complex because of its biological origin and lower availability to the anaerobic biomass [16–18]. WAS biodegradability may be affected by operating conditions of the aerated tank in the wastewater treatment line [19]. Sludge originating from an extended aeration process is less biodegradable than sludge from a high-load process [20]. Moreover, Ekama et al. [19] showed that unbiodegradable organics of WAS, as determined from aerobic conditions, remain unbiodegradable under anaerobic digestion conditions. The anaer- obic biodegradability of sludge has thus been shown to be linked 1385-8947/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2010.03.059