Bioelectricity production from food waste leachate using microbial fuel cells: Effect of NaCl and pH Xiao Min Li a , Ka Yu Cheng b , Jonathan W.C. Wong a,⇑ a Sino-Forest Applied Research Centre for Pearl River Delta Environment, Department of Biology, Hong Kong Baptist University, Hong Kong Special Administrative Region b CSIRO Land and Water, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Underwood Avenue, Floreat, WA 6014, Australia highlights  Anolyte with 100 mM NaCl gave the highest power density and lowest internal resistance.  Increases in power output may be maintained via NaCl addition in a continuous mode.  The highest power density was obtained under alkaline conditions.  The highest COD removal efficiency and CE was obtained in neutral and alkaline MFCs.  Optimal anodic pH for food waste leachate treatment with MFC ranged from 6.3 to 7.6. article info Article history: Received 4 July 2013 Received in revised form 6 September 2013 Accepted 8 September 2013 Available online 16 September 2013 Keywords: Bioelectrochemical systems Waste-to-energy Food waste leachate NaCl pH abstract Microbial fuel cells are a promising technology for simultaneous treatment and energy recovery from food waste leachate. This study evaluates the effects of NaCl (0–150 mM) and pH on the treatment of food waste leachate using microbial fuel cells. The food waste leachate amended with 100 mM NaCl enabled the highest maximum power density (1000 mW/m 3 ) and lowest internal resistance (371 X). Increasing the anodic pH gradually from acidic to alkaline conditions (pH 4–9) resulted in a gradual increase in max- imum power density to 9956 mW/m 3 and decrease in internal cell resistance to 35.3 X. The coulombic efficiency obtained under acidic conditions was only 17.8%, but increased significantly to 60.0% and 63.4% in the neutral and alkaline pH’s MFCs, respectively. Maintaining a narrow pH window (6.3–7.6) was essential for efficient bioelectricity production and COD removal using microbial fuel cells for the treatment of food waste leachate. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Food wastes are the largest component of municipal solid wastes in many urbanized societies (30–55% by weight), and anaerobic digestion is considered as the most environmentally beneficial treatment option for food wastes (Levis and Barlaz, 2011). Food waste leachate produced from the hydrolysis/acido- genic stage of two-stage anaerobic digesters is rich in volatile fatty acids (VFAs) (Xu et al., 2011), which can serve as good organic feed stocks to drive electricity production in microbial fuel cells (MFC) (Logan, 2008; Logan and Rabaey, 2012). MFC are bioelectrochemi- cal systems that can convert chemical energy stored in an organic substrate directly into electrical energy. Electrochemically active microorganisms are involved in this process to catalyze oxidation of organic compounds using an insoluble electrode (anode) as elec- tron acceptor (Logan et al., 2006; Rabaey et al., 2007). A number of studies have shown that electrochemically active microorganisms can utilize VFAs from food waste fermentation as carbon sources for current generation in MFC (Choi et al., 2011; Freguia et al., 2010; Li et al., 2013; Mohanakrishna et al., 2010; Nam et al., 2010; Oh and Logan, 2005; Teng et al., 2010). Although MFC technology has been suggested to complement anaerobic digestion for bioenergy recovery with several unique advantages over the conventional bioenergy technologies (Li and Yu, 2011; Pham et al., 2006; Rozendal et al., 2008), previous study suggested that the relative low bioelectricity output from a food waste leachate treating MFC was due to the high internal resis- tance (R int )(Li et al., 2013). One of the factors that strongly influ- ence the R int of MFC is ionic conductivity of electrolyte (Liu et al., 2005; Logan et al., 2006; Torres et al., 2008). Earlier studies indi- cated that increasing the conductivity or ionic strength of the ano- lyte and catholyte could result in improved MFC power output (Fan et al., 2008; Lefebvre et al., 2012; Liu et al., 2005). Generally, power densities of MFCs could be facilitated by high conductivities of up to 20 mS/cm (Logan and Rabaey, 2012). However, increasing ionic 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.09.037 ⇑ Corresponding author. Tel.: +852 3411 7056; fax: +852 3411 2355. E-mail address: jwcwong@hkbu.edu.hk (J.W.C. Wong). Bioresource Technology 149 (2013) 452–458 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech