Evaluating and modeling biogas production from municipal fat, oil, and grease and synthetic kitchen waste in anaerobic co-digestions Chenxi Li, Pascale Champagne ⇑ , Bruce C. Anderson Department of Civil Engineering, Queen’s University, Kingston, ON, Canada K7L 3N6 article info Article history: Received 25 April 2011 Received in revised form 24 July 2011 Accepted 25 July 2011 Available online 3 August 2011 Keywords: Anaerobic co-digestion Fat, oil, and grease Synthetic kitchen waste Methane production Linear and non-linear modeling abstract The feasibility of using synthetic kitchen waste (KW) and fat, oil, and grease (FOG) as co-substrates in the anaerobic digestion of waste activated sludge (WAS) was investigated using two series of biochemical methane potential (BMP) tests. Ranges of ideal substrate to inoculum (S/I) ratio were determined for the FOG (0.25–0.75) and KW (0.80–1.26) as single substrates in the first experiment. The second exper- iment, which estimated the methane production performances of FOG and KW as co-substrates for WAS co-digestion, was conducted based on the optimal parameters selected from the results of the first exper- iment. Results indicated that co-digestions with FOG and KW enhanced methane production from 117 ± 2.02 mL/gTVS (with only WAS) to 418 ± 13.7 mL/gTVS and 324 ± 4.11 mL/gTVS, respectively. FOG exhibited more biogas production than KW as co-substrate. Non-linear regression results showed that co-substrate addition shortened the lag phases of organic biodegradation from 81.8 (with only WAS) to 28.3 h with FOG and 3.90 h with KW. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Producing methane from organic residues (e.g. primary and activated sludge) through anaerobic digestion processes has been applied to the on-site, co-generation of electrical power and heat in wastewater treatment plants (Zitomer et al., 2008). This technol- ogy can significantly reduce the operating costs at wastewater treatment facilities and stabilize the organic residues. A significant reduction in greenhouse gas emissions can also be realized. How- ever, the anaerobic digestion process has a number of limitations including slow reaction rates compared to aerobic processes, long retention time requirements (20–30 days), sensitivity to waste loads and toxic materials, and its complex operation (Lin et al., 1997; Hwang et al., 1997; Navia et al., 2002). The energy content of the gas may also vary and is dependent on the nature of the substrate. To enhance biogas production and assist in municipal organic waste management, anaerobic digestion with the addition of co- substrates, i.e. co-digestion, has been considered an effective, low-cost, and commercially flexible approach to reduce process limitations and improve methane yields (Alatriste-Mondragón et al., 2006). However, surprisingly few reports have focused on full-scale applications of this concept, and consequently the suc- cessful implementation of this approach in Canadian municipali- ties has been limited (De Baere, 2000; Mata-Alvarez et al., 2000; Natural Resources Canada, 2002). The City of Kingston (Ontario, Canada), a typical medium-size Canadian municipality, recently upgraded one of its two wastewater treatment facilities (Ravens- view Water Pollution Control Plant) to yield higher quantities of methane to decrease on-site operational costs. In this case, an anaerobic co-digestion process with the addition of low-cost muni- cipal organic wastes could also be considered for implementation as an efficient and economical solution. As such, municipally avail- able organic wastes including fats, oils and grease (FOG) and kitch- en waste (KW), which can be collected in close proximity to the treatment facility, could be employed as the potential co-sub- strates. Cotrell (2008) reported a 50% increase in biogas production at a full-scale digester using FOG as a co-substrate. Kabouris et al. (2008) also investigated FOG as a co-substrate and achieved signif- icantly higher methane production. Carucci et al. (2005), Gunasee- lan (2004), Gómez et al. (2006), Labatut et al. (2010), and Li et al. (2002) evaluated food wastes, which are also the main components of KW, and were successful in enhancing methane yield production. To determine the suitability of a specific organic substrate for anaerobic digestion, the biochemical methane potential (BMP) test has been proven to be a relatively simple and reliable method for the comparison of the extent and rates of waste conversion to methane (Hansen et al., 2004; Owen et al., 1979). To evaluate co- digestion using BMP tests, it is important to consider the substrate to inoculum ratio (S/I) on a total volatile solids basis (TVS). Deter- mining the ideal S/I ratio is necessary to achieve the maximum ultimate methane production. Chynoweth et al. (1993) indicated 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.07.103 ⇑ Corresponding author. Tel.: +1 (613)533 3053; fax: +1 (613)533 2128. E-mail address: champagne@civil.queensu.ca (P. Champagne). Bioresource Technology 102 (2011) 9471–9480 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech