Recovery and pre-treatment of fats, oil and grease from grease interceptors for biodiesel production Marvin Joseph Montefrio * , Tai Xinwen, Jeffrey Philip Obbard Division of Environmental Science and Engineering, Faculty of Engineering, National University of Singapore, 9 Engineering Drive 1, EA-03-12, Singapore 117576, Singapore article info Article history: Received 4 October 2009 Received in revised form 16 March 2010 Accepted 14 April 2010 Available online 8 May 2010 Keywords: Biodiesel Fatty acid methyl esters Esterification Grease interceptors FOG abstract Fats, oil and grease (FOG) can be recovered efficiently from grease interceptors for biodiesel production. FOG is susceptible to hydrolysis because of its inherent high moisture content and the presence of lipases associated with food residuals in the grease interceptors. This study reveals that the FFA content of FOG derived from grease interceptors did not exceed 8% (w/w) due to constant influx of fresh FOG from waste- water. However, if the FOG is allowed to hydrolyze without dilution, the FFA content can reach 15% (w/w) in more than 20 days. Experiments were conducted to optimize reaction parameters for the esterification of FOG prior to the conventional alkali-catalyzed biodiesel production process. Sulphuric acid (H 2 SO 4 ) was a more efficient catalyst than Fe 2 (SO 4 ) 3 in reducing the acid value to 61 mg KOH/g under identical reaction conditions. At reaction temperatures of 650 °C, only H 2 SO 4 was capable of reaching the recom- mended acid value within 24 h. The optimum methanol to FFA ratio for an H 2 SO 4 -catalyzed reaction was 20:1, whereas for Fe 2 (SO 4 ) 3 it was above 26:1. Esterification occurred under static, non-mixed conditions, although conversion rates were low. The rate of conversion increased with mixing speed, with a 200 rpm orbital shaking speed as optimum. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Domestic and commercial food establishments generate large volumes of wastewater, in the form of grey water or sullage, that contains significant amounts of fats, oil and grease (FOG). FOG must be separated from wastewater prior to entering the sewage system, primarily because of its propensity to block municipal sewer lines and disrupt the effective operation of downstream treatment processes [1]. Hence, grease separators (i.e. grease traps and interceptors) 1 are installed between wastewater effluent points and the sewer system to allow FOG to be trapped in a chamber, while FOG-free water exits to the sewer [3]. In developed countries that have stringent pollution control laws to protect the sewage system, grease interceptors (GIs) gener- ate huge volumes of FOG annually. For example, in a study conducted by the National Renewable Energy Laboratory [4] in the United States, 30 metropolitan areas generated an average of 6 kg of GI FOG per year per person. This figure is even larger than the estimated volume of restaurant waste cooking oil (WCO) generated in the US, which is just around 4 kg/person/year. The motivation for separating FOG from wastewater is not en- tirely associated with problems related to disposal in sewage sys- tems. The recovered FOG can be recycled as a valuable resource, and is sold to companies for use as an additive for animal feed, soap, cosmetics, and compost [5]. In some cases, for example in Singapore, FOG extracted from GIs is brought to centralized facili- ties where it is treated in anaerobic digesters. The methane gener- ated in the process is used to generate electricity to offset the on- site energy demands of the facilities. Although FOG from GIs can be recycled in a variety of applications, there is a potential to convert this low value waste stream into an even more valuable product, i.e. biodiesel. Biodiesel is a fast emerging valuable commodity as it represents a potential solution to abate greenhouse gas emissions in the transport sector. However, there are already concerns that biodie- sel, specifically those derived from agricultural crops, pose more detrimental environmental impacts than benefits. In a recent study conducted by Fargione et al. [6], it is noted that most biodiesel pro- duced globally is derived from crops grown on land converted from rainforests, peatlands, savannas and grasslands. Crop production results into a net ‘‘carbon debt” i.e. a release of more CO 2 than what can be reduced from the displacement of fossil fuels. The major advantage of biodiesel derived from FOG is that it does not have any environmental implication associated with land use conver- sion. Hence, it not only offsets the carbon impact of fossil fuels, but also that of crop-based biofuels that may actually be environ- mentally damaging. 0306-2619/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2010.04.011 * Corresponding author. E-mail address: marvin.planeteer@gmail.com (M.J. Montefrio). 1 Grease traps are passive interceptor devices that have a rated flow rate of 50 gallons per minute (GPM) or less. Grease interceptors, on the other hand, are installed outside of buildings and have a rated flow rate of greater than 50 GPM [2]. Applied Energy 87 (2010) 3155–3161 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy