AbstractsBiology & Animal Science

Feasibility Study for a Community Scale Conversion of Trap Grease to Biodiesel

by Jingjing Wang

Institution: University of Cincinnati
Department: Engineering and Applied Science: Environmental Science
Degree: MS
Year: 2012
Keywords: Environmental Studies; trap grease; biodiesel; extraction; inventory of trap grease
Record ID: 1942361
Full text PDF: http://rave.ohiolink.edu/etdc/view?acc_num=ucin1330024170


The world is experiencing fossil fuel depletion, global warming and environmental deterioration due to the overuse of fossil fuels. Biodiesel, as an alternative fuel, is considered as part of the solution. Biodiesel has experienced rapid development and commercialization in the past decade, and the technology for biodiesel production has greatly improved in handling multiple feedstocks. But the development of the biodiesel industry is still facing challenges. The major obstacle to the wide use of biodiesel is that biodiesel is not cost-competitive compared with diesel fuels. The industry is constantly searching for low-cost, or even no-cost feedstocks. Therefore, trap grease can potentially serve as a promising biodiesel feedstock to boost the biodiesel industry. Trap grease is a mixture of oils, food debris and kitchen wastes. It is generated in grease traps in restaurants. In most municipalities in the US, trap grease, after being pumped out from grease traps by grease haulers, is either sent to wastewater treatment plant or directly to landfills. An intensive literature review has been conducted and the following facts have been obtained. In the US, grease is the number one cause of clogging of public sewers, which results in costly sanitary overflow or combined sewer overflows. Various utilization ways of trap grease include composting, land application, anaerobic co-digestion, making biodiesel, combustion, incineration and rendering, etc. If trap grease is utilized as a feedstock for biodiesel production, it is not only beneficial to the biodiesel industry, but also helps solve the trap grease disposal issue. However, the challenge lies in the extraction of the oil fractions from this highly heterogeneous low grade feedstock. The goal of this study is to evaluate the feasibility of a community scale conversion of trap grease to biodiesel. Trap grease sample used for this study was obtained from the Metropolitan Sewer District of Greater Cincinnati (designated as MSD-TG). The MSD-TG mainly consists of water (58.94%), free fatty acids (FFAs) (20.69%) and unextractable part/solids (18.17%), with the lipid part of the MSD-TG being almost all FFAs. This study uses waste cooking oil (WCO) to extract the oil faction from the MSD-TG. WCO is also a low-cost biodiesel feedstock oil and using WCO as the solvent removes the solvent recovery step in the pretreatment process. The optimum extraction conditions were studied. It was found that 60° is the optimum extraction temperature. And at 60°, the optimum extraction duration is 90 minutes and the optimum extraction ratio is 4:1 (for every 10g of the MSD-TG 40mL (36g) of WCO is used). The extraction performance of WCO was evaluated by comparing it with three other organic solvents, methanol, hexane and isopropyl alcohol/hexane (2:1, v/v). WCO shows comparable performance among the four solvents. Based on the survey from trap grease haulers, the quantity of the grease trap waste (as semi solids) generated in Cincinnati is estimated to vary from 1.48 to…