(498f) Possibility of Multi-Fuel Production From Trap Grease by Combination of Heat-Driven Upgrading and Methane Fermentation

Trap grease, which is a free-floating aggregate on the surface of the tank between restaurant and sewer, is either an oil or sludge-like grease including food scraps and water. It is a low-quality mixture of fats and oils, and is not recycled as a fuel in Japan. However, oily components such as glycerides and fatty acids in the grease a re considered to be a feedstock for alternatives to fossil fuels such as diesel and heavy oil. Furthermore, we consider that residues discharged during extraction of such oily content from the grease may be converted into biogas via methane fermentation. In the present study, first, we proposed a heating-driven liquefaction and phase separation for recovery of the oily content, and investigated the possibility of the obtained oil to use as an alternative to heavy oil in terms of impurity and property. From the investigation, the oily content was a clean fuel, especially a low-sulfur fuel. Hence, the heat-driven upgrading was useful for recovering a high-quality oil content from trap grease. In addition, we showed this upgrading can be successfully scaled up to a small demonstration phase. Unfortunately, the recovered oil could not meet some of fuel properties for replacement of high-grade heavy oil. Therefore, some improvements were proposed, and then their effectiveness was experimentally evaluated. Second, to evaluate the possibility of the residues to produce biogas, several types of residues from different restaurants were characterized in terms of volatile solid (VS), total nitrogen, etc, and then biogas productivity of the individual residues was examined using a batch-type methane fermentation. The results showed that the residues were applicable for methane fermentation and the biogas productivity ranged from 0.5 to 0.9 L/g-VS. These residues are considered to be good feedstocks for methane fermentation. From a series of investigation, the combination of the heat-driven upgrading of trap grease and methane fermentation of the residue from the grease upgrading can produce not only an alternative to heavy oil but also biogas. We expect both fuels may be used in a dual-fuel engine to generate electricity.