부산대학교 도서관

This study analyzed the characteristics of food waste from a food waste digestion plant (with a capacity of 80 tons per day) situated in Chungju-si, Republic of Korea. Additionally, the sedimentation technique for the removal of grit was evaluated, as improper removal of grit in food waste can result in machinery failure, abrasion, clogging, sediment accumulation in digesters, and reduced treatment efficiency. The food waste exhibited total solids and volatile solids percentages of 16.2% wt. and 14.8 wt.%, respectively. Notably, the average particle size of the grits from the food waste sample measured 99 μm. Food waste containing particles larger than 1,000 μm predominantly comprised rice and leafy vegetables, whereas grit within the same particle size range predominantly consisted of hard seeds and woody shells. Conversely, food waste and grit with particles under 1,000 μm exhibited a muddy texture. The food waste demonstrated pseudo-plastic fluid behavior with a viscosity ranging from 5 to 300 Pa·s at shear rates between 1 - 30 s-1. During the design process of a settling tank aimed at achieving an 80 wt.% removal efficiency for grit present in food waste, the calculated ratio of effective length to effective depth (L/D ratio) was found to be 6,359. This value exceeds the design criterion, which specifies that the L/D ratio should be below 10. Even with the assumption of complete removal of the surface active agent from the particle, the L/D ratio was found to be 5,785. By adjusting the viscosity of the food waste to match that of water, it became feasible to achieve an L/D ratio of 0.018. Furthermore, employing a hydrocyclone resulted in an L/D ratio of 2.12. Consequently, it was concluded that pre-treatments aimed at reducing the viscosity of food waste could render both the sedimentation technique and the use of hydrocyclone for grit removal feasible.