Exploring The Co-composting Potentials of Raw Grease Trap and Grease Trap-Derived Soaps: Insights into Grease Trap Modification, Calcium Supplementation, and Microbial Community Analysis

Managing waste with grease traps poses a challenge because of the potential environmental issues associated with its disposal. In this study, two approaches were investigated to increase the biodegradability of grease trap waste: 1) converting raw grease trap waste into soap and 2) supplementing grease trap soap as inoculum with calcium material. The preparation of grease trap soap was optimized to attain a soap yield of 103% by utilizing a water-to-ethanol ratio of 9:1 at 80 °C for a processing time of 3 hours. A comparison of the composting results revealed higher nitrate yields with increased ratios of grease trap soap. Specifically, composting with 100% raw grease traps yielded 523.4 mg kg-1 nitrate, whereas composting with 100% grease trap soap produced 1,331.0 mg kg-1 nitrate. This indicated greater biodegradability of the modified grease trap, as evidenced by the BOD values, which were 3.81 times greater in the grease trap soap than in the raw grease trap waste. Microbial community analysis revealed distinct patterns between the compost mixed with 100% raw grease traps and that mixed with 100% grease traps. While both compost types contained predominant microorganisms linked to oil-degrading bacteria and biosurfactant producers, notable differences in microbial taxa were detected. Despite the high nitrogen content of grease trap soap compost, the germination index of mung bean seeds revealed that increasing grease trap soap loading tended to reduce the germination index. The addition of calcium hydroxide and calcium carbonate to the compost system, which uses grease trap soap as the inoculum and raw grease trap waste as the feedstock, could result in an increased germination index.