Technology Development for Utilizing Trap Grease and Sewer Grease for Biodiesel Production

摘要

Fats, oils and greases (FOG) in the wastewater stream have long been a nuisance to the environment because they clog sewer pipes, causing overflows and damages. FOG can be classified as trap grease if obtained directly from food services, or sewer grease if mixed with FOG in the sewer system. This paper evaluated the technical feasibility and several sustainability parameters of converting trap/sewer grease into biodiesel. Both sewer and trap grease have FFA levels higher than the acceptable level (15-20%) of the current biodiesel industry. Due to emulsion, the lipid fraction of the sewer grease cannot be directly obtained by heating. Two innovative technologies, glyceroloysis and in-situ transesterification, were tested to make biodiesel from these FOGs. For trap grease, the results of glycerolysis showed that crude glycerin was effective in reducing the FFA% to < 1 wt%, with an optimum condition of 230 °C for 150 min and 1:1 molar ratio between glycerin and FFA. The study on the time series of the mono-, di-, tri-glycerides (MAG, DAG, TAG), FFA and glycerin was conducted to better understand the reaction mechanisms. For sewer grease, a direct transesterification process (in-situ conversion) was developed to extract the lipid and make biodiesel in one step. The optimum condition was determined as 20% (of dry sewer grease) H2SO4, 65 °C and 7hr, which gave a 85.43% extraction rate (biodiesel+unreacted FOG vs. total FOG) and a 76% FOG-to-biodiesel conversion rate (biodiesel vs. total FOG) were achieved.