281747 Comparison of 1- and 2- Step Biodiesel Production From Activated Sludge Using Supercritical Methanol and Economic Analysis
In recent times, demand of renewable fuels like biodiesel has escalated due to spurs from the 2007 Renewable Fuel Standard that mandates the production of 1 billion gallons of biodiesel by 2022, as well as environmental and energy security concerns. One of the reasons why biodiesel is not yet cost-competitive with petroleum fuels is due to the high cost of feedstock. A high-potential feedstock for biodiesel production is activated sludge obtained from wastewater treatment plants, which is relatively cheaper to use. Researchers have shown that the fats present in the sludge can be transformed to biodiesel. However, drying of sludge prior to oil extraction and reaction is a major operating cost of this process since it is so high in water content. Thus, the most efficient process to convert the oils from activated sludge to biodiesel will need to have high water tolerance. In this case, supercritical methanol works suitably as a reactant and catalyst.
A study was conducted to determine the yield of biodiesel produced from reacting wet sludge using only supercritical methanol. Activated sludge was obtained from a Tuscaloosa, AL wastewater treatment plant and an approximate composition of 93% water and 7% solids was reacted with methanol in a 450 ml Parr® reactor using a methanol: solids ratio of 30:1 (mass basis) at 300 °C for 3 - 12 hours. Analysis of the product by Gas Chromatography-Mass Spectrometry (GCMS) showed a number of fatty acid methyl esters (biodiesel) such as methyl linoleate and methyl palmitoleate; and an average biodiesel yield of 7 %. A series of experiments were conducted for the direct transesterification (1-step) optimization based on temperature, reaction time and methanol volume for the production of biodiesel from wet sludge. For this, an oleagineous (oil-storing) yeast - Rhodotorula glutinis was used as a model system for sludge (to reduce inconsistencies in sludge batch variations) and gave biodiesel yields as high as 21 %. Furthermore, the 2-step method of hydrolyzing the fats to fatty acids followed by esterification was also examined for changes in yields. This study will show the results of both methods compared and the economic analysis for the prospect of scaling up.