(510e) Production of Biodiesel by Direct Transesterification of Activated Sludge Using Supercritical Methanol

Fatty acid methyl esters (biodiesel) can be produced by using activated sludge generated from wastewater treatment facilities.  However, drying of sludge prior to oil extraction is a major operating cost of this process. To address this challenge, the authors have conducted a study to determine the yield of biodiesel produced from reacting wet sludge using only supercritical methanol.

Activated sludge was obtained from a wastewater treatment plant in Tuscaloosa, AL and filtered to a composition of 90% water. This was reacted with methanol using varying methanol:solid ratios at 275, 300, and 325 °C for 1 - 9 hours. Two reactor set-ups were used in this study: 1) a 450ml batch Parr ® reactor, and 2) a 46ml batch reactor.  Analysis of the product by Gas Chromatography-Mass Spectrometry (GCMS) showed a number of fatty acid methyl esters (biodiesel) like methyl oleate and methyl palmitate. Since sludge contains approximately 5% lipids which varies with time (season) and treatment conditions, a model system of oleagineous yeast - Rhodotorula glutinis was also used to evaluate the production of biodiesel in a system similar to sludge. 

The average sludge biodiesel yield obtained on the Parr reactor was 7.1 ± 3.9% based on initial solids while the average sludge biodiesel yield obtained on the 46ml batch reactor thus far was 2.2 ± 0.4%. The average biodiesel yield obtained from Rhodotorula glutinis was 20.7 ± 5.8%. This work shows the results of optimization on temperature, reaction time and methanol volume for the production of biodiesel from sludge and Rhodotorula glutinis with high water content and will also show the proposed mechanism for this reaction.