Theses and Dissertations

Issuing Body

Mississippi State University


Hernandez, Rafael A.

Committee Member

Estevez, L. Antonio

Committee Member

Hill, Priscilla

Committee Member

French, W. Todd

Date of Degree


Document Type

Dissertation - Open Access


Chemical Engineering

Degree Name

Doctor of Philosophy (Ph.D)


James Worth Bagley College of Engineering


Dave C. Swalm School of Chemical Engineering


Biodiesel is a renewable fuel that can supplement petroleum fuel supply. A major deterrent to commercial biodiesel production from traditional feedstock like soybean, canola or rapeseed oils is the high cost of feedstock: 70 - 95% of total biodiesel production cost. Therefore, a relatively cheaper feedstock is needed to make the price of biodiesel cost-competitive with petroleum diesel. Activated sludge from wastewater treatment plants is a relatively cheaper feedstock and relatively easy to obtain. However, drying of this sludge prior to oil extraction is a major operating cost of this process, as high as 50% of biodiesel production cost. The goal of this research is to address this challenge by investigating the feasibility of using activated sludge from municipal wastewater for cost-efficient biodiesel production with little or no drying of the feedstock. First, the use of water-tolerant catalysts for biodiesel production was investigated to determine the level of water tolerance of these catalysts for the case where the sludge could be dried to an extent. The study investigated porous metal oxide and zeolite catalysts with tunable basicities, acidities and hydrophobicities and proposed a reaction mechanism for the most active catalyst. Next, the alternative where the catalysts were not very tolerant of moisture was considered, and the feasibility of a non-catalytic means of producing biodiesel from wet microbial media using supercritical methanol was also investigated. A model system of oleaginous yeast, Rhodotorula glutinis, was used to evaluate the production of biodiesel in a system similar to sludge. Since the non-catalytic method showed the highest tolerance for water at 90% moisture content, the optimum reaction conditions for highest FAME yields were determined. Two methods of the non-catalytic process, 1-step and 2-step processes, that could produce high FAME yields were studied and compared in terms of FAME yields and kinetic rate constants. With these results, an economic analysis was performed to investigate the cost efficiency of both methods of the non-catalytic process and recommend one with great potential for producing biodiesel from activated sludge at a cost-competitive price.