Theses and Dissertations

Issuing Body

Mississippi State University


Hernandez, Rafael

Committee Member

French, W. Todd

Committee Member

Estévez, L. Antonio

Committee Member

Magbanua, Benjamin, Jr.

Committee Member

Hill, Priscilla

Date of Degree


Document Type

Dissertation - Open Access


Chemical Engineering

Degree Name

Doctor of Philosophy


James Worth Bagley College of Engineering


Dave C. Swalm School of Chemical Engineering


The utilization of activated sludge as feedstock for biofuel and oleochemical production was investigated. Initial studies included optimization of biodiesel production from this feedstock through in situ transesterification. Results of these studies indicated that activated sludge biodiesel is not economically viable. This was primarily due to relatively low yields and the high economics of feedstock dewatering. Strategies to increase biofuel yield from activated sludge were then evaluated. Bacterial species present in activated sludge are known to produce a wide variety of lipidic compounds as carbon and energy storage material and as components of their cellular structures. In addition to lipidic compounds, activated sludge bacteria might also contain other compounds depending on wastewater characteristics. Among these bacterial compounds, only the saponifiable ones can be converted to biodiesel. The unsaponifiable compounds present in the activated sludge are also important, not only for biofuel production, but also for a wide variety of applications. Characterization of lipids in activated sludge revealed that it contains significant amount of polyhydroxyalkanoates, wax esters, acylglycerides and fatty acids. It also contains Template Created By: James Nail 2010 sterols, steryl esters and phospholipids as well as small but detectable amounts of hydrocarbons. This indicated that activated sludge could be also an inexpensive source of oleochemicals. Another strategy that was evaluated was lipid-enhancement by fermentation of activated sludge. Since the majority of products from petroleum oil are used as transportation fuel, the aim here was to increase the saponifiable lipids in activated sludge bacteria by applying a biochemical stimulus (i.e. high C:N ratio). Results showed that application of this stimulus increased the amount of saponifiable lipids, particularly triacyglycerides, in the activated sludge. Furthermore, fermentation homogenized the lipids in the sludge regardless of its source. This solidified the concept of utilizing wastewater treatment facilities as biorefineries. To support the utilization of other compounds in raw activated sludge for biofuel production, a model compound was chosen for catalytic cracking experiments. Results indicated that catalytic cracking of 1-octadecanol over H+ZSM5 proceeds via dehydration, producing octadecene. The octadecene then undergoes a series of reactions including β-C─C bond scission, alkylation, oligomerization, dehydrocyclization and aromatization producing aromatics, paraffins and olefins suitable for fuel applications.