Date of Award:

5-2013

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biological Engineering

Committee Chair(s)

Ronald C. Sims

Committee

Ronald C. Sims

Committee

Charles D. Miller

Committee

Randolph V. Lewis

Committee

Byard Wood

Committee

James Bonner

Abstract

Microalgae are the preferred crop for the production of biodiesel. Microalgae are microplants that have the ability to harness sunlight more efficiently than other plants and store 20-80% lipids per g of dry algae in their cells. Microalgae have the extraordinary ability to grow in brackish water or wastewater. Microalgae can be grown in municipal wastewater to uptake phosphorus and nitrogen and remediate the wastewater of these nutrients. Microalgae thus cultivated accomplishes a dual role of wastewater treatment and provides a sustainable feedstock for biofuels and other bioproducts.

This study focused on efficiently harvesting microalgae from water using modified starch. Modified starch, or in this case, cationic starch, is an organic compound that when used to harvest microalgae in large quantities has shown no environmental concerns. Moreover, starch is inexpensive, biodegradable, and is abundantly found in nature. For this research, cationic starch was synthesized using cationic functional groups3-methacryloyl amino propyl trimethyl ammonium chloride, and biogenic amines. The synthesized cationic starches were tested for their ability to remove suspended solids using wastewater from Logan City, Utah wastewater treatment lagoons and from a single strain of microalga Scenedesmus obliquus grown in photobioreactors. Cationic starches showed superior solids removal efficiencies compared with the traditionally used and toxic aluminum sulfate. The dosage of cationic starches was significantly lower than aluminum sulfate to harvest equivalent quantities of microalgae.

The microalgae harvested using cationic starches were able to produce higher quantities of acetone, butanol, ethanol, biodiesel, and Escherichia coli when compared with the bioproducts from aluminum sulfate harvested microalgae. Higher yields could be due to the carbohydrate nature of starch, which provided additional carbon to produce higher bioproduct yields. Cationic starches represent an organic form of microalgae harvesting, which can improve the potential for the use of microalgae for our future energy needs.

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