Date of Graduation

8-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Chemical Engineering

Advisor/Mentor

Robert R. Beitle

Committee Member

Christa Hestekin

Second Committee Member

Edgar Clausen

Third Committee Member

Daniel Lessner

Fourth Committee Member

Jamie Hestekin

Keywords

Pure sciences, Applied sciences, Algae, Bioprocessing, Hollow fiber membranes, Propanediol

Abstract

Propylene glycol dinitrate (PGDN) is an important component used in the formulation of energetic materials. A renewable, environmentally-friendly and effective production technique for the production of 1,2-propanediol, an important precursor to PGDN, is desired. While fermentation of 1,2-propanediol has been achieved, it suffers from major limitations such as expensive feed sugars and relatively low yields. It is hypothesized that algae sugars could serve as a feedstock for the microbial synthesis of 1,2-propanediol, thereby reducing production costs and enhancing sustainability.

Algal biomass produced from an Algal Turf Scrubber® has proven to have significant potential as a source of fermentable materials. However, to commercialize the production of 1,2-propanediol and other bulk chemicals from algae, growth rates need to be optimized. It has been suggested that the addition of carbon dioxide gas can enhance the growth rates of algae. This dissertation demonstrates a novel method of gas delivery to thin-film aqueous systems utilizing a unique hollow fiber membrane manifold that is ideal for use in ATS® systems. It was determined that hollow fiber membranes are more effective at delivering gas to liquid compared to traditional bubbling and a porous diffuser, particularly at shallow depths. A mass transfer model was developed to describe the transport of carbon dioxide gas into water in such systems.

In addition to the need for increased growth rates, further challenges lie in the recovery of fermentable materials from algal biomass. While methods of extraction have been developed for other algae components, such as algal oils and proteins, most of the techniques are not suitable for the recovery of fermentable carbohydrates. Very few techniques have focused on the extraction of carbohydrates, and those that do lack economic efficiency due to long processing times and high costs associated with enzymes and/or energy requirements. By combining mechanical means of disruption, such as abrasive material, with sonication, it could be possible to reduce processing times, thereby lowering energy costs. Based on this hypothesis, a novel technique for the extraction of algal sugars was developed. This technique, deemed “sonic abrasion,” was found to extract nearly twice as much sugar than sonication alone, and adequate carbohydrate concentrations for use in fermentation processes could be achieved.

Finally, the feasibility of utilizing algal derived sugars to ferment 1,2-propanediol from Thermoanaerobacterium thermosaccharolyticum was investigated using a 10 g/l synthetic algal sugar mixture. When compared to a 10 g/l glucose feed, it was found that the synthetic algal sugar mixture was capable of producing nearly twice as much 1,2-propanediol whilst producing fewer by-products.

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