Date of Award

5-1-2017

Degree Type

Dissertation

Embargo Date

6-14-2019

Degree Name

Doctor of Philosophy (PhD)

Department

Biomedical and Chemical Engineering

Advisor(s)

Radhakrishna Sureshkumar

Subject Categories

Engineering

Abstract

Microalgae represent a promising source of renewable biomass for the production of biofuels and valuable chemicals. However, the development of high throughput microalgal cultivation methods and energy efficient biomass harvesting technology is necessary to improve the economic viability of large scale microalgal biomass production.

The issue of poor distribution and absorption of light is one of the hurdle that can be addressed to improve the productivity in microalgal cultivation systems. As it happens, microalgal photosynthetic activities have shown great dependence on the irradiance to which the microalgal cells are exposed. Quantitatively, microalgal growth increases with increasing light intensity until a saturation level beyond which the microalgal photosynthetic machinery can be subject to photodamage. Qualitatively, most microalgal species have exhibited a propensity for wavelengths in the blue and red regions of the visible electromagnetic spectrum whereas other wavelengths can induce photoinhibition. Further, a change in the incident light can lead to photoacclimation where the microalgal species activate the preferential synthesis of certain compounds or completely alter their metabolic activity.

Despite such importance of light for microalgal growth and biomass production, only a small fraction of microalgal cells receives an optimal irradiance in current microalgal cultivation systems (open and enclosed ponds). The remaining microalgal cells are found either in the over illuminated zones (e.g. top surface of open culture) of the cultivation systems where they are exposed to photoinhibition or in the poorly illuminated zones where their growth is limited. In this dissertation, this issue is addressed by developing a multi-fold approach to improve the distribution and absorption of light in microalgal photobioreactors.

First, a plasmonic film light filter technology is developed. By virtue of enhancing the irradiation of blue and red lights using silver nanospheres and gold nanorods, this technology can enhance microalgal biomass production by up to 50% and increase photosynthetic pigments production by up to 78%. A short light path capable Tris-Acetate-Phosphate-Pluronic (TAPP) microalgal cultivation and harvesting system is also developed. Adding to the interesting light manipulation features, this energy efficient microalgal cultivation and harvesting system that exploits the thermoreversible sol-gel transition properties of the copolymer pluronic can increase the harvesting rate of microalgal biomass via gravimetric sedimentation by a factor of ten. Further, the adhesion properties of microalgal cells on the surface of photobioreactors are studied as a way to control the impacts of biofouling on light penetration and light absorption in microalgal cultivation systems. Furthermore, the rheological properties of microalga C. reinhardtii broths are studied and the interesting properties of such complex fluids are used as tools to control the periodical motion of microalgal cells from dark sections to well illuminated sections of typical photobioreactors for enhanced microalgal growth.

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Available for download on Friday, June 14, 2019

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Engineering Commons

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