Date of Award:

12-2025

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

Liyuan Hou

Committee

Liyuan Hou

Committee

R. Ryan Dupont

Committee

Jixun Zhan

Abstract

Wastewater treatment systems are increasingly challenged by a complex mix of pollutants including excess nutrients, organic dyes, and persistent chemicals like per- and polyfluoroalkyl substances (PFAS). Conventional treatment technologies often struggle to effectively and affordably remove these contaminants. This study explores the use of two diatom species, Phaeodactylum tricornutum and Navicula cryptocephala var. veneta, both single-celled microalgae with silica-based cell walls, as an environmentally sustainable approach to tertiary wastewater treatment. Diatoms offer dual functionality through surface adsorption properties and metabolic flexibilities, making them promising candidates for integrated treatment strategies.

To test the trophic flexibilities of diatoms, P. tricornutum was grown under mixotrophic (mix of metabolism for organic carbon in addition to photosynthesis) and photoautotrophic (photosynthesis only) conditions. Mixotrophic conditions were implemented through the addition of organic carbon using glucose, glycerol, sodium acetate, and sodium pyruvate, respectively. Cultures supplemented with glycerol and sodium pyruvate showed the greatest improvements in growth, nutrient uptake, and lipid production, demonstrating the potential of mixotrophic growth to enhance performance in carbon-rich waste waters. In contrast, naturally occurring non-axenic N. veneta cultures were analyzed to assess diatom-bacteria interactions under different lighting and carbon regimes. Although bacterial species associated with plant-like growth promotion were present, no cooperative benefits were observed. Instead, elevated carbon conditions favored rapid bacterial growth, which ultimately suppressed diatom abundance, highlighting the need for microbial community studies in mixed systems to assess diatom capabilities in tertiary wastewater treatment.

To assess pollutant removal, both live and dried diatom biomass were tested for their ability to adsorb organic dyes. Dried biomass, especially from P. tricornutum, achieved high dye removal efficiencies due to favorable surface interactions between the dye molecules and the silica-based frustules. N. veneta showed moderate performance, supporting its potential as an alternative biosorbent. However, when tested against perfluorooctanoic acid (PFOA), a representative PFAS compound, neither diatom species demonstrated measurable adsorption, indicating that additional surface engineering would be required to target these resistant contaminants.

This work demonstrates that diatoms can play a valuable role in sustainable wastewater treatment. Their ability to simultaneously assimilate nutrients and bind synthetic dyes makes them a cost-effective and low-energy option for tertiary treatment applications. While further development is needed to expand their capabilities to emerging pollutants like PFAS, the findings support continued research into diatom-based technologies as part of a broader push toward more circular and biologically integrated wastewater treatment systems.

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