Publication Date

5-2023

Date of Final Oral Examination (Defense)

January 2023

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Biology

Department

Biology

Supervisory Committee Chair

Kevin Feris, Ph.D.

Supervisory Committee Member

Lisa Warner, Ph.D.

Supervisory Committee Member

Marcelo Serpe, Ph.D.

Abstract

Agricultural and municipal wastewaters contain vital elements necessary for algal growth (i.e., N, P, Mg, K). One way to capture these elements, in an environmentally friendly way, is through struvite production (NH4MgPO4·6H2O), however, this process is costly to implement. High-value secondary commodities coupled to struvite production can enable implementation of this nutrient capture strategy for agricultural and municipal wastewater systems. In this study, struvite was tested as a nutrient source for cultivation of high-value algal biomass with the main focus on high-value lipids such as Eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). We compared the growth of microalgal strains C. reinhardtii, N. oculata, and P. tricornutum in two different growth media that include a standard media (Chu 13 and F2), and media supplemented with municipal struvite as the primary nitrogen and phosphorus source. A second experimental factor (temperature and nutrient stress) was used to evaluate stress effects on algal lipid production when struvite is used as the primary nutrient source for growth. Growth response, lipid content and quality, and nutrient sequestration were evaluated. Data indicate that all three species produce more or the same amount of biomass in struvite-amended treatments relative to controls, respectively (0.43 g/L struvite vs. 0.16 g/L in controls for C. reinhardtii, 2.76 g/L for struvite and 2.58 in controls for P. tricornutum, N. oculata control compared to struvite-amended treatments (0.15 g/L vs. 0.32 g/L, respectively). Lipid productivity and lipid profiles varied with respect to stress and media type as a function of algal strain. Overall, stress and media had a limited effect on polyunsaturated fatty acids PUFA’s production with linoleic acid being the only fatty acid to illustrate a significant response to nutrient stress in N. oculata (104.52 ug/mg compared to 5.84 ug/mg in struvite media). C. reinhardtii had a significant increase in linoleic acid in struvite amended media compared to standard media (13.2 ug/mg vs 7.96 ug/mg). P. tricornutum was the only strain out of the three to produce Eicosapentaenoic acid (EPA); however, while none of the treatments had a significant effect on EPA production, EPA was not produced in F2 under temperature stress. Based on the biomass composition of the algal we cultivated under our experimental conditions the highest market value of the biomass was a high-protein cattle feed. Although few lipids illustrate significant responses to our temperature and nutrient stresses, the directional trends in the responses observed across strains and lipids suggest future studies that limit single nutrients (i.e. N or P), rather than simultaneous limitation of N and P may result in more positive effects on yields of targeted lipids.

DOI

https://doi.org/10.18122/td.2084.boisestate

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