Date of Graduation

12-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Chemical Engineering

Advisor/Mentor

Jamie A. Hestekin

Committee Member

Robert Beitle

Second Committee Member

Christa Hestekin

Third Committee Member

Thomas A. Costello

Keywords

Biological sciences, Applied sciences, Health and environmental sciences, Eicosapentaenoic acid, Fatty acids, Microalgae, Photo bioreactor, Porphyridium cruentum, Swine waste water

Abstract

One of the major nutritional requirements in our diet is an adequate intake of omega-3 specially eicosapentaenoic acid (EPA). In the present study, the effects of two temperatures (16°C & 20˚C) and light intensities (140 & 180µE/M2.S) and four nitrate levels (0.075, 0.3, 0.5 and 0.7g/L) on the cell growth and lipid productivity of Porphyridium cruentum, one of the most promising oil-rich species of microalgae, were investigated. A growth comparison was carried out using pure CO2 and 5% CO2/air. Additionally, the ratio of the fatty acids with omega-3 and omega-6 groups at various growth conditions were compared, since an appropriate proportion of omega-6 (arachidonic acid(ARA)) to omega-3(EPA) is vital for healthy nutrition. Lower EPA production and consequently higher ARA/EPA ratio occurred when 5%CO2/Air was utilized as CO2 supplementation. The highest biomass productivity (143 mg/L.day) and EPA (13.08%w/w) were achieved at 20˚C, 140µE/M2.S and 0.3g/L nitrate, while lipid content was the lowest (0.5%w/w) at this condition. The optimal growth condition to produce the lowest ARA/EPA, 2.17, was achieved at 20°C, 140µE/M2.S (pure CO2) and 0.5g/L nitrate.

The possible growth of P. cruentum in ultra-filtered swine wastewater was also evaluated in this study. P. cruentum was grown in different waste dilutions (total nitrogen concentrations of 12.4, 49.4, 82.4 and 115.3mg/L) to achieve the optimum nutrient condition for producing EPA. Various salinities (0-3.2%) were examined in the optimum nitrogen concentration. The data were compared to L1-medium and the results generally demonstrate better growth of P. cruentum in swine waste with higher lipid productivity and lipid content. The maximum lipid productivity (143mg/L) and lipid content (4.71 mg/100g biomass) was achieved in 3.2% salinity swine waste with 82.4mg/L nitrogen concentration while control medium with 2.5% salinity resulted the highest biomass productivity (3.76g/L). Markedly higher biomass productivity, lipid productivity and lipid content were achieved from swine waste culture diluted with seawater compared to saltwater. Higher C16:0, 18:2 and C20:5 (EPA) and lower C18:0 and ARA/EPA were achieved from swine waste culture compared to the control medium. Generally, the minimum ARA/EPA(1.33) was obtained at 82.4mg/L nitrogen concentration and 3.2% salinity in swine waste diluted with seawater.

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