Date of Graduation

12-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Chemical Engineering

Advisor/Mentor

Hestekin, Jamie A.

Committee Member

Beitle, Robert R. Jr.

Second Committee Member

Hestekin, Christa N.

Third Committee Member

Costello, Thomas A.

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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