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Cultivation of Nannochloropsis Salina in Diluted Anaerobic Digester Effluent under Simulated Seasonal Climatic Conditions and in Open Raceway Ponds

Sheets, Johnathon P
http://rave.ohiolink.edu/etdc/view?acc_num=osu1373452229

Abstract Details

2013, Master of Science, Ohio State University, Food, Agricultural and Biological Engineering.
Concerns about unsustainable fossil energy use have led to increased research and development for cost-effective and renewable transportation fuels. Microalgae have gained considerable interest as a biofuel feedstock due to their ability to be grown in areas unsuitable for crops, high growth rates and high oil content. However, massive commercial nutrient and freshwater requirement in open raceway pond cultivations have drawn concerns regarding the economic sustainability of the microalgae to biofuel process, prompting research towards culturing microalgae with nutrients from freely available wastewater streams. Anaerobic digestion (AD) is an organic waste treatment process that utilizes microorganisms to produce biogas for renewable energy. Digested liquor from AD, or AD effluent, is rich in nitrogen and phosphorus. To reduce nitrogen and phosphorus runoff, research has been conducted to culture microalgae with diluted AD effluent for nutrient removal and lipid-rich biomass production. Most previous research cultured freshwater algae strains with diluted AD effluent. However, to reduce freshwater consumption, attention should be focused on culturing marine strains with AD effluent as a nutrient source. Culturing any microalgae strain requires analysis of the effects of seasonal climatic conditions on growth prior to scale-up in open raceway ponds. Collection of these data will improve prediction of biomass and lipid productivity in realistic outdoor cultivations. However, some factors encountered in outdoor systems are difficult to simulate in laboratory settings. Evaluation of the effects of predator contamination on biomass, lipid, and fatty acid production is required for prediction of biofuel yield. Finally, economic analyses are critical to evaluate future research opportunities that can improve the microalgae to biofuel process. In this study, specific growth rate, biomass productivity, total nitrogen (TN) removal, lipid and fatty acid content of Nannochloropsis salina were analyzed for their response to simulated seasonal climatic conditions using municipal wastewater AD effluent as a nutrient source. Results were compared with cultures using commercial under equivalent TN levels for proper comparison. Data collected from simulated conditions were used to predict biomass growth in open raceway ponds during July, August, October and November culture periods in Wooster, Ohio, USA (lat. 40.8050&#xb0;N). Preliminary experiments showed the favorable AD effluent loading ratio was 7% (v/v), with a maximum specific growth rate of 0.327 &#xb1; 0.016 d-1, biomass productivity of 204 &#xb1; 12 mg L-1 d-1 and TN removal of 97%. Under simulated seasonal conditions, N. salina specific growth rate was significantly affected (p<0.0001) by average daily light exposure when cultured in either diluted AD effluent or commercial nutrients. The media temperature levels tested (10-25&#xb0;C) did not have significant effect on specific growth rate. Using average daily light exposure as the only effect, quadratic models predicting specific growth rate showed high correlation cultures using commercial nutrients (R2=0.898) and diluted AD effluent (R2=0.910). While total lipid content (0.26-0.32 g g-1 dry weight) and total fatty acid content (0.575-0.661 g g-1 lipids) were unaffected, fatty acid profile was significantly affected by lighting conditions, with a 29% increase in C20:5 (eicosapentaenoic acid, EPA) and 43% increase in C20:4 content for varied illumination culture over constant illumination cultures. Using the quadratic models attained under simulated seasonal conditions, accurate prediction (22% error) was attained for specific growth rate of N. salina cultured in an 850-L open raceway pond using AD effluent as a nutrient source and July culture period with highest average light exposure, highest average media temperature, fed batch cultivation mode and no predator contamination. Cultures in August with fed batch operating mode and 1060-L volume were exposed to predator contamination and showed inadequate prediction. October and November cultures with predators and semi-continuous operating mode (1060-L) also showed inadequate prediction, indicating models must account for additional operating conditions. When contaminated with predators, N. salina lipid content declined from 0.37 &#xb1; 0.02 to 0.26 &#xb1; 0.01 (g g-1 dry biomass weight), total fatty acid content declined from 0.671 &#xb1; 0.070 to 0.335 &#xb1; 0.029 (g g-1 lipids) and EPA content declined from 0.272 &#xb1; 0.03 to 0.084 &#xb1; 0.011 (g g-1 lipids), drastically reducing the net value of N. salina biomass. The results from this study demonstrated the effects of realistic seasonal conditions on N. salina culture using AD effluent as a nutrient source. While limited light and predators can diminish biomass lipid and fatty acid productivity, AD effluent was successfully shown to be a suitable nutrient replacement for commercial nutrients under simulated seasonal climatic conditions. Data attained will be used to improve modeling of large-scale open raceway ponds in a seasonal climate.
Yebo Li, PhD (Advisor)
Peter Ling, PhD (Committee Member)
Brian McSpadden Gardener, PhD (Committee Member)
119 p.
Agricultural Engineering
Nannochloropsis salina, anaerobic digester effluent, microalgae biofuels, open raceway ponds, seasonal climatic conditions, nutrient removal

Recommended Citations

Citations

  • Sheets, J. P. (2013). Cultivation of Nannochloropsis Salina in Diluted Anaerobic Digester Effluent under Simulated Seasonal Climatic Conditions and in Open Raceway Ponds [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1373452229

    APA Style (7th edition)

  • Sheets, Johnathon. Cultivation of Nannochloropsis Salina in Diluted Anaerobic Digester Effluent under Simulated Seasonal Climatic Conditions and in Open Raceway Ponds. 2013. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1373452229.

    MLA Style (8th edition)

  • Sheets, Johnathon. "Cultivation of Nannochloropsis Salina in Diluted Anaerobic Digester Effluent under Simulated Seasonal Climatic Conditions and in Open Raceway Ponds." Master's thesis, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1373452229

    Chicago Manual of Style (17th edition)

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