Theses and Dissertations at Montana State University (MSU)
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Item Algal biofilms and lipids: bicarbonate amendment and nitrate stress to stimulate lipid accumulation in algal biofilms(Montana State University - Bozeman, College of Engineering, 2022) Rathore, Muneeb Soban; Chairperson, Graduate Committee: Brent M. Peyton; This is a manuscript style paper that includes co-authored chapters.Algal biofuels are compounds obtained by transesterification of algal lipids to fatty acid methyl esters (FAMEs) which can be used as biodiesel. Algal biofilms have a potential for commercial applications of algal biomass for biofuel production and provide concentrated biomass requiring less water removal to reduce biofuel production costs. Lipid production in algal biofilms is low as compared to planktonic algal growth systems and strategies for enhancing lipid content in algal biofilms need to be developed. The overarching goal of the studies presented herein was to develop lipid accumulation strategies in algal biofilms using nutrient stresses to increase triacylglycerides (TAGs) and FAMEs. First, a reactor was designed for photoautotrophic biofilm growth incorporating a novel algal biomass harvesting mechanism. Chlorella vulgaris biofilm growth was demonstrated to establish the reactor characteristics under three different inorganic carbon regimes and the presence of excess calcium to facilitate biofilm attachment and accumulation. Excess calcium resulted in precipitate formation and increasing ash content in biomass and caused difficulty in biofilm detachment. However, the highest biomass accumulation was observed in the bicarbonate and the bicarbonate with calcium treatments. Second, two different algal strains were tested for lipid accumulation under two nutrient conditions: nitrate limitation and bicarbonate addition. Algal strains included, an extremophilic freshwater diatom RGd-1, a Yellowstone National Park (YNP) isolate, and oleaginous chlorophyte C. vulgaris. High bicarbonate content at low nitrate concentration in the bulk medium provided the highest lipid accumulation as determined by Nile Red fluorescence and Gas Chromatography Mass Spectrometry (GCMS) analysis of extracted FAMEs (7-22 % wt/wt). For prevention of biomass loss and quick response to nutrient stresses to stimulate lipid accumulation, the growth medium was exchanged after initial biofilm accumulation and operated in batch mode. This was implemented to quickly introduce nutrient stresses using fresh medium to vary bicarbonate and nitrate concentrations as needed. Thus, the work presented here demonstrated enhanced lipid production in algal biofilms with nitrate stress and bicarbonate amendment is a viable strategy to increase lipid accumulation. Increased lipid content may help offset the cost for biodiesel production with more lipid product and lower processing requirements for water removal.Item Sodium bicarbonate amendment for enhanced astaxanthin production from Haematococcus pluvialis(Montana State University - Bozeman, College of Engineering, 2019) Erturk, Berrak; Chairperson, Graduate Committee: Brent M. Peyton; Christian Lewis and Brent M. Peyton were co-authors of the article, 'Sodium bicarbonate amendment for enhanced astaxanthin production from Haematococcus pluvialis' submitted to the journal 'Algal research' which is contained within this thesis.Haematococcus pluvialis is a freshwater green microalga that is widely considered to be the richest natural source of the high value carotenoid astaxanthin. The use of bicarbonate salts as a means of efficiently delivering inorganic carbon in microalgal cultivation is a relatively new concept and its application is continuously growing. Previous studies have largely focused on increasing the lipid content in microalgae via the use of high concentrations of sodium bicarbonate under nitrogen deplete culture conditions. Lipid accumulation is directly related to astaxanthin production as astaxanthin is dissolved and stored in lipid bodies in H. pluvialis. Because of this relationship in H. pluvialis, the effects of sodium bicarbonate addition on astaxanthin production was investigated in this study. Due to its complex life cycle, H. pluvialis is commonly cultivated in two stages called the 'green' and 'red' stage. Different approaches have been proposed in each stage to increase the astaxanthin production, namely by growing microalgae under nutrient-limited conditions or resuspending the cells into nutrient deplete conditions. In this study, H. pluvialis (UTEX 2505) was cultivated in stirred (120 rpm) batch reactors containing MES-Volvox medium with a 12 h:12 h light/dark cycle. Sodium bicarbonate (2.5 mM) was used as an additional inorganic carbon source in the green stage and 50 mM of sodium bicarbonate was used as a trigger mechanism to induce astaxanthin production in the red stage. Following the trigger, the astaxanthin accumulation rate increased from 0.13 mg L ^-1 day ^-1 to 0.64 mg L ^-1 day ^-1 with an astaxanthin concentration of 1.56 + or - 0.01 mg L ^-1 and 3.95 + or - 1.25 mg L ^-1 respectively. Whereas, an addition of 2.5 mM sodium bicarbonate at the green stage increased the final astaxanthin accumulation rate up to 2.12 mg L ^-1 day ^-1 and the astaxanthin concentration to 11.2 + or - 0.56 mg L ^-1. Increasing biomass in the green stage resulted in higher astaxanthin content at the end of the red stage. In addition to increasing the total astaxanthin content, 2.5 mM of sodium bicarbonate led to faster nitrogen utilization during the green stage. With this faster utilization of nitrogen, the cultures were grown with a one-stage cultivation approach, where the astaxanthin production occurred in continuous mode.