Studies on CO2 Sequestration by Microalgae.

Akhila, N. (2014) Studies on CO2 Sequestration by Microalgae. [Student Project Report] (Submitted)

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Abstract

Microalgae have been identified with potential for CO2 sequestration and simultaneous bioenergy production. Vast biodiversity, higher growth rate and simple nutritional requirements with wide environmental adaptations make them an ideal feedstock for industrial production of valuable products. In this context, evaluation of various culture parameters to improve algal biomass yield, lipid quality and lipid extraction conditions towards bioenergy production is necessary. An indigenous Scenedesmus sp. was selected for the study due to its higher specific growth rate and biomass productivity. Cultivation parameters such as pH, nitrogen source, nitrogen concentration, light intensity, CO2 supplementation, external bicarbonate supplementation, organic carbon supplementation were individually optimized for maximizing biomass and lipid yield. The lipid quality was evaluated by fatty acid profiling of lipid extracts by gas chromatography technique. The mechanism and ability of the microalgal strain to utilize CO2 under open outdoor conditions were evaluated in raceway ponds. In addition, various methods of lipid extraction and biomass pre-treatments like ultrasonication, homogenization, steam pre-treatment were evaluated to maximize lipid yield directly from wet algal biomass. Scenedesmus sp. could tolerate up to 15% CO2 v/v and maximum growth was observed when CO2 was supplemented through an infusion system in low density polyethylene photo bioreactor compared to direct aeration in bubble column reactor. The strain showed maximum growth between pH 9 - 11. Highest growth was observed when cultivated with nitrate as nitrogen source (~ 1gL-1 biomass yield) compared to urea and ammonium salts. It was observed that with increase in nitrate levels the biomass yield increased and lipid content decreased. The strain could tolerate up to 40mM external bicarbonate supplementation with maximum growth at 15mM. The strain had the ability to grow under mixotrophic conditions i.e., organic carbon supplementation (glucose and glycerol) up to 0.2 M. The biomass yield increased by three fold (2.1 gL-1) compared to autotrophy (~ 0.7gL-1). The strain had an average lipid content of 15% w/w biomass with palmitic (C-16:0), oleic (C-18:1) and alpha linolenic acid (C-18:3) as major fatty acids. An increase in oleic acid levels was observed under nutrient deprived and high light intensity growth conditions. The fatty acid yield increased under mixotrophic and CO2 supplemented conditions compared to control cultures indicating the role of these parameters in lipid metabolism. Among the various pre-treatment conditions homogenization and steam (autoclave) treatments improved lipid recovery directly from wet algal biomass. The study suggested that Scenedesmus sp. has the ability to grow under open conditions and fix the external CO2 with increased biomass yield. Further the increase in lipid yield under CO2 supplemented conditions suggest that the strain has dual benefit of both CO2 mitigation and simultaneous lipid production. Accumulation of oleic acid in the biomass makes the lipid substrate ideal for biofuel production since presence of monounsaturated fatty acid improve the fuel properties. Evaluation of pre-treatment conditions suggest that particle size reduction of algal biomass improve the lipid yield by twofold and homogenization/steam pre-treatment of wet biomass recovered lipid yield up to 17% w/w (1.5 fold) compared to control suggesting that lipids can be extracted directly from wet biomass avoiding the energy intensive drying process.

Item Type:	Student Project Report
Uncontrolled Keywords:	Microalgae, CO2 sequestration, Scenedesmus
Subjects:	500 Natural Sciences and Mathematics > 07 Life Sciences > 04 Microbiology > 01 Algae
Divisions:	Plant Cell Biotechnology
Depositing User:	Food Sci. & Technol. Information Services
Date Deposited:	17 Jun 2015 10:11
Last Modified:	17 Jun 2015 10:11
URI:	http://ir.cftri.res.in/id/eprint/11840

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