Mixotrophic cultivation of microalgae using industrial flue gases for biodiesel production

Abstract

In the present study, an attempt has been made to grow microalgae Scenedesmus quadricauda, Chlorella vulgaris and Botryococcus braunii in mixotropic cultivation mode using two different substrates, i.e. sewage and glucose as organic carbon sources along with flue gas inputs as inorganic carbon source. The experiments were carried out in 500 ml flasks with sewage and glucose-enriched media along with flue gas inputs. The composition of the flue gas was 7 % CO2, 210 ppm of NO x and 120 ppm of SO x . The results showed that S. quadricauda grown in glucose-enriched medium yielded higher biomass, lipid and fatty acid methyl esters (FAME) (biodiesel) yields of 2.6, 0.63 and 0.3 g/L, respectively. Whereas with sewage, the biomass, lipid and FAME yields of S. quadricauda were 1.9, 0.46, and 0.21 g/L, respectively. The other two species showed closer results as well. The glucose utilization was measured in terms of Chemical Oxygen Demand (COD) reduction, which was up to 93.75 % by S. quadricauda in the glucose-flue gas medium. In the sewage-flue gas medium, the COD removal was achieved up to 92 % by S. quadricauda. The other nutrients and pollutants from the sewage were removed up to 75 % on an average by the same. Concerning the flue gas treatment studies, S. quadricauda could remove CO2 up to 85 % from the flue gas when grown in glucose medium and 81 % when grown in sewage. The SO x and NO x concentrations were reduced up to 50 and 62 %, respectively, by S. quadricauda in glucose-flue gas medium. Whereas, in the sewage-flue gas medium, the SO x and NO x concentrations were reduced up to 45 and 50 %, respectively, by the same. The other two species were equally efficient however with little less significant yields and removal percentages. This study laid emphasis on comparing the feasibility in utilization of readily available carbon sources like glucose and inexpensive leftover carbon sources like sewage by microalgae to generate energy coupled with economical remediation of waste. Therefore on an industrial scale, the sewage is more preferable. Because the results obtained in the laboratory demonstrated both sewage and glucose-enriched nutrient medium are equally efficient for algae cultivation with just a slight difference. Essentially, the sewage is cost effective and easily available in large quantities compared to glucose.

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“…The micoalga S. quadricauda was obtained from the mother cultures maintained as quadrant streak plates in a freezer from the previous studies [25]. The isolated colonies were looped out and sub-cultured into freshly prepared Bold's basal medium (BBM from Sigma-Aldrich) in a 500 mL Erlenmeyer flask with 300 mL working volume.…”

“…The lipids were extracted from powdered biomass through solvent extraction procedure using hexane [25]. The solvent was introduced into the 50 mL round bottom flask containing the biomass along with a stir bar to reflux heat for 60 min at 70°C.…”

The advances and limitations in biodiesel production: feedstocks, oil extraction methods, production, and environmental life cycle assessment

“…The LCA research works reported that the land required for agricultural systems was 96% higher than for the algal biodiesel production (245). Moreover, microalgae cultivation can be associated with carbon capture from flue gas emissions and wastewater treatment (52,246). It was reported that 1 kg of algal biodiesel fixes about 0.6 kg of CO 2 (247).…”

MAB2.0 project: Integrating algae production into wastewater treatment

“…As microalgae can remove this excess amount of nutrients from the AD effluent, its application leads to saving on operational cost and capacity while producing biomass as added value product. Furthermore, anaerobic digestion derived biogas is often used on-site to generate power in gas engines with flue gas emission, of which CO 2 content is a potential carbon source for microalgae (16,17).…”