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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In the present study, an effort has been made to sequester automobile exhaust gases from a petroleum based engine using microalgae Scenedesmus quadricauda. The automobile selected for the present study was a two wheeler motorcycle. S. quadricauda was subjected to un-suspended/attached non-enclosure cultivation onto a silicone matrix coated stainless steel pipe, protracted to the motorcycle silencer outlet through which, the exhaust gases passed out. The automobile exhaust gases initially contained 13% of carbon dioxide, 2.4% of carbon monoxide, 0.2% of nitric oxide, 0.08% of nitrogen dioxide, 0.1% of sulfur dioxide and 0.05% of sulfur trioxide concentrations, which were removed up to 62, 57, 65, 66, 64 and 65% respectively by S. quadricauda from the attached growth experiment. The present study results showed that the exhaust gases played a crucial role in inducing biomass and lipid yields up to ≥2 and ≥ 0.6 g L − 1 respectively. The tolerance of S. quadricauda to the exhaust gas components' toxicity and its efficiency in treating them followed by the biomass and lipid productivities were better than anticipated in the present study.

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This article has been retracted. Please see the Retraction Notice for more detail: https://doi.org/10.1186/s42834-020-0046-z