Potential of Monoraphidium minutum for carbon sequestration and lipid production in response to varying growth mode

• Monoraphidium minutum remediated flue gas.
• Intermittent CO2 supply maximizes lipid accumulation while growing autotrophically.
• Max. biomass productivity was observed in mixotrophic growth.
• Higher C/N of lyophilized biomass showed higher lipid accumulation.
• Resultant biodiesel met with European biodiesel standard.

Mixotrophic growth at flask level and, autotrophic–mixotrophic and autotrophic growth in photobioreactor by utilizing CO2/air/flue gas were checked for the isolated strain of Monoraphidium minutum from polluted habitat. Our study confirmed that it is a saturated fatty acid rich (30.92–68.94%) microalga with lower degree of unsaturation oil quality (42.06–103.99) making it potential biodiesel producing candidate. It showed encouraging biomass productivity (80.3–303.8 mgl−1 day−1) with higher total lipid (22.80–46.54%) under optimum glucose, fructose, microalgal biodiesel waste residue and sodium acetate fed mixotrophic conditions. The pH control by intermittent CO2, continuous illumination with 30% flue gas, and utilization of biodiesel glycerin were effective schemes to ameliorate either biomass productivity or % lipids or both of these parameters at photobioreactor scale (7.5 L working volume). The modulation of environmental variables (pH control, CO2 and organic substrates concentration) could augment % saturated fatty acids, such as C16:0.

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