Exploration of fast growing Botryococcus sudeticus for upstream and downstream process in sustainable biofuels production

• Botryococcus sudeticus grown in open condition can produce 71 t ha−1 y−1 of dry biomass.
• A two-step transesterification yields 0.195 g biodiesel yield/g dry biomass.
• Higher heating value (HHV) of B. sudeticus biodiesel was estimated up to 39 MJ/kg.
• The lipid extracted residual biomass produced 0.165 g bioethanol/g residual biomass.

This study explores an integrated approach on biodiesel and bioethanol production from the indigenous strain Botryococcus sudeticus. The alga was isolated from the freshwater pond and mass cultivated in 25 m2 open raceway pond. A two-step combined harvesting technique such as coagulation and flocculation was standardized. The results showed that 150 ppm of ferric chloride and 15 ppm of organic polymer Poly-(D) glucosamine increases the harvesting efficiency and the biomass yield was achieved up to 99%. Based on the areal and volumetric biomass productivity, it is estimated that the alga B. sudeticus can produce 71.1 t ha−1 y−1 of dry biomass. The dry biomass was analyzed for its chemical compositions. The results revealed that, the alga accumulates 4.5% of hydrocarbon, 22.6% of lipid, 23% of carbohydrate and 19.5% of protein, respectively. Sequential stages of esterification and then transesterification were studied to convert the FFA and triglycerides into biodiesel. Triacylglycerides and free fatty acids were converted to alkyl esters with up to 89% efficiency and the biodiesel yield was estimated up to 0.195 g/dry biomass. Further, the exploitation of lipid extracted residual biomass was explored for bioethanol production. The results indicate that 0.165 g bioethanol/g residual biomass was obtained at 30 °C fermentation for 168 h.

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