SUSTAINABLE OCEAN TECHNOLOGIES CURRENT SCIENCE, VOL. 118, NO. 11, 10 JUNE 2020 1731 *For correspondence. (e-mail: dhara@niot.res.in) Mass culture of marine microalgae Chlorella vulgaris (NIOT-74) and production of biodiesel G. Dharani*, D. Magesh Peter, J. T. Mary Leema, T. S. Kumar, K. Thirupathi, A. Josephine, R. Kirubagaran and M. A. Atmanand National Institute of Ocean Technology, Ministry of Earth Sciences, Chennai 600 100, India Biodiesel production using marine microalgae as an alternate fuel source is receiving international atten- tion in view of its economic and environmental advan- tages. The present study evaluated the feasibility of biodiesel production from the marine microalgae; Chlorella vulgaris (NIOT-74). Outdoor mass cultures of marine microalgae were done in different photobio- reactors and raceways with marine C. vulgaris (NIOT- 74) as a model organism. The study demonstrated the feasibility of producing biodiesel and provided an evaluation of the physico-chemical properties of bio- diesel (B100) and blend (B10) according to ASTM standards. A cost-effective electroflocculation method with 90.12% harvesting efficiency was developed and tested. The biodiesel produced from C. vulgaris (NIOT-74) was tested in two-stroke and four-stroke engines and was also used to test drive a vehicle. Keywords: Biodiesel, Chlorella vulgaris, fuel proper- ties, photobioreactors. Introduction INDIA imports about 219.15 MT of petroleum, valued at US$ 90 billion (Rs 5.65 lakh crore) of which the auto- mobile sector alone is reported to consume 70% of the total petroleum diesel stock 1 . India has a unique pattern of petroleum diesel consumption with five times more diesel consumption than gasoline in contrast to world- wide consumption standards of more gasoline than petro- leum diesel. During the last two decades, Indian diesel consumption has increased several folds from 5 (1970– 71) to 45 million metric tonnes (2006–07) 2 . This necessi- tates an urgent need for an alternative to petroleum diesel fuel for India 2 . Research activities have been focused on developing alternate fuels so that the huge cost involved in the import of petroleum diesel could be curtailed. Bio- diesel is produced mostly from vegetable oil (edible and non-edible oil) or animal fats 3 . This is a major challenge to our food security as the potential market for biodiesel surpasses available plant and animal oil production 4 . An ideal feedstock is a fuel source with low green-house gas emissions and little or no competition with food produc- tion 5 . One such alternative is marine microalgae. Algal biodiesel performs as efficient as petroleum diesel with no sulphur and minimal emissions of particulate matter, CO, hydrocarbons, and SO x (ref. 6). To translate biodiesel production from marine microalgae to a commercial re- ality, multifaceted research and development is essential starting from isolating and identifying suitable strains, to optimizing different stages of mass scale operations for biomass production, harvesting, and lipid extraction 2 . For any commercial venture on marine microalgae, it is perti- nent to evaluate the performance of the strain under out- door conditions 7 . The cost of marine microalgal biomass production can be brought down considerably by using natural sunlight and outdoor cultivation systems 8 . India being a tropical country has the advantage of sunlight to take up outdoor marine microalgal culture in an effective way to reduce cost of microalgal biodiesel production 9 . Majority of the studies on biodiesel production from marine microalgae are restricted to indoor cultures due to the difficulties in maintaining the outdoor cultures con- tamination free in the ever-changing weather 7 . Hence, the study attempted to investigate the growth performance of marine microalgae in different custom-designed outdoor photobioreactors under phototrophic and mixotrophic conditions. The opportunities and constraints for biodie- sel production from marine microalgae were also eva- luated. Materials and method Strain and culture conditions Of the 200 marine microalgal strains screened from NIOT (National Institute of Ocean Technology) culture collec- tions the best performing strain, Chlorella vulgaris (NIOT-74; NCBI accession number – JF894249) was used for all the experiments in this study. Cultures (500 ml) were grown aseptically in the laboratory at 25 ± 1°C, light intensity of 120 μmol photon s –1 m –2 (provided by cool-white fluorescence tubes) and a 16:8 h dark : light photoperiod. Sterilized natural seawater enriched with f /2 medium 10 (1 ml/l of seawater) in 1000 ml Erlenmeyer flask was used as culture medium for the indoor cultures.