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Micro-algae are to be an attractive way to produce bio-diesel due to high photosyntheticÂ yields and lipid accumulation in cells. This high productivity combined with possibility toÂ uptake CO2 stimulated its utilization as a biological mitigation method of CO2, at onceÂ as an alternative renewable source of energy. Growth characteristics and chemicalÂ composition of micro-algae can be altered by culture environment. Nutrient sufficiency,included magnesium element (Mg2+) is important factors on overall biochemicalÂ composition. In study, Nannochloropsis sp was cultivated in Erlenmeyer 250 mlÂ containing 200 ml f/2 medium. There are three groups of treatment with different level
of magnesium (Mg2+), i.e. 0 (M0); 0.1mgL-1 (M1); and 1.0 mgL-1 (M2). All treatment wasÂ designed triplicate in batch system. Culture was then aerated continuously with sterileÂ atmospheric air (1.5 L.min-1). Cells were harvested on 25th day after inoculation andÂ analyzed. Data showed that Chlorophyll-a increased linearly with time and maximumÂ at 18th days of growth period, i.e. 23.57; 26.44; and 27.74mgL-1, for M0; M1; and M2,respectively. Chlorophyll-a content decreased significantly when pH dropped to 5-6.Enrichment with Mg2+ increased the chlorophyll-a content 12.2-17.7%. Dry cell reachedÂ 375-400mgL-1 in all treatment. Lipid content of Nannochloropsis sp in control (M0) isÂ 55.3%, higher than M1 and M2. Saturated fatty acid tends to increase from 80.70 (M0)
to 96.70 (M1) and 94.53% (M2). Fatty acid of M0 and M1 was composed dominantly byÂ palmitic acid (C16:0), i.e. 49.19-70.75% total fatty acids. Meanwhile, M2 treatment wasÂ dominantly by lauric acid (C12:0), i.e. 32.98%.
Keywords: CO2 biological mitigation, chlorophyll-a, fatty acid, lipid, agnesium,
microalgae, Nannochloropsis sp, photosynthesis.
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