Enhanced biomass and lipid production for cultivating Chlorella pyrenoidosa in anaerobically digested starch wastewater using various carbon sources and up-scaling culture outdoors

The mixotrophic growth of Chlorella pyrenoidosa and lipid accumulation in anaerobically digested starch wastewater (ADSW) were enhanced using six carbon sources in the laboratory and then up-scaled outdoors. The microalgae can utilize monosaccharides (glucose, fructose and galactose) as carbon sources for mixotrophic growth in ADSW when they cannot use maltose, sucrose or starch. Compared to the blank ADSW culture, the addition of 0.8% monosaccharides improved the algal concentration by more than 2.2-2.5 times during laboratory axenic culture. Moreover, the cellular lipid content in the biomass increased by 50.5-93.4%. The fatty acids analysis indicated that more than 44-51% of the lipids were covered with saturated fatty acids (C14:0, C15:0, C16:0 and C18:0) in the presence of 0.8% monosaccharides, whereas only 28% were covered in pure ADSW culture. Up-scaling the culture outdoors showed that the addition of sugar caused severe bacterial contamination in the algal system. Fortunately, the rapid growth of bacteria did not collapse the algal system. Similar to the results of the laboratory culture, both the algal growth and lipid accumulation were enhanced with addition of the three monosaccharides during outdoor culture. This result suggests that adding the three monosaccharides to ADSW is a potentially effective way to enhance both the biomass and lipid production.