Cultivation of energy microalga Chlorella vulgaris with low–toxic sludge extract

Abstract

Chlorella vulgaris was cultivated in different proportions of activated sludge extracts, which was from the treatment of synthetic wastewater containing tetrachlorophenol. The growth period of C. vulgaris could be shortened for about 10 days when sludge extract was mixed into BG11 culture substrate, and the growth of C. vulgaris was promoted during the period of adaptation and logarithmic period. In the stable and decay period, when the proportion of sludge extract increased to 50%, cell proliferation was inhibited. There was an evident positive correlation between the total and average amount of starch polysaccharide with sludge concentration. When C. vulgaris was cultivated with pure sludge extracts, the total amount of starch and polysaccharide was up to 103 and 125 mg/L. Therefore, the low-toxic sludge extracts were more beneficial to the accumulation of carbohydrates. In the 100% sludge extracts culture medium, chlorophyll-a in C. vulgaris was accumulated to 30.2 mg/L on the 25th day. Through the analysis of algal cells' ultrastructures, it was shown that the photosynthesis was strengthened greatly with low-toxic sludge extracts. The results show that the rich heterotrophic carbon source in the sludge extract can be used as an excellent medium for Chlorella. It provides new ideas for the harmless utilization of surplus sludge as a resource. At the same time, the use of nutrients in the sludge extract to cultivate Chlorella is of great significance to low-cost algae cultivation.

Strategy for Managing Industrial Anaerobic Sludge through the Heterotrophic Cultivation of Chlorella sorokiniana: Effect of Iron Addition on Biomass and Lipid Production

“…This fact can be affected by the differences in each matrix's initial TOC content and other components, which is clearest observed in TN's concentration accomplished by Tan et al [14], which is approximately half of the value achieved in this study (597.6 mg L −1 ). Additionally, Chen et al [13] obtained a TOC of 268 mg L −1 in their synthetic industrial sludge extracts. These variations in final nutrient concentration must be considered before it is used for microalgae cultivation, depending on the species and culture conditions (mixotrophic or heterotrophic) to avoid growth inhibition [14].…”

“…Generally, culturing strategies that promote both biomass and lipid production must improve the microalgae cultivation system efficiency. Anaerobic sludge extracts contain high concentrations of ammonium and phosphate [13]; thus, removing these nutrients using microalgae systems has been extensively studied. However, a study on the effect of iron supplementation during microalgae growth in anaerobic liquid digestate has shown that iron plays a significant role in the population dynamics of symbiotic life.…”

“…A potential strategy to reduce biomass production costs is to replace some nutrient sources in culture media with anaerobically digested waste sludge (ADWS) [13]. ADWS, supplemented with volatile acids, was shown to produce a higher quantity of microalgal biomass than nitrogen and phosphate from traditional sources under mixotrophic growth conditions [14].…”

“…However, ADWS from industrial processes brings additional challenges due to the limited composition and potential contaminants. Even so, a recent study demonstrated that after pretreatment, the use of synthetic wastewater supplemented with tetrachlorophenol for Chlorella vulgaris growth under mixotrophic conditions promoted starch production [13].…”