Chlorella vulgaris was cultivated in different proportions of activated sludge extracts, which was from the treatment of the 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 logarithm. 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, shows 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 and resource utilization of surplus sludge. At the same time, the use of nutrients in the sludge extract to cultivate chlorella is of great significance to low-cost algae cultivation.
Low – toxic sludge extract based algae cultivation system was used in this study.
Sludge extract was more favorable for C. vulgaris growth during the period of adaptation and logarithm.
Day 20 was optimal to obtain maximal algal biomass.
The effect of sludge extract on the organelles of C. vulgaris was analyzed by the sub-microstructure of cells.