Abstract: Aimed to investigate the flocculating effect and impairment of three kinds of flocculants on Isochrysis galbana, spectrophotometry and gravimetric method were adopted to determine the flocculating rate, and morphological observation and total ester measurement were made to evaluate the flocculating impairment on algae cell. The results showed that ferric chloride and alum showed higher flocculating velocity (less than 4 hours). For flocculating >90% of algae cells, a dose of ≥20 mg·L^-1 of ferric chloride or at least 80 mg·L^-1 of alum was required. At a dose of 80 mg·L^-1 of alum, the algal total lipid productivity was the highest (29.9%), while the impairment on the cell integrity was the least, suggesting that 80 mg·L^-1 of alum could be used as the flocculant to harvest I. galbana for biofuel production.

Key words: cadmium stress, ROS, NO, Ca, plant hormone.