Abstract: Microalgae are important photosynthetic microorganisms playing important roles in energy conversion and carbon cycle. At present, algae biotechnology is mainly used in carbon fixation and pollution control, production of bio-energy, food, medicine, feed, and other value-added by-products, etc. However, there are still many technical bottlenecks need to be addressed such as energy-intensive microalgae harvesting, which is one of the main obstacles that hinders microalgae industry. Traditional harvesting methods such as sedimentation, filtration, and centrifugation are either of low efficiency or high cost for microalgae harvesting due to low concentration in medium and the relatively small size of microalgal cells. Biological flocculation method, mediated through flocculating algae, fungi, bacteria and/or microbial flocculants extracted from microorganisms, is considered as one of the most promising techniques for algae harvesting due to advantages of high safety, high recovery efficiency, low fundamental investment， low operating energy consumption, and no secondary pollution to the environment, etc. This paper critically reviewed different microalgae harvesting methods with particular focus on the current status and prospects of biological flocculation.

Key words: microalgae, flocculating microorganisms, biological flocculation, harvesting