Method for treating eutrophicated water body by using microalgae

The invention discloses a method for treating eutrophicated water body by using microalgae, which comprises the following steps of: selecting microalgae capable of efficiently absorbing nitrogen and phosphorus as algae seeds, and performing domestication such as reducing the nitrogen and phosphorus content and adapting to the water body to be treated by regulating culture medium ingredients; and performing amplification culture step by step, introducing the algae seeds into a primary eutrophicated water body treatment tank, making the nitrogen and phosphorus flowing into the water body of theprimary treatment tank greatly absorbed by the microalgae, discharging into a secondary treatment tank for sedimentation and filtration, discharging most of the treated water, flowing back a little water to the primary treatment tank along with the microalgae, and recycling to fulfill the aim of improving the water quality finally. In the method, the defects of high technical investment, high cost, complex technology, secondary pollution and the like in the prior art are overcome. The COD of the eutrophicated water body treated by the method can be reduced by about 95 percent, the BOD can be reduced by about 93 percent, the total nitrogen can be reduced by about 97 percent, the total phosphorus can be reduced by about 97 percent, and the eutrophicated water body treated by the method completely meets the national type III water quality standard.