Abstract: Microalgae immobilization technology is a technology that immobilizes free microalgae cells on a carrier and changes it into a solid biocatalyst to be utilized.Immobilization can significantly improve the stability and longevity of algae cells,and is convenient for collection.At present,the "embedding method" in which microalgae cells are encapsulated in gel polymer by fixing method is often adopted due to its advantages of relatively simple operation,lower cost,less damage to cells,larger cell retention,etc.In order to explore the effect of immobilized microalgae on the removal of phosphate and ammonian from aquaculture waste water,Scenedesmus obliquus was used as algae species,and sodium alginate embedding technology was used to carry out purification comparative tests of different algae embedding densities(S-1 group:2.52×10⁴cells/mL,S-50 group:1.26×10⁶cells/mL and S-100 group:2.52×10⁶cells/mL),and the effects of embedding density on the growth of algae cells were also investigated.The results showed that the embedding density had a significant effect on the removal of phosphate and ammonian and the growth rate of algae cells(P<0.05).The higher the embedding density was,the better the removal effect of phosphate and ammonian was.The final removal rates of phosphate for S-1,S-50 and S-100 groups were 61.11%,83.33% and 88.89%,respectively.And the final removal rates of ammonian were 39.95%,50.00% and 57.53%,respectively.The main reason may be that the higher the concentration of algae cells was,the more effective algae cells participating in the reaction were and the higher the amount of nutrients absorbed was,so the efficiency of removing phosphate and ammonian per unit time was high.The growth rate K value of S-1,S-50 and S-100 groups of S. obliquus was S-1 > S-50 > S-100.The growth rate K value gradually decreased with the increase of embedding density of algae cells.This may be due to the fact that the more the cell embedding density was,the greater the mass transfer resistance of CO₂,O₂ and nutrients was,and the lower the permeability of algae-spheres was.All these factors could cause subsequent algae cell proliferation to be affected.