Conditions Optimization Of Immobilized Isochrysis Galbana For Aquaculture Tailwater Treatment

Tailwater from industrial seawater aquaculture is a nutrient-rich tailwater with low pollutant concentrations,which can easily lead to eutrophication in local waters.Due to its characteristics of high salinity,low pollutant concentration and great change in water quality,there is a lack of mature treatment technology at present,and it is urgent to develop efficient and widely applicable treatment technology for Marine aquaculture tail water to reduce its ecological risks.This paper intends to use microalgae immobilization technology,focusing on the study of Isochrysis galbana,in order to determine the optimal immobilization conditions using sodium alginate.The project will also compare and analyze the advantages and disadvantages of immobilized and free-living microalgae in the removal of aquaculture tailwater,and explore the effects of trace elements on their removal efficiency.The aim of this research is to provide scientific evidence for the treatment of pollutants in seawater aquaculture tailwater.Experimental results:（1）The optimal immobilization conditions for encapsulating Isochrysis galbana using sodium alginate were:2%sodium alginate solution,2%calcium chloride solution,3.7 mm algal sphere particle size and 1×10⁶cells/ml initial algal cell density.Scanning electron microscopy observations revealed that Isochrysis galbana grew and aggregated in the pores,with an average diameter of 4.33±0.32μm.（2）The initial concentrations of NH₄⁺-N,TN,TP,and COD in the tailwater were0.92±0.08 mg L^-1,144.61±8.59 mg L^-1,0.18±0.01 mg L^-1,and 1.32±0.03 mg L^-1,respectively.Compared with free-living cells,the immobilized algal spheres of sodium alginate were significantly more effective in removing pollutants from the tailwater.After 10 days of treatment,the immobilized and free groups had removal rates of96.88%and 30.93%for ammonia nitrogen（NH₄⁺-N）,71.13%and 8.28%for total nitrogen（TN）,48.08%and 14.43%for total phosphorus（TP）,and 42.42%and 6.57%for chemical oxygen demand（COD）,respectively;the immobilized and free groups with added trace elements had removal rates of 93.95%and 62.27%for NH₄⁺-N,61.05%and 20.35%for TN,52.89%and 38.46%for TP,and 39.39%and 19.19%for COD,respectively.Conclusion:In this experiment,when sodium alginate was used to immobilize Isochrysis galbana,the algae spheres prepared had certain hardness and mass transfer characteristics,and nutrients and metabolites could enter and leave freely.The immobilized Isochrysis galbana could proliferate in the pores of the spheres,and their growth and distribution were good.The immobilized Isochrysis galbana can grow in the tailwater of high nitrogen mariculture and prolong its growth period.Compared with the free Isochrysis galbana,the immobilized Isochrysis galbana has significantly improved the removal rates of NH₄⁺-N,TN,TP,and COD in the tail water.