Study On Removal Of Algae From Seawater By Tannic Acid Enhanced Modified Clay And Activated Persulfate

Harmful algal blooms（HABs）occur frequently in different water environments,which seriously threaten aquatic organisms,fishery economy,tourism and human health.In order to reduce the harm of HABs,it is very important to develop emergency algae removal technology.In this paper,tannic acid compound chitosan modified kaolin and tannic acid coupled with divalent iron activated persulfate were developed to remove algae in seawater.The main research contents are as follows:（1）Tannic Acid Enhanced Removal of Chlorella salina from Seawater by Chitosan Modified KaoliniteThe chitosan（CS）modified kaolinite（K）was prepared and the structure of CS-K was characterized.The Chlorella salina was chosen as a model and the tannic acid（TA）was further used to enhance the removal of Chlorella salina from seawater by chitosan-modified kaolin（CS-K）.The change of total nitrogen（TN）,total phosphorus（TP）and p H after algal removal with addition of TA/CS-K was also investigated.The results show that the removal efficiency was 87%at 24 h when the dosage of TA/CS-K（the ratio of CS-K to TA was 1:1）was 0.4 g/L,which is higher than that of CS-K（52%）and TA（65%）.In addition,we found that the removal efficiency is as high as 82%at 3 h when the ratio of CS-K to TA is 5:1 and the loading is 0.9 g/L.With increasing loading of TA/CS-K,the values of TN,TP,and p H slightly decreased.Furthermore,after modified by chitosan,the surface of kaolin changed from negative charge（Zeta potential of-20 m V）to positive charge（Zeta potential of+25 m V）,suggesting that CS-K can flocculate and precipitate algae cells,while TA can inhibit the growth of algae and even kill chlorella salina.（2）Removal of Phaeocystis globosa in seawater by Fe²⁺activated persulfate coupled with tannic acidUsing Phaeocystis globosa as a model alga,a tannic acid coupled with divalent iron activated persulfate（PS）algaecide was developed.The removal efficiency of the algicide for Phaeocystis globosa in seawater was evaluated.The effects of PS,TA and Fe²⁺for the removal efficiency of Phaeocystis globosa were investigated,and the changes of TN,TP,COD and total organic carbon（TOC）before and after algae removal were analyzed.The results show that the removal efficiency was 76%at 180 min when the dosage of Fe²⁺/TA/PS(the concentration of Fe²⁺,PS and TA was 0.1g/L,0.24g/L and 0.01g/L,respectively)was 0.35 g/L,and the algal cell density was 1.5×10⁹cells/L,which was higher than that of Fe²⁺/PS(the concentration of Fe²⁺and PS was 0.1g/L and0.24g/L,respectively)（52%）.In addition,compared with Fe²⁺/PS system,theflocculation foemed by Fe²⁺/TA/PS system are more compact and the sedimentation speed is faster.After algae removal,the concentrations of TN,TP,COD and TOC decrease,indicating that the Fe²⁺/TA/PS system has a potential application prospect in the treatment of red tide and improvement of water quality.