Removal Of Algae And Phosphorus From Eutrophic Water By Modified Clay

Eutrophication of water body is an urgent environmental problem in the world.Phosphorus is one of the limiting factors for algae growth.Excessive phosphorus in eutrophic water and sediment will lead to algae overgrowth,and even population explosion will form water blooms.Immobilization of phosphorus from water and reducing the content of bioavailable phosphorus are the keys to inhibit algae proliferation and treating eutrophic water.In this thesis,four kinds of new composite modified bentonite were prepared.Through characterization and beaker experiment,PAC-La with the best performance in the early stage was selected for sediment column and eutrophic water remediation experiment,and the water quality index and the concentration of lanthanum and phosphorus in sediment were detected to evaluate the application value of composite modified clay in actual eutrophic water remediation.The research work and achievements of this thesis were as follows:（1）Four kinds of composite modified bentonite were characterized,and the results showed that the surface of modified bentonite presents a rough multi-layer structure.After modification,the Zeta potential values all increased in different degrees.The adsorption experimental data of four kinds of composite modified bentonite were more in line with Langmuir isothermal adsorption model,and the maximum saturated adsorption capacity of PAC-La was the largest（44.677 mg/g）,while that of PFS-La was the smallest（29.385 mg/g）.Quasi-second-order kinetic model and particle diffusion model can better fit the kinetic process of phosphorus adsorption by composite modified bentonite.The influencing factors of phosphorus and algae removal by composite modified bentonite were analyzed.Except PAFC-La,the phosphorus and algae removal effects of the other three materials all increased with the increase of dosage concentration.With the increase of p H from 5 to 10,the phosphorus and algae removal efficiency of PAS-La and PFS-La increased first and then decreased,while the phosphorus and algae removal efficiency of PAC-La increased with the increase of p H,and had no significant effect under acidic and alkaline conditions.（2）PAC-La was used to carry out the deposition column experiment.After the experiment,the concentration of Cl^-in the deposition column will increase,the concentration of TN will decrease,the concentration of TP will decrease,and the concentration of ammonia nitrogen will also decrease in general,and the concentration of Chla will decrease rapidly.The concentration of La³⁺in the sedimentary column first increased and then decreased to the initial concentration,and the concentration of Al³⁺did not change much.With the addition of PAC-La,some unstable phosphorus in the sediment of the sedimentation column will be converted into stable phosphorus,but the conversion was not obvious because of its low unstable phosphorus content.Among them,the addition of PAC-La in sediment will cause the proportion of NH₄Cl-P in TP to decrease,that of BD-P to decrease,and that of Na OH-P and Res-P to increase.After PAC-La was added,the lanthanum content in the upper layer of sediment increased more,the lanthanum content in the middle layer increased less,and the lanthanum content in the lower layer hardly increased.In addition,with the addition of PAC-La,Sophora alopecuroides and Haematococcus verticillata in the experimental group grew better,and the plant length,weight and root length were better than those in the control group.Although the CAT activity and POD activity of the plants had slightly increased,the changes were small.（3）The eutrophic water body was treated jointly by Sophora alopecuroides,Haematococcus verticillata and PAC-La.After PAC-La was applied,the flocculation effect was produced immediately,and the algae in the water settled to the bottom.The water analysis results showed that the transparency of water increased from 28.950 cm to 51 cm,the concentration of Cl^-increased from 64.980 mg/L to 94.971 mg/L,the concentration of TN decreased,the concentration of TP decreased from 0.821 mg/L to0.040 mg/L,the concentration of ammonia nitrogen in water also showed a downward trend,and the concentration of Chla decreased rapidly from 202.838μg/L to 23.199μg/L.The concentration of La³⁺in the sediment column first increased and then decreased to the initial value,while the concentration of Al³⁺did not change much.With the addition of PAC-La,some unstable phosphorus in the sediment was transformed into stable phosphorus,and the contents of NH₄Cl-P,BD-P and Na OH-P in the sediment all decreased,while the contents of HCl-P and Res-P increased.After PAC-La application,the content of lanthanum in the upper layer of sediment increased more,the content of lanthanum in the middle layer increased less,and the content of lanthanum in the lower layer hardly increased.After the application of the PAC-La,Sophora alopecuroides and Haematococcus verticillata grew normally,and the water quality remained at a good level until the end of the experiment.Therefore,the PAC-La has a wide application prospect in the remediation of eutrophic water bodies.