Research On Preparation Of Lanthanum Modified Bentonite And Its Application In Phosphorus Removal From Secondary Wastewater

Phosphorus removal from domestic sewage is of great significance and is an important and sustainable way to realize sewage treatment and resource recovery.Due to the substandard total phosphorus（TP）concentration in the tail water of sewage treatment plant,it is necessary to explore the effective advanced phosphorus removal process.Lanthanum-modified bentonite（LMB）exhibits a broad development prospect in the application of phosphorus removal in water treatment based on the excellent adsorption capacity for phosphate.In this study,LMB applied to phosphorus removal in secondary wastewater was inveatigated.Firstly,LMB preparation was conducted by microwave radiation heating method,which then was applied for advanded phosphorus removal including the influence of different factors on the phosphorus adsorption performance by LMB.In addition,LMB adsorption combined with ultrafiltration process,served as the pretreatment technology,was developed to solve the problems of solid-liquid separation and phosphorus recovery.And the phosphorus removal efficiency and ultrafiltration membrane fouling in the combined process also were investigated.Based on single factor experiment and response surface methodology,the optimal parameters for LMB preparation of modifier dosage,microwave time,solid-liquid ratio,and microwave power were 1.77 mmol/10 g,4 min,1:3.5,and 700 W,respectively.Moreover,LMB prepared by microwave heating method maily affected the cations exchange among the bentonite layers with the increased bentonite layer space by 0.28 nm and micropores numbers based on X-ray diffraction,scanning electron microscopy,infrared spectroscopy and specific surface area and pore size analysis.The effects of dosage,adsorption time,stirring rate,initial TP concentration,p H value,coexisting anions（Cl^-,HCO₃^-and F^-）and dissolved organic matter on LMB adsorption performance were investigated when applying for phosphorus removal.The results showed that TP concentration could be decreasing from 2.02 mg/L to less than 0.5 mg/L within 10 min with LMB dosage and stirring rate of 1 g/L and 120 r/min,respectively.However,high concentration of HCO₃^-,F^-,and dissolved organic matter had a great impact on the phosphorus removal.In addition,LMB adsorption kinetic was conformed to the pseudo-second-order kinetic equation,and the adsorption isotherm followed the Langmuir isotherm model with the maximum LMB adsorption capacity of 6.83 P mg/g.Additionally,phosphorus in the secondary sedimentation tank effluent could be removed effectively in LMB adsorption/ultrafiltration process.The results showed that TP concentration was mainly reduced in the LMB pretreatment accounting for around 90%-95%of the total removal rate in LMB adsorption/ultrafiltration process.LMB adsorption pretreatment also could promote dissolved organic matter removal by ultrafiltration membrane effectively with the maximum removal rates of DOC and UV₂₅₄ in the combined process of35.5%and 22.2%,respectively.Moreover,in order to explore the influence of LMB adsorption pretreatment on ultrafiltration membrane fouling,the change of membrane flux,resistance,and fouling model also were further conducted.The results showed that LMB pretreatment could effectively slow down the membrane flux decreasing and reduce the irreversible membrane fouling.Furthermore,the practical application of LMB adsorption/ultrafiltration process also was explored for advanced phosphorus removal of the secondary sedimentation tank effluent with TP concentration decreasing from 0.82 mg/L to 0.08 mg/L.In addition,CODcr,ammonia nitrogen and total nitrogen also could be removed limitedly while the turbidity removal rate reached 87.5%.Moreover,in terms of the operation cost,the expense of LMB treatment was about 0.026 yuan per ton of sewage with the dosage of 47 g.