Development Of Resin-based Zero-valent Iron And Its Application For Phosphorus Removal

Phosphorus（P）is considered a key factor in the eutrophication process of water.The removal and recovery of phosphorus from the effluents of wastewater treatment plants（WWTP）are of great significance for reducing eutrophication and alleviating phosphate rock depletion.In this study,a composite adsorbent（n ZVI-402-Cl）was successfully prepared by reducing and immobilizing Fe³⁺as nanoscale zero-valent iron（n ZVI）on IRA-402 strong alkaline anionic resin using in situ reductive deposition method to remove phosphate from simulated wastewater and secondary effluent from wastewater treatment plants.A number of structural characterization,phosphate removal performance studies and corresponding equipment applications were carried out around n ZVI-402-Cl.The characterization and experimental results are as follows.1.Scanning electron microscopy（SEM）and dispersive spectroscopy（EDS）results show that n ZVI particles and their oxidized fraction are loaded on the surface and inside of the anion exchange resin,and the iron content increases gradually from the outside to the inside.Combined with the X-ray diffraction（XRD）results,it can be inferred that n ZVI was loaded into n ZVI-402-Cl in an amorphous form and formed a core-shell structure of iron oxides/n ZVI.It was found to have good stability in the p H range（3.0-11.0）by analyzing the loss of Fe elements on n ZVI-402-Cl under different p H environments.2.At different p H（3.0-11.0）,n ZVI-402-Cl had a high phosphate adsorption capacity,with a maximum adsorption capacity of 56.27 mg P/g at p H 7.2.Excellent selectivity made n ZVI-402-Cl maintained its high phosphate adsorption capacity regardless of the coexistence of interfering sulfate and nitrates anions.Especially,the nanoconfinement of n ZVI in anion exchange resin could reduce the negative effects of humic acid on phosphate removal.The regeneration test showed that recovery efficiency can reach～95%after using n ZVI-402-Cl five times.In column mode,n ZVI-402-Cl column generates>840 bed volume（BV）clean water([PO₄^3-]<0.5 mg/L)from the simulated phosphate-contaminated water.In contrast,the values of the IRA-402 column are only～625 BV.When faced with real wastewater（WWTP II effluent）,the effective treatment volume of n ZVI-402-Cl was increased by 104%compared to IRA-402 with a penetration point of 0.1 mg P/L.Finally,the FT-IR,HRTEM,and XPS results showed that n ZVI-402-Cl adsorbed phosphate mainly through the ion exchange effect of trimethylammonium functional group and metal sites on the resin backbone.3.In the optimization test of the parameters of the phosphorus removal equipment developed based on adsorbent materials,five different lipid packaging and filling methods were used to change its stacking density,water flow rate and other parameters to find out the optimal operating conditions.When the third method of delivery（i.e.,uniform delivery）was used and the resin was packed with large mesh bags,the equipment had the best treatment effect with a water flow rate of 6.70 L/min,and the total phosphorus concentration in the water column decreased from 1.98 mg/L to 0 mg/L within two hours.The p H remained stable during the treatment process and the total phosphorus concentration decreased to 0.5 mg/L at about 40 min of treatment.When the second stage wastewater from a wastewater treatment plant in Yangluo,Wuhan,was treated with this method,the total phosphorus concentration in the effluent was reduced from 0.25 mg/L to 0 mg/L within two hours,and the treatment was basically complete with a treatment rate of 50 L/h.In addition,through the economic cost accounting and analysis,in the service life of 3 years,the economic benefit of composite phosphorus removal resin is much higher than the common phosphorus removal agents in the market.