Study On The Removal Of Nitrate From Groundwater By Biochar Loaded With Nanometer Iron Metal

With the acceleration of our country urbanization process and the rapid growth of industry and agriculture,the substandard discharge of urban domestic wastewater and industrial wastewater,and the excessive use of nitrogen fertilizers in agriculture,our country groundwater resources have been polluted to varying degrees,of which nitrate is a kind of extensive pollutants can induce various tumors and other diseases in the human body.In order to effectively remove nitrate in water,different types of technologies have been developed,mainly including biological denitrification,physical chemistry,and chemical reduction.Because nano-zero-valent iron（n ZVI）has better activity than micro-scale zero-valent iron,chemical reduction of nitrate in water by n ZVI is a hot spot in current research.However,single nano-zero-valent iron has poor stability,is easy to agglomerate,and is easily affected.p H influence and other issues.In this paper,biochar was used as a carrier to prepare supported nano-zero-valent iron composite materials,nano copper-palladium catalyst composites,and supported nano-iron composite materials;through experiments to explore its ability to remove nitrate and reduce products.The structure and composition of the composites were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,and X-ray photoelectron spectroscopy（XPS）.Through experiments,the ability of these composites to remove nitrate and the reduction path of nitrate were studied,and the mechanism and reduction characteristics of nitrate reduction by these composites were explored.The main contents and results of this paper are as follows:（1）Study on supported nano-zero-valent iron composite materials for reducing nitrate.Through the SEM characterization,it is found that the particle size of the nano-iron particles is mainly distributed between 50-200nm,and they are distributed on the surface of the biochar in a relatively regular circle and necklace;the removal ability of nitrate is different under different iron-carbon ratios.The nano-zero-valent iron composite prepared under the condition of 1:2 has the best nitrate removal rate;in the p H range of 4.05～9.88,the removal rate of nitrate can reach more than 94%.The supported Fe/BC composite material can reduce the agglomeration of nano-iron particles and improve the reactivity of nano-iron,thereby increasing the removal rate of nitrate.（2）Study on the reduction of nitrate under the supported nano-zero-valent iron and copper-palladium catalyst system.The diffraction peaks of elemental Fe⁰ and iron oxides were detected by XRD.In the XPS spectra before and after the reaction,the iron form content and the iron valence state changed.The TEM image shows that the copper and palladium are uniformly distributed on the biochar,and the particles are dispersed in a loose surface;In Fe/BC-（Cu-Pd）catalytic system,the nitrogen selectivity under the condition of Cu:Pd ratio of1:4 is 48%;in the p H range of 4.05～9.88,the removal rate of nitrate reached more than 98%;under the condition of coexisting anions,the order of inhibiting the reduction rate of nitrate-nitrogen is:PO₄^3->CO₃^2->SO₄^2-.The addition of copper-palladium catalyst increases the removal rate of nitrates.In the Fe/BC-（Cu-Pd）catalytic system,NO₂^-will be adsorbed on the surface of Cu or Pd and further be absorbed by the active sites of Cu or Pd.The adsorbed active hydrogen is converted into nitrogen and ammonia nitrogen,thereby increasing the selectivity of nitrogen.（3）Study on the removal of nitrate by supported nanometer iron-based metal composite materials.From the SEM image,it is observed that the nano-copper particles aggregate on the surface of the nano-iron particles;when the reaction is 15 minutes,the copper loading amount is 2.5%-10%corresponding to the removal rate of nitrate up to 99.3%;the p H value is for the supported type nano-iron-copper composite materials have little effect on nitrate removal,and the nitrate removal rate can reach more than 98%after 30 minutes of reaction;the total nitrogen removal rate of iron-based composite materials is 13.8%-18.7%,the total nitrogen removal rate of supported iron-based composites is 25.8%-29.5%.The metal copper or palladium obtained from the supported iron-based composite material improves the reaction activity of nano-iron,can effectively remove nitrate,and shorten the reaction time.