Study On The Preparation Of Nano Zero-valent Iron By Green Modification And Its Removal Of Nitrate Nitrogen From Wastewate

With the rapid development of metallurgy and food industries,the content of nitrate nitrogen in groundwater is too high,which brings harm to human health and organisms and crops,destroys the ecological environment and hinders economic development.The World Health Organization（WHO）and the Environmental Protection Agency（US-EPA）have specified maximum contaminant levels（MCL）for nitrates as 50 mg/L（NO₃^--N）and 10 mg/L（NO₃^--N,in nitrogen）.Therefore,the efficient removal of nitrate in water has become an urgent problem.The main research contents of this project are as follows:（1）In this study,Fe⁰（referred to as n ZVI）was modified and then used for the removal of nitrate nitrogen,and two green materials for nitrate nitrogen removal were synthesized,the first was to use green tea extract to reduce and introduce copper ions to obtain green modified nano-zero-valent iron-copper bimetals（GT-n ZVI/Cu）;The second is to reduce GT-PAC-n ZVI by porous activated carbon loading and green tea extract,and then vulcanization modification to obtain porous activated carbon supported nano-zero-valent iron vulcanization modified material（GT-PAC-n ZVI/S）.Characterization methods such as SEM-EDS,XRD and XPS were used to characterize and analyze the two materials.（2）The effects of GT-n ZVI/Cu and GT-PAC-n ZVI/S on the univariate conditions during nitrate nitrogen reduction were investigated,including the initial p H of the solution,the amount of material added,the reaction temperature,and the nitrate nitrogen balance experiment.The results of GT-n ZVI/Cu removal of nitrate nitrogen showed that the nitrate nitrogen removal rate and nitrogen conversion rate of 72.92%in 75 minutes when the initial p H of the solution was 3,the addition amount was 8 g/L and the Cu load was 30%.It exhibits excellent reducing properties,and polyphenolic antioxidants make GT-n ZVI/Cu stronger antioxidant properties.The results of GT-PAC-n ZVI/S removal of nitrate nitrogen showed that when the initial p H=7,the addition amount was 4 g/L,the temperature was 60 o C,the carbon-iron ratio was 1:10 and the iron-sulfur ratio was 1:0.3,the nitrate nitrogen removal rate could reach 93.00%and the nitrogen conversion rate was 22.10%in 95 minutes.The experimental results show that the two materials have good removal effect on nitrate nitrogen,and although the removal rate of GT-PAC-n ZVI/S is reduced compared with GT-n ZVI/Cu,the p H conditions of the removal process of nitrate nitrogen are milder,and the amount of GT-PAC-n ZVI/S is less,which is conducive to reducing costs.（3）The removal mechanism of nitrate nitrogen by SEM-EDS,FTIR,XRD,XPD and XPS was analyzed.The results show that the removal of nitrate nitrogen is enhanced by complexation,reduction and adsorption of both materials.The above two material preparation methods have feasibility and certain economic value,and have excellent removal performance for nitrate nitrogen,excellent nitrogen conversion and oxidation resistance.It shows that both materials have great application potential in the field of nitrate nitrogen treatment in wastewater.