Enhanced Nitrate Removal And High Selectivity Towards Dinitrogen For Groundwater Remediation Using Biochar-supported Nano Zero-valent Iron

Groundwater plays a very important role in the development of society and human life,but the pollution of nitrate in the groundwater is increasing.It is of great significance to find more economic,environmentally friendly and efficient materials to remove nitrate from groundwater.Nano zero-valent iron is a commonly used groundwater remediation material,but it has problems such as a narrow working pH range.In this paper,nano zero-valent iron/biochar composites were prepared by using biochar as carrier for nitrate removal.In this paper,the feasibility of nano zero-valent iron/biochar composites for the removal of nitrate and the feasibility of reducing nitrate to dinitrogen are explored.The main conclusions are as follows:（1）The mass ratio of nano zero-valent iron/biochar has a great influence on the performance of composite materials.1:2 is the best nano zero-valent iron/biochar mass ratio,which can achieve 96.2%nitrate removal rate and 61%dinitrogen selecivity;the composite can effectively remove nitrate（75.0-97.0%）in the pH range of 2-12,but the highest dinitrogen selecivity can be achieved only at pH 5.Cl^-,SO₄^2-,PO₄^3-and hardness have inhibitory effects on nitrate removal and dinitrogen selecivity,among which inhibition of PO₄^3-is the most significant.When the composite material is treated with actual groundwater samples,nitrate removal efficiency（78.2%）and dinitrogen selectivity（46.03%）is lower than laboratory experiments,but still higher than nano zero-valent iron and biochar.（2）The performance of nano zero-valent iron/biochar composites synthesized by 600°C biochar is better than other pyrolysis temperatures.The composites prepared with bagasse biochar are better than wheat straw biochar.In summary,nano zero-valent iron/600°C bagasse biochar（mass ratio 1:2）,which has the highest nitrate nitrogen removal rate（98.77%）and the highest dinitrogen selecivity（72.82%）,is an ideal nitrate removal material.（3）Biochar pretreated with HCl and formic acid had little effect on the removal of nitrate by composites,but had a negative effect on dinitrogen selectivity.NaOH pretreated biochar had negative effect on nitrate removal and dinitrogen selectivity by the composites.The nano zero-valent iron/biochar composite follows the first-order kinetics of nitrate removal,and the reaction rate constant is 0.36（mg L）^1-n/min.