Study On Remediation Of Nitrate Pollution In Groundwater With In-situ Reaction Zone Of Biochar-supported Zero-valent Iron

Nitrate nitrogen pollution has become a ubiquitous problem around the world,which poses a serious threat to the ecological environment and human health.Remediation of nitrate nitrogen pollution in groundwater has become a hot research topic in recent years.Zero-valent iron in-situ reaction belt remediation technology is a new remediation technology,which has the advantages of small soil excavation,easy control of reaction conditions and low operating cost.However,there is a lack of systematic research on the zero-valent iron in-situ reaction zone remediation technology,and few scholars have studied the migration and distribution of remediation agents in media.Therefore,in this study,biochar loaded with zero-valent iron was used to prepare remediation materials,and the removal mechanism of nitrate nitrogen was determined.One-dimensional column experiment was used to study the migration and distribution of remediation materials in aquifer media,and two-dimensional simulated tank was used to repair nitrate nitrogen,so as to monitor the influence range of its reaction zone and the rule of groundwater chemical change.The specific research contents and results are as follows:（1）The zero valent iron on the surface of biochar can react with NO₃^--N or DO in the solution.Electrons escape from the core and shell of zero valent iron to form Fe²⁺,and form NO₂^--N,NH₄⁺-N and N₂ at the same time.The main product is NH₄⁺-N.In addition,as an intermediate product,a small part of NO₂^--N can be converted to NH₄⁺-N.The carboxyl group on the surface of biochar will exist in the form of ester and react with water,zero valent iron and Fe²⁺to form quinone group.The generated quinone group can provide H⁺for the reaction,generate N₂ from NO₃^--N and convert itself into ester group.（2）The larger the particle size of aquifer medium is,the better the migration ability of BC-ZVI material in aquifer medium is.When the particle size is 2-4 mm,the migration ability of BC-ZVI material is the best.When the flow rate increased,the hydraulic effect increased,and the shear force on the surface of the medium also increased.The BC-ZVI particles originally trapped and deposited on the medium returned to the aqueous phase,and the migration ability of BC-ZVI material in the medium increased,and the migration ability of BC-ZVI material was the best when the flow rate was 3.15 cm/min.The higher the concentration of restorative injection is,the more unfavorable the migration of BC-ZVI material in the medium,and the migration ability of the material is the worst when the concentration of restorative injection is800 mg/L.（3）After the injection of BC-ZVI grout,NO₃^--N near the injection well is effectively reduced,and a stable reaction zone is formed 10-20 cm around the injection well to effectively remove NO₃^--N polluted groundwater.The formation range and repair ability of the reaction zone are not uniform.The longer the distance from the injection well,the remediation effect and the strength of the reaction zone become weaker.