Research On Nitrate Removal Method And Its Applications In Wastewater Treatment

Nitrate（NO₃^-）is found in almost all bodies of water and has the potential to harm the ecosystem,plants,animals,and people.As a result,it is critical to work on creating NO₃^-removal technology that is both safe and effective while also being ecologically friendly.In recent years,NO₃^-pollution in water has been addressed using biological procedures,physicochemical methods,chemical processes,electrochemical methods,and other technologies.Because of their simplicity,high denitrification efficiency,and low operation cost,zero-valent iron（ZVI）denitrification in chemical processes and electrochemical denitrification have gotten a lot of attention.Both tactics,on the other hand,have their own set of drawbacks.In ZVI denitrification,for example,nanometer-scale ZVI is often used,with ammonia nitrogen（NH₄⁺-N）as the major product.Cathode materials are limiting the advancement of electrochemical denitrification technology.The composition of real wastewater is complex,resulting in an unsatisfactory electrochemical reduction efficiency.In order to increase denitrification efficiency and alleviate NO₃^-pollution,in this paper,the ZVI denitrification process was perfected,cathode materials with high reducing activity were developed,and the influence of common components in real wastewater on NO₃^-reduction were investigated.The specific research contents of the research are as follows:（1）150μm ZVI(ZVI₁₅₀)was used as a reductant to remove NO₃^-and NH₄⁺-N was removed by folding point chlorination in order to develop a suitable denitrification technology for large-scale application.The effects of the operating parameters of ZVI₁₅₀ denitrification process on the NO₃^-reduction were systematically studied.And the corresponding kinetic models were established to describe the NO₃^-reduction process.The results were shown that when the p H=3.5 and n(ZVI₁₅₀:NO₃^--N)=12.50,the efficiency of NO₃^--N reduction reached 97.8%.In the overdose of ZVI₁₅₀,the reaction conformed to the nth-order kinetics.In the moderate amount of ZVI₁₅₀,the reaction followed the pseudo-first-order reaction.In both cases,the pseudo-second-order adsorption kinetics had good applicability.Then,the optimum condition of folding point chlorination was studied.When n（Cl₂:NH₄⁺-N）=1.8 and p H=7.5,the concentration of NH₄⁺-N was 3.7 mg/L in water.（2）A new type of Co₃O₄/Cu electrode was prepared by electrodeposition and calcination at high temperature.The preparation conditions of the electrode were optimized and the electrodes were characterized by SEM,EDS and XRD.In addition,the effects of operating conditions on NO₃^-reduction were studied.The results were shown that the Co₃O₄/Cu electrode which was prepared by electrodeposition of cobalt on a substrate for 10 min and then calcined at 500°C had large specific surface area,good crystallinity and high catalytic activity.Its reduction efficiency was 2.2,1.3 and 5.5 times that of Cu,Cu/Zn and Ti,respectively.After optimizing,the optimal electrolytic parameters were determined as follows:the initial concentration of NO₃^--N was 50 mg/L,the concentration of Cl^-was 500 mg/L,the current density was 10 m A/cm² and p H=7.0.After 60 min of electrolysis,the efficiencies of NO₃^--N reduction,NH₄⁺-N generation and total nitrogen removal were 87.6%,34.7%and52.8%,respectively.（3）The real wastewater has complex components and different properties.Experiments without background interference are difficult to simulate the real situations.Therefore,the effects of operating parameters and common pollutants(e.g.PO₄^3-,CO₃^2-,Ca²⁺and organic matter)on the efficiency of NO₃^-reduction were investigated in water.After optimizing,the efficiency of NO₃^--N reduction reached 80.2%.In the existence of PO₄^3-（more than 50 mg/L）,NO₃^--N reduction was inhibited.This can be attributed to the competing adsorption of interference ions and NO₃^-in the surface of the electrode,and the density functional theory calculations proved this.The interference of PO₄^3-can be alleviated by adding Ca²⁺to the solution,which was harmless to NO₃^-reduction.When studying the influence of organic compounds on NO₃^-reduction,glucose was selected as the target pollutant and chemical oxygen demand content was taken as the evaluation index.Because organic matter can be degraded by cathodic reduction or anodic oxidation in long-term electrolysis,the existence of organic matter also had a negative impact on NO₃^-reduction.Finally,2.5 L real wastewater was treated by electrochemical method.The feasibility and practical application of this method were illustrated from the aspects of reduction efficiency,operation cost,electrode stability and recycling efficiency.This work can lay a foundation for real wastewater treatment...