Study On The Reaction Of Nitrate With Nano-Zero-valent Iron And Its Modified Materials

Lakes and rivers are precious fresh water resources.Excessive use of agricultural nitrogen fertilizer,industrial nitrogenous wastewater and substandard discharge of urban domestic sewage have caused the nitrate content of various rivers and lakes rising continuously,thus causing serious harm to human health.Therefore,it is of great significance to study the method of removing nitrate from water in an efficient and economical way to improve the utilization of water resources and alleviate water pollution.Nano-zero-valent iron?NZVI?has the advantages of low cost and high efficiency in removing nitrate.Nano-zero-valent iron?NZVI?has a much higher specific surface area and reducing power than ordinary zero-valent iron?ZVI?,making NZVI more conducive to large-scale repair of nitrate pollution.However,NZVI is prone to agglomeration due to its larger surface energy and static magnetic force between particles.And because of the high activity of NZVI,it is easily passivated by reacting with dissolved oxygen.In this study,hydroxypropyl methylcellulose?HPMC?was used to coat NZVI to form nanocomposite H-NZVI to improve the agglomeration of NZVI,enhance the stability of NZVI and the ability to remove nitrate.The effects of HPMC and NZVI coating ratio,initial pH,dissolved oxygen,coexisting ions and experimental temperature on the reaction of H-NZVI with nitrate were studied.The concentrations of nitrate,ammonia nitrogen and nitrite during the reaction were investigated.Variety.In order to reduce the conversion rate of nitrate to ammonia nitrogen during the reaction of NZVI with nitrate,the conversion of nitrate to nitrogen is promoted in order to increase the removal rate of total nitrogen.In this study,we also tried to use micro-electrolysis system composed of activated carbon?AC?and nano-zero-valent iron?NZVI?to react with nitrate to compare the micro-electrolysis system composed of different zero-valent iron?common zero-valent iron and nano-zero-valent iron?and activated carbon.The difference in nitrate removal effect,nitrate selective conversion rate,and total nitrogen removal rate.Moreover,the ratio of different zero-valent iron to activated carbon,the initial pH of the solution,dissolved oxygen,and the effect of coexisting anions on the reaction were investigated.The main results of the study are as follows:?1?NZVI produced under the existing experimental conditions When the initial concentration of nitrate is 40mg/L,the average off-selling of NZVI is 11.99 mg-N/g.The average denitration amount of H-NZVI was 13.47 mg-N/g.The average denitration of H-NZVI is generally more than 20%higher than that of NZVI.And from the SEM and TEM images,it can be seen that HPMC effectively coated NZVI to improve its dispersibility.It shows that the effective coating of HPMC effectively improves the ability of NZVI to remove nitrate.?2?Whether it is NZVI,H-NZVI or NZVI/AC,various influencing factors?dissolved oxygen,initial pH,coexisting anions,experimental temperature?have similar effects.That is,the lower the dissolved oxygen,the lower the initial pH,and the higher the experimental temperature,the more advantageous it is for the nano-zero-valent iron and its various modified materials to remove nitrate.The order of inhibition of nitrate removal by various coexisting anions on various types of nanoparticles is PO₄^3->CO₃^2->SO₄^2->Cl.?3?H-NZVI broadens the range of solution pH to NZVI.Under alkaline conditions,H-NZVI can also achieve a nitrate removal rate of 85%to 100%.Acidic conditions are more advantageous for?N?ZVI/AC combined with microelectrolysis to remove nitrate and TN.When the initial solution has a pH of 7.0,NZVI/AC can remove 100%nitrate and the TN removal rate is 38.9%.?4?NZVI and NZVI have a total nitrogen removal rate of about 10%after reaction with nitrate,indicating that the conversion product of nitrate is mostly ammonia nitrogen,and only a small part is converted into nitrogen and nitrite.The removal rate of TN in the micro-electrolysis system composed of NZVI/AC and nitrate can be maintained at more than 35%.