Treatment Of Wastewater Containing Low Content Of Nitrate By Reduced Iron Powder

Nitrate is a wide spread contaminant of ground and surface waters worldwide,and it is a potential human health threat especially to infants?Because of the high concentration of residual nitrate nitrogen after the biodegradation,the total nitrogen of wastewater would exceed standards,which discharge into the environment will still have an impact on the human body and the environment.In addition,the nitric acid wet method used in the production of iron oxide red in China,a large amount of high concentration ammonia nitrogen wastewater was produced by converting nitrate in the production process.In view of the above two problems,this paper proposed the use of reduced iron powder?Fe⁰?to treat low concentration nitrate wastewater.Through the analysis of nitrogen transformation in the reaction process,the path of nitrate reduction conversion was deduced and reaction kinetics analysis was used to investigate the reaction conditions of promoting the reaction products to be environmentally harmless.The reaction mechanism was also preliminarily discussed.The influences of pH,temperature,Fe²⁺concentration,the dosage of Fe⁰ and initial nitrate concentration on the reduction of nitrate radical by reduced iron powder have been researched.The results indicated that:the initial pH value and Fe²⁺concentration are the main influence factors,while the reaction temperature is a secondary factor.In the process of the reduction of NO₃^-by Fe⁰,the electron transfer of the metal surface is the main reduction reaction mechanism,and Fe²⁺can be used as an electron donor or electron transfer carrier to promote the occurrence and progress of the reduction reaction between Fe⁰ and NO₃^-.Nitrate removal rates increased with increasing amount of Fe⁰,and decreased with increasing initial nitrate concentration.In order to explore the feasibility of the zero-valent iron treating the wastewater containing low content of nitrate nitrogen under neutral conditions,SEM and EDS were employed to examine the morphology of Fe₃O₄ and the as-synthesized ferrite loaded zeolite?FZ?composed by coprecipitation method,the Fe₃O₄ particles are scattered in small clusters on the zeolite.Fe²⁺entered inside the crystal structures through ion exchange,and both play a role in the reaction.Therefore,Fe⁰ synergistic with FZ can restore NO₃^-in neutral or even alkaline conditions,and the FZ prepared by alkali washing pretreatment of zeolite powder has better effect.The removal efficiency of nitrate of Fe⁰?Fe⁰/quartz sand and Fe⁰/activated carbon from wastewater in an upstream fixed bed reactor was studied.When the initial nitrate concentration was 50 mg·L^-1,the initial pH was 6 and the volume ratio of Fe⁰ and activated carbon was 0.5,the removal efficiency of NO₃^-could account for 75.99%,and the proportion of ammonia in the reduction products was low.The process met pseudo first order reaction,and the reaction constant was 0.084 min^-1.The addition of quartz sand or activated carbon could effectively reduce the hardening of iron powder in the reactor.The zeolite had high removal efficiency of ammonia nitrogen and good adjustment to the pH values of the effluent.