Experimental Study On Removal Of Nitrate From Groundwater By Sponge Iron-Activated Carbon Composite Material PRB Technology

As an important part of water resources,groundwater is increasingly polluted by nitrates.In this paper,sponge iron-activated carbon is used as a medium filler for Permeable Reactive Barriers?PRB?to repair nitrate-contaminated groundwater through chemical reaction.By artificial groundwater contaminated by nitrates,static experiment exploring sponge iron-activated factors nitrate removal,through the continuous flow influent simulation PRB dynamic experiment,the effect of sponge iron-activated carbon on the repair of contaminated water and the effects of adding other substances such as SO42-,Cl-,CO32-and natural organic matter?NOM?on the repairing effect were studied.Through the study of different influencing factors,the experiment draws the following conclusions:?1?The sponge iron-activated carbon is mixed to form a large number of tiny primary batteries in the solution to improve the removal rate of nitrate nitrogen;the dense oxide film attached to the surface of the sponge iron can be removed by acid removal before the reaction to increase the removal rate of nitrate nitrogen by 4 times;the higher the ratio of iron to carbon in solution,the better the removal of nitrate nitrogen;when the pH value is between 6 and 8,there is no significant effect on the removal rate of nitrate nitrogen;the same time the higher the reaction temperature the higher nitrate removal;sponge iron-activated carbon reduction nitrate reaction accords with quasi-first-order kinetic equation,with the increase of the influent concentration of nitrate nitrogen,the reaction rate constant is also increased K_obs.?2?When the influent flow rate is between 1.0 cm/h and 5.6 cm/h,the effect of sponge iron-activated carbon on nitrate removal is worse with the increase of flow rate,and the lower the ammonia nitrogen content is.;when the pH of the influent is neutral,the removal rate of nitrate nitrogen and the lowest nitrite and ammonia nitrogen content are generated.When the concentration of SO₄^2-added is less than the concentration of nitrate nitrogen in the solution,the removal of nitrate nitrogen by sponge iron-activated carbon is promoted,and the inhibition is observed when the concentration is greater than the concentration of nitrate nitrogen.Adding Cl^-and CO₃^2-will inhibit the removal of nitrate from sponge iron-activated carbon.The higher the concentration of Cl^-,the more obvious the inhibitory effect,but the inhibitory effect of CO₃^2-concentration between 15 mg/L and 60 mg/L is not related to the concentration of dosing.The addition of NOM inhibits the removal of nitrate from sponge iron-activated carbon and inhibits it more significantly with time.?3?Analysis of the surface of sponge iron shows that elemental iron on the surface of sponge iron is the main substance.After the reaction,the elemental iron on the surface of the sponge iron is reacted,and the formed iron oxide and iron hydroxide block the pores on the surface of the sponge iron,resulting in a decrease in the removal of nitrate nitrogen by the sponge iron-activated carbon in the later stage of the reaction.