Study On The Effect Of Sponge Iron On Nitrogen Transfer In Sewage Water

At the present time, water eutrophication in China is worse and worse, whichexacerbating the shortage of water resources and having great influence on the economic growthof the country and the basic guarantee for people’s lives. Being one of the biggest challenges inour country, the low removal rate of nitrogen cause water eutrophication and that has beenseriously taken into consideration. Therefore, it is very important to strengthen the treatmenteffeciency of nitrogen in the sewage treatment and to exert strict control over the emissions ofnitrogen. Sponge iron is a reducing agent with spongelike small holes. Sponge iron used forchemical reduction of nitrate is discovered early. As an efficient, economic denitrificationtechnology, the relevant research and application is a concern. At the present time, a lot ofresearches have been carried on and achieved some results.In this experiment, the sponge ironhas been used to study the reaction products and mechanism.Certain concentration solution ofKNO3is prepared as simulated wastewater. By studying the initial solution pH, the sponge irondosage, the sponge iron particle size, the initial concentration of nitrate, sponge iron-zeoliteratio, reaction time and other factors, the role of sponge iron in the reaction is explored andreaction mechanism is analyzed.The results indicated that: The low inflow pH is beneficial to generation of ammonianitrogen and reduction of nitrate nitrogen. The dosage of sponge iron lower than2.25g, theremoval rate are keep steady in41⁴5%, higher than2.25g,decreasing with the dosage.thegeneration of nitrite is increasing with the dosage.the best dosage is1.5g. The smaller thepartical size, the higher the removal rate. The smaller partical size have higher specificsurface area and contact area.the best size is2².5mm. The max removal rate was got whenthe concentration of raw water is4.41mg/L, when the concentration of raw water larger than4.41mg/L, the removal rate of nitrate decreases. The generation of nitrite is increasing withthe dosage. Sponge iron:zeolite=1:2，the removal rate reach the maximum. The add of zeolitedo beneficial to reduction of nitrate nitrogen. The removal rate reaches the maximum whenthe time comes to75min, after that, gradually decrease.The mechanism: the electrons required to reduction NO₃^-is provided by Fe⁰and theelectron transfer on metal surface is a major reduction mechanism.When the reaction take palce between the sponge and nitrate,and the product is ammonianitrogen,the apparent rate constant is kobs=14.59（mg/L）^1-n· s^-1，The reaction order of the isn=-0.878.Through these experiments, the reaction products and removal rate of nitrate in thereaction are explored and reaction mechanism is analyzed.there are different reaction products,such as ammonia nitrogen, nitrogen,nitrite depend on different experimentalconditions,but nitrogen is the most wanted product.how to obtain more nitrogen is one of theresearch objects from now on.in the future,the accurate reaction pathway and mechanismshould be studied and try to improve the proportion of nitrogen in all products;Based onsingle logistic regression,the experiment should be optimized under best condition;to studythe role of zeolite and zeolite-sponge iron in this system;To study the iron-carbonmicro-electrolysis and its influence to the results. Based on it,more work need to be done tostudy how to increase the N2generation by the sponge iron materials in denitrificationtechnology in the future and apply the results into sewage treatment plants.