Reduction of nitrate by Metallic iron and zinc

• Main Authors: Lin, Wei-Yu, 林偉宇
• Other Authors: Chen, Shiao-Shing
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/03212078670858293040

碩士 === 國立臺北科技大學 === 環境規劃與管理研究所 === 92 === Metallic iron and zinc (Feo、Zno) were employed to reduce the nitrate in this study. Oxygen and sulfate both are the most common oxidants in the water which affects the reduction of nitrate by metal. Results indicated that the existence of oxygen, the reduction rate of nitrate by metal would be reduced about 20~30%. The changes of pH were different between aerobic (initial ORP＞100 mV )and anoxic (initial ORP around 0 mV)environment. pH changed up and down between 6 and 7 until the reaction was stable, but pH rose smoothly to 9 under aerobic conditions. ORP not only caused the different changes of pH, but also the production of metal when reaction was over. Take Feo for example, iron would turn to Fe2O3 under aerobic environment, but Fe(OH)3 would be produced under anoxic environment. The same surface area concentration(m2/L) of Feo and Zno were used to compare the nitrate reduction rate. The reaction rate constants of Feo(0.088 m2/L) is 0.069 hr-1, and Zno (0.084 m2/L) is 0.221 hr-1, which shows that Zno is superior to Feo. A pseudo-second-order reaction of Zno was detected under anoxic condition, and all the other reactions like Feo or Zno under aerobic or anoxic conditions were pseudo-first-order reactions. Through stoichiometric calculations, hydrogen-produced reaction was found combining the reducing reaction by Zno but not Feo. The 23 factorial design was used for investigating three factors that affects the reduction rate of nitrate by Feo. Three factors were ORP, dosage of Feo (560 mg/L and 800 mg/L) and the existence of sulfate. The effect was determined as the followings： ORP＞the existence of sulfate＞stoichiometric ratio. ORP was the greatest factor during the reduction of nitrate. Sulfate was not reduced under aerobic condition, on the contrary, sulfate was totally reduced under anoxic condition. The existence of sulfate lowered the reduction rate of nitrate about 10.5 % under anoxic condition, and an interval of 10% between different dosage of Feo. The kinetic model of nitrate and sulfate which could fit data well was setup by experimental data and consistent with the proposed mechanism.