Remediation of Ground Water Contaminated by Nitrate Nitrogen and Chromium Using Zero-Valent Iron PRB Technology

Through continuous flow experimentation,the reactivity characteristics of zero-valent iron(Fe0)-PRB with ground water contaminated by nitrate,chromium and the combination of nitrate and chromium were investigated.The products of nitrate and chromium deoxidized by zero-valent iron were also analyzed.The interaction between the nitrate and chromium which were synchronously deoxidized by zero-valent iron was also studied.In this paper,zero-valent iron with 0.15-0.42 mm particle size and activated carbon with 0.15 mm particle size were used as reaction packing media;their mass ratio was 1∶1.The results showed that nitrate could be effectively deoxidized by zero-valent iron.The NO3——N removal efficiency was 95% when the influent NO3——N mass concentration was 20 mg/L.NO2——N was the transitional deoxidization product,while NH4+-N was the main final product in the effluent.The pH increased from 7.1 in the influent to 9.0 in the effluent,and the total iron mass concentration in the effluent was below 0.60 mg/L.Chromium could be deoxidized by zero-valent iron more effectively for the chromium contaminated ground water which was treated by PRB.The Cr(Ⅵ) removal efficiency was 96% when the influent Cr(Ⅵ) mass concentration was 10 mg/L.The redox products such as Fe3+ and Cr(Ⅲ) precipitated on the packing media during the process.Thus,they could not be transported into the downstream.The pH increased from 7.0 in the influent to 8.0 in the effluent,and the total iron mass concentration in the effluent was below 0.30 mg/L.For the treatment of ground water contaminated by both nitrate and chromium,the results showed that the Cr(Ⅵ) removal efficiency by the zero-valent iron was not affected by the co-existence of NO3——N,while the NO3——N removal efficiency decreased with the existence of Cr(Ⅵ).