Nitrate Removal from Groundwater by Heterotrophic/Autotrophic Denitrification Using Easily Degradable Organics and Nano-Zero Valent Iron as Co-Electron Donors
Heterotrophic/autotrophic denitrification (HAD) is an effective approach to remove nitrate from contaminated groundwater. To improve its performance, easily degradable organics (methanol, ethanol, oxalic acid, and sodium acetate) and nano-zero valent iron (nZVI) were selected as co-electron donors for HAD, and their effectiveness in enhancing HAD to remove nitrate from simulated groundwater was evaluated. It was found that the removal efficiency of HAD to nitrate was significantly affected by the species of easily degradable organics as their different biological availability. Among the tested organics, ethanol-supported HAD system exhibited a better removal efficiency, and after 10 days reaction, it could achieve a high nitrate removal rate to 85.6% with an initial concentration of 90.94 mg/l, and at the end of the test (27 days), nitrate was almost completely removed in the interaction of heterotrophic denitrification (HD) and autotrophic denitrification (AD), and there was no nitrite and ammonium accumulation (< 0.1 and 1.0 mg/l). Moreover, the initial C/N ratios (0.2, 0.5, 1.0, 2.0, and 4.0) of simulated groundwater had a significant influence on nitrate removal by HAD. Increasing the C/N from 0.2 to 2.0 could markedly enhance nitrate removal efficiency, but continuously increased to 4.0 the removal rate just decreased; nevertheless, the accumulation of nitrite and ammonium were closely related to both the C/N ratios and species of organics. The synergistic effect between HD and AD process plays a vital role in the mixotrophic environment. Therefore, this research provides an effective method for nitrate removal from contaminated water with low organic carbon.
KeywordsHeterotrophic/autotrophic denitrification (HAD) Easily degradable organics Nitrate Groundwater Co-electron donors
The authors gratefully acknowledge the financial support by the National Natural Science Foundation of China (No. 41502240), the Natural Science Basic Research Plan in Shaanxi Province of China (No. 2017JM4005), the Fundamental Research Funds for the Central Universities (No. 3102017zy056), the Key Laboratory of Groundwater Contamination and Remediation, China Geological Survey (CGS) & Hebei Province (No.KF201610), and the Seed Foundation of Innovation and Creation for Graduate Students in Northwestern Polytechnical University (No. Z2017192).
- Aminzadeh, B., Torabian, A., Azimi, A. A., Nabi Bidhendi, G. R. N., & Mehrdadi, N. (2010). Salt inhibition effects on simultaneous heterotrophic/autotrophic denitrification of high nitrate wastewater. International Journal of Environmental Research, 4, 255–262.Google Scholar
- Ezzatahmadi, N., Ayoko, G. A., Millar, G. J., Speight, R., Yan, C., Li, J., Li, S., Zhu, J., & Xi, Y. (2017). Clay-supported nanoscale zero-valent iron composite materials for the remediation of contaminated aqueous solutions: a review. Chemical Engineering Journal, 312, 336–350.CrossRefGoogle Scholar
- Park, J.-H., Kim, S.-H., Delaune, R. D., Cho, J.-S., Heo, J.-S., Ok, Y. S., & Seo, D.-C. (2015). Enhancement of nitrate removal in constructed wetlands utilizing a combined autotrophic and heterotrophic denitrification technology for treating hydroponic wastewater containing high nitrate and low organic carbon concentrations. Agricultural Water Management, 162, 1–14.CrossRefGoogle Scholar
- Ponder, S. M., Darab, J. G., Bucher, J., Caulder, D., Craig, I., Davis, L., Edelstein, N., Lukens, W., Nitsche, H., Rao, L., Shuh, D. K., & Mallouk, T. E. (2001). Surface chemistry and electrochemistry of supported zerovalent iron nanoparticles in the remediation of aqueous metal contaminants. Chemistry of Materials, 13, 479–486.CrossRefGoogle Scholar
- Repert, D. A., Barber, L. B., Hess, K. M., Keefe, S. H., Kent, D. B., LeBlanc, D. R., & Smith, R. L. (2006). Long-term natural attenuation of carbon and nitrogen within a groundwater plume after removal of the treated wastewater source. Environmental Science & Technology, 40, 1154–1162.CrossRefGoogle Scholar
- Simon, F. G., & Meggyes, T. (2000). Removal of organic and inorganic pollutants from groundwater using permeable reactive barriers: part 1. Treatment processes for pollutants. Land Contamination & Reclamation, 8, 175–187.Google Scholar