Experiment and multicomponent model based analysis on the effect of flow rate and nitrate concentration on denitrification in low-permeability media.

To better understand the combined effects of flow rate and NO3- concentration on denitrification rate and NO3- removal efficiency in the low-permeability media, a set of column experiments with different flow rates and injected NO3- concentrations were conducted. Denitrification processes under these different conditions were simulated using the PHREEQC code that couples the biogeochemical reactions and hydrological transport processes. In these reactive transport models, Monod kinetics were applied to describe the denitrification process. It was found that, among the experiments conducted in this study, the low flow rate (0.023 m/d) resulted in the low denitrification rate but high NO3- removal efficiency. Meanwhile, NO3- removal efficiency was the highest (85%) under moderate NO3- concentration of 1.29 mmol/L, although denitrification rate increased in response to the increase of NO3- concentration. The model results also indicated that NO3- removal efficiency of 97% can be achieved with relatively low flow rate and high influent NO3- concentration. The results in this study provide insights into NO3- remediation, and the temporal and spatial flow rate, as well as NO3- concentration distribution, should be pre-evaluated for the effective removal strategies.