This paper presents a mathematical model for an in-situ hydrogenotrophic denitrification and oxidation process in an experimental scale aquifer. This model was developed to investigate the stable denitrification performance of the aquifer as well as the effects of varying the molar ratio of nitrate load to hydrogen gas injection (N/H ratio) on the effluent quality in terms of nitrate and nitrite concentrations under a long-term operation. The model could fairly predict the effluent quality in terms of nitrate and nitrite concentrations in the aquifer, in response to the sudden decrease in H2 gas injection as well as different N/H ratios. Furthermore, the model clearly demonstrated that denitrification and nitrification proceeded in each zone injected with H2 gas or O2 gas, respectively, and that stable treatment can be achieved. There were some differences between the experimental data and the model results for nitrate, nitrite, dissolved oxygen, and dissolved hydrogen at the H2-injection zone, implying that mass transfer rates in biofilm should be taken into consideration for more precise modeling. A sensitivity analysis showed that effluent quality in terms of nitrate concentration was the most sensitive to changes in maximum nitrate and nitrite utilization rates.
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