Apparent kinetics phenomena of denitrification in sediments and its causes

Intrinsic kinetic constants are very important for biogeochemical process simulation and environmental management engineering design. However， the intricate mass transfer-reaction coupling effects in sediments lead to the acquisition of apparent kinetic constants in conventional studies， with the underlying environmental dependency mechanisms remaining poorly resolved. This study systematically investigated the drivers of apparent kinetic phenomena through integrated laboratory column experiments and numerical simulations， anchored in diffusion boundary layer theory. Flow-through sediment reactors experiment and inversion results showed that the denitrification kinetic constants increased nonlinearly with the influent concentration and flow rate， showing a significant apparent kinetic phenomenon. When Da was not much less than 1， the reaction system often exhibited an apparent kinetic phenomenon； the increase of kinetic constants caused by changes in influent concentration and flow rate was due to the increase of the diffusion flux of nitrate nitrogen. But the specific reasons were different between the two conditions. The increase of kinetic constants from influent concentrations was due to the increase in concentration difference of nitrate at both sides of the diffusive boundary layer， while the increase of constants caused by flow rates was due to the thinner boundary layer. In order to avoid the simulation error caused by the misuse of kinetic constants， it is necessary to identify the apparent kinetic phenomena before simulations.