Modelling denitrification process in a static mixer–reactor using lattice-Boltzmann method

Abstract

Nitrate removal in wastewater systems is crucially important to maintaining the quality of potable water as well as protecting vulnerable ecosystems. In this study, a denitrification model was incorporated into lattice-Boltzmann model (LBM) to investigate denitrification efficacy of wastewater treatment in a static mixer–reactor. The model was used for simulating the effects of six solid and porous obstacle configurations, different inlet velocities, and inlet methanol concentrations on denitrification within a static mixer–reactor with six different configurations. The results show that all the obstacles and porous blocks could improve the denitrification efficiency. However, the performances of these configurations could be affected differently by the inlet conditions. At a low velocity (u=0.5u0), the denitrification rates are almost twice as that at u=1.5u0. However, at a high inlet velocity, there were small differences of the denitrification efficiency among different configurations. Furthermore, the rectangular obstacle had the greatest effects on the denitrification rates at the low inlet velocity while its performance at a higher velocity was almost comparable to those of the porous blocks. It is also found that at a high inlet methanol concentration (C2-u = 2.0C2-u0), all the configurations increased the denitrification efficiency of up to 10%, compared to clear channel. However, the rectangular obstacle resulted in a decrease of about 3% in denitrification at a low inlet methanol concentration (C2-u = 0.5C2-u0) while all other configurations could improve the performance. Although at a low methanol concentration, the solid obstacles could dwindle the performance, the porous blocks did enhance denitrification rates in all the inlet methanol concentrations. This implies that the porous configurations have a wider range of operational conditions, compared to other obstacle configurations. A proper design of static mixer–reactors without any moving part is able to improve the denitrification efficiency in wastewater treatment. The present model is a useful tool to evaluate the performance of different reactor configurations under combinations of all significant parameters, such as inlet velocity and methanol concentrations.