CFD simulation and analysis of reactive flow for dissolved manganese removal from drinking water by aeration process using an airlift reactor

Abstract

Removal of soluble manganese Mn(II) from natural water using dissolved oxygen as an oxidant is an important process in the production of drinking water. This process can be performed in multiphase devices, and airlift reactors have been regarded as an efficient system for carrying out aeration. To simulate this process, it is necessary to understand the oxidation kinetics of soluble Mn(II) coupled to multiphase hydrodynamics and inter-phase mass transfer. The objective of this paper is, therefore, to develop a three-dimensional Euler-Euler two-phase model, aiming to simulate a reactive flow for Mn(II) removal from drinking water by aeration process using an airlift reactor. Based on the previous experimental data, the mathematical models were firstly validated by comparing the liquid residence time distribution and mass transfer, and then the dependence of manganese oxidation on the initial Mn(II) concentration and pH values were analysed. Afterwards, the dependence of manganese oxidation on the initial Mn(II) concentration and pH values were numerically analysed, as well as the effect of the autocatalytic reaction due to the addition of MnO2, and compared to the results from a one-dimensional axial dispersion model. Using CFD, it was found that the local and global models agreed successfully with experimental data and correctly described the auto-catalytic effect of MnO2 on the oxidation by aeration process. While the level of spatial heterogeneity increased with pH, the simulations highlighted surprisingly that it decreased with a rise in the initial concentration of MnII, whereas it remained constant when the amount of MnO2 was increased.