Modeling of tubular membrane contactors for ozonation of water reveals reduced bromate formation with static mixers

Abstract

Bromate formation and insufficient micropollutant degradation are two major problems in wastewater ozonation. The conventional process using bubble columns has the drawback of an inhomogeneous ozone distribution, causing increased bromate formation. Membrane contactors are a promising alternative as they can dissolve ozone bubble-free. This work presents a simulation of a tubular membrane contactor in COMSOL Multiphysics that includes flow, mass transfer, ozone decay, and reactions of organic molecules and bromide with ozone and hydroxyl radicals. Gaseous ozone and water flow on the lumen and shell side of the membrane, respectively. Static mixers are placed in the water channel, coaxial between the membrane and housing. The simulations show a 75% increase in ozone flux through the membrane, a homogenized ozone distribution, and 13 times higher degradation of a medium-oxidizable micropollutant in the presence of additional static mixers. Furthermore, static mixers enable the use of a lower gaseous ozone concentration, resulting in 31% lower bromate formation at the same ozone exposure without affecting micropollutant degradation. Overall, we demonstrate that membrane contactors with static mixers can be used as a strategy to reduce bromate formation.