Ozone dosing systems for water treatment

This #TechnicalTuesday, #teamWRc Graduate Water Process Engineer, Gabriel Pronek, discusses how his mathematical model demonstrates ozone as an effective reagent for contaminants in water.

I’ve recently been looking into mathematical modelling of ozone dosing systems for water treatment. Ozone is a powerful oxidant, with huge application in contaminant removal from water. It breaks down organic molecules such as pesticides and pharmaceutical by-products and can be used as an alternative to chlorine for disinfection.

For my model, I was considering the dissolution of ozone in water, as well as it’s reaction with a model contaminant, X. The system would typically consist of a single tank split into various stages with the use of baffles. Some of these stages would then be aerated with ozone that is electrochemically produced onsite. I visualised the compartments as a series of equal, perfectly mixed tanks in series. I modelled the ozone dissolving in two stages and then reacting with the contaminant in the others. The model was based around the assumption that two of the chambers would be aerated, with the others allowing for sufficient residence time for the reaction(s) to take place. The model assumed counter current flow for the gas and water, so an intermediate residence tank was required.

The model demonstrates ozone as an effective reagent for contaminants in water. On the graph below, the blue line represents ozone concentration, and the orange line represents contaminant concentration. Ozone was shown to rapidly react with the contaminant, with very small concentrations of both leaving the system.

This model was an initial analysis of ozone for water treatment; however, there is scope to improve the calculations. More accurate results could be obtained by the effects of hydrostatic pressure and gas side streams. In a real system, there will likely be multiple different contaminants reacting with the dosed ozone. Additional tracking for the concentrations of each of these contaminants along with other commonly occurring substances could be implemented into the calculations. Physical and chemical parameters such as pH and Temperature will also influence dissolution and reaction rates.