Effect of three-dimensional mixing conditions on water treatment reaction process

The performance of water disinfection facilities traditionally relies on Hydraulic Efficiency Indicators (HEIs), extracted from experimentally derived Residence Time Distribution (RTD) curves. This approach has often been undertaken numerically through computational fluid dynamics (CFD) models, which can be calibrated to predict accurately RTDs, enabling the assessment of disinfection facilities prior to the construction of disinfection tanks. However, a significant drawback of the conventional efficiency methodology prescribed for disinfection tanks is associated with the respective indicators, as they are predominantly linked to the internal flow characteristics developed in the reactor, rather than the disinfection chemistry which should be optimized. In this study three-dimensional numerical models were refined to simulate the processes of chlorine decay, pathogen inactivation and the by-product formation in disinfection contact tanks (CTs). The main objective of this study was to examine the effect of three-dimensional mixing on the reaction processes which were modelled through finite-rate kinetic models. Comparisons have been made between pathogen inactivation and disinfection by-product accumulation results produced by a RANS approach against the findings of a Segregated Flow Analysis (SFA) of conservative tracer transport. CFD Results confirm that three-dimensional mixing does have an effect on the reaction processes, which, however, is not apparent through the SFA approach.