Use of Innovative Techniques to Enhance the Hydraulic Disinfection Efficiency of Drinking Water Contact Tanks

Impact of Modified Inlets on Residence Times in Baffled Tanks

“…RTD curves and BFs. An ideal inlet, which would be identical to the cross‐section of the channels in the tank, was modeled by Kattnig (2014) and was estimated to have a BF of about 0.8. This result can be attributed to the difficulty in achieving perfect plug flow (i.e., a BF of 1.0) as a result of dispersion arising from wall effects (Greene et al 2006).…”

“…Hydrodynamic analysis. The ideal inlet modeled by Kattnig (2014) allows for a better emulation of river‐like flow in which average longitudinal velocities are nearly constant throughout the cross‐section; this implies advection‐dominated flow and minimal diffusive action. Therefore, it is suggested that inlet modifications that lead to the quickest homogenization of longitudinal velocities and dissipation of vertical velocities will lead to higher mixing efficiency in the disinfection system.…”

“…This necessitates a turbulence closure scheme. Ultimately the renormalization group (RNG) k‐ ဓ model was used whenever possible because it handles free shear turbulence well and has been successfully used to correctly predict flow in disinfection tanks by Kattnig (2014) and Taylor et al (2012) while still being computationally inexpensive. Similarly favorable results were obtained using the standard k‐ ဓ model for the same purpose by Wilson and Venayagamoorthy (2010) and Gualtieri (2006).…”

“…Mesh independence was assumed to be achieved when the BF parameter changed negligibly with an increase in cell count. Using this metric, Kattnig (2014) showed that for the baffled contact tank at hand, mesh independence was obtained at about one million cells. As a conservative measure and because of the impinging jet(s) at the inlet leading to issues with resolving the flow accurately, about 1.4 million cells were used for each model.…”

“…The baffles create a more channeled environment for the water by increasing length‐to‐width ratios of flow to encourage transport through advection, which is superior to diffusion for mixing purposes (Kattnig 2014, Amini et al 2011, Li et al 2006, Peplinski & Ducoste 2001). It also limits the creation of dead zones of stagnated water by guiding the flow through portions of the tank that would otherwise be short‐circuited (Kattnig 2014; Zhang et al 2013; Amini et al 2011; Kim et al 2010; Wols et al 2010, 2008; Evans et al 2003). In small communities in which financial budgets for drinking water disinfection are limited, baffled systems provide a cost‐effective solution for ensuring adequate contact time.…”