On an average day, a large municipal water treatment plant generates approximately 380 million liters per day (MLD). Most of this water bypasses the 23-ML finished water reservoir and is supplied directly to the system. When the demand is low during the night, 7.6 MLD of water enters the reservoir, and the same amount of water exits the reservoir through the same gates when the demand is high during the daytime. Because of the way the reservoir has been operated, the age of water can be high, resulting in greater disinfection byproduct formation. In this analysis, a commercial software package for computational fluid dynamics model (CFD), ANSYS CFX, was used to calculate water age distributions in 3D space and time. The existing reservoir with current operation was first evaluated, and then the effects of structural and operational modifications on water age were quantitatively evaluated. The structural modifications consisted of installation of baffles and flap gates to create a one-directional flow pattern through a serpentine channel. The operational modification was made by operating a pump every 7 days, which is currently operated only every month to exercise the pump. The average water age became 8.5 days older in 16 days in the existing reservoir, and change in water age was reduced from 8.5 to 5.5 days by either structural or operational modification. The structural modification would require the reservoir to be taken out of service for an extended period of time and also require a capital investment, while the operational modification was manageable by the plant. Therefore, the operational modification was preferable.
.jpg "Shinjiro Miyawaki, n/a (he/him/his) photo")
