Passive and Active Methods for Enhancing Water Quality of Service Reservoir

Abstract

Knowledge of flow pattern and water age distributions in service reservoirs is of the utmost importance for ensuring water quality supplied to the customers. In this article, a balancing reservoir was first investigated as a benchmark case. Using the computational fluid dynamics (CFD) method coupled with dynamic meshes, the flow pattern and water age distributions in the reservoir were simulated under actual service conditions. The calculated flow pattern indicated the migration and evolution of flow recirculation regions in the reservoir, which would lead to nonuniform lateral and vertical distributions of the water age, and therefore residual chlorine concentration. A passive flow control method, by adjusting the original circular nozzles to elliptical nozzles, was explored to enhance the water quality. It was found that using elliptical nozzles could assist fluid mixing in the reservoir. The water in the modified reservoir with elliptical nozzles had 5% lower age values than those of the original. Next, bubble plumes were used as an active method to enhance the water quality in the balancing reservoir. It was found that bubble plumes could enhance the fluid mixing significantly in both the vertical and lateral directions. Consequently, the modified reservoir with bubble plumes had 10% lower age values than those of the original reservoir. Therefore, the use of bubble plumes is suggested to be a viable approach for enhancing the water quality in a balancing reservoir, which is deemed to be novel in this field.