Modelling the influence of evaporation on residual chlorine in water storage tanks using CFD :

Abstract

Water storage tanks are usually utilized in water distribution systems (WDS) to meet the water demand fluctuations. Long residence periods experienced in these tanks can cause immoderate loss of the disinfectant residual due to the numerous processes that occur in water. Low-level disinfectant residual can encourage microorganism regrowth in the distribution system, leading to unsafe water. Chlorine is the most common disinfectant used to disinfect water supplies. However, variations in the rate of chlorine decay in these storage tanks is one of the greatest limiting factors in ensuring adequate water treatment process and giving guarantee to its efficiency. These variations could be due to some inadequately tested mechanisms of chlorine reactions in bulk fluid, chlorine reactions with storage tank walls, and evaporation. This study presents Computational Fluid Dynamics (CFD) modeling approach to assess the influence of evaporation on residual chlorine in water storage tanks. Simulations together with experimental measurements were performed in laboratories as well as at the water treatment plant in order to gain a better understanding of the influence of evaporation on residual chlorine in water storage tanks. Findings from this study indicate that an increase in the evaporation rate accelerates the rate at which residual chlorine is lost. This study can contribute to the existing literature about monitoring chlorine decay in storage tanks and therefore help the managements of water and sewerage treatment plants to come up with appropriate tools and design of storage tanks. It is concluded that temperature is the main factor influencing evaporation, which in turn causes disappearance of residual chlorine within the water storage tanks.