Author(s): J. K. Yang; S. N. Chan; K. W. Choi; J. H. W. Lee
Keywords: Dense jet; Chlorine disinfection; Total residual chlorine; Numerical modelling
Abstract: Concentrated dense sodium hypochlorite (NaOCl) solution is commonly used in sewage treatment plants for disinfection of treated sewage. In view of the importance of sewage disinfection to the environmental impact, it is essential to understand the mixing and reaction of chlorine with sewage for disinfection dosage optimization. In this study, a laboratory experiment of dense chlorine jet discharging into stationary treated sewage is conducted. To ensure safe operation of the experiment, the set-up is first tested with sugar solution with density similar to that of dense chlorine solution. Then, experiments of dense NaOCl solution discharging into tap water and treated sewage are conducted. Numerical models are also developed based on the OpenFOAM computational fluid dynamics code and the Distributed Entrainment Sink Approach (DESA). The predicted ambient total residual chlorine (TRC) profiles and dilutions at different jet cross-sections agree well with experimental observations. Measurement of ambient TRC shows that the chlorine consumption is rapid within the first three minutes of NaOCl discharge. Chemical reaction slows down as TRC accumulates in the tank.