Abstract
A concentrated 10% chlorine solution (in sodium hypochlorite) with a specific gravity of 1.2 is used for the disinfection of treated primary effluent in the Stonecutters Island Sewage Treatment Works (SCISTW) in Hong Kong. The chlorine solution is injected in the form of coflowing dense jets into a sewage flow of approximately , with a target dosing rate of (or an initial dilution of 5,000 to 10,000). The large sewage flow to chlorine dosing flow ratio has resulted in insufficient mixing and high chlorine demand as a result of the fast reaction of chlorine with organic and inorganic substances in the sewage. An integral jet model is developed to predict the jet mixing in the initial contact region of chlorine and sewage, accounting for chemical kinetics of the chlorine–sewage reaction. The model is calibrated using field data obtained from experiments using real sewage and chlorine solution in a field-scale physical model inside the sewage treatment works. The mathematical model is used to guide experimentation of various alternatives to reduce the chlorine demand. It is found that under the same chlorine dosage, diluting the concentrated chlorine solution by four times (i.e., containing 2.5% available chlorine) and doubling the number of injection jets can result in the reduction of chlorine demand by 10–15%. The chlorine dosage optimization was supported by extensive field measurements and three-dimensional (3D) computational fluid dynamics (CFD) simulations.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgments
This research was commissioned by the Drainage Services Department (DSD) of the Hong Kong Special Administrative Region (HKSAR) Government (Contracts HATS 02/2014 and HATS 03/2014). The support and assistance of DSD engineers and on-site staff at SCISTW are well-appreciated. The assistance of Daniel Tsang in the field work and laboratory analysis is gratefully acknowledged.
References
ANSYS FLUENT 15.0 [Computer software]. ANSYS, Canonsburg, PA.
Choi, K. W., Lee, J. H. W., Kwok, K. W. H., and Leung, K. M. Y. (2009). “Integrated stochastic environmental risk assessment of the Harbour Area Treatment Scheme (HATS) in Hong Kong.” Environ. Sci. Technol., 43(10), 3705–3711.
Chu, V. H., and Lee, J. H. W. (1996). “General integral formulation of turbulent buoyant jets in cross-flow.” J. Hydraul. Eng., 27–34.
EPD (Environmental Protection Department). (2014). “EPD clean harbour.” ⟨http://www.cleanharbour.gov.hk/en/home.html⟩ (Jan. 1, 2017).
Haas, C. N., and Karra, S. B. (1984). “Kinetics of wastewater chlorine demand exertion.” J. Water Pollut. Control Fed., 56(2), 170–173.
Jafvert, C. T., and Valentine, R. L. (1992). “Reaction scheme for the chlorination of ammoniacal water.” Environ. Sci. Technol., 26(3), 577–586.
Lee, J. H. W., Chan, S. N., Choi, K. W., and Qiao, Q. S. (2015). “Fluid mechanics of chlorine disinfection for the Hong Kong Harbour Area treatment scheme.” Proc., 36th IAHR-Congress, International Association of Hydro-Environment Engineering and Research, Madrid, Spain.
Lee, J. H. W., and Chu, V. H. (2003). Turbulent jets and plumes: A Lagrangian approach, Springer, New York.
Lee, J. H. W., Huang, J. C., Choi, D. K. W., and Chan, S. N. (2014a). “Report on review of in-plant effluent quality data.”, Drainage Services Dept., HKSAR Government, Hong Kong.
Lee, J. H. W., Huang, J. C., Choi, D. K. W., Chan, S. N., and Qiao, Q. S. (2014b). “Review of in-plant sewage treatment and disinfection processes.” Drainage Services Dept., HKSAR Government, Hong Kong.
Lee, J. H. W., Huang, J. C., Qiao, Q. S., Choi, D. K. W., and Chan, S. N. (2016a). “Report on model testing of chlorine demand in the flow distribution chamber.” Drainage Services Dept., HKSAR Government, Hong Kong.
Lee, J. H. W., Qiao, Q. S., Chan, S. N., Choi, D. K. W., and Huang, J. C. (2016b). “Field experiments of chlorine demand in disinfection of treated primary effluent.” J. Environ. Eng., 04017073.
Lee, J. H. W., Qiao, Q. S., Chan, S. N., Choi, D. K. W., and Tsang, D. M. H. (2016c). “Report on model testing of chlorine demand in the flow distribution chamber–Experiments with pre-diluted NaOCl solution.” Drainage Services Dept., HKSAR Government, Hong Kong.
Lin, S., and Evans, R. L. (1974). “Chlorine demand study of secondary sewage effluents.” Water Sewage Works, 121(1), 35–44.
Qiao, Q. S., Chan, S. N., Choi, K. W., and Lee, J. H. W. (2016). “A study of a chemically reacting chlorine dense jet discharging into treated sewage.” Proc., IAHR-IWA Int. Symp. on Outfall Systems, International Association for Hydro-Environment Engineering and Research, Madrid, Spain.
Sawyer, C. N., McCarty, P. L., and Parkin, G. F. (1994). Chemistry for environmental engineering, 4th Ed., McGraw-Hill, New York.
Thomann, R. V., and Mueller, J. A. (1987). Principles of surface water quality modeling and control, Harper and Row, New York.
Wright, S. J. (1994). “The effect of ambient turbulence on jet mixing.” Recent research advances in the fluid mechanics of turbulent jets and plumes, P. A. Davies and M. J. V. Neves, eds., Vol. 255, Springer, Dordrecht, Netherlands, 13–27.
Information & Authors
Information
Published In
Copyright
©2017 American Society of Civil Engineers.
History
Received: Feb 13, 2017
Accepted: May 18, 2017
Published online: Sep 6, 2017
Published in print: Nov 1, 2017
Discussion open until: Feb 6, 2018
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.