Abstract
Conventional designs of chlorine contact tanks in potable water treatment plants are insufficient in terms of disinfection efficiency due to low hydraulic and mixing efficiencies. Strong interaction of the turbulent flow with the solid baffles may adversely affect hydraulic, mixing and disinfection performance of the contact system. Recirculating and jet zones created in the tank may require high chlorine dosages to yield adequate disinfection levels, which can result in the formations of high disinfection by-products (DBPs) in the treated water. The use of treated water by the consumers with high chlorine dosages and DBPs may lead to environmental and health problems in the long-term. Disinfection efficiency of the tank can be increased by the modification of the baffles and required disinfection levels can be achieved using lower chlorine dosages. In this study, performance of a patented baffle design is evaluated by means of numerical simulations on a full-scale contact tank. Self-decomposition of the chlorine, pathogen inactivation and formation of Trihalomethane (TTHM) by-product are simulated using a second-order numerical model. Numerical results show that the new baffle design yields 3-log inactivation by using 40% less chlorine concentration than the conventional design and the amount of DBP can be decreased by 43%.
Highlights
Chlorine Contact Tanks (CCTs) have been used in municipal water treatment plants for the removal of potential pathogens and viruses from the surface and ground waters
The optimized dimensions of the patented slotbaffle design (SBD) used in the contact tank are depicted in Fig 2 [12]
While 3-log inactivation of the Giardia pathogen is achieved using 25 mg / L chlorine dosage for conventional baffle design, the SBD provided the same inactivation level using 15 mg / L, which is a significant reduction in the chlorine usage
Summary
Chlorine Contact Tanks (CCTs) have been used in municipal water treatment plants for the removal of potential pathogens and viruses from the surface and ground waters. Disinfection performance of a contact tank can be evaluated with respect to required chlorine dosages for the suggested inactivation level. Angeloudis et al numerically investigated disinfection performance of several contact tank designs using a first-order chemical model, which provides chlorine self-decomposition, pathogen inactivation and by-product formation [3]. Effect of the inlet configuration on the disinfection performance of a contact tank was investigated by Angeloudis et al using a first-order chemical model for the chlorine [6]. Hydraulic and mixing efficiencies, as well as disinfection efficiency of a full-scale contact tank in Eskisehir Municipal Water Treatment Plant in Turkey is investigated by means of three-dimensional numerical simulations. In the second stage of the numerical studies, disinfection simulations were carried out for the chlorine selfdecomposition and pathogen inactivation with focus on the formation of DBP formation
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