Disinfection optimization by a better control of ozonation process

Currently, ozonation installations in French drinking water treatment plants are operated in order to ensure an ozone residual of 0.4 mg/L at the outlet of the contactor with a contact time of 4 minutes which guarantee, with regards to the USEPA tables, a 4 log virus inactivation. Veolia Water has launched a thorough study concerning hydraulics in ozonation contactors which goals are (1) to reach the disinfection level desired through a better supervision of operating conditions, (2) to guarantee good hydraulic performances to reduce ozone production and ozonation-by products (bromates). The validation of these objectives is related to a relevant control of every ozonation tank with a Ct criteria considering from now their geometry, which condition their hydraulic efficiency. In comparison with CSTR method, the Ct₁₀ method has been judged as the most relevant. Veolia is working with such a tank control, which definitely requires the determination of its hydraulic efficiency. Considering that numerical modelling of the ozonation contactors will be very long and expensive, the project team is working on the determination of an analytical model expression for hydraulic efficiency. The objective is to create an innovative tool which enables plant operators themselves to easily determine the hydraulic efficiency of inter or post ozonation tank.