Ozone Transfer Efficiency

Ozone transferred is difference between the amount fed (ozone feed) and the amount he leaves the system (ozone out). Ozone transfer efficiency can be expressed as follows:

Transfer Efficiency (TE) ={(Ozone Feed) – (Ozone Out)}/(Ozone Feed)

The transfer efficiency is effected by various factors including bubble size, temperature, pressure, gas/liquid ratio, concentration of ozone in the feed gas(related to ozone generator output), water chemistry, etc. The following relationships between key variables and TE exist:

1. TE decreases as applied ozone dose increases.
2. TE increases as water quality decreases (ozone demand increases)
3. TE increases as the water chemistry favors the formation of hydroxyl radicals (high pH and low alkalinity)
4. TE decreases as gas/liquid ratio increases.
5. TE increases with decreasing bubble size.
6. TE increases with increasing concentration of ozone in the feed gas.

The design of the mixing/contact system are important for the TE. Different types of mixing systems have application given site specific conditions and economics. In the case of fine bubble diffusers the flow pattern through the contact vessel and the depth of the diffusers are critical to the TE. Beyond the normal factors effecting TE, the configuration of the side stream injection system will have an impact on TE, e.g. removing gas immediately after the injector or in the contact chamber.

Background

1. Ozonation is an absorption process
2. Mass transfer rate dependent on
    Physical properties of phases
    Concentrations at the interface
    Degree of turbulence
3. Two-film model (Referring to the diagram below)
    N = (kL x a) x (CL*-CL) x VL
    CL* = f(CG, P, T) – Henry’s law
    CL = f(mixing conditions)
    kL.a = f(hydrodynamic & operating conditions, reactor configuration)
    CL: Concentration of Ozone in Liquid
    CG: Concentration of Ozone in Gas