In a porous diffuser reactor, the water to be treated is made to flow through one or more chambers, the bases of which consist of porous diffusers giving off very fine bubbles of ozonized gas. For optimum gas-liquid contact, the water is usually fed in from the top of the chamber to ensure countercurrent mixing. Ozone may be injected into any or all of the chambers. In all cases, countercurrent mixing is preferable. The porous diffusers are of the DP 230 disc type. In this type of reactor, the depth of water above the porous diffuser should be from 5 to 7 m. In pre-ozonation stages, some of the pollutants in the water (detergent, algae, etc.)
There are two types of turbine reactor. In the first type, the water to be treated is fed into the suction area of a turbine, which sends the water down through the stream of ozonized gas being injected upwards. This produces a fine emulsion of gas and water, which diffuses throughout the upstream section of the chamber to be again projected downwards by the turbine. All the water to be treated is sent several times through the turbine to ensure good mixing. The turbine blades must be carefully designed to split the gas bubbles and ensure efficient diffusion of the gas mixture throughout the liquid. The second type of reactor uses a turbine with submerged motor located at the bottom of the chamber. The specially designed turbine sucks through the ozonized gas together with a certain amount of water, to produce an emulsion of fine bubbles. To ensure efficient gas diffusion, this type of turbine is custom-built to match the depth of immersion, the gas flow rate and the water recirculation rate at the plant in question. This type of turbine will provide excellent performance provided it is operated at its nominal rate. Under such conditions, it is capable of treating quite heavily polluted water, which makes it suitable for preozonation work. The turbine's speed of rotation must be matched to the flow rate of ozonized air/oxygen to be injected. The number and layout of turbines will depend on the hydraulic characteristics of the treatment tank.
The injector contacting method is commonly used in Europe, Canada, and the United States (Langlais et al., 1991). Ozone is injected into a water stream under negative pressure, which is generated in a venturi section, pulling the ozone into the water stream. In many cases, a sidestream of the total flow is pumped to a higher pressure to increase the available vacuum for ozone injection. After the ozone is injected into this sidestream, the sidestream containing all the added ozone is combined with the remainder of the plant flow under high turbulence to enhance dispersion of ozone into the water. Figure illustrates typical in-line and sidestream ozone injection systems.