Having the proper ozone equipment is only part of the solution. Ozone is a gas and is generated in situ. Making sure that this ozone gas is transferred into a liquid and then mixed properly is very important. This process is known as ozone mass transfer.
Making sure that the ozone is properly dissolved and allowed a complete chemical reaction of the gas is how to ensure a reliable ozone mass transfer. Most failures of ozone applications are the results of faulty ozone mass transfers.
The Solubility of Ozone and Importance of Choosing Correct Mass Transfer Devices
Temperature has an effect on the different solubility of ozone. Ozone is able to dissolve more and easier in cooler water. Because of this, ozone doses for the for the same applications will differ from country to country. When a proper ozone mass transfer is conducted, it will enhance the solubility levels of ozone, thereby ensuring required actions of ozone. A list of simple mass transfer devices are:
1) Hydro injector/ venturi/ eductors
2) Diffusers
3) Static mixers
4) Mass multipliers
5) Combination of the above
Venturis: These devices use high water pressure to suck the ozone into the water. They achieve at least 90-95% efficiency because of their design. The pump required has to be sized properly, or there will be ozone leakages.
Diffusers: These are devices that bubble ozone across water in order to diffuse it into the water. They work under normal water pressure. The number of diffusers needed will be determined by the volume of air, and surface area of the contact tank. Diffusions requires a minimum bubbling height of 5-6 meters for maximum efficacy. Some problems that arise from diffusing is the channeling of bubbles, and inadequate gas liquid contact. Because the diffusers is always in contact with high concentration ozone, it is important that the diffuser is made of the right material. SS or ceramic diffusers are the most preferred materials. For waters with high turbidity, diffusers are not recommended. Ozone destructors are also needed for the destruction of any unused ozone.
Static Mixers: These are devices placed in a pipe that are always used in conjunction with venturis. If used after venturi injections, they increase the ozone mass transfer. The material of construction is also very important here as well. SS 316 are normally used.
Mass Multipliers: These are devices that are placed in pips that discharge water mixed with ozone under high pressure into the water. They are normally used for large applications and in conjunction with venturis. Mass Multipliers are normally made of Kynar plastics.
Combination of Devices: A combination of mass transfer devices are often used. Combinations work efficiently and will guarantee higher percentage of mass transfer. However, in larger applications, it can also increase the cost it takes for mass transfer. This is something that is very important to keep in mind when planning your method of mass transfer.
Other factors that determine the efficiency of the ozone mass transfer are:
1) pH of the water: needs to be between 7-8 pH.
2) Temperature of the water: the higher the temperature the less the ozone will dissolve.
3) The concentration at which the ozone is used. The higher the concentration, the more ozone will dissolve.
4) The pressure: ozone mass transfer under pressure is recommended and this can reduce ozone dose, since efficiency is very high.
5) The design of the contact tank: ensures that the diffused ozone is efficiently mixed in the water.
Other Forms of Ozone Mass Transfer: There are also some unconventional types of ozone mass transfer that can be used with equal efficacy. U Tube devices are one of these methods. U Tubes have water that is forced into the tube under pressure and the water mixes within the pipelines when the direction of the water if forcibly changed. Essentially, it is like using a diffuser system under pressure. A U Tube system that is designed properly can have an efficiency of over 95%.