Two steps are used to determine the amount of ozone required. First is the CUMULATIVE need, which is the number of milligrams of ozone necessary to oxidize the number of milligrams of contaminates present. This is the stoichiometry of the reaction representing the consumption of ozone, normally in mgO3/mg substance. When several contaminates or substances are present, the totals for each are added together. This includes metals, minerals, organics, pesticides and etcetera. When this need is satisfied, the reaction is done. This is the calculation for oxidization, coagulation, flocculation, precipitation, color removal (ie. 1-3mgO3/mg Carbon) and etcetera.
Second is the DISINFECTION calculation, measured in mg/L of ozone over a specific period of contact time, usually minutes. This is a concentration & time (C t or C t) needed for inactivating living organisms, from single cell to higher life forms. It is the disinfection calculation for pathogens and pests, such as; algae, amoebae, bacteria, virus and etcetera.
The cumulative demand must be satisfied before a concentration of ozone can be held stable for any period of time in solution.
Both steps require adequate injection, mixing and time for the small amount of ozone to physically contact the target. One mg/L is only 1/1000 of a gram dissolved in one kilogram (1000 grams) of water, or 1:1,000,000. The time required for contact and/or reaction can be from several seconds to many minutes and is the obvious reason for the “t” in the C t. The ozone must physically contact the target to react with it.
It is not just economical and beneficial, but almost essential, to remove substrates or turbidity prior to the disinfecting steps, so that the target organisms are not shielded from the disinfectant. Organisms can be attached to, as well as enclosed within, the turbidity or other particles. This principle applies to other disinfectants as well ozone.
If excess ozone is produced, OFF GAS can be a problem, so don’t waste ozone and don’t pollute with it. Attention to this will also minimize production costs.
If there is any trick to using ozone, it is to make only as much as is needed and then place it correctly to do what is required. This automatically assumes the following:
1. The raw water quality is known. (= test it).
2. The desired specifications for the finished water quality are decided prior to designing the system. (= the shotgun approach works poorly here).
3. The operation must allow sufficient time at appropriate points in the treatment sequence for the ozone to chemically react with the targets. (=design it)
Ozone will react when injected into water and there will be a reaction of some kind with everything in that water. This means everything, not just the contaminant targeted for treatment. Basically, ozone will try to do it all, even attempting to react with the containers and piping.