Ozone is a naturally occurring gas. It reacts rapidly with organic materials (about 3,000 times faster than chlorine) and, unlike with
chlorine, there are no toxic residues. The reaction by-product of ozone is oxygen, which is usually welcomed in aquaculture systems. Ozone is commonly used in effluent water treatment as well as in recirculation systems for two main reasons: disinfection by the killing of harmful pathogens, and improved water quality through enhanced microflocculation. Ozonation is commonly installed immediately prior to protein skimmers, since their efficiency is markedly improved thereby.
Because ozone is such a powerful oxidant, it is important to know what is contained in the water to be ozonated. This is particularly important when sizing ozone generators. Ozone is not selective; it will react with almost anything it contacts including tan- nins, acids, metals, etc. There are some organic compounds that do not react with ozone and if the reactions are slow, ozone may not be effective. A detailed water analysis should be available to the
supplier of the ozone generator, as well as a list of target pathogens. Ozone's can oxidize iron, manganese, sulfides and arsenic, which are commonly found in ground water. These precipitate and can be removed through micro-filtration.
The key benefit of ozone in water treatment is disin- fection by removing pathogens. Effectiveness depends on the ozone concentration and the time the ozone is retained in the water i.e. the contact time. There is a wide range of concentration requirements for pathogens found in aquaculture systems. For bacteria and viruses, effective concentrations range from 0.03 to 1 ppm, with retention times from 1 to 10 minutes. Fungi generally require much greater concentrations and contact times for 99% kill rates. Keep in mind, the concentrations and retention times listed for pathogens are for target- ing a specified organism; there will be other organ- ics in the water which will also be consuming ozone, so actual concentrations may need to be higher, or contact times longer to ensure efficiency.