Features Structures & Equipment Water and irrigation
Ozone Water Sterilization

November 2015 — How effective is it? Many major municipalities throughout the world are using ozone water sterilization in their water treatment plants because ozone is a powerful disinfectant and leaves no chemical residue in the water.

The air we breathe is 21 per cent oxygen, 78 per cent hydrogen, with the remainder composed of carbon dioxide, argon and other gases.

We can produce 92 per cent grade oxygen by using swing adsorption technology in oxygen generators.

This process strips out the oxygen from the air from all the other gases and produces pure oxygen. This is then fed into a plasma ozone reactor that changes the oxygen to produce ozone gas.

EFFECTIVE PROCESS
Ozone is an oxidant that kills bacteria, pathogens, algae and mould or any living cell in the air or water.

For example, after one minute of contact time at 1 mg/litre of ozone, some 99.999 per cent of all bacteria are killed.

The ozone gas, when applied to disinfect water, turns back into oxygen within a very short period of time. This is a plus since oxygen is very beneficial within the rootzone.

Ozone is a colourless gas that is said to have an odour similar to the smell of the air after a major thunderstorm has occurred.

Ozone has far greater disinfection effectiveness against bacteria and viruses when compared to chlorination. Its oxidizing properties can reduce the concentration of manganese, iron and sulphur, and they eliminate odour problems. Organic particles can be removed post-filtration with special media filters.

As mentioned earlier, ozone turns back into oxygen over a short period of time, ranging from a few minutes to 30 minutes. The rate of ozone degradation will vary according to the chemistry of the water, water temperature and the pH levels.

With the ozone process, irrigation water is pumped through a venturi injector that creates a vacuum pulling the ozone gas into the water stream while oxidizing the water being treated. As the fine bubbles of ozone gas are mixed in the water, the oxidant nature of ozone kills bacteria on contact.

Coupling this with post filtration systems results in pure clean water.

ADVANTAGES OF OZONE
Ozone is effective over a wide pH range and rapidly destroys bacteria, viruses and pathogens.

It has stronger germicidal properties than chlorination, and is a strong oxidant with a short reaction time.

The treatment process has no chemical residue in the water.

Ozone eliminates a wide variety of inorganic, organic, microbiological and odour problems.

DISADVANTAGES OF OZONE
There are higher initial equipment costs as compared to chemical treatment.

Ozonation provides no germicidal or disinfection residual to inhibit or prevent re-growth. However, this can be overcome by periodically repeating the ozonation process.

The system may require pre-treatment for hardness reduction or pre-filtration if the water has high organic content.

Ozone is less soluble in water as compared to chlorine or other chemicals, and therefore requires special mixing techniques.

It may be more difficult to find professionals proficient in ozone
water treatment, especially for greenhouse crops.

CONCLUSION
Ozone is a very effective way for sterilizing recycled irrigation water for greenhouse crops. There are associated costs in setting up the initial wastewater reclaim and sterilization process, but the benefits outweigh the initial outlay since growers can save from 35 per cent to 40 per cent in water and fertilizer costs. These savings will easily cover the costs for setting up an ozone water sterilization system as the payback is typically two to three years or shorter.

Eric Labbate is the CEO of Climate Control Systems Inc., which has been manufacturing greenhouse automation systems for climate management, fertigation management, and ozone water treatment systems since 1985.