Ozone has been used for the purification of water for more than 100 years throughout the world. The main applications are drinking water, swimming pools and industry. 95% of all water bottles that you buy have been disinfected with ozone.
Within Dutch horticulture relatively little is known about the effects of ozone and too often wrong conclusions have been drawn from past experiences. In Canada, where emission standards for the environment have been an issue for a while, suppliers have noted the introduction of ozone by 1 in 10 farmers in recent years.
However, Ozone is no stranger to horticulture, it was used in the past as a water disinfectant. "This description as a water disinfectant is wrong terminology for this technique. Water disinfectant only suggests killing fungi, bacteria and viruses, like a UV system or heater does. Ozone does so much more than just disinfect," says Cees de Haan of AgroZone.
"With disinfection through UV or heating, microbiology is killed while the dead matter remains in the water. There’s also a large buildup of plant derived substances, such as phenols and root exudates in the water. The substrate and drain water gradually becomes polluted and cloudy."
The T10-value decreases. UV systems therefore have a low return and the water has to be discharged unnecessarily. Accumulation of organic pollution inhibits the crop growth and feeds the biofilm in the pipes. This biofilm is a breeding ground for bacteria and viruses.
Ozone is a powerfully oxidizing, natural gas. Oxidizing means burning. Ozone oxidizes dissolved organic substances and dead matter from the water. The water becomes crystal-clear again, so the T10 value goes up and the buildup of biofilm is avoided.Oxygen level
Due to the low oxygen level of 4-5mg/l in drain water, crops become more sensitive to Pythium, for example, and fertilizers will not be optimally absorbed. By heating the water, the oxygen level drops even further, to almost zero. The latest ozone techniques are able to increase the oxygen level in the water to 20-30mg/l. These are values far above the natural limits that have a positive contribution to the root system, resistance and enhanced fertilizer uptake. Biofilm consists of anaerobic bacteria that are repelled by the high levels of oxygen released after the ozone application.
Plant protection products
Examination by WUR Bleiswijk has shown that the most recent ozone techniques are able to remove 98% of plant protection products from the water, without additional carbon filters.
This meets the purification requirement for discharge water per January 1, 2018 and you may continue to discharge if cultivation makes it desirable or necessary.
Ozone is produced on location from oxygen extracted from compressed air and dissolved in water. When ozone has performed its oxidizing and disinfecting function it becomes oxygen again. The dissolved oxygen level in the water is thus increased to some 300%.
The great strength of ozone therefore is that ozone not only disinfects the water, but really cleans it. This is done entirely without chemicals or residues, and is therefore very environmentally friendly. In addition, inhibitory substances are removed and the oxygen level is increased considerably. No other technique offers these advantages.
Depending on how ozone is used, one can opt for a complete disinfection of the water or for a regulatory effect. In this case, ozone is not used for a complete disinfection, but more for its regulating function in order to remove organic substances and inhibitors.
There are two ways to apply ozone
Partial stream treatment, where the ozone system circulates only in the refuse drain silos, removes dissolved organic substances, inhibitors and PPP and increases the T10 value and the oxygen level.
This system is used in combination with an existing UV disinfectant. The result is crystal-clear water, a higher capacity of the UV disinfectant and more oxygen for your plants.
Mainstream treatment; here the system works - as the sector is accustomed to - as a kind of disinfectant. Ozone disinfects the drain water and then the system circulates in the refuse drain, clean drain and rainwater silos. The central ozone system can treat every silo in the company. Here too dissolved organic substances, inhibitors and PPP are removed and the oxygen level is increased.
Ozone as water disinfectant is more than the killing of organisms, ozone is:
• Disinfection of water
• Removal of growth inhibitors
• Oxygen boost
• T10 value increase
• Removal PPP
All ozone systems are subject to the VAMIL and MIA tax arrangements. Provincial laws also frequently apply. Treated and untreated drain water
A main stream system
This article was written by Cees de Haan. He has 20 years experience with ozone and specializes in chemical-free water treatment for cooling towers and industrial water treatment. Owner of AgroZone, which focuses on ozone applications in horticulture, since 2008.