Ozonisation is based on the conversion of stable oxygen (O2) from air to unstable ozone gas (O3). The ozone gas is produced by an ozone generator in the greenhouse. Ozone is injected directly in the drain water and induces oxidation of microorganisms (fungi, microorganisms, and viruses) and organic matter leading to their destruction. The oxidative action of ozone is twofold: a direct oxidation of organic compounds by the ozone and an indirect oxidation due to the production of free radicals (O-H) coming from the decomposition of the ozone in the water. Ozone is lethal for humans at a concentration of 4ppm. Therefore the necessary precautions must be taken. Above, the use of ozone is restricted at the European level. Ozone is registered as a biocide (Biocidal Products Regulations (EU) 528/2012 framework). Above, this gas is very corrosive what can lead to damage to the irrigation installation when incorrect materials are used. The efficacy of the disinfection is dependent on various factors: the concentration of organic matter in the drain water, the flow, the contact time, and the concentration of ozone in the solution. Recommendations for a complete disinfection are 8 – 10 g of O3/m3 of treated water, for a contact time of 1 to 2 seconds. When coupled with peroxide the ideal ratio is 0.15g/g of H2O2/O3. These parameters allow 2 to 6 m3/h of the solution to be treated. Investment costs vary from 30 000 to 100 000€ depending on the capacity of the installation. Energy consumption varies from 1.5 kWh to 6.2 kWh.

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Benjamin Gard

Association Provençale de Recherche et Expérimentation Légumière (APREL), France
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