The use of peroxides for water disinfection in horticulture

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Peroxides are used to prevent rock wool or flow mats from becoming green, clogging pipes and drippers because of a biofilm or lime scale and work curatively against algae, duckweed, root exudates and bacteria in the water. Hydrous peroxides break down into environmentally friendly components (H2O and O2) but are not yet allowed for spraying on plants. Frequent irrigation with peroxides can cause phytotoxicity but weekly doses of 200 ppm are well tolerated by a large range of tested hydroponic plants and Ficus benjamina. Be careful when using at an early and vulnerable plant stage. Dosage is product dependent and the level of peroxide drops quickly in a circuit that contains plants. However, peroxides that are stabilized with performic acid, peracetic acid and silver (2.2-7.5 € kg-1) are effective for a few weeks. Companies that use drip irrigation might invest in a pumping system (€ 1 800-2 400 depending on tube diameter) that continuously doses peroxides into the water. In this case, a peroxide stabilized with an acid is necessary to avoid clogging with salt or calcium deposits. For contamination of small basins, ebb/flow floors and cultivation tables, a single manual application in the storage tank with more stable peroxides is sufficient (monthly or two-monthly). This is more effective than frequently adding a low dose. Peroxides can also be used to clear turbid drain water before disinfection by low pressure UV. To follow up the concentration of peroxide in the water, measurement strips can be used. All product applications were considered safe enough for crops until a concentration of 500 ppm. H2O2 has the added value that it degrades some crop protection products.

Ilse Delcour

Proefcentrum Voor Sierteelt (PCS), Belgium
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