WATER SANITIZING AGENTS SUCH AS CHLORINE AND CHLORINE DIOXIDE INTERACT WITH PEAT SUBSTRATE AND SUSPENDED SOLIDS

Recirculation of irrigation solutions to conserve water and reduce runoff increases the risk of plant pathogens, algae, and clogging of irrigation equipment with biofilm. A range of sanitizing water treatment technologies are therefore used in greenhouses, such as chlorine, chlorine dioxide, copper, and activated peroxygens. When these technologies are applied to a recirculating irrigation solution, suspended solids from peat, plant parts, and sediment create a demand on the sanitizing agent active ingredient, thereby reducing efficacy for control of target microorganisms. Total suspended solids (TSS) were as high as 105.6 mg L^-1 in recirculated irrigation water based on a survey of 13 greenhouse locations, with organic matter representing an average 62% of the TSS. Rapid reduction of the oxidants chlorine (sodium hypochlorite) and chlorine dioxide occurred in the presence of 50 mg L^-1 of fine screened peat in solution, with less effect of the peat solution on active ingredient levels of copper ionization, copper salt, or activated peroxygens. This research emphasizes the need for adequate filtration to remove suspended solids when sanitizing irrigation water.