Scaling from dissolved and suspended solids in irrigation water reduces the efficiency of greenhouse irrigation systems. Water deposits and biofilms inside pipes reduce water flow and often clog irrigation emitters (Fig.1). These biofilms are best described as a slimy buildup of bacteria and fungi on surfaces. Biofilms are common problems on greenhouse plants, plant racks, walls, floors, and cooling pads (Fig. 2).
The clogging of emitters with scale and biofilms requires constant maintenance if not properly controlled. Reduced or occluded water flow results in dead plants. Scaling inside irrigation system pipes also has the potential to harbor plant pathogens in the biofilms, such as Pythium. Greenhouse managers often solve problems with biofilms in greenhouses using conventional fungicides and surface disinfectants, which are typical quaternary ammoniacal formulations, bleach solutions, or hydrogen dioxide. Injection into the water lines with chemical oxidants can keep pipes clean (Fig. 3). Common oxidants for injection include chlorine, either sodium or calcium hypochlorite, or ozone. Other water treatment systems include UV-C radiation or heat pasteurization.
Chlorine injection systems for greenhouses either use sodium hypochlorite injection, concentrated bleach, or calcium hypochlorite dissolved into a concentrate and injected. Both chemicals provide effective biocidal activity with some residual control of plant pathogens, but require specialized equipment for injection. Sodium hypochlorite also leaves sodium hydroxide residues, which are toxic and unsightly.
Our work at CSU has shown that some control of Pythium can be achieved with chlorine injection; however, the effective doses are greater than that required for drinking water treatment. Still, the primary purpose of chlorine injection is controlling biofilms. Where UV-C sterilization and heat pasteurization are effective, neither provide any residual disinfection downstream from the injection site for biofilm or pathogen control.
Walking greenhouse tradeshow floors, we see many new technologies becoming available for inexpensive, onsite generation of ozone. These systems are readily adaptable to most existing greenhouse irrigation systems for injection into irrigation water. These machines generate ozone gas and peroxide-free radicals from ambient air, requiring no chemical storage and just a source of electricity. With the continuous injection of ozone into the irrigation water, biofilm buildup in your water system
is reduced. These systems can include UV-C radiation chambers for additional water sanitation (Fig. 4).
Our work at CSU with ozone injection technology is demonstrating that biofilms can be easily managed (Fig. 5). We are observing considerable decreases in bacterial populations in recycled irrigation water for hydroponic production. The bacteria populations that we are monitoring are those that cause biofilm buildup in hydroponic irrigation systems. The installation of these technologies can reduce water use,
allowing waste water capture and water recycling, reduced fertilizer use, and reduced waste water leaving the greenhouse—all saving money and precious water.