DISINFECTION OF DRAIN WATER IN GREENHOUSES USING A WET CONDENSATION HEATER

A wet condensation heater has been modified to disinfect drain water i n greenhouses in addition to providing heating and CO2. Various kinds of microorganisms (bacteria and fungi) and one virus (tobacco mosaic v irus [TMV]) originating from either pure cultures or substrate extract s were introduced into the disinfection circuit above the heater. Wate r was checked downstream for the number of microorganisms surviving th e heat treatment. Fungi were destroyed after 30 s at 58.9 degrees C, a nd most of the bacteria except some spore-forming bacteria such as Bac illus polymyxa were destroyed after 45 s at 65.2 degrees C. Complete e limination of TMV particles was more difficult to achieve but their nu mber was greatly reduced, limiting the probability of plant infection. The microbial density was significantly decreased at relatively low t emperatures (less than 75 degrees C for 2 min) and so the efficacy of the heater was attributed to a combined effect of both temperature and UV irradiation from the flame. Addition of a nonpathogenic microorgan ism to the substratum is proposed to compensate for the lack of comple te efficiency observed with high flow rates of drain water. This intro duced microorganism could occupy the free space and limit an invasion by a pathogen surviving the treatment.