Disinfection of drain water in greenhouses using a wet condensation heater

Abstract

A wet condensation heater has been modified to disinfect drain water in greenhouses in addition to providing heating and CO2. Various kinds of microorganisms (bacteria and fungi) and one virus (tobacco mosaic virus [TMV]) originating from either pure cultures or substrate extracts were introduced into the disinfection circuit above the heater. Water was checked downstream for the number of microorganisms surviving the heat treatment. Fungi were destroyed after 30 s at 58.9 °C, and most of the bacteria except some spore-forming bacteria such as Bacillus polymyxa were destroyed after 45 s at 65.2 °C. Complete elimination of TMV particles was more difficult to achieve but their number was greatly reduced, limiting the probability of plant infection. The microbial density was significantly decreased at relatively low temperatures (less than 75 °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 microorganism to the substratum is proposed to compensate for the lack of complete efficiency observed with high flow rates of drain water. This introduced microorganism could occupy the free space and limit an invasion by a pathogen surviving the treatment. © 1994.