Monitoring bacterial populations in an agricultural greenhouse production system irrigated with reclaimed wastewater

While much attention has been given to evaluations of potential health risks associated with the irrigation of crops by treated urban waste water in open fields, no information is available concerning irrigation with waste water in. closed greenhouses in soilless cultivation. The fate of human pathogens originating from waste water applied in a greenhouse environment. and throughout the marketing chain, has never been assessed. The aim of this study was to examine the fate of indicators of faecal pollution in a greenhouse production system for roses irrigated with waste water under soilless cultivation. Rose plants grown in mineral (perlite) or organic (coconut fibre) soilless media were irrigated with potable or secondary (treated) urban waste water. Prior to chlorination, 2 CFU Escherichia coli ml(-1), a bacterium used as all indicator of faecal pollution, were detected in the treated effluent water source. Following routine chlorination. no E. coli were detected in the source water. fertigation solution. or soilless media. In addition, E. coli was not found on leaf surfaces. in the air inside or outside the greenhouse, or in the vase water of the cut-flowers. The 0.6 - 0.7 CFU E. coli ml(-1) identified in the drainage solution demonstrated that some viable E. coli cells survived chlorination, and accumulated to reach detectable levels in the leachates. Chlorination also suppressed the population of coliforms and total aerobic bacterial counts throughout the greenhouse water system, as well as all total fungal and yeast Counts in the source water.