Irrigation of Olives with Reclaimed Wastewaters and Deficit Strategies Affect Pathogenic Bacteria Contamination of Water and Soil

This study aimed to evaluate pathogenic bacterial contamination of the water-soil-plant system in potted olive trees irrigated with reclaimed wastewater. Desalinated water (DW) obtained by treating municipal wastewater (SW) and reclaimed water (RW) obtained by mixing SW with the brine (BR) produced by DESERT technology (tertiary treatment by ultrafiltration, active carbon and reverse osmosis) were used. Two different irrigation regimes were compared: full irrigation (FI) and regulated deficit irrigation (RDI). During two irrigation seasons the concentrations of Escherichia coli, enterococci, spores of sulfite-reducing Clostridia (SRC) and Salmonella spp. were monitored in water, soil and fruit samples. Microbial concentrations in DW were always below the threshold for reuse in agriculture, while RW showed the highest level of contamination for all observed parameters. RDI management appeared to increase the soil content of SRC spores with respect to FI. Sporadically low SRC spore contamination was recorded in some fruits only in 2018, regardless of the irrigation source, probably because of accidental contamination during sampling or post-harvest handling. This study encourages the creation of a better regulatory framework reference, with specific guidelines for the use of RW as part of integrated environmental systems for the management of sustainable agriculture.