Utilization of reclaimed wastewater for irrigation of field-grown melons by surface and subsurface drip irrigation

Shortage of water in arid and semiarid areas throughout the world makes utilization of marginal water for agricultural irrigation a necessity. The marginal water most used for irrigation in Israel is secondary-treated urban effluents. In spite of the water treatment process, these waters often contain higher levels of bacterial human pathogens than the potable water from which they were derived. Utilization of the treated effluents for irrigation in Israel is strictly regulated according to the water quality and the irrigated crop. Due to health concerns, and a lack of experimental data, the treated effluents are not yet used for irrigation of vegetables. In the present study we have evaluated safety and agronomic issues involved in irrigation of summer melon with secondary-treated urban effluents, administered to the production field by surface and sub-surface drip irrigation according to the national regulations. Two water qualities were compared, secondary-treated wastewater and potable water. The effluents contained higher levels of EC, pH, Na and Cl, N, P, K, microelements, and heavy metals than the potable water. Potable water was applied by surface drip irrigation, and three irrigation regimes were compared for the treated effluents. These included surface irrigation, and subsurface irrigation at 20 or 40 cm below the soil surface. No differences in yield quantity and quality were found between treatments. Na concentrations and SAR levels of the soil were higher under irrigation with the effluent. Contamination by E. coli, fecal coliforms, and total coliform bacteria were found on the melon peel of all treatments, and the quantity and quality of the contamination did not vary significantly between treatments. E. coli and fecal coliforms were found in the surface 0-2 cm soil samples of treatments irrigated with both water qualities by surface drippers, but no contamination was found in the treatments irrigated by subsurface irrigation. The fact that the microbial contamination of the fruit was not prevented by subsurface drip irrigation or by irrigation with fresh water suggests that environmental factors, rather than an irrigation treatment affect, were the cause for the microbial spread. Further analysis is required concerning effects of environmental factors, such as the interaction between weather conditions and distance from the effluent oxidation ponds on temporal geospatial distribution of the bacterial human pathogens and the potential for subsequent contamination of fresh produce in the field.