Effects of ten years treated wastewater drip irrigation on soil microbiological properties under Mediterranean conditions

Abstract

Water shortage in most countries of the southern Mediterranean basin has led to the reuse of municipal wastewater for irrigation. Despite numerous advantages for soil fertility and crop productivity, recycling wastewater in the soil also has several ecotoxicological and sanitary problems. To evaluate the chronic soil contamination and the cumulative impact of wastewater, we compared two plots, all under orangegrove that had been drip irrigated for 10 years. The first plot was irrigated with treated wastewater; the second one was irrigated with groundwater. No negative effects of treated wastewater drip irrigation treatment were observed on the measured soil parameters (pH, organic matter and cation exchange capacity). A slight increase in the concentration of soil enteric bacteria and soil fungal densities was recorded in the wastewater plot reaching a maximum value in the first soil layer (0 to 20 cm). This result was recorded essentially around the emitters. Groundwater plots and wastewater plots exhibited similar repartitions of soils DNA quantity with depth, with the highest values in the upper layer and a progressive decrease with soil depth. For both soils, DNA quantity was positively affected by soil organic matter content. This work confirms that, under suitable conditions, treated wastewater use in irrigation can have positive effects, not only in the aspects of soil quality, but also in social terms, as it allows the maintenance of irrigated agriculture in areas where groundwater has been polluted by seawater intrusion.

Keywords: Treated wastewater, groundwater, drip irrigation, enteric bacteria, soil DNA.

African Journal of Biotechnology Vol. 12(39), pp. 5761-5770