Impact of the use of treated wastewater for irrigation on the physico-chemical quality of soils: A case study from Ain Defla, Algeria

The use of treated wastewater is considered a good alternative for the different agricultural irrigation practices and the sustainable management program for the conservation of water and soil in semi-arid areas. The main objective of this research work is to determine the impacts of the reuse of treated wastewater (TWW) on some soil properties with the collection and analysis of 68 samples from the Ain Defla wastewater treatment plant (WWTP) over a three-year period, under a turf cultivation system. Soil samples were taken at depths ranging from 0 to 20 and 20 to 40 cm and then analyzed for pH, electrical conductivity (EC) and overall mineralization. The results showed large changes, over time, in the chemical properties of the soil due to irrigation with treated wastewater compared to the control, with median pH values varying from 8.12 in 2015 to 8.15 in 2016 and 8.91 in 2017. The pH increased significantly from 8.12 in non-irrigated soil to 8.22 in soil irrigated with treated wastewater. There was a significant difference between the two horizons (8.15 at the surface and 8.24 at depth). The electrical conductivity went from 0.25 μS/cm in 2015 to 0.37 μS/cm in 2016 to drop to 0.15 μS/cm and 2017. The electrical conductivity has doubled between the non-irrigated soil (0.14 μS/cm) and the irrigated one (0.28 μS/cm) while it has not changed between the two horizons (0.27 μS/cm on the surface and 0.24 μS/cm in depth). The results obtained during these three years show that treated wastewater is a main source of increase in mineral salts in the soil which could lead to the degradation of the environment in general and that of the physico-chemical quality of soil in a particular. Also, it was found that treated wastewater can be a potential source of essential nutrients for plants by accumulation in soils.