Hydraulic conductivity of a soil irrigated with treated sewage effluent

Effluent disposal on soil solves the immediate problem of contamination caused by direct discharge into rivers; nevertheless, other problems may appear if no agricultural management is applied. Among the current concerns about effluent reuse in agriculture, the most critical one regards the charge of soil physical properties, particularly of the hydraulic conductivity. This paper aims to determine the hydraulic conductivity in an Oxisol area irrigated with treated domestic sewage effluent (Effluent treatment) and with treated groundwater (Water treatment), during 24 months, by comparing the results with those of an area under natural conditions (Control treatment). The unsaturated soil hydraulic conductivity K was measured in the experimental area using the instantaneous profile method from 12.5 to the 187.5 cm deep (every 25 cm). The determination of the saturated hydraulic conductivity K sat was carried out in laboratory using the falling head method. The results showed that the soil hydraulic conductivity changed in both areas, i.e., the Water and Effluent treatments, when compared to the Control area. Irrigation with treated water and with effluent showed similar changes in the K(θ) function, due to a high Na content in both irrigation waters. The irrigated areas had a significant decrease of K(θ) at high water contents compared to the Control treatment; a significant decrease of K sat was also observed in the irrigated areas. K(θ) increased in the irrigated soil at low water contents, suggesting soil structure and macro- and microporosity changes. Changes in the hydraulic conductivity were more pronounced in subsurface soil layers (to about the 1-m depth), which could be a consequence of the concentration of sodium in the leaching fraction and its subsequent increasingly damaging effect in the soil subsurface.