Effects of irrigation with different effluents on saturated hydraulic conductivity of arid and semiarid soils

The use of recycled wastewater that has undergone various treatments (effluent) for irrigation is becoming one of the main means by which to mitigate the pressure on freshwater resources. The main objective of this study was to improve the basic understanding of the effects of irrigation with various effluents on the saturated hydraulic conductivity (K_s.) of arid and semiarid soils. Clay, loamy, and sandy soils were sampled from experimental plots irrigated with freshwater or secondary effluent for >3 yr, and were used in column experiments. Leaching the loamy and clay soils with reverse osmosis (RO) effluent, which contained low electtolyte concentrations, led to clay swelling and dispersion and thereby decreased the soil K_s, In these soils, the high concentration of suspended solid particles and dissolved organic matter (DOM) in oxidation pond (OP) effluent caused significant pore clogging, which reduced the K_s. Leaching the soils with ultrafiltered effluent maintained high K_s values due to the low concentration of suspended solid particles and DOM, their small sizes, and the relatively high electrical conductivity of this effluent. The relatively large average pore size in the sandy soil prevented pore clogging and K_s reduction when leached with RO and OP effluent. Secondary effluent irrigation increased the soil exchangeable Na percentage (ESP) compared with freshwater irrigation but did not change the organic matter con tent in the soil. In the loamy and clay soils, this higher ESP of the effluent-irrigated soils resulted in greater reductions in K_s when leached with deionized water than occurred in freshwater-itrigated soils.