WaterSubject

Soil column studies were conducted with two soils to assess the effects of irrigation with wastewater on soil and groundwater quality. Upon the application of wastewater, exchange occurred between solution sodium (Na⁺) and exchangeable cations (Ca²⁺, Mg²⁺, K⁺), whereby these cations were released into solution. The average exchangeable sodium percentage (ESP) of the soils increased during leaching from 9 to 21 and 28.8 to 29.7 after applying 5.0 and 3.5 l (about 7 and 6 pore volumes) of wastewater to the soils columns, respectively. Adverse effect of high Na⁺ concentration in the wastewater on raising ESP was less pronounced in the soil having initial high ESP than in the soil with low initial ESP. Salinity of the soils was also increased with the application of wastewater and Mg²⁺ and K⁺ were leached from the soils. These losses would be more severe on soils having a low cation exchange capacity and if, uncorrected could lead eventually to their deficiencies for plant growth. When the soil columns were leached with distilled water the flow rate of one soil decreased to zero after 2.2 pore volume indicating damage to soil structure. Irrigation with wastewater, which is generally more sodic and saline than regional groundwater, increases the rate of soil sodification of shallow groundwater. A relatively simple chromatographic model was used to estimate final ESP profiles in the soils assuming the condition of local equilibrium. This approach had a limited success for one of the soil. Since the final leached concentrations are in good agreement with those of wastewater, we attribute these differences to non-uniform flow through the column. In terms of practical soil and water management, our study reveals that relatively simple means can be useful to predict the water quality in soils, their discharge to ground water, and the hazard of soil structure deterioration.In arid and semi-arid regions, water resources of good quality are becoming more and more scarce and are being allocated with priority for urban water supply. Therefore, there is an increasing necessity to irrigate with water that already contain salts, such as saline groundwater, drainage water, and treated wastewater. Salinity and sodicity are the principal water quality concerns in irrigated areas receiving such waters. Saline-sodic irrigation water, particularly in case of limited rainfall and high evaporation, may significantly increase soil sodicity. For instance, irrigation with saline-sodic water (EC = 3–8.5 dS m^?1 and SAR = 14–26 (mmol_c l^?1)^1/2) increased soil sodicity. Excessive exchangeable sodium (Na⁺), associated with pH > 8.5, caused a degradation of the physical properties of soils, and adversely affected water and air movement, soil erodibility and plant growth. The sodification of soil as a result of alkali water irrigation has been the subject of several studies, which related the changes in soil with various indices of irrigation water quality. Exchangeable sodium percentage (ESP) is generally used to judge the intensity of sodification.

Predicting the movement of solutes through the soil started from the time when use of fertilizers in agriculture began. One of the early studies dealing with the movement and interaction of two chemical species was given. They assumed that equilibrium was attained in the exchange of two ions between the solution and soil surfaces. The chromatographic processes related to adsorption/exchange reactions could be used to predict the impacts of the composition of irrigation water on both the solution and the exchange phases in soils. UNSATCHEM is a transient chemistry model which predicts the mobility and retention of solutes in soils based on the chemical composition of the air-exchange-mineral-solution phases of the soil and the amount and composition of the applied water.

In some parts of arid and semi-arid regions in Iran, such as Hamadan plains in the state of Hamadan, sugar beet and wheat crops are being irrigated with sewage effluent, drainage water, and wastewater from a power plant due to inadequate availability of fresh surface water and ground water. The wastewater from the power plant has a saline-sodic composition. Both the wastewater volumes and the areas involved in wastewater irrigation are increasing as a function of time. Continuous disposal of wastewater from thermal plant (which contains appreciable amounts of Na⁺ ions) through irrigation in closed systems poses a serious threat of soil salinisation and sodification. These problems may affect sustainability of crop production in the long run.

Hence, we performed soil column leaching experiments with wastewater to evaluate the impact of wastewater use on concentrations of different cations and anions of agricultural soils and their leaching towards ground water. We assessed the effect of wastewater use on soil sodicity and salinity to determine the ability of a relatively simple chromatographic model in predicting solution and exchange phases. Soil columns were also leached by distilled water to assess the effect of good quality water on properties of soils, after the soils were irrigated by wastewater for crop production.