Evaluation of Agriculture Soil Quality by Treated Wastewater Reuse in Arid Regions: Case Study in Sistan and Baluchestan Province, Iran

In this paper, the reuse of reclaimed wastewater for irrigation of agricultural land and its effect on soil quality has been investigated in an arid region of Iran. For this purpose, two pilots of 2,000 m2 area with a variety of plants were selected near the effluent discharge of a wastewater treatment plant (WWTP) in Zahedan and Zabol cities in Sistan and Baluchestan Province. The wastewater treatment systems at Zahedan and Zabol were activated sludge (extended aeration) and aerated lagoons, respectively. In this study, 14 types of native plants were selected and seeded in 18 rows and treated wastewater was reused for irrigation of the pilots. The samples were taken from the effluent of the WWTP and analyzed from the viewpoint of quality. Results showed that indicators of sodium adsorption ratio (SAR), sodium percentage (Na%) and electrical conductivity (EC) were higher than standard levels set by the Food and Agricultural Organization (FAO). Other parameters such as total dissolved solids, pH, biochemical oxygen demand, chemical oxygen demand and turbidity were in the standard range. To assess soil quality, sampling was conducted in two stages that included irrigation with fresh water and irrigation with treated wastewater. Soil analysis showed that soil structure is loamy with high salinity and alkalinity. Soil quality in the 12 month period after irrigation was studied and investigated; although the treated wastewater quality in some cases was beyond the FAO irrigation standard range, there was no adverse effect on the soil quality, e.g. EC, SAR and exchangeable sodium percentage (ESP). In the Zahedan pilot, the values of soil EC, SAR and ESP decreased to 82%, 75% and 66% after irrigation with treated wastewater. The soil quality of the Zabol pilot decreased after 6 months, but on continuation of the irrigation for 12 months, the values for EC, SAR and ESP decreased to 49%, 25% and 24%, respectively. The results show that the reuse of reclaimed wastewater is an economical and beneficial method for irrigation of agriculture land in the arid regions of Iran. Finally, an artificial neural network model, which adopts a back propagation algorithm with momentum and adaptive learning rate, was applied. The effect of each parameter on the performance of the Zahedan pilot was compared, using the partitioning connection weights method. The result is ECeffluent > ECsoil > SARsoil > BOD5 > ESPsoil > SAReffluent. In addition, many strategies were proposed to optimize the working conditions of the system.