Design and Testing of a Separation and Desalination Device for Farmland Saline–Alkaline Water in Arid Areas

To solve the problem of soil salination and to desalinate saline–alkaline water in arid areas, this study involved the design and testing of a separation and desalination device for farmland saline–alkaline water that is suitable for arid areas. The results of this study indicate that after the pretreatment of farmland saline–alkaline water, the water yielded by the pretreatment device had a mean turbidity of <1 and a mean silt density index (SDI) of <3, which met the working conditions of nanofiltration (NF) and reverse osmosis (RO) membranes. When used to filter saline–alkaline water, the composite NF–RO membrane system achieved a desalination rate of 97.06%, a total hardness removal rate of 97.83%, and a Cl(−) removal rate of 99.65%, which satisfied the standard for irrigation water quality. Some indicators of the yielded water reached the hygienic standard for drinking water, thus successfully reutilizing water resources. The circulating solar collector tube of the device was designed with a collection area of 6 m(2), which could basically satisfy the heat demand of the flash tank for distillation. The design of the flash tank and the shell-and-tube circulating condenser met the requirements for vapor condensation. The crystals in the solar salt box precipitated under solar action. X-ray diffraction was used to identify the primary compound of the crystals as NaCl, suggesting that the precipitates have potential value as industrial salts. This study offers new technical references and helpful engineering guidance for arid saline–alkaline enrichment areas facing the problem of saline farmland irrigation water.