Simulation of agricultural drainage water concentration for the recovery of salts

Salt removal from drainage waters is becoming increasingly important for sustained irrigated arid land agriculture where inadequate drainage infrastructure exists. Solar evaporation and concentration systems are currently in development in California for this purpose. Integrated on-farm drainage management (IFDM) systems seek to reduce salinity impacts in arid land agriculture through sequential reuse of water on increasingly salt tolerant crops. The final stage in the system calls for recovery of salt, possibly in purified form, for removal from the system. A critical element in this last stage is final concentration of the drainage brine from the halophyte component of the IFDM system. This study investigates solar brine concentration using a horizontal shallow basin solar concentrator and a liquid film solar-assisted concentrator, explores the concept of enhancing the solar gain, mass transfer, and evaporation rate through more novel approaches, analyzes the chemical compounds in the salt obtained by selective crystallization and precipitation, and examines preliminary methods to increase purity of crystallized salt for industrial uses and other markets.; A mathematical model was developed to simulate evaporation of water and salt concentration in a shallow solar concentrator and an inclined open-film or tilted concentrator. The model predicts brine and collector surface temperature, water evaporation rate, and salinity of the concentrated solution. Three different evaporation rate models were evaluated and compared. Experimental results obtained from the concentrators were compared with model results relating evaporation rate to geometry and climatic conditions. The tilted concentrator yields productivity and efficiency that are 20% higher than the horizontal concentrator.; Crystallized salt with initial concentration of 94.7% sodium sulfate from the 33% concentrated brine obtained by precipitation was purified up to 99% after rinsing with a saturated sodium sulfate solution to remove surface contamination (e.g. magnesium sulfate). Further investigation will be needed to obtain higher purity. Higher recovery of sulfate and means to recover other products and dispose of residual salts still need further development.