High Recovery Desalting of Brackish Water by Electrodialysis: Field Tests at Yuma Desalting Test Facility and at La Verkin Springs

摘要

An ED (electrodialysis) pilot plant achieved high desalting recoveries of nearly 95 percent at the YDTF (Yuma Desalting Test Facility, Arizona) and 92 percent at LVS (La Verkin Springs, Utah) during over 4000 hours of operation. Brine TDS (total dissolved solids) concentrations of nearly 100 000 gram/cu meters were obtained at LVS, which is a greater brine concentration than is possible using RO (reverse osmosis). The LVS required ED energy (while producing a product TDS concentration of about 1000 gram/cu meters) is estimated to be about one-third the energy requirements of a commercially available distillation brine concentrator. Lowering product TDS concentration by ED requires increased equipment size and energy consumption. Special modifications of a standard ED design by its manufacturer were required for the pilot plant to achieve the high brine concentrations through a minimization of both the wastage of water and the dilution of brine that usually occurs with polarity reversal. During initial ED operation (at the YDTF) about 60 000 gram/cu meters brine TDS concentration caused the bronze brine-recirculation pump to erode and lose its required capacity and contributed to electrical shorting at the stack electrodes in nonflow areas. Subsequent replacement of the pump by one of plastic and the electrodes by ones specially encapsulated with plastic for higher electrical insulation allowed the pilot plant to operate for over 2000 hours producing high brine concentrations without additional equipment problems. The ED process has been shown to be highly feasible technically for achieving very high brine concentrations and desalting recoveries, which are particularly important to inland-desalting applications where brine-disposal volumes need to be minimized because of the high brine-disposal costs.