Parametric tests of an electrodialysis reversal. (EDR) system with aliphatic anion membranes

Abstract

During 1980, parametric studies were performed at the U.S. Department of the Interior, Roswell Test Facility, for the purpose of comparing the performance of aliphatic anion membranes to standard anion membranes in an electrodialysis reversal (EDR) system. An Ionics AQUAMITE × EDR unit was used to desalt a high sodium chloride, 4100 mg/S, TDS feed water. During these tests, the product salinity averaged 388 mg/l at an average production rate of 25,800 USGPD. The use of aliphatic membranes reduced the desalting energy consumption from 8.1 kwh/KGal with standard membranes to 6.8 kwh/kGal with aliphatic membranes at 73% recovery and, at 92% recovery, from 14.6 kwh/kGal for standard membranes to 11.0 kwh/kGal for the aliphatics. Slightly higher water recoveries were also possible with the aliphatic membranes as they exhibited less water transfer. A maximum recovery of 94% was obtained without operational problems despite calcium sulfate (gypsum) supersaturation levels of up to 165% in the waste Stream. Additional tests were conducted to evaluate the performance using a separate brine reed of inferior quality water (14,000 mg/l TDS) in order to obtain nearly complete recovery of the better quality brackish feed water. The separate brine feed allowed very high recoveries of the simulated Virginia Beach feed water while maintaining moderate brine stream concentrations. As a result, energy consumption was reduced from 11.9 kwh/kGal, for the maximum recovery case without separate brine feed, to 7.5-8.1 kwh/kGal using the separate brine feed approach. During these tests, extension of the time period between polarity reversal from 20 to 30 minutes was also investigated. This was found to improve power consumption slightly and increased the production by as much as 7.6% at very high water recoveries. It was concluded, as a result of these tests, that the following characteristics would be desirable for an EDR plant to treat a high sodium chloride 4100 ppm water: 1. Aliphatic anion membranes for reduced' energy consumption 2. Separate feed for brine and electrode flows for nearly complete recovery of a limited higher quality brackish water resources 3. 30-minute reversal cycle to improve production and increase recovery.