Scale inhibitor and recovery optimization for a brackish water supply: pilot test results and full-scale experiences

Pilot testing was conducted at a brackish water reverse osmosis water treatment plant to identify operational constraints associated with effective scaling control. The test program involved testing select inhibitors/dispersants, feed water pH, and operating recovery as part of a full-scale retrofit from a hollow fiber to spiral-wound reverse osmosis membrane facility. The test results indicated the facility could be operated at elevated recovery, but was sensitive to conditioning with sulfuric acid. Use of sulfuric acid addition to control calcium carbonate scaling was determined to increase calcium sulfate scaling. Membrane autopsy data confirmed calcium sulfate scaling onto the membrane surface with minimal biological and organic content. It was determined that recovery could be increased from 65 to 75 percent by discontinuing sulfuric acid addition and feeding only scale inhibitor. Scale inhibitors with dispersant properties were recommended for full-scale implementation.