25~(th) Annual WateReuse Symposium Comparison of Two RO Concentrate Reduction Technologies on Chemical Usage, Energy Consumption, and Life Cycle Environmental Impacts

摘要

Nearly all available water resources with good quality are fully utilized in the southwest region. Advanced treatment processes,such as reverse osmosis (RO), are currently being used to desalt the brackish groundwater, surface water, and reclaimed water sources. Most two-stage or three-stage brackish water RO systems operate at approximately 85 percent recovery or less, losing 15 percent or more water as a high salinity concentrate stream. Technologies that can recover more from the precious resources and reduce the volume of the concentrate are key interests. Recent completed and ongoing studies suggested that the intermediate concentrate chemical precipitation (ICCS) process provides one of the most cost-effective and energy efficient steps approaching zero liquid discharge (ZLD) concentrate management. As illustrated in Figure 1,the ICCS process utilizes lime softening (conventional type using solids contact clarifier or pelletized type using fluidized bed reactor) to precipitate calcium carbonate and magnesium hydroxide at high pH, co-precipitating the sparingly soluble ions that can cause membrane scaling and limit membrane recovery (such as silica, barium, strontium). Through addressing the factors limiting RO recovery, it stabilizes concentrate to allow higher recovery (60 to 70 percent recovery) in subsequent secondary RO system, enhancing the overall recovery from 85 percent to 94 to 95 percent. Even though it is not a ZLD technology, it helps to reduce the size and costs of the downstream concentrate management processes.