(412b) RO-ED-UF-WAIV Hybrid for near-ZLD Brackish Water Desalination

A hybrid process has been developed which desalinates brackish water sources resulting in high recoveries (> 95%), near zero liquid discharge, and reduced energy consumption compared to conventional ZLD. The process as shown in Figure 1 involves electrodialysis to remove salt and recover water from RO concentrate. By operating the ED with extremely high concentrations in the brine stream, low electrical power is required. The scaling in the ED brine stream is prevented by a seeded crystallizer which is coupled to a submerged UF unit to effect liquid solids separation. The superconcentrate from the ED is the only waste stream and represents only 1-5% of the original feed water. This superconcentrate is evaporated to near dryness using a wind aided intensified evaporation device (WAIV) that is composed of vertical wetted surfaces of high packing density (20 ? 40 m2 wetted surface / m2 footprint) which gives 20 fold evaporation enhancements over a conventional evaporation pond and uses less than 5% of the energy required by thermal/mechanical evaporators. While individual processes have been examined in the past (e.g. RO-ED), this particular process flow scheme including membrane aided crystallizer and WAIV has never before been studied or operated. In the present talk we present accumulated data from 35 batches of pilot scale EDR operation, capable of treating 2 m3 RO concentrate/day. ED current was at 200 A/m2 for most of the batch runs and cell pair voltage drops ranged from 0.3 ? 0.9 V. RO concentrate was generated with a low pressure RO pilot unit equipped with ~30 m2 membrane area and capable of producing 18-24 m3/day of RO product from raw brackish water (3000 mg/L TDS) from the Mashabe Sadeh wellfield. Both RO and ED operated throughout with no signs of scaling and fouling. WAIV operation on ED concentrate allowed further concentration of the waste stream from 10% to 30% TDS and enhanced concentration of magnesium salts. Based on pilot data, an economic analysis was updated and showed that this process was more economical than alternative near-ZLD processes proposed in the literature. Keywords Zero Liquid Discharge (ZLD), Brackish water desalination, RO, UF, Recovery Ratio, WAIV