Energy Consumption and Gypsum Scaling Assessment in a Hybrid Nanofiltration-Reverse Osmosis-Electrodialysis system

Hybrid and integrated membrane systems are often proposed as a way to increase the water recovery in desalination plants. Four different configurations of seawater desalination plants were compared: a standard single-stage seawater reverse osmosis (SWRO), a hybrid SWRO-electrodialysis (ED) system, a nanofiltration (NF)-SWRO system, and an NF-SWRO-ED. Based on the laboratory results, the overall water recovery, energy consumption, scaling risk, and the composition of the generated waste brine were projected. An NF-SWRO-ED system was found as the best choice. The proposed system is able to produce highly concentrated brine, close to saturation with respect to sodium chloride. The brine can be further used in evaporated salt production or in the chlor-alkali industry.