Effects of nanofiltration on desalination of flue gas desulfurization wastewater by electrodialysis: Treatment effect, fouling property and techno-economic analysis

This study seeks to compare the treatment effect and fouling property of the nanofiltration (NF) – electrodialysis (ED) hybrid system and single ED system, and launches a techno-economic analysis for the flue gas desulfurization wastewater treatment. The optimal operation conditions of ED and NF process were determined, and the fouling properties of NF membranes and ion exchange membranes (IEMs) were explored. Morphology and chemical structure analysis concluded that NF membranes are more susceptible to fouling than IEMs, ascribing to the discrepancy of driving force and fouling mechanisms. The economic impact of membrane fouling was calculated in detail, including costs of increased membrane resistance and pressure drop of feed channel, decreased water permeability, membrane replacement and cleaning-in-place (CIP). We have found that the major factor of increased operating cost resulting from fouling comes from the membrane replacement cost (≥66%), followed by additional energy cost (≥4.1%) and with only a minor contribution from the CIP costs (≥0.8%). Overall, the total operating cost for the NF-ED system was 35.9% more expensive than the single ED system with a total cost of 2.95 ¥/m3. The results can provide a useful reference for the application of membrane technology in water and wastewater treatment.