Interaction mechanisms between fouling and chemical cleaning on the ageing behavior of ion-exchange membranes during electrodialysis treatment of flue gas desulfurization wastewater

Chemically irreversible fouling (CIF) and erosion caused by chemical cleaning would result in the changes of desalination performance and membrane properties of the ion-exchange membranes (IEMs), which were defined as membrane ageing. Roles of CIF and chemical erosion in the ageing process and the interaction mechanisms have been systematically investigated during the electrodialysis treatment of flue gas desulfurization wastewater. The main foulants contributed to CIF were anionic polyacrylamide (APAM) and CaSO4 for anion-exchange membranes (AEMs) and CaSO4 for cation-exchange membranes. The variation in the ageing behaviors has undergone three main stages. The general tendency of desalination rates was initially decreased, subsequently increased, and gradually declined at last. Membrane morphology and chemical structure of the aged IEMs transformed as a result of the CIF as well as the alternant NaOH and HCl cleaning. Chemical erosion caused the degradation of functional groups and polymer matrix, which was demonstrated by the changes in ion exchange capacity, contact angle, thermal stability and mechanical strength. Cleaning efficiency was limited by CIF, while chemical erosion would in turn affect membrane fouling behaviors. The extended Derjaguin-Landau-VerweyOverbeek analysis verified that the antifouling ability of aged AEMs enhanced with a decrease of the total interaction energy of APAM-AEM.