Foulant identification and fouling control with iron oxide adsorption in electrodialysis for the desalination of secondary effluent

Electrodialysis (ED) is one of a number of attractive options in the desalination of secondary effluent, but membrane fouling is still an issue that needs to be resolved. This study investigated potential foulants and the fouling control of ED during desalination. Cation and anion exchange membranes were found to be fouled with different components in secondary effluent. Protein and calcium ion were the most responsible for the fouling of anion and cation exchange membranes, respectively. Pretreatment using iron oxide particles (IOPs) as an adsorbent contributed greatly to the reduction of irreversible fouling caused by organic matter present in the secondary effluent. IOP pretreatment also improved the quality of the treated water significantly.

The ED of the secondary effluent was investigated with and without pretreatment using IOPs and potential foulants. Fouling resistances were examined while analyzing the foulants that were attached to the membrane surface and the variation of electrical resistances. The proteins present in the secondary effluent fouled ion exchange membranes more than polysaccharides, while calcium was the major inorganic foulant in the ED of the secondary effluent. Metal ions (e.g., Ca2þ) caused more serious fouling on the CXM, but organics did more on the AXM. Furthermore, the AXM was fouled relatively irreversibly more than the CXM. This might be associated with the stronger deposition of organics at the AMX membrane. To mitigate membrane fouling caused by ROM, the secondary effluent was pretreated using different types of IOPs. Of the IOPs tested, magnetite which was prepared by precipitation was found to be the most effective in removing ROM from the secondary effluent. When the secondary effluent was pretreated with precipitated magnetite, a substantial reduction in reversible (48.3%) and irreversible (57.8%) electrical resistance was achieved for the anion exchange membrane. With ED alone (i.e., without pretreatment), the DOC removal efficiency was just 7.7%, while with pretreatment using magnetite, the DOC This work was supported by the UniBiz grant of the Small and Medium Business Administration. The authors extend thanks to the Educational Innovation for Resources Recycling program, the Ministry of Environment, Korea for their support.