Membrane Fouling Characteristics of Pre-oxidation/Ultrafiltration Combined Process for Manganese Removal

In order to remove manganese from drinking water, the effect of ultrafiltration after pretreatment with three oxidants (NaClO, ClO₂ and KMnO₄) on removing manganese and characteristics of membrane fouling were studied. Mn²⁺ could be effectively removed by the three combined processes, and the concentration of Mn²⁺ after ultrafiltration was less than 5 μg/L with the removal efficiency of more than 99%. The filter cake layer on the ultrafiltration membrane surface was one of the important reasons for the membrane fouling and the rapid decrease of membrane flux. It was found by SEM that the morphology of the filter cake layer on the membrane surface was significantly different after pretreatment with different oxidants. The particle size of the filter cake layer after pretreatment of KMnO₄ oxidation was larger, and there was obvious space between the particles. However, size and content of the particles in the filter cake layer after pretreatment with ClO₂ and NaClO were small and low, and the space between the particles was not obvious, thus forming a relatively dense filter cake layer. According to the analysis of XPS and FT-IR，the main components of the filter cake layer were mixture of Mn3⁺ and Mn⁴⁺. The surface of the filter cake layer was rich in hydroxyl groups, which had a strong coordination adsorption effect on the free Mn²⁺ in water.