Understanding ultrafiltration fouling of ceramic and polymeric membranes caused by oxidized iron and manganese in water treatment

Ultrafiltration (UF) with ceramic membrane has attracted growing attention in drinking water treatment. In this regard, a ceramic and a polymeric UF membrane process with in-line preoxidation has been applied for iron and manganese control in water. The effect of water chemistry including pH, ionic strength and hardness on the characteristics of oxidized iron and manganese aggregates, and subsequent UF fouling behavior were evaluated. The fouling of constant flux dead-end UF membranes was assessed using blocking low and resistance-in-series model analyses. Results suggest that the water chemistry has not possessed notable impact on the overall iron and manganese removal efficiencies but did contribute to the extent of fouling caused by manganese dioxide aggregates. The resistance of the cake layer and its compressibility could be explained by the manganese dioxide aggregate properties, such as size, ζ-potential and fractal dimension, which were controlled by the water chemistry. However, the cake formed by ferric hydroxide aggregates induced very low and comparable resistance to the membranes under all conditions, in line with the similar aggregate properties. The fouling behavior of ceramic membrane was generally similar to that of polymeric one, however, the reversibility of the fouling differed from one another. Overall, this work provides further insight on the fouling of ferric hydroxide and manganese dioxide in water treatment.