Respective role of iron and manganese in direct ultrafiltration: from membrane fouling to flux improvements

Abstract

Manganese contamination in the surface water has captured ever-increasing attention in the drinking water supply, especially in the fields of membrane filtration. In the present study, an innovative gravity-driven membrane (GDM) process, combining the supplementary effects between the bio-cake layer and ultrafiltration (UF) membrane, has been constructed with expects to treat the iron-and manganese-containing surface water. The results indicated that iron and manganese were deeply eliminated by GDM process with both concentrations of less than 0.05 mg/L in the membrane permeate, and the presence of iron and manganese would also measurably contribute to the removals of organic foulants. Furthermore, little impacts of the presence of iron and manganese on the occurrence of flux stabilization were observed. During the treatments of iron- and manganese-containing surface water, the stable fluxes of GDM process were substantially attributed to the coverage and porosities of bio-cake layer on the membrane surface, regardless of the limited effects of EPS accumulation. The generated manganese oxides would improve the roughness and porosities of bio-cake layer, as well as reduce its coverage and the thickness of basal layer, facilitating flux improvements by approximately 18%. Instead, the iron involvement would engineer a thicker basal layer, increase the coverage and reduce the porosities of bio-cake layer, leading to a flux reduction (~17%). Therefore, GDM process is a cost-effective strategy for decentralized water supply, especially for the treatments of iron- and manganese-containing surface water.