Aquatic humic substances, iron, and manganese removal by ultrafiltration and nanofiltration membranes combined with coagulation–flocculation–sedimentation

Abstract

Iron and manganese removal is made conventionally by oxidation methods; however, when aquatic humic substances (HS) are present, they can affect the removal, with another treatment process being necessary. This study focused on performance of ultrafiltration (UF) and nanofiltration (NF), preceded by coagulation, flocculation, and sedimentation stages for iron, manganese, and HS removal, with two water sources that present superior levels of humic compounds, and measured by dissolved organic carbon (DOC) and UV absorbance at 254 nm. Coagulation, flocculation, and sedimentation combined with UF/NF efficiently removed dissolved iron, HS, apparent color, and turbidity. Almost total iron removal was already attained in the prior steps of coagulation, flocculation, and sedimentation, obtaining final values of dissolved iron of less than 0.001 mg L−1 for the two types of water studied. However, the complete system did not appear effective (less than 50% efficiency) in dissolved manganese removal, although a significant reduction in the HS was achieved (approximately 80% after UF and 90% after NF measured as DOC, for two types of water). Pretreatment was shown to be effective in reducing the loss of filtration flow because of the removal of high-molecular-weight HS, thus minimizing the formation of fouling on the membrane.