Manganese removal by hydrogen peroxide and biofiltration

Biofiltration has gained more attention as an alternative filtration for the removal of manganese (Mn) in both groundwater and surface water. This study investigated the potential of biofiltration as pretreatment at the Bennery Lake Water Treatment Plant located in Halifax, Nova Scotia, for the removal of manganese and dissolved organic carbon (DOC) from pH 6 natural lake water. A bench-scale study identified the effect of oxidant enhancement with hydrogen peroxide (H₂O₂), nutrient enhancement with phosphorus (P) and medium type (granular activated carbon (GAC) and anthracite) on a biofiltration system. Addition of both the nutrient, phosphorus (300–500 µg/l), and the oxidant, hydrogen peroxide (0·5 mg/l) enhanced the biofiltration performance, achieving 98% manganese removal and 27% (1·3 mg/l) DOC removal. Overall, the medium was not a significant factor for manganese removal, while GAC removed significantly more DOC than anthracite, although further treatment would be required for either medium to achieve lower DOC concentrations. These results show direct biofiltration of surface water at pH 6 can remove manganese below the 50 µg/l aesthetic guideline from a manganese loading of over 1 mg/l. This work highlights a potential mechanism and implication of biological roughing filtration technique for the removal of manganese and DOC from natural surface water.