Long-term monitoring of Mn and Fe removal in biofilters from a converted plant

Conversion from physicochemical to biological treatment in water treatment plants has received increased attention due to the potential benefits of biofiltration. However, information is limited about the operational performance of converted water treatment plants for iron (Fe) and manganese (Mn) removal over a long-term period. In this study, Fe and Mn removal from biofilters was investigated in a converted plant from November 2011 until April 2021. The plant comprises an aeration unit followed by a modified up-flow roughing filter (URF) and by two rapid sand filters (RSF) in parallel. Data analysis was based on Fe and Mn concentrations collected from 222 water analysis reports. Results showed that 98% of Fe and 95% of Mn concentrations in treated water were below the local regulatory limits of Fe , 0.2 mg/L and Mn , 0.1 mg/L. Fe was mainly removed in the URF (68%), and Mn was removed nearly equally by the URF (46%) and the RSF (47%). The combination of the URF with RSF produced total Fe and Mn removal efficiencies of 95% and 88%, respectively. No significant differences between the seasonal variation of Fe and Mn concentrations in the URG and RSF were found. The effectiveness of biofiltration technology without the use of chemical reagents or nutrient substrate additions, was demonstrated over a long-term period of monitoring.