Integrating activated carbon into conventional sand filtration boosts biological Mn(ii) removal efficiency†

Abstract

Efficient manganese removal at water treatment plants is becoming increasingly significant due to growing health and aesthetic concerns associated with Mn in drinking water. Recently, biological granular activated carbon (GAC) filtration has demonstrated effectiveness in removing dissolved Mn(II) biologically. However, most water treatment plants continue to rely on conventional sand filtration. To enhance biological Mn(II) removal on the basis of sand filtration remains a challenge. This study aimed to explore whether partially integrating GAC into sand filters could significantly enhance Mn(II) removal. Results showed that even a 25% replacement of sand with GAC enabled rapid filter maturation and Mn(II) removal efficiency that was statistically comparable to the 100% GAC filter (p > 0.05), with marked improvement over the 100% sand filter. Solid analysis revealed that GAC media facilitated biomass accumulation that was 25 times greater than that observed with sand, and biogenic MnO_x also adhered more strongly to GAC surfaces. This caused the GAC portion of the GAC–sand filter to play a dominant role in Mn(II) removal. Additionally, the GAC media fostered both biomass growth and MnO_x accumulation in the underlying sand layer, enabling the sand portion to remove more Mn(II). This proof-of-concept study highlighted a promising strategy for addressing Mn issues by integrating GAC into sand filtration systems without requiring substantial infrastructure modifications.