Aging of manganese precipitates as a possible cause for decreasing performance of rapid sand filters for drinking water treatment

The objective of the experiment is to determine the aging of Fe and Mn precipitates forming a coating on grains in rapid sand filters. Rapid sand filtration (RSF) is a widely used technology in drinking water purification to remove NH4+ , Fe2+ and Mn2+ via oxidative processes. It has been found that the removal performance of RSFs changes over the duration of implementation, in particular for Mn. Effective oxidation of Mn2+ in RSFs requires microbial and surface catalysis. More particularly, Mn-oxides formed by Mn2+ oxidation can be effective catalysts for Mn2+ oxidation. We hypothesize that aging and alteration of Mn precipitates, forming the reactive coating around sand grains, contribute to the subsequent decrease in Mn removal efficiency. To test the hypothesis, we will combine XRF and XAS analyses of coatings obtained from RSFs of different operation lifetime.