Our work investigates the settling behaviour of natural granules applied in drinking water treatment plants. We show that these natural granules have a tendency to show a considerably large deviation in terms of their settling velocity; this is contrary to what many velocity prediction models assume. In the current work, we present and discuss the factors which contribute to the observed deviation in drag and settling velocity. It connects full-scale operations and research.

The build-up and subsequent remobilization of microscopic particles can cause discoloration of drinking water during distribution. We theoretically investigated the relevant transport processes and dependencies on flow conditions and particle properties. The presented theoretical framework is intended as a starting point for a numerical tool to help water utilities determine regions of high discoloration risk and reduce these risks, e.g., by designing more efficient pipe cleaning programs.