Concentration-driven models revisited: Towards a unified framework to model settling tanks in WWTPs

This contribution introduces a new perspective on the modelling of settling behaviour aimed at providing a unified description of the processes taking place both in primary and secondary settling tanks for a more detailed operation and control in Water and Resource Recovery Facilities (WRRFs). First, experimental evidence is provided pointing out the flocculation state of sludge as an important common source of distributed behavior in different settling processes. Subsequently, a unified model framework considering several particle classes is proposed in order to describe this distributed settling behaviour as well as the effect of variations in flocculation state on the settling process. The result is a set of PDEs that are valid from dilute concentrations where they correspond to discrete settling to concentrated suspensions where they correspond to compression settling and can thus be used to model both primary and secondary settling tanks