Primary sedimentation modelling with characterized setting velocity groups.

Within a plantwide water and resource recovery facility context, an important requirement for a primary sedimentation unit model is the correct fractionation of the settleable portion (primary sludge - PS) of the raw wastewater total suspended solids (TSS) according to the (i) unbiodegradable particulate organic (UPO), (ii) biodegradable particulate organic (BPO), and (iii) inorganic settleable solid (ISS) components. This paper focuses on improving a current TSS- based primary settling tank (PST) model to account for correct proportions of these three components, with characterized settling velocity groups. The steps taken towards development of the primary sedimentation unit model involved the development of a discrete particle settling model in Microsoft Excel and the utilisation of well characterised municipal wastewater data from previous studies in the discrete particle settling model, to reproduce PS and settled wastewater outputs in settling fractions of UPO, BPO and ISS, via steady state and dynamic calculations and under strict material mass balances.