Developing and Validating a Model to Assess Sewer Sediment Issues from Changing Wastewater Inflows and Concentration

Abstract

Sewers are critical for the maintenance of both public and environmental health in urban areas through their transport of wastewater for treatment. Despite significant costs associated with excess sewer solids deposition causing blockages and reduced hydraulic capacity, there are still gaps in our knowledge of sewer solids processes. This is particularly a concern with the implementation of Decentralised Water Recycling (DWR) and further reductions in per capita water consumption. This will reduce wastewater inflow to and increase the concentration of solids in sewers, leading to increased blockages and reduced hydraulic capacities in sewers. Sewer solids can be divided into two main groups based on their size: gross solids and sewer sediments. This paper details the development, initial calibration, and validation of a comprehensive sewer sediment transport model to assist in quantifying the impacts of changing wastewater inflows and concentration. This model aims to facilitate the transition to more sustainable cities by reducing the uncertainties in the implementation of sustainable water measures, such as DWR and water use reduction. OpenFOAM, an open-source computational fluid dynamics package, was used to develop the sewer sediment model. This model has components that model flow, suspended sediment transport, bed load transport, and deposited bed development. Model calibration, using a square hydraulic flume, shows model results for flow and sediment transport are promising. Model validation experiments in a pilot-scale sewer system show that reducing sewer inflows are going to be a concern for sewer solids, especially in non-ideal or ageing sewers.