Stochastic Approach to the Modelling of Gross Solids Mass Flow in Sewer Systems

The movement of large organic solids in sewers has not been studied until recently. New European Regulations require that these solids are controlled so as not to be seen in the environment once escaped from combined sewer overflows. Hence there is now a greater imperative to understand how these solids move and are discharged from sewer networks. A study over the last 5 years has investigated all aspects of the origins and movement of these solids in real sewers in Scotland. Computational modelling is essential to predict the behaviour of these ‘gross' solids in sewer networks. A stochastic model has been developed to simulate their movement by predicting the probability of transition of any given solid among three different states (suspension, near bed and immobile state). This new modelling approach has been developed using continuous time Markov Chain and Kolmogorov system equations. Simulation has been carried out using the InfoWorks hydraulic model and tool box MATLAB/SIMULINK. This paper presents an application of the stochastic approach to simulate the gross solids movement in a sewer network using this probability based approach.