Mathematical Modelling of In-Sewer Processes as a Tool for Sewer System Design

The objective of this paper is to evaluate the potential impact of insewer processes (COD components transformation and hydrogen sulphide production) on the design of sewer systems. The tool used for such analysis is a mathematical model derived from the WATS model (Wastewater Aerobic/anaerobic Transformation in Sewers) able to describe the processes occurring in the sewer system both under aerobic and anaerobic conditions. The model is applied to three catchments with, respectively, 10,000, 50,000 and 250,000 inhabitants connected to gravity sewer systems different in terms of type (separate or combined), slope, length, travel time, wastewater temperature. The simulation results enable to assess the effect of the in sewer transformations in terms of hydrogen sulphide formation and transformation of the biodegradable organic matter that is necessary for biological nutrients removal at the WWTP.