Temperature Modeling in Activated Sludge Systems: A Case Study

A model of temperature dynamics was developed as part of a general model of activated‐sludge reactors. Transport of heat was described by the one‐dimensional, advection‐dispersion equation, with a source term based on a theoretical heat balance over the reactor. The model was compared to several reference models, including a tanks‐in‐series model and the dispersion model with heat components neglecting biochemical‐energy inputs and other activated‐sludge, heat‐balance terms. All the models were tested under steady‐state and dynamic conditions at a full‐scale facility, the Rock Creek wastewater treatment plant in Hillsboro, Oregon, using meteorological data from a station located 16 km from the plant. The dispersion model and tanks‐in‐series model matched in situ temperature data with absolute‐mean errors less than 0.1°C. Neglecting biochemical‐heat‐energy inputs in the activated‐sludge reactor underestimated temperatures by up to 0.5°C. The biochemical‐heat‐energy inputs accounted for 30 to 40% of the total heat flux throughout the year.