Plant-wide modelling and analysis of WWTP temperature dynamics for sustainable heat recovery from wastewater

Wastewater heat recovery up-stream of wastewater treatment plants (WWTPs) poses a risk to treatment performance, i.e. the biological processes. In order to perform a sustainability analysis, a detailed prediction of the temperature dynamics over the WWTP is needed. A comprehensive set of heat balance equations were included in a plant-wide process model and validated for the WWTP in Linkoping, Sweden, to predict temperature variations over the whole year in a temperate climate. A detailed model for the excess heat generation of biological processes was developed. The annual average temperature change from influent to effluent was 0.78 degrees C with clear seasonal variations. 45% of the temperature change arises from processes other than the activated sludge unit. Hence, plant-wide energy modelling was necessary to predict in-tank temperature in the biological treatment steps. The energy processes with the largest energy gains were solar radiation and biological processes, while the largest losses were from conduction, convection and atmospheric radiation. Tanks with large surface areas have significant impact on the heat balance regardless of biological processes. Simulating a 3 degrees C lower influent temperature, the temperature in the activated sludge unit dropped by 2.8 degrees C, which had a negative impact on nitrogen removal.

Automated summary

Wastewater heat recovery up-stream of WWTPs poses a risk to treatment performance, requiring detailed prediction of temperature dynamics and comprehensive heat balance equations for analysis. Developing a detailed model for excess heat generation in biological processes is essential for predicting temperature variations and maintaining treatment efficiency.