Modeling the Temperature Pattern of a Covered Anaerobic Pond with Computational Fluid Dynamics

Abstract

This paper presents the development of a 3D computational fluid dynamics (CFD) model of a covered deep anaerobic pond treating raw sewage. The model was based on an unsteady-state laminar flow which was solved in accordance with the finite volume method and simulated the hydrodynamic pattern and thermal energy balance of the anaerobic pond throughout a year of operation. The model input included hourly ambient air temperature, monthly soil temperature profile, daily influent wastewater temperature and velocity, which were incorporated through an external routine in C++. Numerical simulation was validated by temperature measurements from the experimental pond. The mean relative error and correlation factor out of 164 temperature values of the simulated pond, in comparison with the experimental one, was 9.34% and 0.91, respectively. The average temperature of the simulated pond throughout the experimental period was 18.9 ∘C. The validated 3D thermal model can be used as a tool for assessing and evaluating the impact of various design modifications (changes in construction material, adding insulation, installing a heat exchanger, etc.) on the thermal behaviour of an anaerobic pond, aiming at its average temperature increase which will, in turn, positively affect its organic removal performance. The thermal model presented, is the first stage of a complete anaerobic pond model which will include wastewater quality transport and basic biochemical reaction mechanisms of the anaerobic decomposition process present in an anaerobic pond. The complete anaerobic pond model will be able to predict the effluent COD of the pond.