Effects of flux chamber configuration on the sampling of odorous gases emissions

Abstract

Flux chambers are commonly used to measure emission rates of odorous compounds at passive liquid surfaces in wastewater treatment plants. Different flux chambers configurations are found in the literature and the main concern regards to the mixing inside the chamber, which is linked to impact on the overall mass transfer between emitting surface and headspace, and the sampling recovery efficiency. However, aspects related to the airflow and mass transfer inside the chambers influence the measured emission rates. The mass transfer coefficients in the liquid and gas phases are functions of the friction velocity on the liquid surface. This work investigates the airflow and odorous compounds transport (with different Henry’s law constants) inside a flux chamber using Computational Fluid Dynamics, to determine the influence of inlet airflow rate (2, 5 and 10 L min−1), inlet configurations (4, 6 and 8 inlet holes) and the inclusion of internal fans on the surface friction velocity and emission rate. The results showed a complex flow inside the chambers and a concentration field that reaches steady state after 6 residence times. The use of an internal fan promoting downward flow increased turbulence and produced values of friction velocity at the liquid interface closer to those found in the near surface flow in the boundary layer, whereas all other configurations tested showed much lower values of friction velocity. Therefore, the use of a fan is recommended.