Effects of ﬂux chamber conﬁguration on the sampling of odorous gases emissions Willian L. Andreão a , Jane M. Santos a,⇑ , Neyval C. Reis Jr. a , Ademir A. Prata Jr. b , Richard M. Stuetz b a Departamento de Engenharia Ambiental, Universidade Federal do Espírito Santo, Av. Fernando Ferrari 514, 29.060-970 Vitória, ES, Brazil b School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052, Australia article info Article history: Received 13 February 2019 Received in revised form 28 May 2019 Accepted 9 June 2019 Keywords: Flux chamber Odour emission Hydrogen sulphide Acetic acid Computational ﬂuid dynamics Friction velocity 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 litera- ture 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. Ó 2019 Elsevier Ltd. All rights reserved. 1. Introduction Anaerobic microbial activity at wastewater treatment plants (WWTP) can generate unpleasant odorous emissions that may be noticed in surrounding residential areas leading to complaints [1–3]. The main odorous compounds emitted from WWTP belong to families of chemical compounds such as sulphur, nitrogen and other volatile organic compounds (for instance, phenols, aldehy- des, ketones, alcohols and volatile fatty acids). Primary and sec- ondary settlement tanks, certain secondary treatment options, such as sequencing batch reactors during the settle and decant phases, biological aerated ﬁlters awaiting backwash, lagoon- based treatment systems such as anaerobic lagoon and waste sta- bilisation ponds can represent a signiﬁcant source of atmospheric odour emissions from passive liquid surfaces in WWTP, causing impacts on air quality and human health [4,5]. The direct assessment of odour emissions from passive liquid surfaces can be performed by using enclosure methods such as portable wind tunnels [6–9] and dynamic ﬂux chambers [10–12]. However, the use of any enclosure method to sample odorous gases is likely to disturb the emitting surface and may not repre- sent the real emission rate [13]. In order to establish policies and control strategies for odours emissions and to use dispersion mod- els for odour impact assessment, it is necessary to measure the cor- rect emission rate, but so far there is no universally accepted enclosure device-based measurement method. The so-called US EPA ﬂux chamber [10,11] is the design widely adopted worldwide but a range of different ﬂux chamber shapes (rectangular and cylindrical) and sizes (base area and height) have been presented in the literature [13,15]. Nonetheless, limited reporting of experimental details and measurement results (e.g., velocity and/or concentration proﬁles) are available to support a comparison of these sampling devices, in particular for the applica- tion of an internal fan. The ﬂux chamber was originally designed to be a mixing cham- ber [11,16–19] that has a well-mixed headspace to ensure that the odorous gas concentration is uniformly distributed throughout the ﬂux chamber and the collected samples are representative of the ﬂuid inside the chamber. The mixing in small ﬂux chambers is pro- vided by the air ﬂow patterns produced by the sweeping air sys- tem. However, in larger chambers, the use of a small fan or an https://doi.org/10.1016/j.ijheatmasstransfer.2019.06.029 0017-9310/Ó 2019 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: jane.santos@pq.cnpq.br (J.M. Santos). International Journal of Heat and Mass Transfer 140 (2019) 918–930 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt