Development of an odorant emission model for sewage treatment works

Abstract

In the field of odour assessment, much attention has been paid to the measurement of odour concentration. Whilst the concentration of an odour at a receptor is a useful indicator of annoyance, the concentration at the source tells only half the story. The emission rate - the product of odour concentration and air flow rate - is required to appreciate the significance of odour sources. Knowledge of emission rates allows odour sources to be ranked in terms of significance and facilitates appropriate selection and design of odour control units. The emission rate is also a key input for atmospheric dispersion models. Given the increasing importance of odour to sewage treatment works operators, there is a clear need for predictive methods for odour emission rates. Theory suggests that the emission of odorants from sewage to air is controlled by mass transfer resistances in both the gas and liquid phase. These are in turn controlled by odorant and emission source characteristics. The required odorant characteristics are largely known, and mass transfer from many different types of emission sources have been studied. Sewage treatment processes can be described by one or more of six characteristic emission sources, these being quiescent surfaces, channels, weirs and drop structures, diffused aeration, surface aeration and flow over media. This paper describes the development of odorant mass transfer models for these characteristic emission types. The models have been applied in the form of spreadsheet models to the prediction of H2S emissions and the results compared with commercial VOC emission models.

Dispersion of Odorous Gaseous Compounds Emitted from Wastewater Treatment Plants

“…The detection and perception of odours by humans is an extremely complex process. The main factors determining whether an odour causes annoyance are the concentration of the odorous compound in the air, the "odour quality", the odour appearance frequency and the odour duration (Piringer et al 2007;Nicell 2003Nicell , 2009Gostelow et al 2001Gostelow et al , 2004Gallego et al 2008).…”

Mass transfer inside a flux hood for the sampling of gaseous emissions from liquid surfaces – Experimental assessment and emission rate rescaling

“…By knowing the values of the mass transfer coefficients in the interior of the flux hood, it is possible to estimate the bias in the measured emission rate, compared to the values that could be expected in the field in the absence of the sampling device, especially for compounds with volatilisation controlled by conditions in the gas phase. In the present analysis, the calculated by the volatilisation model proposed by Gostelow et al (2001a) for passive liquid surfaces is adopted as a proxy for the values in the field. The friction velocity, which is one of the input variables for the model, is estimated based on the wind speed at 10 m height ( ) by applying the correlation of Smith (1980).…”

Dynamic Modeling of Hydrogen Sulfide within Enclosed Environments in Biosolids Recovery Facilities

“…Prediction of H 2 S emissions throughout WRRF units has been carried out by resorting to different models, such as WATER9 (USEPA, 2001), BASTE (Corsi and Card, 1991), TOXCHEMþ (Melcer et al, 1994) or the model proposed by Gostelow et al (2001b), among the most commonly used. Main H 2 S removal mechanisms considered include volatilization, stripping, adsorption, absorption, biodegradation (USE-PA, 2001) and oxidation (Santos et al, 2009).…”

“…Alternative approaches exist for empirical derivations of these coefficients, as described by USEPA (1994), Mackay and Matsugu (1973) and Mackay and Yeun (1983). However, several authors have demonstrated the expressions often over or underestimate emission rates (Ferro and Pincince, 1996;Jones et al, 1996;Gostelow et al, 2001b;Santos et al, 2006) by factors of up to 12 times , depending on the operational process, and therefore local determination of transfer coefficients is advised. When modelling emissions within enclosed environments, some models, such as WATER9 (USEPA, 2001), are based on the assumption of the equilibrium of volatile compound concentration between the gas and liquid phase, rather than mass transfer phenomena (Tata et al, 2003).…”

“…Under non-quiescent flow conditions, as induced by weirs or drop structures, the mass transfer is affected by phenomena such as airborne droplets, falling wastewater film or air entrainment in the tailwater (Corsi and Quigley, 1996). Generally, most models estimate these emissions as a dependent variable on parameters such as drop height, flow rate, hydraulic weir load or tailwater depth (Melcer et al, 1994;Corsi and Quingley, 1996;Gostelow, et al, 2001b), using adaptations of the equations proposed by Rahmé et al (1997) or Nakasone (1987).…”