Real-time Odour Dispersion Modelling for Industrial Sites Application: State of the Art and Future Perspectives

In the field of odour impact assessments resulting from industrial activities, the use of atmospheric dispersion models appears to be crucial. These mathematical tools are able to estimate the ambient air odour concentration at the receptors nearby a plant, as indicated in some guidelines and laws. Generally, the odour concentration is evaluated through emission olfactometry monitoring, and subsequently, based on the dispersion modelling software, impact maps are created at specific percentiles (odour concentrations that are reached for a certain number of hours a year). However, in this way, it is not possible to know the specific odour event as it occurs; therefore, it would be ideal to have a real-time estimation of the odour fallout in the plant's surroundings. Currently, there exist some scientific papers and several commercial which propose some kind of real-time odour monitoring. Overall, these tools aim to monitor the odour events that occur on-site in real-time and to model atmospheric dispersion. The present work seeks to summarise what is currently available for real-time estimation of odour emission and dispersion, with the purpose of highlighting the potential, the eventual limitations, and the principal aspects to be studied and investigated. These considerations may help to develop a newer approach in order to stimulate the research towards the highest possible accuracy of these systems

Estimation of the Odour Emission Capacity of High-load Wastewater

The Odour Emission Capacity (OEC) is an experimental parameter that quantifies the odour potential of a liquid, in terms of ouE/m3 liquid , based on the stripping of odorants contained in a known amount volume of liquid. The method was implemented for the first time in 1998 by Frechen and Köster and standardized in 2015 in the German technical standard VDI Guideline 3885/1. In particular, the sampling steps of gas phase for the dynamic olfatctometry analysis were fixed at 2, 6, 16 and 32 minutes. This work aims to propose a modified methodology to evaluate this parameter in wastewater which come from the sewer systems and industrial wastewater treatment plants (WWTP) characterized by high odour load (e.g. oil-refinery desalter water, oil-well water). The implementation of a system of dilution for the sampled gas, has appeared to be an important aspect to take into account in case of high odorous load, because it allows to perform the analysis also with smaller liquid volume (i.e. 1 L), a necessary condition for lab logistics and safety considerations as the safeguard of the involved operator’s health (e.g. panel members, lab analysts). In order to improve the accuracy of the result and optimize the methodology, a different approach was studied through the increase in the number of odour concentration measurements and the modification of the sampling times. Results show that increasing the time of analysis from 32 min to 2 days, the trend of the time-varying integral of OEC reaches a quasi-stationarity respect the same curve associated to the OEC estimated with the standard methodology

Validation study of WindTrax reverse dispersion model coupled with a sensitivity analysis of model-specific settings

In last years, atmospheric dispersion models have reached considerable popularity in environmental research field. In this regard, given the difficulties associated to the estimation of emission rate for some kind of sources, and due to the importance of this parameter for the reliability of the results, Backward dispersion models may represent promising tools. In particular, by knowing a measured downwind concentration in ambient air, they provide a numerical value for the emission rate. This paper discusses a critical validation of the WindTrax Backward model: the investigation does not only deal with the strict reliability of the model but also assesses under which conditions (i.e. stability class, number, and location of the sensors) the model shows the greatest accuracy. For this purpose, WindTrax results have been compared to observed values obtained from available experimental datasets. In addition, a sensitivity study regarding model-specific parameters required by WindTrax to replicate the physics and the random nature of atmospheric dispersion processes is discussed. This is a crucial point, since, for these settings, indications on the numerical values to be adopted are not available. From this study, it turns out that the investigated model specific settings do not lead to a significant output variation. Concerning the validation study, a general tendency of the model to predict the observed values with a good level of accuracy has been observed, especially under neutral atmospheric conditions. In addition, it seems that WindTrax underestimates the emission rate during unstable stratification and overestimates during stable con-ditions. Finally, by the definition of alternative scenarios, in which only a portion of the concentration sensors was considered, WindTrax performance appears better than acceptable even with a small number of concen-tration sensors, as long as the positioning is in the middle of the plume and not in the strict vicinity of the source

Experimental evaluation on liquid area sources: Influence of wind velocity and temperature on the wind tunnel sampling of VOCs emissions from wastewater treatment plants

The investigation of Volatile Organic Compounds (VOCs) emission from wastewater basins is a challenging issue. In particular, the quantification of an accurate emission rate appears quite tricky, since the release of VOC compounds from this type of source, and the subsequent dispersion into the atmosphere, is ruled by different complex phenomena, potentially affected by a variety of external chemical and physical parameters. In this regard, the wind velocity and the liquid temperature represent variables that are worth investigating. Given this, the present paper discusses an experimental study aimed at evaluating the influence of these variables on the emission rate of VOCs (i.e. acetone, toluene and butanol) in solution with water at low concentrations (0.5 mL/L and 5 mL/L). The experimental trials are conducted using a wind tunnel system, changing the sweep air flow from 0.02 m/s to about 0.06 m/s and the liquid temperature from 20 °C to 35 °C. This study reveals that while the wind velocity seems to slightly influence the emission rate of VOCs estimated by wind tunnel sampling, the effect of the temperature appears much more significant. This behaviour is also confirmed by experimental trials conducted on real-case industrial wastewater, coming from an equalization tank. In view of this, the approach commonly applied to evaluate the influence of wind velocity (i.e. a dependence of the odour emission rate on the square root of the wind velocity) appears not fully consistent with the experimental results obtained at low concentrations by wind tunnel sampling. Also, the influence of temperature seems more pronounced in the case of butanol, in accordance with the theoretical trend of Henry constant as a function of temperature

VALIDATION STUDY OF WINDTRAX BACKWARD LAGRANGIAN MODEL

In last years, atmospheric dispersion models have reached considerable popularity in environmental research field. In this regard, given the difficulties associated to the estimation of emission rate for some kind of sources, and due to the importance of this parameter for the reliability of the results, backward dispersion models may represent very promising tools. This paper discusses a critical validation of the Windtrax backward Lagrangian model: the investigation does not only deal with the strict reliability of the model but also assesses under which conditions (i.e. stability class, number, and location of the sensors) the model shows the greatest accuracy. For this purpose, Windtrax results have been compared to observed values obtained from available experimental datasets. From this study, it turns out a general tendency of the model to predict the observed values with a good level of accuracy, especially under neutral atmospheric conditions. In addition, it seems that Windtrax underestimates the emission during unstable stratification and overestimates during stable conditions. Finally, by the definition of scenarios in which only a portion of the concentration sensors was considered, Windtrax performance appears better than acceptable even with a small number of sensors, as long as the positioning is not in the strict vicinity of the source

Variability in odour impact assessment due to different cloud cover estimation approaches: A northern Italy case study

For atmospheric dispersion models, Cloud Cover (CC) is an input that controls turbulent diffusion. This study analyses the influence of various approaches to estimate CC in odour dispersion modelling: given the normative relevance of these assessments, it is pivotal to understand the result of different operational choices about this parameter. Results seem largely comparable regardless the different CC approach. Both, micrometeorological parameters from CALMET simulations and CALPUFF odour impact maps appear almost overlapped. The outcome of the present study is that CC algorithms, do not significantly influence odour impact: this result strengthens the regulatory use of models for odour assessments

Quantification of odour annoyance-nuisance

This paper analyzes the state of the art of the methods and models used for the characterization of odour annoyance and it preliminary advances proposals for the evaluation of the olfactory nuisance. The use of a sensorial technique, such as dynamic olfactometry, is proposed for the analysis of odour concentrations, odour emission rates and odour dispersions. Secondly a simple model for the quantification of environmental odour nuisance, based on the use of FIDOL factors, i.e. frequency, intensity, duration, hedonic tone and location, is developed