Health and Safety Middle East Logo

Environmental Odour Monitoring

Published: 10th Sep 2010 in AWE International

A real-time odour impact monitoring system was installed at the Sivos des 60 Bornes waste water treatment plant (WWTP), which treats the waste water of two towns, St-Hilaire-de-Riez and St-Jean-de-Monts, on the French coast in the region of Vendée. The users’ objective was to minimise odour nuisances generated by pumping stations of the waste-water system and by various components of the WWTP.

The system (called OdoScan®) enabled the user to identify the main source of odour emissions, in this case the outlet of the deodorisation process of the pre-treatment building of the WWTP. Continuous odour monitoring by site operators allowed immediate and direct action on the source responsible for nuisances, thereby appreciably reducing the number of complaints received by the Sivos during the 2008 summer season. Finally, an analysis of the average impact on the surrounding area helped the user to identify that pumping stations are a potential weak spot in terms of nuisances experienced, but more importantly, that generally, very low levels of odour were experienced by residents.

 

Introduction

Odour nuisances generated by industrial activities on the French coastline have been regularly identified by vacationers as bothersome over the past few years. These nuisances create a new set of problems between tourists, owners and managers of tourist sites, elected community officials, and local industry.

Waste treatment activities in these communities are particularly affected by such problems. During the summer season, the quantity of waste to be treated can often amount to more than 10 times the usual off-season load. This overload causes an increase in odour emissions from treatment sites, and a heightened risk of occurrence of odour nuisances.

The installation of odour control equipment on problematic sources is usually the ideal solution. However, to ensure that the investment in such technologies has a real impact on nuisance reduction, it should ideally be accompanied from the outset by an assessment of the odour sources that might generate nuisances, within or outside an industrial site, as well as by monitoring of the improvements achieved.

Indeed, while some sources are often perceived as the main culprits in generating odour nuisances, and treated as such, many odour sources with a significant environmental impact are overlooked, so the odour problem persists.

This article details the installation of a tool for monitoring nuisance odours in the towns of St-Hilaire-de-Riez and St-Jean-de-Monts on the French Vendéan coast, a major summer vacation resort area. Together, the two towns host more than 100,000 visitors per week during the summer season, in addition to their usual 15,000 residents.

Historically, the main source of nuisance identified by elected officials, residents and tourists was the waste water treatment plant (WWTP).

The site of the Sivos des 60 bornes WWTP is in the town of Saint-Hilaire-de-Riez, in the Vendée department. This plant treats all the waste water of the town of Saint-Jean-de-Monts and one third of the waste water of Saint-Hilaire-de-Riez.

The site is near 60 bornes beach. The coastal road passing in front of the plant links departmental route 123 (D123) to the southern subdivision of the town of Saint-Jean-de-Monts (900 metres as the crow flies). To the north, the plant is separated from this subdivision by an area of sand dunes (the ‘Pré Salé’), wherein lies a residential zone and a campground. They are the plant’s closest neighbours, 180 metres from the nearest odour source on the site.

To the southeast, the village of Les Becs borders the beach at a distance of 1 kilometre, but residences further east are even closer (Le Petit Bec
at 500 metres). Finally, towards the northeast, besides the residences along the D123, the public forest of Pays de Monts acts as a vegetation buffer prior to the town centre of Saint-Jean-de-Monts. The figure 1 (opposite) illustrates the above description.

Methodology - Identifying the odour sources

The first step entails identifying the sources that could create olfactory nuisances. An initial examination of the region led to the identification of two potential sources: the WWTP and the pumping stations.

The pumping stations are the elements of the sewage system that propel the sewage towards the WWTP. Six pumping stations were identified in areas near residential or vacation resort areas.

The WWTP contains several potential emission sources. The purification process uses a biological treatment of waste water, which includes the usual stages: intake, aeration, and settling. The site presently includes the following installations:

• A waste water intake building (contains a grit chamber and skimmer)
• A buffer pond
• An aeration pool, adjustable according to the charge to be treated
• Two clarifiers for settling
• A sludge collection and treatment building

Gaseous effluent deodorisation systems have been installed on these components. The buffer pond, for instance, is deodorised by a photochemical system. The skimmer has also been equipped with a photochemical unit designed to reduce odour concentrations.

Finally, the two sludge intake and treatment buildings employ chemical (acid-base) scrubbers designed to purify the building’s air prior to atmospheric release.

Thus, a total of 14 odour emission sources were identified as potential generators of odour nuisances in the environment. The following figure shows these sources.

The inclusion of pumping stations into the assessment of odour problems allows a better understanding of the influence such installations may have on nuisance odour generation. While emissions from these stations are potential nuisance sources, it is entirely possible for the WWTP to be blamed instead, as the odours produced are comparable.

Odour monitoring system

The OdoScan® odour management technology developed by Odotech for continuous odour monitoring was chosen for the site.

The system allows operators to monitor the principal odour source(s) of their facilities. The system comprises a computer, software for real-time odour dispersion modeling, and a meteorological station.

Samples are taken from the odour sources on the site and analysed by a dynamic dilution olfactometer in accordance with European standard EN 13725.

The software parameters are programmed to model the atmospheric odour dispersion in real time and to display the resulting odour plume in odour units per cubic meter of air (o.u./m3).

In order to calculate the odour plume, OdoScan®’s atmospheric dispersion model combines real-time data from the meteorological tower with the odour concentration values already measured, and displays the odour plume superimposed on the map of the site. This allows the operator to instantly visualise the impact of the odour, 24/7. The AERMOD dispersion model, a world reference for atmospheric dispersion, is used. The following figure illustrates the concept.

The dispersion model incorporates the characteristics of emission sources and receptor points or surfaces, as well as the real-time meteorological data in order to calculate the odour concentration in ambient air at several user-defined locations.

Olfactometry

Dynamic dilution olfactometry entails presenting a panel with sample dilutions created by a calibrated olfactometer for measuring the gas flow. The air-odour mixes are presented to panelists at odour sniffing ports.

The objective is to determine the odour perception threshold for a gas sample. The odour perception threshold is defined as the odour level at which 50% of an odour panel perceives the odour, while the other 50% does not. By definition, the odour perception threshold is equivalent to one odour unit per cubic meter of air (o.u./m3). The number of dilutions of the odour sample necessary to obtain 1 o.u./m3 is equal to the odour concentration of the sample in odour units per cubic meter of air (o.u./m3).

Dynamic Dilution Olfactometer

The olfactometric analyses were performed using the ODILE® Dynamic Dilution Olfactometer, in compliance with European standard EN13725. The measurements obtained are objective and relate directly to the individual perception of the odour.

Results and discussion - Odour diagnosis

The odour diagnosis consists of assessing the relative magnitude of each odour source. This initial analysis pinpoints the most significant sources in terms of odour flow rates.

Table I shows the odour flow rates measured at the sources of the WWTP.

The following figure shows these flow rates as a percentage of the overall emissions of the site. The total odour flow rate of the Sivos des 60 bornes WWTP is estimated at 50 million odour units (peak), with all components operating. This number is at the low end of the range for this type and size of facility. Of this overall emission, it appears that the open surfaces (the three ponds) constitute minority emission sources at less than 11%. Inversely, pretreatment deodorisation accounts for more than three quarters of all emissions. This predominance is due to two independent causes: firstly, the exhaust concentration was relatively high relative to the buffer pond and sludge deodorisations, and secondly, the volume flow rate for the outlet is the largest on the site (10,000 m3/hr, nearly 40% of the site volume flow rate).

This situation is typical. The deodorisation of the pretreatment had never been identified as a potential source of nuisance odour. First of all, owing to its very nature, a deodorisation outlet is rarely suspected to be the cause of a nuisance, as the deodorising equipment is usually considered effective. In addition, the deodorisation outlet is nearly 15 metres above ground, so that the odours it releases seldom cause a nuisance on the site itself, where operators might potentially recognise the odour. Indeed, the odour plume disperses high up, over long distances, and only hits the ground outside the site property limits. Operators have a natural tendency to identify ground installations as potential nuisance odour sources, since these sources make up their daily olfactory environment.

From an overall perspective, the site produces 50 million odour units per hour at peak times, for a volume flow rate of just under 25,600 m3/hr. In terms of emission average, this yields 2,000 o.u. for each cubic metre of gas effluent, a relatively low output for a facility of this size. The table shows the odour flow rates of the different pumping stations.

The following observations can be made:

• The total odour emissions of the stations come to 4.42 million odour units per hour
• Les Sauges, Les Demoiselles and Top Loisir are the greatest odour producers, accounting for 92% of the emissions of the six stations and a peak flow rate of 36%
• Plant elements with odour control equipment account for 8% of the odour emissions at a peak flow rate of 60%
The following figure summarises these proportions.

Comparison with the pumped water flows shows that the quantity of odour generated is not a function of the quantity of effluent treated. Indeed, the Immortelles pumping station pumps the largest quantity of waste water but produces one of the lowest odour emissions. Odour flow rate is primarily a function of the time the pumped waste water spends in the system, as well as the nature of the effluent. Depending on the origin of the effluent, it may be more or less charged with odour-producing molecules.

The odour diagnosis results show that the pumping stations are a potential source of environmental nuisance. Since the odours from the pumping stations may be readily associated to those from the WWTP, they must be included in the analysis of odour complaints, and thus in the continuous odour monitoring system.

The odour flow rates obtained from the odour diagnosis were used as reference values in the atmospheric dispersion modeling software of the OdoScan® system.

Real-time odour assessment

The real-time monitoring of odours was used primarily for identifying the origin of odours when complaints were reported. The use of this system allowed operators of the WWTP, as well as municipal employees in charge of pumping stations, to react as soon as a risk of odour nuisances was detected, responding directly at the source responsible for the problem. As a result, a significant reduction in odour complaints was observed during the 2008 summer season.

The following table shows the maximum values at different locations of interest within the study zone. Note that the des Demoiselles campground entrance may be subjected to high odour concentrations.

The values were nonetheless relatively low. While the odour perception threshold is by definition 1 o.u./m3, the odour recognition threshold is usually set at 5 o.u./m3. At this threshold, people can identify the nature of the odour as well as its source, if they know about it. Thus, the residential zones of des Becs and des Begonias never reached the odour recognition threshold over a one-year period.

The modeling of odours is largely dependent on meteorological parameters. The following figure shows the degree to which different meteorological parameters can have a direct impact on the dispersion of odour, and therefore on its perception by those concerned.

The wind direction is comparable but the extent of the plume is completely different for the two scenarios. Note that in the left-hand diagram, the odour plumes are very narrow. The complaint risk is much lower than for the right-hand diagram, where the odour plumes are very wide. As a result, a long stretch of the beach is subject to odours.

The usefulness of this type of equipment lies in enabling the start-up of specific odour control measures when problems arise (chemicals in the sewer system, boosting the scrubber treatment, increasing fresh airflow in buildings, etc).

The on-demand reduction of odours allows the operator to avoid the costs of continuous odour treatment while ensuring that the quality of life for residents near the sources remains unaffected.

Impact study

The impact study consists of consolidating the entire real-time monitoring data set to perform analyses of the exposure of nearby residents to odours over a longer period.

Hourly maxima

This situation refers to the worst combination in terms of meteorological conditions and emissions of odourous effluent. Examination of the Figure reveals that this situation raises the odour concentration within a radius of 1000 metres to a level of 4 odour units per cubic metre.

This means that it is possible to detect and recognise the plant site odours within a 1 kilometre radius in the event of particularly unfavorable meteorological conditions.

The most unfavorable impact thus appears to be substantial under maximum operating conditions, at the des Demoiselles campground, the point nearest the site. In the event of poor weather conditions and intense plant operation, all of the other locations monitored could be subject to complaints.

The following figure shows the most unfavorable situation for the pumping stations only.

The des Sauges and des Demoiselles pumping stations are the sources with the strongest impact. While this was predictable from the estimated odour flow rates, it yields a perception threshold (1 o.u./m3) range of up to 300 metres for the two points. The other two locations were negligible over their range (<100 metres).

Threshold breaches

Two threshold breaches were investigated. The first concerns the breach of the perception threshold, e.g. the percentage of time for which more than one half of the population detects an odour coming from the site. See Figure 10.

Mapping the perception threshold (1 o.u./m3) boundary yields 1% of the time, e.g. approximately 90 hours over the whole year, 900 metres from the site.

Note that identification of the odour is not possible at this concentration level.

The 5 o.u./m3 threshold - the concentration necessary for odour recognition - is mapped in the following figure. Its extent does not exceed 1% of the time (e.g. 90 hours per year) at 300 metres.

The following figure deals only with the pumping stations. Only Les Sauges et Les Demoiselles are potentially detectable by their odours at least 2% of the time within a radius of a few dozen metres.

The following table shows the percentage of time where these thresholds were exceeded for each location studied.

The threshold breach numbers reveal a limited impact on the vicinity of the site. In spite of its relative proximity to the site, the Petit Bec subdivision shows a very low potential complaint frequency. On the other hand, that frequency rises to 3% of the time for the neighbouring des Demoiselles location, e.g. 262 hours per year.

Summary - conclusion

The odour monitoring system provides for three types of analyses:

1. The ranking of the odour sources responsible for nuisances
2. Real-time assessment of where nuisances are coming from
3. Assessment of the degree of nuisance generated over time
This triple analysis allows industrial site operators to better understand the nature and the causes of odour nuisances for which they are responsible in the vicinity and to implement proper short and long term solutions.
As a result of the monitoring, it was decided to implement odour control solutions at the des Sauges and des Demoiselles pumping stations, and to optimise the odour control system already in place at the pretreatment facility.
These improvements resulted in a significant reduction in odour nuisances. In addition, the daily use of the OdoScan® system makes
it possible to minimise the number of complaints received by the Town Halls and the WWTP operator.

References

1. COMITÉ EUROPÉEN DE NORMALISATION - CEN 13725, Air Quality Determination of Odour Concentration by Dynamic Olfactometry.
2. CUM. Mesure du nombre d’unités d’odeur (olfactométrie dynamique). Montréal, Communauté Urbaine de Montréal, Service de l’environnement, Direction de l’assainissement de l’air et de l’eau. 1994.
3. PAGÉ, T. et GUY, C.; Odor dispersion modeling. Air & Waste Management Association’s 90th Annual, Toronto, ON, 1997.

Author

Philippe G Micone, General Manager, Odotech, France
After obtaining his Master’s in Chemical Engineering from Ecole Polytechnique de Montréal (Canada), Philippe G Micone completed a joint doctorate with the Institut National Polytechnique de Toulouse with the support of Veolia Water and ADEME (the Agency for Management of the Environment and Energy, France). In addition to being involved in the R&D of electronic noses for the past eight years, Mr Micone provided expertise on a variety of projects through Odotech’s Consulting and Expertise Division. Mr Micone is currently the General Manager of Odotech France, in charge of Odotech’s activities in Europe, Africa and the Middle East.

Odotech ( http://www.odotech.com ) has been in the business of odour management since 1998, with close to 500 interventions in all types of industries. Forty employees in France, Canada and Chile are actively supporting our customers with odour diagnostics; performance studies; modelling studies; establishing liaison committees; preparing odour mitigation plans and preventative programmes; and implementation of odour measurement (e-nose) and real-time modelling tools. More information on odour management can be found on the website above or this blog (blog.odotech.com).

Supporting collaborators/contributors

Thierry Pagé
Odotech Inc., 3333 Queen Mary Road, Suite 301, Montreal (QC) Canada,
H3V 1A2

Jean-Michel Martin
SAUR, 1, avenue Lavoisier, 78064 La roche sur Yon, France

Jacques Baud
SIVOS des 60 Bornes, President, Mairie de St-Hilaire de Riez, France


www.osedirectory.com/environmental.php
 

Published: 10th Sep 2010 in AWE International

Author


Philippe G Micone


Philippe G Micone, General Manager, Odotech, France

After obtaining his Master’s in Chemical Engineering from Ecole Polytechnique de Montréal (Canada), Philippe G Micone completed a joint doctorate with the Institut National Polytechnique de Toulouse with the support of Veolia Water and ADEME (the Agency for Management of the Environment and Energy, France). In addition to being involved in the R&D of electronic noses for the past eight years, Mr Micone provided expertise on a variety of projects through Odotech’s Consulting and Expertise Division. Mr Micone is currently the General Manager of Odotech France, in charge of Odotech’s activities in Europe, Africa and the Middle East.

Odotech ( http://www.odotech.com ) has been in the business of odour management since 1998, with close to 500 interventions in all types of industries. Forty employees in France, Canada and Chile are actively supporting our customers with odour diagnostics; performance studies; modelling studies; establishing liaison committees; preparing odour mitigation plans and preventative programmes; and implementation of odour measurement (e-nose) and real-time modelling tools. More information on odour management can be found on the website above or this blog (blog.odotech.com).

Supporting collaborators/contributors

Thierry Pagé
Odotech Inc., 3333 Queen Mary Road, Suite 301, Montreal (QC) Canada,
H3V 1A2

Jean-Michel Martin
SAUR, 1, avenue Lavoisier, 78064 La roche sur Yon, France

Jacques Baud
SIVOS des 60 Bornes, President, Mairie de St-Hilaire de Riez, France


Philippe G Micone

Website:
http://www.odotech.com


http://www.odotech.com

Contact Us Terms and Conditions Privacy Policy Sitemap Maintenance