Complementarity of odour monitoring systems: Wastewater Treatment Plant La Farfana

  sesion05 garces00The size and location of the sewage water treatment plant La Farfana, in Santiago de Chile, has implied different requirements in terms of monitoring gas odorant and odour, both inside the plant and in its populated environment. The aim of this work is to present the various gas and odour monitoring systems, measured at the emission sources, as in the places in which receptors are found.

Since the plant started its operation in 2003 various systems of monitoring, such as field panels, have been used with participation of neighbours and public officials; panels with specialized monitors; filling out of cards by passive monitors (neighbours); continuous monitoring, 24 hours a day, 7 days a week; odorant gas measurement; modelling of the dispersion of these gases, neighbour complaint phone reception system; campaigns of dynamic olfactometry, roundtables of ongoing work between the company and local communities, etc.

J. Garcés, F. Chávez, Y. Lesty,, >

  Aguas Andinas S.A.. Av. Presidente Balmaceda 1398, Santiago, Chile

  Competing interests: The author has declared that no competing interests exist.

  Academic editor: Carlos N Díaz.

  Content quality: This paper has been peer reviewed by at least two reviewers. See scientific committee here

  Citation: J. Garcés, F. Chávez, Y. Lesty, 2014, Complementarity of odour monitoring systems: Wastewater Treatment Plant La Farfana, Ist International Seminar of Odours in the Environment, Santiago, Chile,

  Copyright: 2014 Open Content Creative Commons license., It is allowed to download, reuse, reprint, modify, distribute, and/or copy articles in website, as long as the original authors and source are cited. No permission is required from the authors or the publishers.

  Keyword: Odour Monitoring, Odour Units, Odorant Gases, La Farfana plant


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     The size and location of the sewage water treatment plant La Farfana, in Santiago de Chile, has implied different requirements in terms of monitoring gas odorant and odour, both inside the plant and in its populated environment.

  The aim of this work is to present the various gas and odour monitoring systems, measured at the emission sources, as in the places in which receptors are found.

  Since the plant started its operation in 2003 various systems of monitoring, such as field panels, have been used with participation of neighbours and public officials; panels with specialized monitors; filling out of cards by passive monitors (neighbours); continuous monitoring, 24 hours a day, 7 days a week; odorant gas measurement; modelling of the dispersion of these gases, neighbour complaint phone reception system; campaigns of dynamic olfactometry, roundtables of ongoing work between the company and local communities, etc.

  The vision of complementarity between the methods used was essential to understand the behaviour of the different units of the plant, as it has also allowed the development of measures which have substantially mitigated emissions, which has been demonstrated by the same systems of monitoring used.



  The treatment of wastewater in the Metropolitan Region of Santiago has been undeniably positive for the environment and the quality of life of the inhabitants of the region. Progressing quickly in water decontamination has been an objective proposed throughout the country and has been met in an especially short time frame. The Metropolitan Region of Santiago and the country in general, in 2014 can now show levels of wastewater treatment of close to 100%.

  Together with the undeniable benefits generated by water decontamination, the externalities generated by unit processes that allow for treatment are also present. In particular, the issue of odorant gas emissions and the reactions from neighbouring communities and environmental authorities have arisen with the process of plant operation. All of the above has occurred in a national and international environment that is increasingly sensitive to the environmental impacts felt by communities from large investment projects.

  In this process there are multiple stakeholders which include neighbouring communities, health and environmental authorities, environmental organizations and the company operating the treatment plant.

  The La Farfana Waste Water Treatment Plant (WWTP) is the largest in the region and the country, treating 50% of the wastewater of Great Santiago. In its 10 years of operation it has developed various gas and odour monitoring systems. It currently treats and average flow of 9 m3/s and serves a population equivalent to 3,000,000 people.

Materials and methods

  The subject of odours from WWTPs is a very new one for the different actors, because these plants have only come to exist very recently in our country.

  Unlike other environmental issues associated with plants, such as the discharges of treated water which are governed by specific rules, there is currently no standard for odours governing the operation of emitting plants, whether emission or immission. Yet at the same time, these odours constitute an impact that can cause discomfort in neighbouring communities. In addition, measuring these odours is complex, because they are associated with human perception, and particularly the perception of annoyance of the affected population, which increases the complexity of the measurement.

  In this context, the La Farfana Plant in its 10 years of operation has developed various monitoring systems that have attempted to include the various manifestations of this environmental problem: gas emissions, odour emission and immission, community perception, odour perception in panels of trained monitors, etc.

  The different methods employed have tried to resolve the fact that while science and technology play the necessary and important roles in the quantification of the problem, they are not sufficient. The participation of other actors and their own perceptions are also relevant to addressing the problem.

  In the operation of the La Farfana plant, different systems have been developed for monitoring, some of which, still operate simultaneously.

   a) Odour panel with incorporation of neighbours and public officials

  The first way to tackle the perception of odours from this plant was performed through a simplified application of the odour panel taken from the VDI 3940.

  These panels were held with groups of 10 people, which included members of the affected community, officials of health and environmental agencies and the rest was performed by monitors with higher levelsof knowledge and education.

   b) Neighbour perception cards (passive monitors)

  Cards were distributed in the homes of the neighbours, and were regularly filled out, regardless of whether they detected any odours. The cards were picked up and processed weekly. Participating houses belonged to different locations around the plant. The information constituted direct information from the community.

   c) Specialised odour panel monitors with University validation

  Following the panel with community and government officials, a transition was performed towards panels that included only personnel trained by a consulting firm, with a selection and evaluation system. In this way it progressed toward a "professionalisation" of the panels. To ensure residents and the authorities of the "scientific rigor" of these panels, validation was incorporated into the reports, by a University belonging to the Council of Rectors.

   d) Odour panel with the grid method

  As an individual exercise and during a period of 7 months, a grid method was developed in a populated area surrounding the plant, in order to determine the presence or absence of odour frequencies (considering the limit of 10%).

   e) Continuous monitoring

  In response to criticism raised by the monthly meeting of the panels, and the lack of information between panels which and the associated delay of information that prevented decision making regarding plant operations, a system of continuous monitoring was developed. This system consisted of a trained and certified monitor covering the plant every day of the year, at various points around the plant and using the immission system for 10 minutes, determining the presence or absence of odour attributed to the plant and recording the duration of the odour perception. This monitor is also trained inside the plant, measuring their perception of the odours emitted by the different units. In this way, when an odour is recorded that is attributable to the plant, it also reports the treatment unit (process unit) that is perceived at the monitoring point. These rounds are carried out 24 hours a day, 365 days a year.

   f) Measurement of gases and dispersion model

  Even when the perception is from odours and not gas, since its inception the plant has measured odorant gases emitted by the different treatment units. DMS, H2S, and Ammonia have been monitored quarterly.

  The dispersion of Dimethyl Sulfide emissions is modelled by the AERMOD program, which provides an idea of the different concentrations from this gas, which could be present in the entire dispersion zone.

   g) Telephone complaint reception system

  The plant has a free telephone communication system, which enables residents who feel affected by the odours of the plant to contact a call centre and file their annoyance perception.

  The call is recorded and reported to the monitor of the continuous monitoring system to go the place where the call originated and perform their own monitoring, and if necessary, indicate which plant unit is responsible for the odour. This perception is based on the information from the meteorological station which is in the plant.

   h) Roundtables with communities

  Parallel to the different monitoring systems, a permanent relationship is developed with neighbourhood organizations surrounding the plant. In the meetings of these "roundtables" the outcome of the various monitoring systems is reported, particularly from telephone calls received from neighbours and when applicable, the activities performed by the plant to minimise possible odorant gas emissions.

   i) Odour maps of the surrounding area

  At the beginning of the operation, the plant prepared an odour 'map' in the area, which provided different emission sources of existing odour within a radius of 5 kilometres, allowing a more precise identification of which odours were attributable to the plants and which were from other odour sources. It should be noted that for the moment, the plant is surrounded by various agricultural activities.

   j) Dynamic olfactometry and dispersion models

  Several dynamic olfactometry campaigns have been implemented, which have slowly allowed the eventual identification of the odour units emitted by the different plant units at maximum, minimum and average values. With this information the AERMOD and CALPUFF models have been used to estimate odour dispersion.

Results and discussion

  Each monitoring system has produced their respective reports and has provided for the generation of different conclusions about the operations of the plant and the behaviour of each of its units.

  For example, Figure 1 presents the total number of calls from neighbours (tri-colour bar) during 2011 and 2012. Different colours show the intersection of information with the perception that develops with continuous monitoring. The relatively high presence of "no odour" may be due to the time lag between the neighbour call and monitor presence, depending on how far away the monitor was from the point in question.

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Figure 1. Calls received 2010-2012

  Upon analysis of the results of the continuous monitoring system for the years 2011 and 2012, we can obtain a view of the records made by people constantly going over the areas surrounding the plant, in this case, in a rural town close to the plant (Figure 2).

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Figure 2. Continuous monitoring results 2012 - 2012

On the other hand, if we analyse the results of odour panels, presented in Figure 3, it can be concluded that the information provided by the latter, even though it is more rigorous from a methodological point of view, it gives less information than continuous monitoring. Moreover, if only the information submitted by the panels were considered, it could be concluded that the plant did not generate odorous gases perceived by residents, during the second half of 2011 and during 2012.

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Figure 3. Result of panels in two areas near the plant

  In the period in which the methodology was developed, the method of distributing cards to be filled out by the residents (2004-2007), a high correlation was established between the time of record distribution and the information delivered by the existing weather station to the inside of the plant. In 80% of cases the registration of annoyance coincided with a wind direction from the plant to the place that filed the record.

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Figure 4. Time distribution of odour registration in cards filled out by neighbours. Average monthly values

  The application of the grid method (year 2007) made it possible to confirm, that of all the monitored points, there was a quadrant where an "odour time" actually occurred, using the standard VDI 3940 and GOAA as a reference.

  Figure 5 shows the results of the application of the method in a populated area surrounding the plant.

  These results were consistent with those reflected by the cards, by the phone call system and later by the continuous monitoring system.

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Figure 5: results of the application of the grid method in sector adjacent to the plant

  Due to space limitations it is not possible to present the results of each of the methods used, but based on experience, a summary of the advantages and disadvantages of each method is presented below.




  1. Panel with neighbours and officials

  2. Neighbour card

  3. Professional Panel


  Includes those affected in quantification of annoyance.

  Includes those affected and allows permanent relationship with the affected population.

  Enables standardised and validated procedure by the authority.


  Difficulties with permanence of panellists.

  When perception decreases, there is a tendency for interest to also decrease.

  Delivery of outdated information, in relation to plant operation problems.

Current situation







  4. Panel with grid

  5. Continuous monitoring

  6.Gases and dispersion model


  Allows detailed study in a specific site. It allows the determination of odour times.

  Allows "online" information. It facilitates the relationship with the operation and with neighbours.

  Allows good estimations of possible impacts, with low costs.


  Specific tool that does not contribute for a long period of time.

  Without regulatory support, it can be challenged by those affected.

  The communities perceive odours and not gases.

Current situation







  7. Telephone complaint reception system

  8. Roundtables with communities

  9. Odour maps of surrounding areas


  It allows a direct relationship and at the time of the perception of the odour by neighbours.

  Allows exchange of perception results. Generates a type of encounter.

  Allows the identification of odour sources and distribute possible responsibility.


  It generates the expectation of the immediate termination of the odour.


  Diffusion not adequate. Generates rivalries between different sources.

Current situation







  10. Olfactometry and dispersion model


  Allows adequate estimation of levels of perception of neighbouring communities. Odour dispersion, not gas, is modelled.


  Little baseline information (bibliography) to validate results. High costs

Current situation



  In summary, the experience in monitoring odours at the LaFarfana Plant allows us to conclude:

  1. The monitoring systems used are complementary, all provide information that as a whole allow a very clear picture of the influence of the plant on its surroundings.
  2. A system of continuous monitoring provides more information than the monthly odour panel system. It loses in methodological rigour, but wins in amount and timeliness of the information.
  3. There are differences between the modelling of odour units and modelling of DMS; but in general, both models express similar behaviour. Measuring DMS and modelling in AERMOD, versus measuring odour units and using the Calpuff model have very different costs. Working with odour units and Calpuff has higher costs.
  4. The experience of the La Farfana Plant has been that the monitoring plans have met several goals; this has included reporting to the authorities, reporting to the community and to those responsible for the operation of the plant. Continuous monitoring, the use of cards and laterthe telephone complaint reception system has allowed the development of a system that allows the estimation of which units or processes are responsible for the emissions.
  5. With the information provided to the operators, it has been possible to introduce changes in the operation and maintenance criteria which have allowed the substantial reduction of the impact of the plant in surrounding towns.
  6. The reliability of the monitoring systems used, as well as the incorporation of neighbours into some of them, has allowed the reduction of the degree of conflict in the relationship between the plant and their residential environment.
  7. In terms of odours, chemistry and analytical methods contribute through quantification, but this is not enough, we need to open up to methods that incorporate citizen perception.


  Funtowicz, S y Ravetz J. 1993. La ciencia posnormal ciencia con la gente. Centro Editor de América Latina.

  Guideline on odour in ambient air “Determinations and assessment of odour in ambient air in Germany with background information and interpretation to the GOAA, Mayo 1998.

  Informes trimestrales de seguimiento ambiental, planta de tratamiento de aguas servidas La Farfana.

  MetodologíaAlemana VDI 3940 “Determination of Odorant in Ambient Air by Field Inspections”, Febrero 2006.

  Resolución de Calificación Ambiental N° 130/2006


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Carlos Nietzsche Diaz Jimenez's Avatar

Carlos Nietzsche Diaz Jimenez

Carlos is the editor-chief of and has been in the odour world since 2001. Since then, Carlos has attended over 90 conferences in odour management, both national and international and authored a few papers on the subject. He has also organized a few international meetings and courses. Carlos owns a small company named Ambiente et Odora (AEO). He spends his free time with his wife and his twins, Laura and Daniel, and of course, writing on

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