COMPOSTING PLANT DESCRIPTION AND ODOR SOURCES
The Toulouse-Ginestous composting site (in France) treats up to 60 tons per day of 30% solids dehydrated WWTP sludge. The sludge is amended with 25 to 50%v bark and screening residues (non degraded bark, recovered from the mature compost). All composting operations are performed in a 10 000 m2 building.
This mixture is composted as 6 m wide windrows with a height of 3 m. Time-sequenced negative aeration is used over a 6 week residence time. The material is then transferred to another indoor platform where it undergoes an 8 week maturation period. The material is then screened to yield equal quantities of mature compost and screening residues.
Figure 1 Composting plan
ELECTRONIC NOSE ODOR MONITORING SYSTEM
The abatement equipment implemented at this facility was properly designed to provide effective reduction of anticipated odor emissions (combined scrubber/biofilters system). However, some processing upsets or operating conditions may trigger effectiveness reductions that can go unnoticed by the plant operator. Unfortunately, some processes can have low odor emissions most of the times and, under certain weather conditions or trigger events, become major nuisance sources.
In the summer of 2005, the plant acquired an electronic nose system in order to further their proactive approach towards odor management: in other words, to detect the potential of odor impacts before they actually affect the population.
Figure 2 View of the biofilter (a), weather station (b) and e-nose (c)
The system configuration was established to ensure monitoring of each key composting process and sources, not only those emitting to atmosphere: 1 e-nose monitors the co-products area, 1 e-nose analyses the air aspiration duct of the composting platform, 1 e-nose is located in the maturation area and 1 e-nose tracks the exhaust of the biofilter.
CONTINUOUS MONITORING SYSTEM RESULTS
The composting plant does not operate in a steady state mode. The composition of the air sent to the odor treatment system will vary continuously depending on the operations, the overall composting situation (number of windrows, stage, etc.) and with the opening of doors. The following figure presents a log of the odor concentrations for the maturation and composting areas, the co-products building stack and the outlet of the biofilter for the first week of June 2006.
Figure 3 – E-nose process and biofilter monitoring
The monitored values indicate significant odor fluctuations for maturation, fermentation and the biofilter. The odor spikes in the maturation area (+) are typical of the patterns induced by frequent door opening and closing during the day. This was expected since the e-nose tracking the maturation area is located near the door used for removal of the finished compost from the building. The information supports significant odor emissions through the opening of doors.
The composting area e-nose (×) is located in the negative aeration duct. The air is then sent to the abatement system, where the exhaust is tracked by another e-nose (○). The behavior of the composting e-nose and the abatement system e-nose present a strong correlation, with a sinusoidal pattern.
Around 7AM each morning, the plant receives up to 60 tons of sludge from the WWTP. This peak reception period creates an immediately measurable rise in odor concentration in the composting area, as evidenced by the daily rising slopes on the blue (×) curve above. The composting odor output (negative aeration system) is in effect the input stream to the abatement system. Small oscillations (of about 20% with respect to the mean value) of the composting output trigger large, lagging oscillations at the exhaust of the biofilters (of about 100% with respect to the mean value). The delay is of about 2-3 hours. This could be indicative of some adsorption by the biofilter media as the odor input to the biofilters rises, followed by a saturation and a delayed reduction of biofilter effectiveness. This type of information is extremely useful for optimized biofilter sizing for odor reduction and assessment of true odor abatement effectiveness.
The co-product odor (-) is relatively constant due to limited activity in the building.
These results illustrate that significant fluctuations exist and are not limited to the odor sources but are also present in the abatement systems, such as biofiltration. Continuous monitoring represents a valuable tool for odor management and will provide better knowledge of odor source behavior compared to discrete samples. Discrete odor sampling cannot ensure representative quantification of the possible range of emissions required for thorough odor impact assessment studies.
Animal productions units are a dynamic and rapidly growing sector of the Canadian economy. Over the last thirty years, they have evolved from a diversified to specialized and intensified production systems. However, rapid growth has led to manure mismanagement, which has resulted in serious odor nuisance and environmental odor problems. The industrialization of animal production as well as demographic changes in rural areas has resulted into difficult cohabitation problems.
Pollution and odours generated from livestock buildings, manure storages and land application activities are major causes of conflicts between producers and their neighbours. The environmental and social issues are presently the greatest challenge faced by Canada’s fast growing livestock industry. As a result, in some regions across Canada the industry cannot take advantage of the increasing international market opportunities.
In response to the need for agri-environmental information and to assess the impacts of animal production on the environment, Agriculture and Agri-Food Canada began work on the development of a set of new environmental indicators. Agri-Environmental Indicators (AEIs) are primarily intended to provide reliable, science-based information on the current state and changes in the conditions of the environment in agriculture, at a national or regional scale. One of the indicators will address the odour issue.
A scooping paper was prepared. It describes the approach for the development of an odour environmental indicator. This paper discuss the suitability and feasibility of three broad areas for the development of an Odour Environmental Indicator - Pressure: pressure indicators can provide information on major farming stresses to populations, that can influence farm management decisions - State: state indicators can provide information on the main outcomes from farm activities, expressed either as risk indicators (estimate of potential environmental and social impact) or state indicators (measure of actual presence and degree of impact), and which are responsive to change in farm management practices. - Response: response indicators provide information on the use by producer of various key management options which may influence the potential impact of agriculture on the social environment.
Odotech with its partners is now in the development process of elaborating and testing a Response odour AEI to address the serious odour issue associated with the livestock industries. The project is followed by an international comity of industry and research experts.
We will announce in this blog papers, results and public repports. Please continious to read us and contact us if you would like to get more info on this initiative.
A significant number of anaerobic digestion projects are underway or under study for the management of the organic fraction of household waste, on farm co-digestion and as an addition to WWTP plants not yet equipped with such systems.
The technology is appealing to many due to a number of interesting characteristics and the current general context. Some of the major drivers are:
- Enclosed operation;
- Production of biogas, an alternative fuel readily useable once purified;
- Reduction of the overall organic mass after processing;
- Funding available;
- Some success stories in Europe (integration of waste management and traditional fuel displacement).
However, these systems come at a significant price tag, of the order of $500 per installed annual ton (often more).
At such a cost, ensuring that the full operating capacity is maintained through its useful life is critical, otherwise the "installed tons" must be replaced by "actual tons". This can instantly cause the cost per ton to creep up. Odor issues are one of the most critical triggers for "loss of processing capacity" in the waste management industry and anaerobic digestion is no exception, even thought these systems were thought to be less odorus or even odorless by some.
Many examples of forced scale back by regulatory agencies due to odor issues are documented. For those who speak french: Ametyst Newscast 1 and Ametyst Newcast 2, a plant designed for 200 kT and running at 50% of its capacity at the time. Closer to us : AD Technologies WMW Article Sept. 2010 discusses two Ontario plants, one of them running at 11% of its 150 kTm capacity, and hoping for an increase to 50% by 2013.
Why and what's to be done?
No simple answer here... Yes, the core of the digestion process itself is less odourus than composting but everything around it is pretty much similar and DOES lead to odor emissions: care must be taken not to fall into a false sense of security (building too close to residential areas, inappropriate air management, not implementing a citizen comittee, etc.).
The odor risks must be considered in the project as early as possible (site selection, process selection, design, odor modeling, operational plans, odor abatement selection, odor monitoring). The concepts and goals of an odor management plan (OMP) are essential here.
Estimated around 2% of the project operating budget, odor planning and odor monitoring will provide a reduced risk of shutdown, reduced processing capacity and no chaotic upgrades at great costs.
For more details regarding the OMP, please see our previous posting on composting or contact us so one of our odor experts can provide additional details or discuss specifics of your project.
The odor pattern corresponds to the interpretation of an odor by the human brain, with all its associations.
As an example: At the age of 2, sitting in the family car at a gas station, you noticed a very strong, penetrating, aggressive odor (gasoline fumes!), but were unable to identify it. With repeated exposure, you began associating the odor of gasoline with the idea of cars, transportation, gasoline stations, road trips, maybe even vacations, etc.
Now, even many years later, as soon as you recognize a light puff of gasoline odor, these connotations come to your mind (consciouly or not). You have also associated a name to the odor (also often based on your exposure experiences and context).
These associations represent the odor pattern. The human brain retains tens of thousands of odor patterns. It is therefore evident that the odor images are specific to each individual, making the assessment of an odor by one person rather biased.
To address this bias, methodologies and modern Dynamic Dilution Olfactometers have been developed to quantify odors using a panel. Due to the multiple functionalities built in the tool, the Olfactometer can quantify odors using four different complementary techniques (a integrated odor quantification and evaluation not achieved by any other instrument):
- Odor concentration and odor threshold determination;
- Odor suprathreshold determination with comparison to a reference gas (i.e. n-butanol);
- Hedonic scale assessment to determine the degree of appreciation (pleasantness versus unpleasantness);
- Evaluation of the relative intensity of odors (the strength of the odor, different from the odor concentration).
When you’re faced with the selection of odor monitoring options at a waste water treatment plant, the decision making process can be confusing: Should I measure H2S? Should I consider using a field olfactometer? What can I learn from an odor study? What about real-time odor monitoring? What are the costs? What are the risks? And, if there are no consequences for emitting nuisance odors or you are not actually receiving complaints, why bother monitoring at all?
If you manage a facility that is responsible for nuisance odor emissions, you should monitor them, and do so in real-time. Here’s why: it is a proactive approach and your best defense against unfounded complaints (or complaints caused by others), it will convey your interest in ensuring your status as a good neighbor, and it will help you optimize your overall operating and capital costs.
Proactive approach and best defense
Real-time odor monitoring with OdoWatch is your best defense against unfounded or targetted complaints. Especially if you have competing odor sources from other neighbors, there is no other way to demonstrate where your responsibility ends and others’ begins. The issue of nuisance odors is an emotional one. Often, a foul odor is the first indicator of something wrong in the environment. People become alarmed and sometimes fearful that they are breathing in toxic gases. If you are tracking the odors emitted from sources at your facility, you are producing the documentation needed to demonstrate and discuss what you are and are not accountable for. You can also use this information in describing the results of your efforts to community members and other stakeholders, and if necessary you could use the information in court (having a traceability of odor emissions, meteorological data and off site odor levels associated with your sources). There is no other method that can provide better odor management information and protection from nuisance complaints.
Optimized odor complaint management
Before real-time odor monitoring, when an odor complaint was received at a waste water treatment plant, the tedious task of investigating began. Often, a staffer would visit the location where the call came from and attempted to diagnose it by smell, if the odor was still present. The time lag between complaint and investigation, and the potential it was due to the occurrence of a peak emission event in the process, did not always result in the ability to identify and solve the problem. But with OdoWatch, plant operators can immediately see if the odor at the location of the complaint could be linked to their operations, and if so, from which monitored process. When your neighbors know that you are investing in the best available technology in order to manage odors, you are on the road to building trust. When you respond to an odor complaint with a copy of the odor plume in the vicinity of their home, they know you are staying on top of the problem and are most likely to identify and address the issue. Your facility is seen as a better neighbor in the process. Also, any odor complaints you receive will be more reliable since the neighbors know you are using advanced systems to monitor and assess your off site impacts.
Finally, using odor monitoring to update predictions of actual odor impacts every few minutes enables you to control odors with efficiency. The OdoWatch system can help you spot, diagnose and correct odor problems as they happen or even before they can be called "problems" – not days or weeks later when the surge of complaints starts coming in. Users of OdoWatch have detected system leaks, trends showing loss of treatment efficiency over time, maintenance issues and chemical dosing errors that they were able to correct rapidly, reducing odors in their vicinity. Making subtle changes can often result in major savings over time. The monitoring can also lead to more efficient equipment design when faced with odor abatement installations and upgrades. The savings can be impressive!
While it’s true that no single method of measuring odors is perfect, real-time monitoring with OdoWatch is the best available technology today. As more people use the technology, their comments and needs are considered by the OdoWatch R&D team, and improvements are built in at each new software release. Each new version, including the upcoming OdoWatch 3.0, provides additional reasons for supporting the implementation of real-time odor monitoring.
Consistent with Kruger’s vision of being a leading supplier of value added water and wastewater treatment equipment and process solutions, we have integrated the Odowatch system in our offerings. Kruger (I. Kruger, Inc.) is a subsidiary of Veolia Water, one of the largest full service water and wastewater companies in the world.
Depending on the goals and the configuration of the source, odor sampling is typically carried out according to one of the following methods:
- Surface sampling through the use of a dynamic flux chamber. The approach allows for the determination of the surface odor flow rate from an unchanneled source such as a windrow, stockpile or lagoon.
- Point source sampling: Typically accompanied by a measurement of the flow rate. Used for sources with significant and confined flows and for efficiency assessments of abatment systems. In certain cases, ambiant sampling (inside a confined space or structure) can also performed.
A surface source is defined as a source of diffuse emissions over an area. Landfills, contaminated sites, compost and manure piles, waste water treatment lagoons, spreading fields are examples of such sources. Gas or odor sampling from surface sources is carried out using inert materials (sampling bags, piping, connections and all surfaces in contact with the gas).
The Odoflux™ flux chamber consists of a cylindrical enclosure with a spherical top. The flux chamber is supplied with a controlled flow of ultra pure air from a cylinder. The sample is taken from the chamber at a controlled flow rate to fill the inert sampling bag. The method allows for the calculation of a flux rate in g/m2-s or in o.u./m2-s.
Point source sampling
A stack, a conduit, a room or a static sample are all candidates for point source sampling. Depending on the characteristics of the source, a protocol may imply sampling and speed measurements according to established guidelines (at various points and at a specified distance of any disturbance).
Additionnally, specific issues such as high humidity, particulate levels, stack temperature or harsh climatic conditions (winter) may require specific protocols to be developped (heated sampling, dynamic dilutions, etc.) to avoid condensation in the sampling train and the samples themselves.
Of course, for both approaches, sampling conditions are to be thoroughly documented (ambient conditions, source conditions, processing data/rates, etc.) for later analysis.
Filled samplings bags are protected from sunlight and heat and are rapidly shipped to the lab where the qualified jury awaits to conduct the analyses in the shortest possible timeframe. In addition to odor concentration measurements, our laboratories can carry out odor intensity measurements, and investigations of odor synergies and hedonic tone.
In a composting site, odors are a given, omnipresent and to be managed :
Incoming organic waste is already odorous;
At the pre-treatment steps (reception, mechanical separation, grinding and other prep processes), sometimes discontinuous but significant releases;
Nearly continuous releases in handling and treatment systems (variable based on technology, design and throughput but never truly “eliminated”);
Also present in the treatment and use of end products and by-products (wastewater, solids, “mature” composts)
Typical odourus chemicals released on a composting site
Sulphides (H2S, DMS, DMDS, CS2, Methanethiol)
Volatile Fatty Acids (Acetic Acid, Butyric Acid, Propionic Acid)
Nitrogen Compounds (Ammonia, Trimethylamine)
+ Many Others depending on Organic waste managed and the process used!
Presence of multiple odor emission sources
There are a number of significant odor sources associated with a composting site and the auxiliary activities:
Transport to site (route to site, waiting queue to reception);
Reception of material;
Pre-treatment of material (bag opening, mechanical separation, mixing/homogenization);
Treatment process releases (composting, digestion, drying,
Building envelope releases (fugitive odor emissions);
Waste material and by-products management:
Waste water ponds;
Screening and blending;
Finished products management.
Typical odor abatement/odor control methods
- Minimize odor emissions (improved processing, recipes)
- Enclose, collect and treat (biofilters and scrubbers)
- Improve dispersion (tall stacks, high vertical velocities)
- Planned operations (avoiding unfavourable met conditions for odor causing activities)
- Additives (inoculants)
- Odor Neutralizers
- Aeration optimization (composting and leachate ponds)
In the « old days » : these odor abatement opions where implemented during a crisis or when forced by new permit.
Now: proactive operators manage odours from the site’s conception, tools and studies are used to optimize the approaches (cost vs required abatement).
Typical odor levels
The following table presents a few typical odor levels (although they can vary widely depending on the specifics of a site, process and materials).
Varies, can be >10 000 O.U./m3
(or biological drying)
Varies, 1000 to >10000 O.U./m3
Varies, but typically 100 to 800 O.U./m3
|Varies, can be >100 000 O.U./m3
NOTE: Odotech has accumulated a large database of odor emissions rates and odor concentrations, please contact us should this be of interest to you.
Odor sampling of a composting windrow
Imagine extracting 10 000 cfm (about 5 m3/s) from the reception hall and exhausting it to atmosphere, leads to 50 000 O.U./s of odor emissions! Same hall but opening of the door during cold weather (hot interior): could easily represent 100 000 O.U./s! Such odor flow rates could be perceived more than a kilometer from the site during certain weather conditions.
The potential off site odor impact of a site is related to many on site factors, more importantly:
Odor concentration and resulting emissions rate (whether forced or fugitive);
The characteristics of the emission release (through a tall stack with high vertical velocity or as ground level fugitives);
Frequency and variability of releases;
Abatement systems in place.
The OMP and its objectives
The implementation of an odor management plan (OMP) is a must for composting sites, just like other risks, odor should be managed not feared or put aside (with fingers crossed). The general objectives of a good OMP are:
- Establish a trust based relationship with stakeholders (elected officials, neighbours, regulatory agencies)
- Rational evaluation of the project and site based on existing and anticipated constraints
- Management of odor events in real time and based on a proactive approach (prevention of off-site odor impacts)
- Continuous improvement and associated off-site odor impact reduction
- Minimization of odor management costs (capital and operational)
- Optimization of odor abatement equipment and processes
- Revenue maximization
- Risk reduction
- Odor traceability