At wastewater treatment plants (WWTP), municipal or industrial, the first intuitive step for odor control is to capture emissions from the most onsite smelly areas. And your nose can tell you which ones they are.
Well, can you really rely on your nose?
Covering primaries, secondaries, DAF or aeration basins would represent major investments: first covers, then gas collection, plus piping, and odor treatment. Millions $ are there: $3M to $8M on covers and engineering + $2M to $5M for scrubbers and piping.
In your odor master planning, it is possible to phase your investment and address first only what will provide you the best bang for the buck.
The question is how far should you go on odor control $ before reaching acceptable off-site odor impact?
It is almost impossible to know from onsite sniffing how far on odor is travelling from diffuse sources. And what about the thousands other different weather conditions that will occur over the seasons by the combination of wind speed, wind direction, temperature, atmospheric pressure, humidity and solar radiation? In your odor master planning, before spending big $ on covers and odor control, why not monitor first in your odor study$.
How much should each source be knocked down? The question is how far should you go on odor control $ before reaching acceptable off-site odor impact?
Classical static odor study (Odor sampling, odor panel and odor distribution modeling) is good but limited to a few entry points. It does not capture all the complexities of the fluctuations induced by variations of the influent, operations and meteorological conditions.
Monitoring odors first with electronic noses at each candidate source for odor control could provide very valuable information:
- Variations, fluctuations, trends of odor emissions
- Peaks, lows and average odor loads
- How far the odors are traveling from each source
- Which sources contribute the most to the off-site odors or odor complaints
- How much should each source be controlled.
If you use a traditional odor study, your engineers may work with as few as 3 snapshot samples to design your odor control master plan that will cost millions... or benefit from thousands of objective data points by using continious odor measurement devices. (It is like seeing 3 pictures to understand the scenario of a story or watching the full movie!)
Your savings could potentially be massive. Think of the cost of under sizing, over sizing or inappropriate design.
|Several industrial and municipal plants are being regulated in order to avoid nuisance odors in the areas surrounding: Wastewater plants, landfills, composting facilities, methanization plants (waste anaerobic digestion), rendering plants, solvent plants, etc.
The question is: what performance criteria make sense?
Historically, odor control performance has been required in terms of chemical compounds not to be exceeded at the stack or in terms of odorous chemical abatement efficiencies. The most frequent are H2S in the wastewater industry and biogas plants and NH3 for composting plants *.
There are two fundamental problems in this approach:
I. People perceive chemicals in terms of odors, not in terms of ppb of H2S, PPM of ammonia or mg/m3 of VOC. It was seen in previous blog posts that
a) Chemical concentrations are poor tracers to predict odor concentrations
b) Chemical compounds are not additive in term of odor perception
c) The vast majority of industrial and municipal odor emissions are composed of a cocktail of numerous odorant chemicals. Removing some specific odorant chemicals does not mean that the odor is gone;
d) The perception thresholds are not yet well established for the vast majority of chemical compounds.
Furthermore, some chemical treatment processes will generate odors themselves with news chemical species (odor neutralizers, biofilters, biotowers, scrubbers and combustion) – zero odor barely exist.
II. The odor problems are in the neighborhood, not at the stack. This biases the selection of odor abatement technologies and their design toward potentially oversized equipment underperforming or un-optimized.
- Specify odor control requirements in terms of odor units per cubic meter (u.o./m3) – equivalent to dilutions to threshold (D/T);
- Specify odor level criteria at the first receptors. This is where the game is. The people needs to be protected, nobody lives in a stack;
- Specify percentiles of exposure. We live in an industrialized world. Is zero odor a realistic objective? Urban and rural odor backgrounds are already at around 5 o.u./m3. The limit for noise is not zero decibels for a plant. Odor nuisances are generated over time from recurrent high odor expositions. Weather conditions have a huge impact on odor dispersion and dictate how far odors travel. Some weather conditions will be particularly unfavourable for odor dispersion. Would it be possible to live with occasional limited odors? This is how it works for noise!
Odor levels not to be exceeded 98% of the time would be an interesting balance between public quality-of-life protection and right to do business.
The big question is how many odor units?
We think that 5 o.u./m3 – as with international regulations – would make sense knowing that ambient background are generally around this value.
The technology is out there
Nowadays, it is pretty easy and accessible to assess the odor control performance based upon odor concentration criteria at the 98th percentile for sensitive receptors:
- Source sampling, olfactometry, and dispersion modeling with a regulatory approved model with local weather data, or
- Odor Continuous Emission Monitoring with electronic noses, local weather data and regulatory approved dispersion model (AERMOD)
This approach would create a fair balance between the quality of life and, the right to operate for plants with affordable odor abatement solutions that target the real problem.
We will soon post an example of an odor regulation based on this approach. We appreciate your continued attention to this issue as we post more information here.
* in California the composting plants are regulated for VOC emissions because they are classified as photochemical reactives with potential to form tropospheric ozone. But there is now serious evidences from works done at UC Davis (CA), University of San Diego and CalRecycle that the composting plants are wrongfully targeted by ozone regulations because the VOC's emitted have very low photochemical reactivity.
Methane in municipal solid waste landfills (MSWL) is produced through anaerobic microbial degradation of organic matter. When the conditions of methanisation are stable in wastes, landfill gas is mainly made up of methane (CH4) and carbon dioxide (CO2) in about equal proportions. The stable production of methane, a source of usable energy, can last several years. However, biogas contains others gases in trace amounts, primarily sulfur compounds and volatile organic compounds (VOCs).
The methane and carbon dioxide are greenhouse gases like some of the trace gases (for example, chlorinated and fluorinated organic compounds). Landfill gas has other environmental and health risks: in addition to the potential of explosion, harmful effects exist because of the presence of hydrogen sulfide (H2S) and of potentially toxic VOCs (benzene, vinyl chloride, dichloromethane, chloroform, toluene, dichlorobenzene, etc) as well as compounds responsible for odors (VOCs, sulfur compounds, etc).
Quantification of landfill gas emission is thus most important but could be time and money intensive considering the extent of surfaces to repeatedly cover. Since heterogeneity must be expected over these large scale areas, a single sampling point method can not be used.
The Instantaneous Surface Monitoring (ISM) (Rule 1150.1, South Coast Air Quality Management District, California) is an interesting method to locate hot spots of landfill gas emissions and determine a cell emission heterogeneity over the full surface. However, this method will not provide the CH4, odorants, odors, toxics and VOC emissions as a quantitative value in emission per unit of surface over time.
We would like to introduce here a method that we have developed with extensive R&D efforts and have been using over a decade on numerous landfills in North America and Europe.
The basis is to perform a overall profile of the methane surface concentrations and to establish the correlation between methane surface concentration and the methane surface flux. The Total Volatile Organic Compound Methane Equivalent (TVOCME) ground concentration cartography is performed according to the recommendations of the instantaneous surface monitoring (ISM) method described in the Californian rule 1150.1. The methane surface flux is measured with a dynamic flux chamber operated according to the recommendations of the US EPA (Klenbusch, 1986).
The analysis of the flux chamber gas can cover several parameters depending on the purpose of the emission assessment : potential toxicity, respect of the standards, potential olfactive nuisance, limonene, careens, camphene, pinene, phellandrene, sulfur compounds, mercaptans, sulfides and VOCs (ethylbenzene, styrene, toluene, benzene, etc).
Several analytical methods are adapted to MSWL emissions characterisation and they are powerful and recognized techniques:
Portable FID, GC-FID or GC-TCD for the methane and the carbon dioxide,
GC-MS with cryogenic trap for the VOCs and the other organics like terpenes (method TO-14A of the US EPA),
GC-PFPD for the sulfur compounds
Olfactometry with dynamic dilution (methods ASTM E679, EN 13725, probit) for the odours.
The following graph presents an example of Total Volatile Organic Compound Methane Equivalent (TVOCME) ground concentration distribution. The red dots are locations selected for "high quality analysis" with flux chamber sampling.
Based on a limited number of flux chamber samplings and measurements (chemical analysis or dynamic dilution olfactometry), the mass flow rate or odor flow-rate of each cell is estimated using a co-krigging method.
The Y axis is surface flux rate (g/m2/s, ou/m2/s)
- Reduces the number of sampling points
- Provides the distribution of surface emissions for optimization of gas collection system
- Evaluates the chemicals or odor flow rates of a complete cell for air quality assessments, odor studies or green house gas emission balance.
ASTM (1997). E679-04- Standard Practice for Determination of Odor and Taste Thresholds By a Forced-Choice Ascending Concentration Series Method of Limits. American Society for Testing and Materials.
CEN European Standard EN 13725 (2003). Air quality - Determination of odour concentration by dynamic olfactometry. Brusssels, CEN.
Klenblusch, M. R. (1986). Measurement of Gaseous Emission Rates from Land Surfaces Using an Emission Isolation Flux Chamber. Las Vegas, NV, U.S. Environmental Protection Agency.
The New York Water Environment Association, Inc. (NYWEA) was founded in 1929, by professionals in the field of water quality as a non-profit, educational organization. Association members helped lead the way toward existing state and national clean water programs. Today the Association has over 2,500 members representing diverse backgrounds and specialties, but all are concerned and involved with protecting and enhancing our precious water resources.
The NYWEA is hosting its 83rd Annual Meeting from February 7th through 9th at the New York City Marriott Marquis Hotel.
Kruger, Inc., a division of Veolia Water, will be exhibiting many of their technologies for water and wastewater plants at Booth 64. One of the technologies featured is Odotech’s OdoWatch®, the world’s first system that measures and monitors odor in real-time. See it up close and schedule a demonstration of how you can use OdoWatch to manage odors and save money at your wastewater treatment facility.
OdoWatch employs a network of electronic noses that perceive odors like the human nose and alerts you before the odors travel offsite. Come by the booth and see the new dispersion modeling application for complex terrains.