determination of odor sources for control

PART VII. ODOR CONTROL TECHNOLOGY

DETERMINATION OF ODOR SOURCES FOR CONTROL

Frederick Sullivan and Gregory Leonardos

Arthur D. Little, Inc. Cambridge, Massachusetts 02140

INTRODUCTION

The successful solution of odor pollution problems first requires an assessment of the nature and extent of the problems. A plant or facility that emits odor from a single source (such as ii stack or vent) requires less effort than a plant with a variety of odor sources that may number in the hundreds. In the latter case, there is a need to assess the problem in such terms as to achieve maximum reduction in odor at a minimal control cost. Quantitative and accurate measurements of the various emission sources and their contribution to the odor in the ambient air must be determined in order to identify and rank the various sources that should receive priority for control. Accurate measurements of odor strength relative to concentration are also useful for defining the degree of control necessary for the single-source situation.

Attempts to relate source odor measurements with ambient odors by the use of diffusion equations have met with varying degrees of success.1.2 Wohlers,l util- izing an evacuated bulb technique for sampling stack gases from a petroleum coking plant, a kralt paper mill, an anion-garlic dehydrating plant, and a roto- gravure printing plant, found that odor measurements at the stacks did not agree in all cases with the calculated dilutions at the distances in the field where the odors were noted. Hogstrom2 demonstrated that a fluctuating plume dispersion model can be used to give realistic estimates of odor frequencies around a point source when the odor thresholds of the chimney gases (sulphate pulp factory) are determined by sampling and sensory methods described by Lindvall.3

Our experience in sampling and evaluating odors has indicated that existing sampling techniques such as ASTM syringe method have seriously underestimated the magnitude of odors emitted by a factor in the range of 2OO-2O,OOO.4

We believe that inadequate sampling and evaluation techniques are the major reasons for reported “failures” of dispersion estimates in predicting ambient odors.

In our technique, we use trained odor chemists to carry out odor surveys of the surrounding areas to define the odor types and intensities perceived off-site and to conduct in-plant surveys to identify all significant odor sources.

T o supplement this, we have developed a source-sampling detailed laboratory odor-evaluation technique to allow comparison of the various odor sources and to make use of predictions based on dispersion equations. We have observed reasonably good correlation between predicted odor intensities from the source analyses determined in the laboratory and those observed by our analysts in the field.

OFF-SITE SURVEY

Odor surveys, in surrounding locales and implant, are an essential first step in determining those sources which must be controlled. A major goal of the off-site

339

340 Annals New York Academy of Sciences

survey is to ascertain the various types and intensities of odors in the vicinity of the plant and to note their frequencies and durations.

In heavily industrialized areas where many plants may be emitting odorous pollutants, an important function of the survey is to trace these pollutants to their respective sources. The problem becomes more difficult when similar types of odors are emitted by different plants in the same area. In a recent assignment involving chlorine emissions, we found four different plants within a one-mile radius emitting chlorine or chlorine-related odors. I t was necessary to observe wind directions, velocity, and odor character carefully in order to identify characteristics from the different plants.

Our surveys are carried out by trained odor chemists. For a representative assessment of an odor situation, observations are performed under a variety of climatic conditions, at different times of the day, and over a reasonable period of time.

The approach used to detect and evaluate odors perceived during a survey is based on the Flavor Profile Methodology.5 This is an objective approach whereby trained personnel describe odor in terms of character notes and assign a total intensity of aroma rating (TIA).

The following seven-point scale is used to denote odor intensity: ) ( = threshold (recognition) I/e = very slight

1 = slight

2 = moderate

3 = strong.

1% = slight-moderate

2% = moderate-strong

Our odor pollution experts have learned to use the names of specific chemicals wherever possible as descriptors of the odors perceived. For example, the odors emanating from a tannery are variable, depending on the operations. Often the principle odor sources are the acid and alkaline water wastes. The animal-related odors associated with alkaline waste waters can be described as caprylic or caproic acid, ammonia, and soap, whereas the acid wastes may be relatable to hydrogen sulfide, sulfite and spoiled protein. This descriptive capability of the trained odor analyst is useful in relating the various odors perceived off-site to their respective sources within the plant.

Prior to the off-site studies, topographic maps and local or city maps are obtained to assist the observers in familiarizing themselves with the terrain and area to be studied. During the surveys, the odor analysts usually drive slowly along a route that has been predetermined, taking into account the prevailing wind conditions. The car windows are open and the analysts are constantly on the alert for odor. When odor is perceived, the car is stopped and observers proceed by foot to determine the intensity, type, and width of the odor path. Wind directions and velocities are measured periodically, since this information is helpful in tracing observed odors to their source. In some instances, surveys have been conducted from a boat or on foot. From results of these surveys, odor maps can be prepared showing wind direction and velocity and the time, location, types, and intensities of odors. FIGURES 1 and 2 are odor maps depicting the odor situation observed at a phenolic resin plant and a coffee-processing plant.

Sullivan & Leonardos: Determination of Sources 34 1

FIGURE 1. Odor map of a phenolic resin plant.

IN-PLANT SURVEY

In addition to evaluating odors around the plant property, the odor analysts also perform observations within the plant. A tour of the plant is made to famil- iarize the analysts with the different processes and their associated odors. This is necessary if environmental odors are to be related to processes or practices oc-

~~~ ~ ~

FIGURE 2. Odor map of a coffee-processing plant.


cumng within the plant. In a tannery, for example, they would examine all areas and processes that are real and potential odor contributors. These would include hide storage and the washing, dehairing, bating, tanning, and retanning operations as well as dump sites, waste liquors, settling basins, and lagoons, and other waste treatment facilities on the plant premises. Odor numbers of the liquid wastes can be developed by serial dilutions to threshold and their potential for contaminating the air can be estimated by taking into account the surface area.

QUANTITATIVE ESTIMATES OF ODOROUS EMISSIONS

Off-site surveys and in-plant reviews are useful for identifying on a qualitative and preliminary basis those sources which appear to be major contributors of odor to the environment. T o determine the relative significance of these sources as contributors of odor in the ambient air, a sampling and evaluation program is required. These sources are selected on the basis of our evaluation of the odor intensity at the source, a consideration of the source air flow, and the extent to which the odor type was consistent with odors observed off-site.

Odor-Sampling Procedure

We use an odor-sampling procedure that was developed in the course of our work on diesel exhaust odor, sponsored by the Environmental Protection Agency (EPA) and the Coordinating Research Council (CRC).e, 7 The procedure in- volves passing a known volume (usually 500 liters) of the odorous air from the source through sorbent traps containing Chromsorb@ 102 (FIGURE 3). The sampling train, which is electrically heated to ensure that odors are not condensed onto the sampling train lines and components, includes a heated filter prior to the sorbent trap, a metal bellows pump, a dry gas meter, and a rate meter for measur- ing volumetric flows. A schematic representation of the sampling train is depicted in FIGURE 4. For continuous sources, the collections are made over a one-hour period. For sporadic emissions, the sampling system can be operated selectively to reflect the operation of the source.

FIGURE 3. Chromsorba trap.

Sullivan & Leonardos: Determination of Sources 343

4- Probe

4- Heated Filter

4- Metal Bellows Pump

4- Odor Sorbent Trap

4- Dry Gas Meter FIGURE 4. Exhaust sampling train. All lines are r electrically heated. Sorbent trap is approximate1 1 X 6 inches, containing 10 g of washed Chromsorb 102.

4- Rate Meter

At our laboratories, pentane is used to elute the trapped odorous components from the sorbent material. The pentane solution containing the odor components is adjusted to a known volume of trapped odorant per p!2 with nonane just prior to use in the odor test room.

The sampling procedure has been applied at a complex coffee-processing facility and has successfully collected different odor types such as the green bean, spent grounds, burnt roaster, and caramelized aromatics associated with soluble coffee. I n addition, the procedure has been applied to collect emissions at jet engine test stands. It is recognized that there may be some situations in which this particular system may not be applicable and in which other adsorbents or sampling techniques may be necessary.

Odor Evaluation Procedure

A panel of four trained analysts is used to determine the odor character and intensity of the trapped components over a range of concentrations expressed as liters exhaust per cubic meter of air (!? exh/m3 air) or as dilutions (liters exhaust: liters of test room air). For a single source sample, as few as five concentrations or as many as 12 or more concentrations may be presented. Presentations made to the analysts are progressively diluted by a factor of 2. With the coffee-processing plant samples, dilutions ranged from 1:625 to as low as 1: 1,280,000.

111 Static Mixer

Sample Introduction

S m g e Pump1 Carbon lDual Channel

Exhaust Fan

FIGURE 5. Dynamic odor test chamber.


A schematic of the odor test facility is shown in FIGURE 5. The dynamic chamber is constructed of aluminum and glass (approximately 6 X 4 X 6 feet) and com- fortably seats a single analyst. Air for dilution of the trapped exhaust is passed through an activated carbon bed before flowing through the chamber at a rate of 100 liters/second. A remotely controlled dual channel syringe pump introduces the test sample solution into a heated side-stream of activated carbon treated air. The sample is vaporized, then mixed with dilution air with use of a static mixer to ensure presentation of a homogeneous sample dilution. T h e diluted sample flows by the analyst in a laminar flow. A communication system is pro- vided for the analyst to report odor characteristics and intensity to the facility operator.

In making the observations, the analyst is not informed regarding the time or order in which the sample concentrations (dilutions) are to be presented, nor is he given information about the nature of the sample. Within a single sitting of one-half hour duration, he may be asked to make observations on two separate samples over five concentration points for each sample, or to evaluate a single sample over as many as nine concentration points. In this latter case, the solution to be injected is prediluted by a factor of 16, with both syringes utilized.

The analyst is instructed to report his observations of the odor character and intensity whenever odor is perceived. A typical evaluation procedure is as fol- lows.

The analyst enters the chamber and becomes adapted to the carbon-treated low-odor background air. A predetermined amount of trapped odorant is then vaporized into the airstream for 15 seconds. This is done remotely by the facility operator, in an adjoining room. When odors are perceived, their character and intensi,ties are reported verbally over the communication system to the facility operator. Following each odorant injection, the analyst is exposed to the clean background air for an interval of approximately two minutes. The entire procedure is repeated the required number of times to establish the dose-response characteristics of the sample for each analyst. Typically, at the lower intensity levels, three presentations of a single concentration or dilution are made to each of four analysts. Thus, for a single dilution, there are 12 presentations to the panel.

Data Treatment

For each odor concentration or sample dilution presented, the odor intensities (TIA’s) reported by each of the four panelists are averaged to obtain a panel average TIA. In addition, a probability of detection (PD) factor for each dilution presented to the panelists is calculated by taking into consideration the number of odor recognitions as a function of the total number of presentations.

A PD factor of one indicates that the panelists detected odor on every presentation for that dilution. A PD factor of 0.5 indicates that a recognizable odor was detected on only six of the twelve presentations.

We have defined the recognition threshold concentration as the lowest concentration (or highest dilution) at which the entire panel could recognize the sample odor on one-half of the Presentations (PD factor of 0.5). The data thus gives information regarding the recognition “threshold” dilution of the source as well as the variation in odor intensity as a function of concentration or dilution. The threshold dilution is useful for determining the amount of odor emitted by each of the various sources. The intensity-concentration (dose-response) char-


TABLE 1 ODOR DATA O N SPRAY DRIER SAMPLED OVER A THREE-MONTH PERIOD

Dilution February March May Avg. Avg. Avg. TIA P.D. TIA P.D. TIA P.D.

1:1250 2.6 1 1:2500 2.4 1 1:5000 2.3 1 1:10000 1.6 1 1:20000 1.2 1 1:40000 1.0 1 1:80000 0.7 0.7

1:320000 0.1 0.2 1:160000 0.6 0.8+

Threshold Dilution 1 :240,000

Source Odor Strength 240,000

2.0 1 2.1 1 1.4 1 1.2 1 0.8 0.9 0.6 0.8 0.25 0.1 0.1 0.3

::it

1 :120.000

120,000

2.0 1 1.8 1 1.5 1 0.9 1 0.4 0.8

8 3 - 0.3 0.1 0.1 0.3 0.1 0.3

1 :60,000

60.000

"Arrow indicates threshold dilution (defined as P.D. 0.5).

acteristics may be used with results from dispersion equations for predicting odor intensities that may arise from each source.

TABLE 1 illustrates the data obtained from the sampling of a soluble-coffee spray drier during a three-month period. The total intensity of aroma (TIA) is the average value for the panel at each dilution, and the PD factor indicates the degree to which a positive response was given by the panelists to the presented dilution.

The threshold dilution for the February sampling occurred between 1: 160,000 and 1:320,000, or interpolating this, at a 1:240,000 dilution. For the other two samples, dilutions of 1: 120,000 and 1 :60,000, respectively, were required. As the table indicates, the average panel total intensity of aroma (TIA) at the threshold dilution as defined is in the threshold to % (very slight) intensity range. The average panel TIA value at a PD factor of one (where a positive response is obtained on all presentations) occurs at the slight (1) intensity level. The table also gives an indication of the degree of variability in the data for a single source sampled over a period of time. The threshold dilution for this odor source over this time period is 1:120,000 with a * twofold variation. Our replicate samples were within this variation.

Source Odor Strength and Odor Emission Rate (Q)

The source odor strength is the reciprocal of the recognition threshold dilution and can be expressed in dimensionless units as suggested by Hogstrom,2 or may be conceptualized in terms of odor mass units/cubic meter. By multiplying the source odor strength by the volumetric flow rate expressed as cubic meters/ second, we can determine the source odor emission rate (Q), which represents the amount of odorous materials emitted/unit time (odor mass units/second).

To use the dose-response data with dispersion estimates, x is designated as the number of dilutions necessary to reduce odor to the threshold level. The threshold dilution is assigned a x value of one and all the other dilutions examined are fixed as multiples or submultiples by two. TIA-x values for three different odor sources a t a coffee plant are listed in TABLE 2. These may be considered as ambient


TABLE 2 TIA-x VALUE RELATIONSHIP

(3 ODOR SOURCES IN COCFEE PLANT)

x-Value

0.75 1.5 3 6

12 24 48 96

TIA Spray Drier

Sub-threshold Threshold

112 1

1 112 1 112-2

2 2 1/2

x-Value

’ 0.5 1 1.0

32 64

128 256

TIA Spent Grounds

Sub-threshold Threshold Threshold

112-1 1-1 112 1 112 1 11s2 1 L

2 112 2 112-3

TIA Green Bean

Sub-threshold Threshold

1 12 1 12 1

1 112 11/2 11t2.2 1 112-2

2

odor concentrations showing the number of dilutions required to reach threshold and also suprathreshold odor intensities (TIA’s). In the case where the threshold dilution occurred between two of the dilutions presented, the x value is in multiples and submultiples by a twofold factor of 1.5. In cases where the threshold dilution coincides with a presented dilution, the x value is a multiple or sub- multiple by a twofold factor of 1.0; x values are obtained from the dispersion estimate and represent ambient odor concentration terms.

The extent to which these various sources may contribute ambient ground-level odors is a function of the effective emission point above ground level and a consideration of how intensity for a particular odor type changes as a function of concentration (or dilution). Also operative in the dispersion of odors in the atmosphere is the wind direction and velocity and meteorological stability con- siderations, as well as a consideration of the terrain and building effects.

The calculated odor emission rate (Q) data for each source can be utilized in

TABLE 3 ESTIMATES OF MAXIMUM X VALUE AT GROUND-LEVEL AS A

FUNCTION OF ODOR EMISSION RATE AND EFFECTIVE STACK HEIGHT

H (effective stack height) 10 Meter 20 MEW 30 Meter 50 Meter 70 Meter 100 Meter Maximum XuIQValue 1.3 x l o 3 3 x lod 1.3 x l o 4 4.4 x lo5 1.9 x 10% 8 x 10% Distance from Source. 0.6 KM 0.18 KM 0.35 KM 1 KM 1.5 KM 3 KM

Q lodor emission rate) +Predicted Maximum x Value b 10’ ,003 ,0007 0.0003 0.0001 O.OOOO4 102 .03 0.007 0.003 0.001 0.0004 lo3 .3 0.07 .03 0.01 0.004 0.002 NoOdor ld Id 108

0.02 t 3 I 0.7 0.3 0.1 .04

” Threshold Odor 30 7 3 1 .4 300 70 30 10 4 2

2o 4 Id 3,000 700 300 100 40 108 30,000 7.000 3,000 1.000 400 Odor Capacity of Atmosphere to Oisperm Odor -lo4 4 -106 -I@ -lo5 -108

Conditions D Stability Wintl Velocity 4.4 m / w (10 m.p.h.1

‘For maximum Xu/value.


atmospheric diffusion equations to determine the extent to which odor could be perceived in the surrounding environment. We use the diffusion equation suggested by Pasquill and modified by Gifford as given in the Environmental Health Series booklet by Bruce D. Turner entitled Workbook of Atmospheric Dispersion Estimates (revised 1970).

In using dispersion estimates, information on the effective stack height (H) of each source is required, since dispersion is principally influenced by this factor.

Solution to the Pasquill equation is facilitated by graphs for various atmospheric conditions on which are plotted curves for various heights of emissions relating distance from the emission point to a parameter:

x u / Q Where Q = odor emission rate

(odorous mass units/sec) u = wind velocity (mlsec) x = odor concentration

(odorous mass units/m3).

Since Q and u are known, the xu /Q value can be determined from the graphs in the EPA workbook, one can solve for x, which is the ambient odor concentration. TABLE 3, which has been derived from the workbook for D stability condi: tions with a wind velocity of 10 mph, directly gives the maximum x value at ground level obtainable for a given odor emission rate (Q) as a function of effective stack height. For each effective stack height (H) we have included in the table the distance from the source at which the maximum ambient ground concentration will occur. As an example, for a 10-meter effective stack height, the maximum (odor intensity) will occur 0.16 km from the source, whereas for a 30- meter stack the maximum odor intensity will occur 0.6 km from the source.

TABLE 4 summarizes the use of the data with dispersion estimates for selected sources krom a cotfee processing plant. ‘l’he source odor strength is determined in the test-room procedure. As mentioned earlier, multiplying this by the flow rate gives the odor emission rate (Q). The stack heights of the five sources are indicated in column (H). The xmaX value is derived from TABLE 3. The predicted odor intensity is then derived from the dose-response characteristic (or the TIA-x value) in TABLE 2. As TABLE 4 indicates, the spent grounds exhaust has the highest predicted maximum odor intensity (moderate-to-strong range), or 2%. The spray drier is predicted to be in the moderate (2) range, and Agglomerator B is expected to contribute more odor intensity at ground level than Agglomerator A.

TABLE 4 PREDICTED MAXIMUM AMBIENT ODOR INTENSITY

(COFFEE-PLANT ODOR SOURCES)

Source Odor Vol Flow Q H Predicted Source Strength (m3/sec) Odor Emission Source \ Max. Maximum

Rate Stack H t TIA

Spray Drier 1 lo5 14 1 . 4 ~ lo6 30m 42 2 Agglornerater A 1 x l o 4 12.8 1 . 3 ~ lo5 3 0 m 4 112 Agglomerater B 7 x lo4 5.8 4x105 20m 28 2

Exhaust 3 . 6 ~ lo5 11.3 4x lo6 2 0 m 280 2 I f 2 Green Bean Drier 4 x lo4 18.6 7.5~ lo5 2 0 m 53 1 112

Spent Grounds


TABLE 5 PREDICTED VS. OBSERVED ODOR INTENSITIES

Predicted Actual

Odor Sourcea Odor Type Intenrity Dinance (kml Intenrity Dirtancs (km)

o.6 i 2.5 0.4.1.0

Spray Drier Soluble Coffm 2.0

Agglomwator B Soluble Coffee 2.0 (Caramelized)

(Caramelized)

(Caramelized) 1:: \ Agglomaator A Soluble Coffea 0.5

Spent Groundr Scrubber Stela Coffee Musty 2.6 0.35 2.0 0.25 Green Been Drier Sour Green Beans 1.5 0.35 (Not Detected)

The green-bean drier is predicted to have a slight-to-moderate (l?L2) intensity. TABLE 5 compares predicted odor intensities with those actually observed dur-

ing an off-site survey of the coffee plant carried out under comparable weather conditions. The agreement between the sampling program and the off-site survey is reasonably good. In this situation, i t is evident that the spray drier and one of the agglomerators require control, since each source, singly, has the capability to contribute odor at a moderate (2) intensity. The spent-grounds exhaust system, which contributes the highest odor intensity, must also be controlled. Odors from the green-bean driers were not detected in the surveys; however, it is possible that these odors were masked by th other coffee-related odors. The extent to which the sources emitting the green-bean odor types should be controlled is clearly de- pendent on the extent to which control is possible with the two major sources of odor. Our experience has been that complaints may be expected when odors ex- ceed low-to-moderate intensities beyond the plant boundaries. Of course, it is also possible to have complaint odor situations at lower intensity levels, depending upon such factors as odor type, frequency, and duration.

CONCLUSIONS

The determination of odor sources for control first requires a thorough assessment of the extent and nature of the problem. The principal question in con- trolling odor from a facility emitting odor from a single point is not to identify but to determine accurately the odor contribution to the atmosphere and the extent to which the odor should be reduced. In all control decisions, the cost of reducing pollutants is a major consideration. The methods we described can be a powerful tool for evaluating cost effectiveness of control techniques.

For plants with a multiplicity of odor sources, the first consideration is to identify the significant contributors of odor. Off-site surveys and in-plant reviews by trained odor analysts are useful to determine on a preliminary and qualitative basis those sources that should receive further study. An indiscriminate sampling program can severely strain the financial resources of a plant, especially if hundreds of possible emission points are involved. Once the major sources are identi- fied, selective samplings and evaluations can be carried out to develop a ranking priority for control.

We believe that the techniques outlined above should be of assistance to those concerned with the control of odorous pollution.


REFERENCES

1. WOHLERS, H. C. 1963. Int. J. Air Water Poll. 7: 71-78. 2. HL~CSTROM, U. 1972. Atrnos. Environ. 6: 103-121. 3. LINDVALL, T. 1970. On sensory evaluation of odorous air pollutant intensities. Nord.

Hyg. Tidskr. (Suppl.) 2. 4. LEONARDOS, G. 1970. Mid-Atlantic States Sectiion, Air Pollution Control Assoc. Semi-

Annual Technical Conf. Odors: Their Detection, Measurement and Control.: 18-36. Rutgers University. New Brunswick, N. J., May 13.

5. SJOSTROM, L. B. 1957. Methodology of the flavor profile. Food Technol. 11 (20). 6. CRC PROJECT Cap~-7-68. 1972. Analysis of the Odorous Compounds in Diesel Engine

Exhaust. Final Report. June. EPA Contract 68-02-0087. 7. REPORT l l T R I C6183-5. 1970. Chemical Species in Engine Exhaust Odors. Final Re-

port. Nov. CRC/EPA.

determination of odor sources for control

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