Science and Technology Journal, Vol. 3 No. II ISSN: 2321-3388
Panel Evaluation of Headspace Odors
of Different Animal Manures
1
2
J.H. Kim1, H.L. Choi2, Y.J. Heor1, H. Ahn3 and H. Kim1,*
Department of Environmental Engineering, University of Seoul, Seoul–130743, Korea
School of Agricultural Biotechnology, Seoul National University, Seoul–151742, Korea
3
School of Nursing, Korea Bible University, Seoul–139791, Korea
E-mail: *h_kim@uos.ac.kr
Abstract—Odor intensity, hedonic tone, and odor characters of chicken, pig, and cow manure were evaluated by
a sensory panel. Two snif ing methods were applied and compared in this study; one was the conventional direct
snif ing method and the other was the dilute gas snif ing method where a small lux chamber was used to dilute
headspace odor from manure before introduce it to the panel. Since animal manures usually produce strong and
offensive odors, when the direct snif ing method applied, the odors could not be easily differentiated; in addition,
between panel members, there were considerable deviations in odor intensity and hedonic tone for the same
sample. On the other hand, when the dilute gas method applied, the difference between panel members could be
reduced. The odor panel evaluation using the dilute gas method could be further improved by letting the panel
members discuss about the odor intensity and hedonic tone of a sample. Finally, in order to precisely describe the
odor characters of a manure sample, “two-stage odor descriptor wheels” were developed in this study.
Keywords: Small Flux Chamber, Direct Snif ing Method, Dilution Method using a Flux Chamber, Two-stage Odor
Descriptor wheel
INTRODUCTION
The public complaints about odors from waste treatment
plants, and composting and concentrated animal feeding
operations (CAFOs) have been increasing [1–2](Schiffman
et al., 2000; Esteban, 1997). Especially, people living near
CAFOs are physiologically and aesthetically affected by
the odors from the facilities [3] (Shusterman, 1999). In
fact, the odors from the CAFOs can affect the health of
animals and animal production, too [4–5] (Wing and Wolf,
2000; Donham, 2000). Therefore, much effort has been
made to control offensive odors from the facilities [6–7]
(Stéphane, 1999; McCrory and Hobbs, 2001). For the proper
control of odors, however, an accurate and objective odor
measurement is required.
In general, the odors from a CAFO are assessed in two
ways; one is based on a human sensory panel, and the
other is based on an analytical instrument, such as a gas
chromatograph (GC) [8-9] (Davoli et al., 2003; Fakhoury
et al., 2000), and a liquid chromatograph (LC) [10]
(Uchiyama and Hasegawa, 1999). Since the instrumental
analysis can quantify individual odorants from a sample
with high reproducibility and accuracy, it will be more
useful in determining odor generation mechanism. Since
most odor sensation is caused by a number of chemicals,
however, results from instrumental analysis often cannot be
compared to the odor intensity evaluated by a human panel
[11] (Gostelow, 2001).
The odor evaluation using a sensory panel is often
performed because it can represent what people actually
smell. In an odor evaluation by a human sensory panel, odor
threshold (the lowest odor concentration to which human
can sense), odor intensity (degree of odor strength), hedonic
tone (degree of disgust), and odor characters (words
describing the feelings caused by odors) are measured [12]
(Gostelow et al., 2003). The currently-applied sensory odor
evaluation methods include ‘the direct snif ing method’
using a certain range of odor category, a dynamic olfactory
method where odors are indirectly measured using a
sophisticated device to dilute odorous gas with odor-free air
Kim, Choi, Heor, Ahn and Kim
in a odor free laboratory and a supra-threshold referencing
method [13] (Sweeten and Akabani, 1994). Of the various
sensory methods for odor measurement, the direct snif ing
method has been the most frequently used since it does not
require sophisticated equipment and can be easily applied
in any cases. In addition, odor measurement can be inished
within a short period of time [12,14] (Koe, 1989; Gostelow
et al., 2003). Therefore, the method can be useful in
preliminary odor assessment. However, the direct snif ing
method often fails to provide consistent and informative
results because panel members often showed large
difference in the odor intensity and hedonic tones [14] (Koe,
1989), especially when sample odor is very strong as in the
case of animal manures.
In this study, odor panel evaluation of chicken, pig, and
cow manure was performed using a small lux chamber
where a manure sample was placed and its headspace gas
was diluted with odor-free nitrogen. The panel evaluation
also adopted supra-threshold referencing method in
which each panel member was asked to compare the odor
intensity of a sample to a reference odor source at a known
concentration. Sweeten and Akabani suggested n-butanol
solution can be used a reference odor source [13]. Then the
results were compared with those from the direct snif ing
method. Finally, “two-stages odor descriptor wheels” were
proposed to precisely describe the odor characteristics of
animal manures.
MATERIALS AND METHODS
EĝĕĊėĎĒĊēę DĊĘĎČē
A small lux chamber was designed to dilute the headspace
gas of animal manure and to introduce it to each odor panel
member (Fig. 1). The chamber consists of a 1 L glass jar
where an animal manure sample of 600 mL was placed.
After the manure was placed, the jar was sealed with a cap
and its headspace was lushed with pure N2 gas at 100 mL
min-1. The headspace was remained lushed for 12 min
before the headspace gas was introduced to panel members
for their evaluation.
The direct snif ing method is applied to the same manure
samples. For the evaluation, a manure sample of 600 mL
was placed in a 1L glass jar and the jar was sealed. Then,
each panel member was asked to open the cover of the jar
and to directly smell the odor. The result from the dilute gas
method was compared with the one from the direct snif ing
method.
N2 in
Sniff port
Gas Flow meter
Diffuser
Sample
Sample
1L Glass Jar
Fig. 1: Schematic Diagram of Small Flux Chamber
SELECTION AND TRAINING OF PANEL
Sensory sensitivity to odor is variable between different
individuals, which often causes accurate assessment of
odor intensity of a sample impossible. Therefore, an odor
panel should be made of individuals with similar olfactory
sensitivity. Thus, screening of odor panels was performed to
exclude individuals with exceptionally low or high olfactory
sensitivity [15] (Ferriera et al., 2003). The screening was
conducted using the so-called odor pen kit (St. Croix Sensory,
Inc, U.S.A), which is commercially available [16] (Lay and
McGinley, 2004). The method using the odor pens follows
the 3-Alternative Forced Choice Method [17] (ASTM, 1997);
in each test, a potential panel is asked to sniff three different
pens (two are blank and the third release odor), and to
distinguish the odorous pen [16] (Lay and McGinley, 2004).
The panel size is also an important issue in a sensory test
of odor. Typically, a panel is made up with 4–10 individuals
[18] (Brennan et al., 1996). In this study, therefore, seven
individuals with similar odor sensitivity (4 men, 3 women)
were selected through the screening procedure. In an odor
evaluation using the panel, 6 discrete categories scale of
0~5 was used; 0 for no odor and 5 for the odor with the
highest intensity [19] (Frechen, 1994).
The selected panel members were trained to distinguish
odors with different intensity using a six category scale
method, in which n-butanol solutions with 6 different
concentrations were prepared and used as references
(Table 1) [19, 20] (Cheremisinoff, 1988; Frechen, 1994).
Training each member was continued until he or she
could distinguish odor intensity of three randomly chosen
n-butanol solutions. Speci ic procedure can be found in
Zhang et al. [21].
Before any odor test, panel members were not allowed
to have any meals, snacks or drink. They were not allowed to
smoke or use cosmetics or perfumes, either. In addition, any
120
Panel Evaluation of Headspace Odors of Different Animal Manures
panel member with a cold or allergy symptom was excluded
from the odor evaluation. All the panel evaluations were
based on the blinded test [22] (Cain, 1980).
Table 1: A Six-scale n-butanol Odor Intensity Reference
Level
0
1
2
3
4
5
n-butanol(ppm)
in Air/in Water
0/0
25/250
75/750
225/2250
625/6250
2025/2250
Category
Description
No odor perceivable
Barely perceivable
Faintly perceivable
Clearly perceivable
Strong
Very strong
Fig. 2: Odor Intensity/ Hedonic Tone Using Direct
Snifϐing Method
PRECEDURE FOR THIS STUDY
An odor evaluation form was made to measure the odors from
manures of three different animals. i.e., chickens, pigs and
cows (Table 2). Although the panel was trained to distinguish
odors of 6 different intensities, they were asked to evaluate
odors from the samples with 11 categories scale; from 0 (for
no odor) tp 10 (for very strong odor). Hedonic tone of each
sample was also evaluated on 11-point scale; from-10 (for
very offensive odor) to 0 (for non-offensive odor).
The panel evaluation using the dilute gas method was
performed in two different ways; in the irst way, each
member individually rated odor of a sample, while in the
second the members were allowed to discuss the intensity
of odor of a sample to reach a consensus. The second
method was designed to reduce the difference between
individual measures and to obtain more precise results [23]
(AWWA, 1993).
RESULTS AND DISCUSSION
PĆēĊđ EěĆđĚĆęĎĔē–CĔĒĕĆėĎĘĔē ćĊęĜĊĊē
DĎėĊĈęĎěĊ SēĎċċ Ćēĉ DĎđĚęĎĔē SēĎċċ
MĊęčĔĉ
Figures 2–4 show the odor intensities and hedonic tones
of different animal manures measured by both direct
snif ing and dilute gas methods, respectively. When the
direct snif ing method was used, odors from different
animal manures could not be distinguished; odors from
all the manures were simply evaluated as having high
odor intensities and low hedonic tones (much offensive)
(Fig. 2). However, when the dilute gas method was used, the
differences in odor intensities and hedonic tones of different
animal manures were more clearly identi ied. Comparing
to other manures, chicken manure produced much more
strong and offensive odors (Fig. 3).
Fig. 3: Odor Intensity/ Hedonic Tone of Using Dilution
Sniff Method
The average standard deviation of odor intensities and
hedonic tones between panels evaluating odors of animal
manures using the dilute gas method based on a small lux
chamber was 1.5 and 1.7, respectively. On the other hand, it
was 2.2 for odor intensity and 1.9 for hedonic tone when the
direct snif ing method was used. The result implies that the
natural odor characteristics of animal manures (e.g., string
odor intensity and offensiveness) makes it hard to identify
difference between them by the sensory panel evaluation
(especially when direct snif ing method is applied). From this
point of view, the sensory panel evaluation with the dilution
method using small lux chamber can be advantageous, since
panel members can avoid being overwhelmed by strong
and offensive odor and can more accurately distinguish
the difference between odors from different materials
(especially the ones with strong and offensive odors).
Fig. 4: Odor
Animal Manure
121
Intensity
and
Hedonic-Tone
of
Kim, Choi, Heor, Ahn and Kim
COMPARISON BETWEEN DIRECTIVE
SNIFFȃINDIVIDUAL AND CONSENSUS
METHOD
THE ODOR CHARACTERISTICS OF
ANIMAL MANURES
After each panel member individually evaluated the odors
from animal manures, he or she was allowed to discuss
others about the odor strength and offensiveness of the
samples and to reach a consensus. Then, the result from this
speci ic test was compared with the one from the evaluation
without post-discussion. In the individual evaluation, the
average standard deviations of odor intensities and hedonic
tones between panels were 1.5, and 1.7, respectively.
However, the standard deviations between panels were
lowered to 1.2 for odor intensity and 1.3 for hedonic tone,
when they were allowed to discuss. The reduced differences
in odor intensity and hedonic tone were attributed to the
possibility of excluding potential outliers though the
discussion between panel members.
Table 2: Evaluation Results of Odor Intensity/
Hedonic Tone by Dilution Sniff and Directive
Sniff Method
Sample
Cow
Swine
Chicken
Cow
Swine
Chicken
Cow
Swine
Chicken
Method
Dilution sniff
(individuals)
Dilution sniff
(consensus)
Directive Sniff
Average (Standard Deviation)
Intensity
Hedonic Tone
3.5 (1.3)
-4.2 (2.1)
5.4 (1.6)
-5.3 (1.5)
7.9 (1.4)
-8.0 (1.5)
3.8 (1.0)
-5.3 (1.6)
5.7 (1.5)
-5.3 (0.8)
8.0 (1.1)
-8.3 (0.8)
6.3 (2.4)
-6.6 (2.1)
8.0 (1.3)
-8.0 (1.5)
7.1 (2.8)
-7.0 (2.8)
Cow
Odor characteristics are usually reported using odor
descriptors, i.e., words or phases of subjective and
described by analogy [12] (Geostelw et al., 2003). However,
since each individual can describe the odor of a sample
in various ways or he does not ind a right word for it, it
is often hard to evaluate the descriptors. To overcome this
problem, recently, the so-called visible odor descriptor
wheel was introduced to allow easy understanding of
odor characteristics of a material [24] (Rega et al., 2003).
Although this approach has been successfully applied to
several studies, it is not suf icient to help a panel to describe
the subtle odor characteristics of a sample. In fact, it is
dif icult to describe ‘odor characteristics of a sample’ with
one or two sentences or words. In this paper, therefore,
“two-stage odor descriptor wheel system” was proposed and
applied to discriminate the odor characteristics of different
animal manures. “Two-stage odor descriptor wheels” are
made of two odor descriptor wheels; irst wheel indicates
10 main descriptors (i.e., loral, fruity, vegetable, food, earth,
offensive, stimulant, ishy, chemical, and medicinal) and
each main descriptor has its own odor descriptor wheel
which has 5 subsequent descriptors that a panel can choose
to assess odor characters of a material in detail.
In the beginning of the assessment with the animal
manures, each panel member was asked to choose
descriptors representing odor characteristics of different
animal manures. Most of the members expressed odors
from the three different manures all offensive by choosing
the descriptor, offensive (Fig. 5). However, when they were
Pig
Fig. 5: Two Stages Odor Descriptors Wheels of Cow, Pig and Chicken Manure
122
Chicken
Panel Evaluation of Headspace Odors of Different Animal Manures
asked to choose descriptors from the second odor wheel
3.
belonging to the descriptor, i.e., offensive in the irst wheel,
the characteristics of the manure odors were distinguished
4.
each other. The panel described that odor of rotten trash
and stale odor were dominant in cow manure odors, while
5.
pig manure smelled like sour milk and rotten trash. Finally,
they described chicken manure produced odor of spoiled
food, rotten trash, or excremental odor.
6.
7.
CONCLUSION
8.
For the olfactory evaluation of chicken, pig, and cow
manures, which naturally have high odor intensities and
9.
low hedonic tones, odor panel tests were performed with
the dilute gas method using a small lux chamber. The result
from the test was then compared with that from the direct
10.
snif ing method. The dilute-gas method showed lower
standard deviations in odor intensity and hedonic tone
of different manure samples. The deviation was further
lowered when the panel members were allowed to discuss
and reach a consensus on the odors from the manures.
11.
12.
If odors from different manures compared, odor from
chicken manure was the most strong and offensive, followed
13.
by odors from swine and cow manures.
Finally, the proposed two-stages odor descriptor wheel
system enabled panel members to visually compare odor
characteristics of different materials. If it is further studied,
14.
it will help assessing different odor sources.
15.
ACKNOWLEDGEMENT
Authors greatly appreciate the support of the R&D
program of MOTI/KEIT (R&D program number: 10037331,
16.
Development of Core Water Treatment Technologies based
on Intelligent BT-NT-IT Fusion Platform).
17.
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BIOGRAPHY
Professor Hyunook Kim is the Dean at the School of Environmental Engineering, University of Seoul, Seoul,
Korea and the Director of the R&D Center of Core Technology for Water Treatment. His major ield is water
& wastewater treatment processes, especially, modeling or process control of them. He also has an expertise
in analysis of trace organic compounds in water and odorants from various sources and advanced oxidation
processes. He currently serves an Associate Editor of Chemosphere, Critical Review in Environmental Science and
Technology, Frontiers of Environment Science & Engineering, and Energy, Ecology and Environment. He received a few
Honors and Awards from Korean government. He has more than 70 publications in peer-reviewed journals and more than
200 reports in international and national conferences.
124