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Olfactometric Characterization of Odour Generation Potential of Piggery Manure Samples
Biolechniques for Air Pollution Abalemeni and Odour Control Policies A J . Drag1 and J . van llam (Ediiors) 0 1992 Elsevier Science Publishers B.V. All righls reserved.
425
Olfactometric Characterization of Odour Generation Potential of Piggery Manure Samples F. Van Wassenhovea, P. Vanrolleghema, H. Van Langenhoveb and W. Verstraetea a
Laboratory for Microbial Ecology, Faculty of Agricultural Sciences, University of Gent Coupure Links 653, B-9000 Gent, Belgium bLaboratory for Organic Chemistry, Faculty of Agricultural Sciences, University of Gent Coupure Links 653, B-9000 Gent, Belgium Abstract The odour problems encountered in industrialized livestock production facilities necessitate a comprehensive study on the fundamentals of odour formation and control. To quantify odour levels, a home-built olfactometer, based on the principle of dynamic dilution and assessment by a panel of testpersons, is used. Our results show that odour concentrations of manure samples subjected to vigorous air stripping decrease exponentially in time; the initial emission diminishes rapidly as a function of the gas volume which has passed through the solution. After a certain stripping time (f30 minutes at 3 wm) the odour generation becomes more or less constant. This constant odour was found to level off at approximately 3 orders of magnitude below the initial concentration. Variations between different manure samples as reflected in changes in initial and background odour levels and exponential stripping-off rates were considerable. Currently,the relation between feed composition, manure storage conditions, etc...and the manure odour generation potential and its characteristics are studied. 1. INTRODUCTION
Although odours have always been associated with livestock production, the trend towards more intensified operations, the encroachment of urban areas into traditionally agricultural land and greater environmental concerns have contributed to make odour control a major problem in manure storage and spreading. Factors affecting odour formation are numerous. Among these, feed composition and addition, feed dispensing methods, animal type and spoilage of feed and water are the most important. The processes that contribute to the odour formation are especially affected by the -anaerobic- fermentation conditions, the microbial ecology, the enzymatic activities and the farm management. Furthermore, the conditions during spreading can influence the odour emission. The evaluation of odour problems is based on chemical and sensory methods. Chemical analysis of piggery wastes resulted in the identification of about 150 volatile organic
426
compounds (Spoelstra, 1980; Yasuhara et al., 1984). Compounds contributing to the problem can be selected by odorogram analysis and concentrations of odorous compounds can be measured. However, because there is a great lack of theoretical knowledge of the dose-response relationship for complex mixtures, the identification of odorant concentrations in terms of perceived odour intensity and character is very difficult. To include the sensorial sensation in an odour description, sensorial methods must be applied. The principle of these methods is to use the human nose as a detector. The quantity measured is the number of dilutions necessary to produce a sample in which the nose fails to detect odour. In this work the odour concentration of the volatile odorous compounds from manure samples are measured by dynamic olfactometry. With the aid of this dynamic dilution system, the maximum potential of a manure sample to emit odour and the odour generation in function of time are determined. 2. MATERIALS AND METHODS
2.1. Manure Samples Fifteen manure sampleswere collected in farms with very different management (piglets, breeding, fattening). Manure ages varied considerably. Half of the samples were taken in Flanders, the other in Walloonia. Samples of 5 to 10liters were stored at 4°Cbefore analysis. Some characteristics of the sampled manures are summarized in Table 1. More details on their composition and analytical methods used can be found in Vanrolleghem et al. (1990).
Table 1 Composition of piggery manure samples subjected to olfactometric analysis. All results are expressed in (gA), except pH (-) and Electrical Conductivity (mS/cm). Total Total Organic-N Total Sample pH EC Solids COD NH4-N (Kieldahl) VFA 30 31 32 33 35 42 43 47 48 49 57 59 60 61 62
7.38 7.70 7.70 7.55 6.27 7.23 7.85 7.24 8.44 8.05 7.80 7.83 8.07 7.75 6.57
21.6 33.6 24.3 23.2 24.4 19.4 24.5 23.1 17.8 34.3 12.7
19.6 94.6 24.6 92.5 39.9 15.2 15.1 39.8 13.1 36.1 132.0 112.3 24.8 15.4 51.1
16.4 55.7 20.4 66.7 58.7 16.9 8.5 54.7 9.0 60.4 72.9 101.9 28.7 14.4 61.4
2.7 5.1 2.7 4.2 2.8 1.7 2.4 2.2 1.2 4.1 4.3 4.6 3.5 1.5 1.2
.,
3.2 6.6 3.3 7.4 4.4 2.2 3.1 3.9 2.4 4.8
8.6
15.1 4.6 2.0 3.5
1.6 3.6 0.1 2.3 19.2 4.8 0.5 16.1 0.5 24.5 5.7 7.2 5.2 0.8 7.0
421
Odour Panel
Figure 1. Scheme of the experimental set-up for dynamic olfactometry. 1:Odour-free compressed air; 2: Flow meter; 3: Flask with 150 ml manure; 4: Empty flask (foam trap); 5a: Predilution system; 5b: Stepwise dilution system; 6: (5a + 5b): Dynamic olfactometer. 2.2. Air stripping and dynamic olfactometry A manure sample of 150 ml was placed into a glass flask and an odour-free airstream was passed through the manure at a flow rate of 400 ml/min (r 3 wm). A scheme of the experimental setup is given in Figure 1. The off-gas airstream was directed to the dynamic olfactometer and the odour concentration was evaluated at various time intervals by 3 preselected panelists. From preliminary olfactometric studies these 3 observers represent the average of an initial panel of 12 persons. During the test, manure samples were maintained at 25°C and 0.2 ml paraffin oil was added to control occasional foaming. According to the principles of dynamic forced choice triangle olfactometry (Dravnieks and Prokop, 1975) a home-built olfactometer was used. This apparatus consists of two units: a predilution system and a stepwise dilution system. The predilution ratios in this device range from 0 to 500. In the stepwise dilution system, six dilution levels are prepared. The lowest dilution level is 5, the highest 160.
2.3. Interpretation A measure of the maximum potential of an odour source (wastewater, manure, ...) to emit odour is named odour generation potential (OGP). Koe and Tan (1990) defined the OGP of a wastewater sample as the quantity of odorous substances that can be volatilized from a cubic meter of wastewater per unit time. The determination of the odorous concentration in the liquid phase isvery difficult but can be related to the release of odorant in the off-gas after air-stripping. The odour concentration of the off-gas can be determined with the aid of a dynamic olfactometer and expressed in odour units (OU).
428
In accordance with Koe and Tan (1990), our results show that odour emissions from manure samples subjected to air stripping decrease exponentially with time. However, in contrast to their findings, after a certain stripping time the odour generation of most manure samples becomes more or less constant. Therefore, the mathematical model adopted by both authors must be extended as follows:
The odour emission measured by dynamic olfactometry may therefore be described by the following kinetic parameters:
OU (0) OU (00)
k ts
= initial odourgeneration potential = constant odour background = air-stripping rate constant = switching time
3. RESULTS AND DISCUSSION
Odour concentrations in the off-gas airstream in function of time were obtained for 15 manure samples. Curve-fitting allowed to determine the kinetic parameters. Figure 2 shows a typical off-gas odour concentration decay in a manure sample with switching point, while Figure 3 illustrates a typical emission profile of a manure sample which showed no switching point during the stripping period studied. Table 2 gives a summary of the kinetic parameter values obtained. Regreision
A
Mean
100000
10000 I
s
. L I
z B
1000
$ 1 100
10 0
30
60
90
Time (minuted
Figure 2 Off-gas odour concentration decay of a manure sample with switching point (Sample 42).
429
Table 2 Summary of olfactometric kinetic parameter values of manure samples. k Sample
ou (0)
30 31 32 33 35 42 43 47 48 49 57 59 60 61 62
OU(W> 135 < 225 150 156 < 80 36 100 410 90 80 2245 < 2000 675 215 < 360
20500 41350 2660 5735 2700 7275 5500 11850 90 17275 9820 13245 3660 215 4095
(Urnin) 0.053 0.025 0.018 0.022 0.017 0.062 0.034 0.023
ts
(min) 41 > 90 69 71
>90 37 50 63 0 100 43 > 90 58 0 > 120
0.000
0.021 0.015 0.008 0.013 0.000
0.009
No clear relationship between these olfactometric data and the physico-chemical characteristics summarized in Table 1could be extracted from the data.
Regression
A
Mean
100000
10000
.m c
B
1
1000
i: LOO
10
0
30
60
90
Time (minutes)
Figure 3 Off-gas odour emission profile of a manure sample without switching point (Sample 31).
430 4. CONCLUSIONS
The odour concentration of 15 manure samples subjected to air-stripping was found to decrease exponentially with time. The initial odour concentration diminishes rapidly, but after a certain stripping time the odour concentration becomes constant for most manures, except samples 31,35,59 and 62. This indicates that during the initial period of aeration the more volatile or less soluble compounds are stripped from the liquid while the remaining odorants which have a lower Henry coefficient and/or are more water soluble give rise to a constant odour background. For that reason the mathematical model given by Koe and Tan (1990) was extended. Olfactometric results showed major variations in exponential stripping off rates, initial odour concentrations and background emissions. Determination of odour generation potential gives powerful1 information usefull for research aimed at reducing odour emissions of piggery manure. Currently, various parameters such as feed composition, manure storage conditions, etc... are studied in relation to the manure odour generation potential and its characteristics. 5. ACKNOWLEDGEMENT This work was supported by the Institute for Scientific Research in Agriculture and Industry (IWONWRSLA). Thanks are due to L. Wolfs for technical assistance in the analysis. 6. REFERENCES
Dravnieks A. and Prokop W.H. (1975). Source emission odor measurement by a dynamic forced-choice triangle olfactometer. J. Air Pollut. Control Assoc., 25,28-33. Koe L.C.C. and Tan N.C. (1990). Odour generation potential of wastewaters. Wat. Res., 12,1454-1458. Spoelstra S.S. (1980). Origin of objectionable odorous components in piggery waste and the possibility of applying indicator components for studying odour development. Agric. Environm., 5,241-260. Vanrolleghem P., Anselme P., Thonart P. and Verstraete W. (1990). Formation and control of odorous compounds in piggery manure. Med. Fac. Landbouww. Rijksuniv. Gent, 55, 1489-1495. Yasuhara A,, Fuwa K. and Jimbu M. (1984). Identification of odorous compounds in fresh and rotten swine manure. Agric. Biol. Chem., 48,3001-3010.
425
Olfactometric Characterization of Odour Generation Potential of Piggery Manure Samples F. Van Wassenhovea, P. Vanrolleghema, H. Van Langenhoveb and W. Verstraetea a
Laboratory for Microbial Ecology, Faculty of Agricultural Sciences, University of Gent Coupure Links 653, B-9000 Gent, Belgium bLaboratory for Organic Chemistry, Faculty of Agricultural Sciences, University of Gent Coupure Links 653, B-9000 Gent, Belgium Abstract The odour problems encountered in industrialized livestock production facilities necessitate a comprehensive study on the fundamentals of odour formation and control. To quantify odour levels, a home-built olfactometer, based on the principle of dynamic dilution and assessment by a panel of testpersons, is used. Our results show that odour concentrations of manure samples subjected to vigorous air stripping decrease exponentially in time; the initial emission diminishes rapidly as a function of the gas volume which has passed through the solution. After a certain stripping time (f30 minutes at 3 wm) the odour generation becomes more or less constant. This constant odour was found to level off at approximately 3 orders of magnitude below the initial concentration. Variations between different manure samples as reflected in changes in initial and background odour levels and exponential stripping-off rates were considerable. Currently,the relation between feed composition, manure storage conditions, etc...and the manure odour generation potential and its characteristics are studied. 1. INTRODUCTION
Although odours have always been associated with livestock production, the trend towards more intensified operations, the encroachment of urban areas into traditionally agricultural land and greater environmental concerns have contributed to make odour control a major problem in manure storage and spreading. Factors affecting odour formation are numerous. Among these, feed composition and addition, feed dispensing methods, animal type and spoilage of feed and water are the most important. The processes that contribute to the odour formation are especially affected by the -anaerobic- fermentation conditions, the microbial ecology, the enzymatic activities and the farm management. Furthermore, the conditions during spreading can influence the odour emission. The evaluation of odour problems is based on chemical and sensory methods. Chemical analysis of piggery wastes resulted in the identification of about 150 volatile organic
426
compounds (Spoelstra, 1980; Yasuhara et al., 1984). Compounds contributing to the problem can be selected by odorogram analysis and concentrations of odorous compounds can be measured. However, because there is a great lack of theoretical knowledge of the dose-response relationship for complex mixtures, the identification of odorant concentrations in terms of perceived odour intensity and character is very difficult. To include the sensorial sensation in an odour description, sensorial methods must be applied. The principle of these methods is to use the human nose as a detector. The quantity measured is the number of dilutions necessary to produce a sample in which the nose fails to detect odour. In this work the odour concentration of the volatile odorous compounds from manure samples are measured by dynamic olfactometry. With the aid of this dynamic dilution system, the maximum potential of a manure sample to emit odour and the odour generation in function of time are determined. 2. MATERIALS AND METHODS
2.1. Manure Samples Fifteen manure sampleswere collected in farms with very different management (piglets, breeding, fattening). Manure ages varied considerably. Half of the samples were taken in Flanders, the other in Walloonia. Samples of 5 to 10liters were stored at 4°Cbefore analysis. Some characteristics of the sampled manures are summarized in Table 1. More details on their composition and analytical methods used can be found in Vanrolleghem et al. (1990).
Table 1 Composition of piggery manure samples subjected to olfactometric analysis. All results are expressed in (gA), except pH (-) and Electrical Conductivity (mS/cm). Total Total Organic-N Total Sample pH EC Solids COD NH4-N (Kieldahl) VFA 30 31 32 33 35 42 43 47 48 49 57 59 60 61 62
7.38 7.70 7.70 7.55 6.27 7.23 7.85 7.24 8.44 8.05 7.80 7.83 8.07 7.75 6.57
21.6 33.6 24.3 23.2 24.4 19.4 24.5 23.1 17.8 34.3 12.7
19.6 94.6 24.6 92.5 39.9 15.2 15.1 39.8 13.1 36.1 132.0 112.3 24.8 15.4 51.1
16.4 55.7 20.4 66.7 58.7 16.9 8.5 54.7 9.0 60.4 72.9 101.9 28.7 14.4 61.4
2.7 5.1 2.7 4.2 2.8 1.7 2.4 2.2 1.2 4.1 4.3 4.6 3.5 1.5 1.2
.,
3.2 6.6 3.3 7.4 4.4 2.2 3.1 3.9 2.4 4.8
8.6
15.1 4.6 2.0 3.5
1.6 3.6 0.1 2.3 19.2 4.8 0.5 16.1 0.5 24.5 5.7 7.2 5.2 0.8 7.0
421
Odour Panel
Figure 1. Scheme of the experimental set-up for dynamic olfactometry. 1:Odour-free compressed air; 2: Flow meter; 3: Flask with 150 ml manure; 4: Empty flask (foam trap); 5a: Predilution system; 5b: Stepwise dilution system; 6: (5a + 5b): Dynamic olfactometer. 2.2. Air stripping and dynamic olfactometry A manure sample of 150 ml was placed into a glass flask and an odour-free airstream was passed through the manure at a flow rate of 400 ml/min (r 3 wm). A scheme of the experimental setup is given in Figure 1. The off-gas airstream was directed to the dynamic olfactometer and the odour concentration was evaluated at various time intervals by 3 preselected panelists. From preliminary olfactometric studies these 3 observers represent the average of an initial panel of 12 persons. During the test, manure samples were maintained at 25°C and 0.2 ml paraffin oil was added to control occasional foaming. According to the principles of dynamic forced choice triangle olfactometry (Dravnieks and Prokop, 1975) a home-built olfactometer was used. This apparatus consists of two units: a predilution system and a stepwise dilution system. The predilution ratios in this device range from 0 to 500. In the stepwise dilution system, six dilution levels are prepared. The lowest dilution level is 5, the highest 160.
2.3. Interpretation A measure of the maximum potential of an odour source (wastewater, manure, ...) to emit odour is named odour generation potential (OGP). Koe and Tan (1990) defined the OGP of a wastewater sample as the quantity of odorous substances that can be volatilized from a cubic meter of wastewater per unit time. The determination of the odorous concentration in the liquid phase isvery difficult but can be related to the release of odorant in the off-gas after air-stripping. The odour concentration of the off-gas can be determined with the aid of a dynamic olfactometer and expressed in odour units (OU).
428
In accordance with Koe and Tan (1990), our results show that odour emissions from manure samples subjected to air stripping decrease exponentially with time. However, in contrast to their findings, after a certain stripping time the odour generation of most manure samples becomes more or less constant. Therefore, the mathematical model adopted by both authors must be extended as follows:
The odour emission measured by dynamic olfactometry may therefore be described by the following kinetic parameters:
OU (0) OU (00)
k ts
= initial odourgeneration potential = constant odour background = air-stripping rate constant = switching time
3. RESULTS AND DISCUSSION
Odour concentrations in the off-gas airstream in function of time were obtained for 15 manure samples. Curve-fitting allowed to determine the kinetic parameters. Figure 2 shows a typical off-gas odour concentration decay in a manure sample with switching point, while Figure 3 illustrates a typical emission profile of a manure sample which showed no switching point during the stripping period studied. Table 2 gives a summary of the kinetic parameter values obtained. Regreision
A
Mean
100000
10000 I
s
. L I
z B
1000
$ 1 100
10 0
30
60
90
Time (minuted
Figure 2 Off-gas odour concentration decay of a manure sample with switching point (Sample 42).
429
Table 2 Summary of olfactometric kinetic parameter values of manure samples. k Sample
ou (0)
30 31 32 33 35 42 43 47 48 49 57 59 60 61 62
OU(W> 135 < 225 150 156 < 80 36 100 410 90 80 2245 < 2000 675 215 < 360
20500 41350 2660 5735 2700 7275 5500 11850 90 17275 9820 13245 3660 215 4095
(Urnin) 0.053 0.025 0.018 0.022 0.017 0.062 0.034 0.023
ts
(min) 41 > 90 69 71
>90 37 50 63 0 100 43 > 90 58 0 > 120
0.000
0.021 0.015 0.008 0.013 0.000
0.009
No clear relationship between these olfactometric data and the physico-chemical characteristics summarized in Table 1could be extracted from the data.
Regression
A
Mean
100000
10000
.m c
B
1
1000
i: LOO
10
0
30
60
90
Time (minutes)
Figure 3 Off-gas odour emission profile of a manure sample without switching point (Sample 31).
430 4. CONCLUSIONS
The odour concentration of 15 manure samples subjected to air-stripping was found to decrease exponentially with time. The initial odour concentration diminishes rapidly, but after a certain stripping time the odour concentration becomes constant for most manures, except samples 31,35,59 and 62. This indicates that during the initial period of aeration the more volatile or less soluble compounds are stripped from the liquid while the remaining odorants which have a lower Henry coefficient and/or are more water soluble give rise to a constant odour background. For that reason the mathematical model given by Koe and Tan (1990) was extended. Olfactometric results showed major variations in exponential stripping off rates, initial odour concentrations and background emissions. Determination of odour generation potential gives powerful1 information usefull for research aimed at reducing odour emissions of piggery manure. Currently, various parameters such as feed composition, manure storage conditions, etc... are studied in relation to the manure odour generation potential and its characteristics. 5. ACKNOWLEDGEMENT This work was supported by the Institute for Scientific Research in Agriculture and Industry (IWONWRSLA). Thanks are due to L. Wolfs for technical assistance in the analysis. 6. REFERENCES
Dravnieks A. and Prokop W.H. (1975). Source emission odor measurement by a dynamic forced-choice triangle olfactometer. J. Air Pollut. Control Assoc., 25,28-33. Koe L.C.C. and Tan N.C. (1990). Odour generation potential of wastewaters. Wat. Res., 12,1454-1458. Spoelstra S.S. (1980). Origin of objectionable odorous components in piggery waste and the possibility of applying indicator components for studying odour development. Agric. Environm., 5,241-260. Vanrolleghem P., Anselme P., Thonart P. and Verstraete W. (1990). Formation and control of odorous compounds in piggery manure. Med. Fac. Landbouww. Rijksuniv. Gent, 55, 1489-1495. Yasuhara A,, Fuwa K. and Jimbu M. (1984). Identification of odorous compounds in fresh and rotten swine manure. Agric. Biol. Chem., 48,3001-3010.