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Subjective odor measurement for the evaluation of agricultural odor control methods Phillips, David Alexander 1979

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SUBJECTIVE ODOR MEASUREMENT FQR THE EVALUATION OF AGRICULTURAL ODOR CONTROL METHODS by 9 1 DAVID ALEXANDER PHILLIPS B.Sc. U n i v e r s i t y of B r i t i s h Columbia, 1976 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN THE FACULTY OF GRADUATE STUDIES DEPT. OF AGRICULTURAL MECHANICS We accept t h i s t h e s i s as conforming t o the r e q u i r e d standard. THE UNIVERSITY OF BRITISH COLUMBIA May, 19 79 (c) D. P h i l l i p s In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department nf Ac^r i^.JhjseJL M<2<.kc^i c <> The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 D E - 6 B P 75-51 I E ABSTRACT Odor measurement i s a u s e f u l t o o l i n the e v a l u a t i o n of a g r i c u l t u r a l odor c o n t r o l methods. S u b j e c t i v e odor measure-ment techniques u t i l i z i n g man's sense of smell as an a n a l y t i c a l i. instrument are d i s c u s s e d . The use of these methods i n e e v a l u a t i n g a g r i c u l t u r a l odor c o n t r o l systems i s a l s o reviewed. A dynamic d i l u t i o n to t h r e s h o l d odor measurement method i s used to e v a l u a t e odorous a i r samples c o l l e c t e d downwind from an on farm a g i t a t e d b a s i n c o n t a i n i n g anaerobic l i q u i d swine manure. Samples were c o l l e c t e d from the time of a g i t a t o r s t a r t u p . I t i s found t h a t s h o r t term s u r f a c e a e r a t i o n of anaerobic l i q u i d swine manure reduces the t h r e s h o l d of the odorous gases being emitted by a t l e a s t two o r d e r s of magnitude. I t i s shown t h a t odor samples with a 'high odor l e v e l ' i n T e d l a r ( P o l y v i n y l F l o u r i d e P l a s t i c ) bags can be s t o r e d f o r 48 hours b e f o r e t h r e s h o l d a n a l y s i s without a s i g n i f i c a n t change o c c u r r i n g i n the odor t h r e s h o l d . I t i s found t h a t odor samples with a 'low odor l e v e l ' * c o l l e c t e d i n T e d l a r bags have a l i k e l y storage l i f e of a t l e a s t 24 hours. * High odor l e v e r i s d e f i n e d here as 5,000 to 10,000 d i l u t i o n s to t h r e s h o l d . ** Low odor l e v e l i s d e f i n e d here as l e s s than 500 d i l u t i o n s t o t h r e s h o l d . i i i . TABLE OF CONTENTS Page ABSTRACT i i . TABLE OF CONTENTS i i i . LIST OF TABLES i v . LIST OF FIGURES v. LIST OF DEFINITIONS v i i i ACKNOWLEDGEMENTS ,x. THESIS OBJECTIVES 1 INTRODUCTION 2 PHYSIOLOGY OF ODOR PERCEPTION 4 Nasal Cavity 4 Olfactory System 5 Peripheral 5 Central 8 THE MOLECULAR BASIS OF OLFACTION 10 ODOR MEASUREMENT-ANALYTICAL TECHNIQUES 12 Quality 12 Accep t a b i l i t y 12 Intensity 12 Det e c t a b i l i t y 13 Sample C o l l e c t i o n 14 Response C r i t e r i a and Indication of Response 22 Interpretation of Responses 23 ODOR MEASUREMENT - AGRICULTURE 25 Vapour D i l u t i o n 29 Threshold Measurement 30 Liquid D i l u t i o n 34 LITERATURE CONCLUSIONS 3 5 TABLE OF CONTENTS (continued) i v . Page MATERIALS AND METHODS 3 7 The Olfactometer 3 7 Sensory A n a l y s i s Procedures 46 THE EXPERIMENTS 4 9 I. Olfactometer D i l u t i o n T e s t 49 I I . Odor Storage Experiment (High Odor Level) 49 I I I . Odor Storage Experiment (Low Odor Level) 50 IV. Short Term A e r a t i o n of Swine Manure f o r Odor Reduction: F i e l d Odor Measurements at the Tank 51 1) The S i t e 51 2) Sampling Devices 54 RESULTS AND DISCUSSION 57 I. O l f actometer D i l u t i o n T e s t 58 I I . Odor Storage Experiment - High Odor L e v e l 61 I I I . Odor Storage Experiment - Low Odor L e v e l 65 IV. Short Term A e r a t i o n of Swine Manure f o r Odor Reduction: F i e l d Odor Measurements at the Tank 69 THE ODOR MEASUREMENT SYSTEM #6 CONCLUSIONS 78 BIBLIOGRAPHY 80 APPENDIX 84 v. LIST OF TABLES TABLE PAGE I Values from o l f a c t o m e t e r d i l u t i o n t e s t showing p r e d i c t e d and a c t u a l v a l u e s 63 II Odor Storage T e s t ; Log D i l u t i o n s and E D J - Q v a l u e s f o r s t o r e d h i g h l e v e l swine manure odor samples 6 7 I I I Odor Storage T e s t : Low odor c o n c e n t r a -t i o n s : P a n e l i s t d i l u t i o n to t h r e s h o l d and E D ^ Q values are shown f o r two experimental t r i a l s 72 IV E v a l u a t i o n of odor t h r e s h o l d s d u r i n g a e r a t i o n o f wastes at the tank; P a n e l i s t D i l u t i o n to T h r e s h o l d and E D c n Values 75 b U V I , LIST OF FIGURES FIGURE PAGE 1 . L a t e r a l and c r o s s - s e c t i o n a l views of 6 the human naval c a v i t y 2. C e l l s of the o l f a c t o r y e p i t h e l i u m 7 3. L o c a t i o n of the o l f a c t o r y b ulbs 9 4. Olfactometer dynamic d i l u t i o n system 38 schematic diagram 5. F r o n t panel of dynamic d i l u t i o n 39 o l f a c t o m e t e r with flow meters (A) and c o n t r o l v a l v e s (B) 6. E x t e r n a l carbon f i l t e r showing the tube 41 shaped f i l t e r i n a frame (A), the two way c r o s s o v e r v a l v e (B) and the flow e q u a l i z a t i o n flowmeters (C) 7. Pressure v e s s e l (A) used to i n j e c t sample 43 i n t o the d i l u t i o n system shown c l o s e d with sample bag e n c l o s e d 8. Panel booth showing sample masks (A). 44 The c e n t e r mask c a r r i e s carbon f i l t e r e d a i r o n l y 9. Close-up of mask with b r e a t h i n g bag (A) 45 showing the non-rebreathing v a l v e (B) on the mask-bag assembly 10. Schematic of the s u r f a c e f l o a t i n g a e r a t o r 53 11. F i e l d gas sampling u n i t showing the 55 sample bag (A), the power source (B), and the small sampling f a n (C) 12. High odor l e v e l bag storage t e s t . Three 66 separate experimental runs are shown 13. Low Odor l e v e l T e d l a r bag storage t e s t 73 v i i . LIST OF FIGURES (Continued) FIGURE PAGE 14. Odor t h r e s h o l d changes f o r samples c o l l e c t e d downwind of the aerated b a s i n on three separate occasions 76 15. Gas chromatographic a n a l y s i s o f the headspace o f m a t e r i a l c o l l e c t e d from a s m a l l s c a l e manure a e r a t i o n experiment. The v a l v e temperature was 50°C, the FI; d e t e c t o r 200°C and the temperature program was i s o t h e r m a l (2 5°C) 7 8 v i i i DEFINITIONS* odor t h r e s h o l d s Odor t h r e s h o l d s can be of f o u r types: odor d e t e c t a b i l i t y , odor i n t e n s i t y d i f f e r e n c e t h r e s h o l d , odor r e c o g n i t i o n t h r e s h o l d , and odor annoyance t h r e s h o l d (see each s p e c i f i c type or d e f i n i -t i o n ) . In each type the odor t h r e s h o l d i s the odorant c o n c e n t r a -t i o n or change i n odorant r e q u i r e d to produce a d e f i n e d o l f a c t o r y e x perience. T h r e s h o l d v a l u e s are not as p r e c i s e as s p e c i f i c a n a l y t i c a l measurements of chemical c o n c e n t r a t i o n s . Since they are dependent on s u b j e c t i v e i n d i v i d u a l v a r i a t i o n , they are s u s c e p t i b l e to s h i f t s with experimental c o n d i t i o n s , m o t i v a t i o n , and other p s y c h o p h y s i c a l d i f f e r e n c e s . T h r e s h o l d v a l u e s are d e f i n e d on the b a s i s of the average, median, lowest, h i g h e s t , e t c . , response from a g i v e n t e s t p o p u l a t i o n . G e n e r a l l y , the median or 50% response from the t e s t p o p u l a t i o n i s the assumed b a s i s u n l e s s s t a t e d otherwise. s u p r a t h r e s h o l d Greater than the t h r e s h o l d . A l s o c a l l e d s u p r a l i m i n a l . I n - s i t u dynamic d i l u t i o n (ISDD) - continuous a d d i t i o n of a d i l u e n t gas to a d i r e c t flow from an odorous source, such as s n i f f i n g a percentage of the ambient a i r through a hand-held c h a r c o a l f i l t e r . I n - s i t u s t a t i c d i l u t i o n (ISSD) - d i r e c t a d d i t i o n of an odorous source of ambient a i r i n t o a f i x e d d i l u e n t gas volume p r i o r to sample e v a l u a t i o n s , as i n a s t a t i c odor t e s t room. O f f - s i t e dynamic d i l u t i o n (OSDD) - continuous a d d i t i o n of a d i l u e n t gas to a continuous flow from a grab sample of an odorous source of ambient a i r , as i n a dynamic o l f a c t o m e t e r . O f f - s i t e s t a t i c d i l u t i o n (OSSD) - a d d i t i o n of a grab sample of an odorous source or ambient a i r to a f i x e d d i l u e n t gas volume p r i o r t o sample e v a l u a t i o n , as i n a s y r i n g e . Category e s t i m a t i o n A p s y c h o l o g i c a l method, i s one of the d i r e c t s c a l i n g approaches i n which the observer's task i s to a s s i g n a predetermined response category to a p e r c e p t i o n or s e n s a t i o n of a s t i m u l u s , or more t y p i c a l l y , a s e r i e s of s t i m u l i . G e n e r a l l y , odor response s c a l e s r e p r e s e n t equal and p e r c e p t i b l y d i f f e r e n t d i v i s i o n s of the s u p r a t h r e s h o l d i n t e n s i t y continuum. They may be i d e n t i f i e d both by numerals and by a d j e c t i v e s (e.g., weak, moderate, and strong o d o r ) . i x magnitude e s t i m a t i o n A p s y c h o l o g i c a l method, i s one of the d i r e c t s c a l i n g approaches i n which the observer's task i s to a s s i g n a value t o a p e r c e p t i o n or s e n s a t i o n of a stimulus or, more t y p i c a l l y , a s e r i e s of s t i m u l i . For example, he may a s s i g n the "standard" odorant a value of "10", one twice as i n t e n s e he may c a l l "20", one h a l f as i n t e n s e , "5", and so on. sensory panel A group of i n d i v i d u a l s t h a t may be s e l e c t e d on the b a s i s of s e n s i t i v i t y t o s t i m u l i , r e l i a b i l i t y , or whose p e r c e p t i o n s are judged to be r e p r e s e n t a t i v e of some l a r g e r p o p u l a t i o n , which i s used to o b t a i n i n f o r m a t i o n concerning the s u b j e c t i v e a t t r i b u t e s of p h y s i c a l s t i m u l i . t r i a n g l e t e s t A p s y c h o p h y s i c a l method f o r determining whether or not a d i f f e r -ence between two s t i m u l i can be d e t e c t e d beyond chance expecta-t i o n i n which i n d i v i d u a l s are r e q u i r e d t o choose which of three s t i m u l i (two of which are a l i k e and one which i s d i f f e r e n t ) i s the odd or d i f f e r e n t one. * Source: Franz 1977. ACKNOWLEDGEMENTS I would l i k e to acknowledge the p a t i e n t a s s i s t a n c e a f f o r d e d to me by my s u p e r v i s o r , Dr. N.R. B u l l e y . F u r t h e r thanks are due t o a l l of the members of the Bio-Resource E n g i n e e r i n g Department who p a r t i c i p a t e d on odor p a n e l s . To the other members of my Committee, my thanks f o r t h e i r d i r e c t i o n . I would a l s o l i k e t o acknowledge the e x c e l l e n t t y p i n g s e r v i c e s p r o v i d e d by Mrs. E n i d Stewart. THESIS OBJECTIVES To determine whether the odor t h r e s h o l d of a gas mixture emanating from anaerobic l i q u i d swine manure changes d u r i n g storage i n T e d l a r * p l a s t i c bags. To e v a l u a t e the e f f e c t i v e n e s s of short-term s u r f a c e a e r a t i o n f o r re d u c i n g the i n t e n s i t y of odors emanat from anaerobic swine manure. P o l y v i n y l F l u o r i d e P l a s t i c . 2. INTRODUCTION Obnoxious odors have always been a s s o c i a t e d with the r e a r i n g of animals i n confinement s i t u a t i o n s . Swine and p o u l t r y o p e r a t i o n s have p a r t i c u l a r l y bad odor problems because manure i s o f t e n handled i n a l i q u i d form which i s g e n e r a l l y under anaerobic c o n d i t i o n s . Odor problems are manifested more s t r o n g l y i n these types of o p e r a t i o n s because they occur on small l a n d bases a l l o w i n g c l o s e c o n t a c t with i n c r e a s i n g suburban p o p u l a t i o n s . Combining the small l a n d based aspect with i n c r e a s i n g r a t e s of s u b u r b a n i z a t i o n and the high odor p r o d u c t i o n c a p a b i l i t i e s of these farming o p e r a t i o n s , the number of complaints concerning odor p o l l u t i o n are l i k e l y to i n c r e a s e . In order to d e a l with t h i s problem odors must be c o n t r o l l e d i n animal r e a r i n g b u i l d i n g s , manure storage f a c i l i t i e s , and d u r i n g manure l a n d spreading o p e r a t i o n s . Many systems have been developed to e l i m i n a t e obnoxious odors from b u i l d i n g s and from s t o r e d manure. However, the e s s e n t i a l aspect of odor e v a l u a t i o n has been n e g l e c t e d i n most a g r i c u l -t u r a l odor c o n t r o l r e s e a r c h . Q u a n t i t a t i v e e v a l u a t i o n of a v a r i e t y of o d o r c c o n t r o l methods i s r e q u i r e d to decide which c o n t r o l methods can b e s t be recommended f o r the job. 3. There are a wide v a r i e t y of methods a v a i l a b l e which have been used to measure or attempt to measure odor. These i n c l u d e o b j e c t i v e chemical and p h y s i c a l measurement methods and s u b j e c t i v e sensory methods. At present, chemical and p h y s i c a l methods have not reached a high enough l e v e l of s o p h i s t i c a t i o n to measure odors a c c u r a t e l y . Work i n t h i s area i s c o n t i n u i n g , but u n t i l more u s e f u l r e s u l t s are obtained, the human nose w i l l have to a c t as a measuring instrument. A p a r t of the r e s e a r c h r e p o r t e d here was made p o s s i b l e when The B r i t i s h Columbia M i n i s t r y of A g r i c u l t u r e i n s t a l l e d a s u r f a c e f l o a t i n g a e r a t o r i n a swine manure storage tank as an odor c o n t r o l measure. The author was allowed access to these f a c i l i t i e s to conduct f i e l d t r i a l s i n c l u d i n g c o l l e c t i o n and a n a l y s i s of odorous gases over time. These samples were e v a l u a t e d by a panel of judges and a l s o the sample c o n t a i n e r e were e v a l u a t e d as to t h e i r s u i t a b i l i t y u s i n g the same odor measurement technique. PHYSIOLOGY OF ODOR PERCEPTION The chemical sense o f s m e l l appears t o have developed d u r i n g the e a r l y stages of e v o l u t i o n i n the animal kingdom. Although man's sense of smell seems t o have degenera-ted and i s c o n s i d e r e d rudimentary when compared t o o t h e r animals, the human nose can d e t e c t many o r g a n i c compounds i n the ppm and ppb ranges (Douek, 1973). The reason man's o l f a c t o r y organs have degenerated r e l a t i v e t o animals c o n s i d e r e d t o be lower on the e v o l u t i o n a r y t r e e may be a t t r i b u t e d t o the t r e e s themselves (Douek, 1973). When the f i r s t monkeys took t o the branches t h e i r environment was changed d r a s t i c a l l y . Because of t h e i r hew vantage p o i n t e y e s i g h t became the dominant u s e f u l sense. Due to t h i s a l a r g e r and l a r g e r p o r t i o n o f the b r a i n was r e q u i r e d t o i n t e r -p r e t t h i s i n f o r m a t i o n at the expense o f the p r e v i o u s l y more developed sense of s m e l l . A l s o , s i n c e b i n o c u l a r v i s i o n was an advantage, s e l e c t i o n r e s u l t e d i n a change i n the bony s t r u c t u r e of th e ' . s k u l l . T h i s caused the areas of o l f a c t o r y r e c e p t i o n to not o n l y be d i m i n i s h e d ;but t o move up i n s i d e the n a s a l c a v i t y . T h e r e f o r e , man's sense of s m e l l has i n e f f e c t y i e l d e d t o h i s sense of s i g h t (Douek, 1973). N a s a l C a v i t y The n a s a l c a v i t y i s a complex set o f chambers l i n e d mainly w i t h c i l i a t e d mucous membrane and d i v i d e d 5. b i l a t e r a l l y by a bony and c a r t i l a g i n o u s system. The g e n e r a l o r g a n i z a t i o n can be seen i n the l a t e r a l and cr o s s s e c t i o n views presented here (Figure 1). T h i s c a v i t y has s e v e r a l f u n c t i o n s the two most important b e i n g r e s p i r a t i o n and s m e l l . A i r i s i n s p i r e d , 10-20% being d i r e c t e d i n t o the upper r e g i o n s of the c a v i t y i n the v i c i n i t y of the o l f a c t o r y c l e f t or s l i t . O l f a c t o r y System. Douek (1973) has d i v i d e d the d i s c u s s i o n of the o l f a c t o r y system i n t o the p e r i p h e r a l o l f a c t o r y system and the c e n t r a l o l f a c t o r y system. The p e r i p h e r a l system i n c l u d e s the o l f a c t o r y e p i t h e l i u m , the o l f a c t o r y glands and the o l f a c t o r y pigments. The c e n t r a l system c o n s i s t s of the o l f a c t o r y bulb and i t s connection w i t h the p e r i p h e r a l o l f a c t o r y system and the b r a i n . P e r i p h e r a l The o l f a c t o r y e p i t h e l i u m v a r i e s i n s i z e but 2 averages 10 cm o v e r a l l c o n t a i n i n g an est i m a t e d ten m i l l i o n r e c e p t o r c e l l s . I t s o u t l i n e i s i r r e g u l a r and i t i s found i n the c l e f t formed by the top of the n a s a l septum, the upper p a r t o f the s u p e r i o r t u r b i n a t e and the ro o f of the n a s a l c a v i t y i n between. Three types of c e l l make up t h i s e p i t h e l i u m : The r e c e p t o r c e l l s , the s u p p o r t i n g c e l l s , and the b a s a l c e l l s . T h e i r g e n e r a l s t r u c t u r e and o r g a n i z a t i o n are shown (Figure 2 ) . A l s o shown are the Bowman's glands and the l o c a t i o n o f the 6. FIGURE 1. L a t e r a l and c r o s s e c t i o n a l views o f the human n a s a l c a v i t y . Fewer sub-fibre pairs in tapering Dense net-work of microvilli on surface of supporting cell Surface of receptor and supporting cells. FIGURE 2. C e l l s of the o l f a c t o r y e p i t h e l i u m 8. o l f a c t o r y pigments. C e n t r a l There are two o l f a c t o r y bulbs l o c a t e d underneath the f r o n t p a r t o f the b r a i n d i r e c t l y above the c r i b i f o r m p l a t e (Figure 3). The o l f a c t o r y bulb i s a complex o r g a n i z a -t i o n o f nerve c e l l s condensing the i n f o r m a t i o n from a myriad of i n d i v i d u a l o l f a c t o r y nerves t o a s m a l l e r number o f secondary nervous pathways. There are a l s o outgoing and incoming nerve f i b e r s connecting the o l f a c t o r y bulbs w i t h the b r a i n . T h i s allows communication of odor s e n s a t i o n t o the b r a i n and a l s o feedback from the b r a i n to the o l f a c t o r y b u l b s . In summary the odorous molecules i n t e r a c t i n some way w i t h primary odor r e c e p t o r s i n the o l f a c t o r y e p i t h e l i u m and raw s i g n a l s are generated by a l a r g e numler of r e c e p t o r s . These s i g n a l s are r e f i n e d i n the o l f a c t o r y b u l b and i n p a r t at l e a s t decoded. F i n a l l y , the b r a i n i n t e r p r e t s the s i g n a l s and a response i s generated. T h i s r e a c t i o n may be a hunger impulse, an a v e r s i o n r e a c t i o n o r one o f many other r e a c t i o n s r e l a t e d t o odors d e t e c t e d i n the environment. 9. FIGURE 3. L o c a t i o n of the o l f a c t o r y bulbs 10. THE MOLECULAR BASIS OF OLFACTION How odorous molecules i n t e r a c t s p e c i f i c a l l y with receptor c e l l s to produce olfactory responses i s regrettably not well understood. I f the s p e c i f i c molecular attributes of a compound which man interprets as a "smell" were known, then the chemical changes required to eliminate or a l t e r the odor would be much clearer. Of the many theories explaining the mechanism of o l f a c t i o n the two receiving most support are the Dyson-Wright vi b r a t i o n theory (Wright, 1957) and the Moncreiff-Amoore stereo chemical theory (Amoore et a l . , 1964). The v i b r a t i o n a l theory postulates that low frequency intramolecular vibrations determine the odor qua l i t y of a molecule. In recent publica-tions by Wright (19 77) i t has been suggested that energy transfers occur between odorous molecules and membrane bound receptor molecules. The energy transfers are thought to be in the low v i b r a t i o n a l range between 100 and 600 wave numbers. If a large enough number of couplings occur per unit time the membrane permeability may be altered i n some way, r e s u l t i n g i n an action p o t e n t i a l i n the nerve. Wright also suggests that there may be up to t h i r t y d i f f e r e n t types of receptors present i n the olfactory epithelium responding to d i f f e r e n t frequencies of vibr a t i o n . 11. The s t e r e o c h e m i c a l theory p o s t u l a t e s t h a t odorant molecules w i t h a p a r t i c u l a r c o n f i g u r a t i o n i n t e r a c t w i t h complementary s i t e s on the membrane s u r f a c e o f the r e c e p t o r . The l o c k and key analogy, s i m i l a r t o t h a t used f o r enzyme f u n c t i o n , i s used t o help e x p l a i n t h i s mechanism. Which of these t h e o r i e s i s the c o r r e c t one remains t o be determined. Both approaches can be used t o e x p l a i n many f a c t s about o l f a c t i o n and both have been used t o a l i m i t e d e x t e n t t o make p r e d i c t i o n s about the odor o f c e r t a i n compounds. I t i s p o s s i b l e t h a t both t h e o r i e s w i l l have t o be combined i n the f i n a l a n a l y s i s o f the p r o c e s s . 12. ODOR MEASUREMENT-ANALYTICAL TECHNIQUES To measure odor i t must f i r s t be deci d e d which dimension of an odor i s most important. Odors can be des-c r i b e d i n terms of t h e i r q u a l i t y , i n t e n s i t y , d e t e c t a b i l i t y and a c c e p t a b i l i t y (Franz, 1977). Q u a l i t y "A dimension of odor i d e n t i f y i n g i t s c h a r a c t e r i s -t i c s through comparison to known o r p r e v i o u s l y sensed odorants. Odor q u a l i t y can be d e s c r i b e d as 'what something sm e l l s l i k e ' , and i s always r e l a t e d to known s t i m u l i or p r e v i o u s l y e x p e r i e n c e d s m e l l s . These c h a r a c t e r i s t i c s , along w i t h i n t e n s i t y , have s i g n i f i c a n c e i n determining a c c e p t a b i l i t y of t h a t odor to the sensor...." A c c e p t a b i l i t y "The continuum w i t h judgements of p o s i t i v e response (acceptance, p l e a s u r e , or l i k i n g ) at the one extreme and a negative response (non-acceptance, d i s p l e a s u r e o r r e j e c t i o n ) at the other extreme. The p o s i t i o n on the continuum at which a given s t i m u l u s i s p l a c e d may d i f f e r w i t h the i n d i v i d u a l , h i s c o n d i t i o n , h i s environment, a t t i t u d e s , e x p e r i e n c e and the l i k e " I n t e n s i t y ".... A q u a n t i t a t i v e a t t r i b u t e of s t i m u l i i roughly - -- c o r r e l a t i v e w i t h the s t r e n g t h o f the s t i m u l u s ; b r i g h t n e s s o f c o l o r s , loudness of sounds, 's t r e n g t h ' o f a t a s t e or s m e l l . T h i s may be measured by category e s t i m a t i o n , magnitude e s t i m a t i o n , or comparisons w i t h r e f e r e n c e odorants. A dimension of odor " D e t e c t a b i l i t y " The minimum c o n c e n t r a t i o n which can be d e t e c t e d as an odor ( i . e . b e i n g d i f f e r e n t from the background) but not n e c e s s a r i l y i d e n t i f i e d as t o odor q u a l i t y . A dimension of odor " I t can be seen t h a t these dimensions i n t e r a c t t o a c e r t a i n e x tent. A c c e p t a b i l i t y depends on both q u a l i t y and i n t e n s i t y and q u a l i t y w i l l depend somewhat on a c c e p t a b i l i t y . When measuring animal waste odors f o r the purpose of comparing odor c o n t r o l systems or to decide whether odor c o n t r o l i s r e q u i r e d , the l e a s t s u b j e c t i v e measurement should be used. Not only are odor q u a l i t y and a c c e p t a b i l i t y the h a r d e s t to measure o b j e c t i v e l y but i n s i t u a t i o n s wherelodor c o n t r o l has a l r e a d y been deemed necessary, these dimensions have a l r e a d y been judged i m p l i c i t l y . The most o b j e c t i v e method f o r odor measurement i s to c h e m i c a l l y or p h y s i c a l l y measure odorant c o n c e n t r a t i o n s which can then be r e l a t e d t o p e r c e i v e d i n t e n s i t y measured under c o n t r o l l e d c o n d i t i o n s . T h i s way a c o r r e l a t i o n i s achieved between the more r e l i a b l e , o b j e c t i v e method and the l e s s r e l i a b l e s u b j e c t i v e method. T h i s type of approach has had l i m i t e d a p p l i c a t i o n i n i n d u s t r i e s where the odor source 14. i s both constant and i n h i g h c o n c e n t r a t i o n , (Duffee 1973). For complex ambient l e v e l odor sources such as those found i n a g r i c u l t u r e , chemical and p h y s i c a l measurement techniques are not s e n s i t i v e enough as y e t . Measurement of animal waste odors has employed d e t e c t a b i l i t y t h r e s h o l d and s u p r a t h r e s h o l d i n t e n s i t y d e t e r m i n a t i o n s . Sensory odor measurement f o r the m a j o r i t y Q f methods can be broken down i n t o s e v e r a l s e q u e n t i a l s t e p s , each o f which i s e q u a l l y important. 1. Sample c o l l e c t i o n . 2. D i l u t i o n and p r e s e n t a t i o n to an i n d i v i d u a l or p a n e l . 3. I n d i c a t i o n of response. 4. I n t e r p r e t a t i o n o f response. ( L i n d v a l l , 1970). Some p o r t a b l e systems combine steps 1 and 2 i n t o a s i n g l e process and t h i s w i l l be i n d i c a t e d when such a system i s d i s c u s s e d . Sample C o l l e c t i o n . Whether odors are e v a l u a t e d on s i t e or i n a l a b o r a -t o r y some k i n d o f sampling procedure must precede any e v a l u a t i o n . Depending on the type o f e v a l u a t i o n the odorous m a t e r i a l may be sampled d i r e c t l y or an odorous air. sample may be c o l l e c t e d i n the v i c i n i t y of the source. Sampling wastes d i r e c t l y f o r subsequent odor a n a l y s i s i s s u b j e c t t o the same r u l e s as would be f o l l o w e d f o r any other a n a l y t i c a l d e t e r m i n a t i o n c a r r i e d out on a heterogenous system. 15. An attempt should be made t o minimize changes i n the sampled m a t e r i a l b e f o r e a n a l y s i s . P h y s i c a l parameters such as pH, temperature and s o l i d s content should a l s o be measured. The author has not found any l i t e r a t u r e d e a l i n g w i t h the e f f e c t of sampling technique (e.g. storage time) on r e s u l t s from sensory a n a l y s i s on d i r e c t l y sampled odorous waste m a t e r i a l s . There i s r e l a t i v e l y more work i n the l i t e r a t u r e d e a l i n g with c o l l e c t i o n o f odorous a i r samples i n the v i c i n i t y . of the source. Again t h e r e are many f a c t o r s t h a t must be c a r e f u l l y noted. These i n c l u d e l o c a t i o n of sampling apparatus, time over which sampling o c c u r s , number of samples taken, a a complete d e s c r i p t i o n o f the sampling device and m a t e r i a l s used and the type of v e s s e l used t o s t o r e the c o l l e c t e d sample. In sample c o l l e c t i o n the s i n g l e g r e a t e s t problem i s the p o s s i b l e s e l e c t i v e a d s o r p t i o n o r a b s o r p t i o n of odorous chemical components i n sampling l i n e s and i n the sample c o n t a i n e r i t s e l f . A l s o , r e l a t e d t o t h i s i s the p o s s i b i l i t y of chemical changes o c c u r r i n g i n the odorous components d u r i n g s t o r a g e . The g r e a t e r the sto r a g e c o n t a i n e r and sample l i n e s u r f a c e area per u n i t volume of c o l l e c t e d gas, the g r e a t e r the e f f e c t the s u r f a c e may have on the r e s u l t a n t odor l e v e l , (Duffee e t a l . , 1973; Wade e t a l . , 1974). The degree of a d s o r p t i o n w i l l be a f u n c t i o n of storage c o n t a i n e r m a t e r i a l . A number of authors have looked a t t h i s problem u s i n g d i f f e r e n t odorants and storage c o n t a i n e r s of d i f f e r e n t composition. They used dynamic d i l u t i o n t o t h r e s h o l d methods to determine whether changes i n odor l e v e l had oc c u r r e d . 16. Heraeon (196 8) r e p o r t e d t h a t 3-5ft p o l y e t h y l e n e bags cause odor d e t e r i o r a t i o n a f t e r 2-3 hours. On the oth e r hand, Dravnieks and Prokop (1975) found t h a t a v a l e r a l d e h y d e / a i r mixture was s t a b l e f o r 48 hours, and e f f l u e n t from two re n d e r i n g p l a n t s was s t a b l e up t o 96 hours a f t e r sampling i n t h i c k - w a l l e d p o l y e t h y l e n e bags. Kenson e t a l . (19 75) t e s t e d T e d l a r , Mylar, Saran t h i c k - w a l l e d p o l y e t h y l e n e , g l a s s and s t a i n l e s s s t e e l storage c o n t a i n e r s u s i n g i n sit,u dynamic d i l u t i o n (IS DD-no storage) as a comparative standard. T h e i r c o n c l u s i o n s suggest t h a t storage f o r up t o 24 hours i n p r e c o n d i t i o n e d c o n t a i n e r s was p e r m i s s i b l e f o r r e n d e r i n g p l a n t and pulp-and-paper odors. Storage was not f e a s i b l e i f c o n t a i n e r s were not p r e c o n d i t i o n e d ( f l u s h e d w i t h sample). Dravnieks e t a l (1978) has r e p o r t e d t h a t r e n d e r i n g p l a n t odors are s t a b l e up t o 48 hours i n T e f l o n p l a s t i c bags. Measurements were made u s i n g a l a r g e p a n e l (9 people) and a dynamic d i l u t i o n t o t h r e s h o l d f o r c e d choice t r i a n g l e measure-ment. Cormack e t a l . (1974) have a l s o found T e d l a r 1PVF) p l a s t i c bags t o be s u i t a b l e f o r sample sto r a g e . G l a s s and s t a i n l e s s s t e e l were found to be unacceptable. I t i s apparent t h a t each odor source i s unique and t e s t s should be c a r r i e d out i n each new s i t u a t i o n t o determine al l o w a b l e aging of samples f o r the c o n t a i n e r b e i n g used. The 17. author has found no p u b l i s h e d data where changes i n odor q u a l i t y due t o storage were being measured although i t i s q u i t e l i k e l y t h a t t h i s occurs. D i l u t i o n and P r e s e n t a t i o n Both t h r e s h o l d and s u p r a t h r e s h o l d measurements r e q u i r e p r e s e n t a t i o n o f d i f f e r e n t l e v e l s of odorants to pane-l i s t s . The method employed f o r d i l u t i o n and the r a t e s and order of p r e s e n t a t i o n vary c o n s i d e r a b l y . In s i t u a t i o n s where odorous m a t e r i a l s are sampled d i r e c t l y and presented to p a n e l i s t s f o r s u p r a t h r e s h o l d i n t e n s i t y e v a l u a t i o n , d i l u t i o n i s seldom employed. However, i n those cases where t h r e s h o l d determinations have been made, d i l u t i o n was g e n e r a l l y c a r r i e d out u s i n g d i s t i l l e d water (Sobel, 1969; Burnett, and Ddndero, 1969). P r e s e n t a t i o n s to p a n e l i s t s f o r these types of e v a l u a -t i o n s were g e n e r a l l y simple, i n v o l v i n g s n i f f i n g at the open, tops of j a r s or f l a s k s . F o r the de t e r m i n a t i o n o f the odor t h r e s h o l d of gaseous samples, both s t a t i c and dynamic d i l u t i o n methods have been employed. Methods to achieve these d i l u t i o n s have been summarized and d i s c u s s e d (Shroeder, 19 75; Duffee et.-al; 19 73; L i n d v a l l , 1970; Dravnieks-and Prokop,' 1975.; Dravnieks, 1977; D o r l i n g 1977) . S t a t i c d i l u t i o n procedures, mainly due t o t h e i r r e l a t i v e s i m p l i c i t y , have r e c e i v e d a l a r g e amount o f use i n the p a s t . So much so t h a t the s t a t i c Syringe D o l u t i o n Technique has been accepted as a standard odor t h r e s h o l d 18. measurement method by the ASTM i n the U n i t e d S t a t e s . Unfor-t u n a t e l y r e s e a r c h has shown the method t o be i n a c c u r a t e due p a r t l y to u n n a t u r a l p r e s e n t a t i o n t o the nose, a d s o r p t i o n d u r i n g sample t r a n s f e r , and s m a l l sample s i z e (Duffee . e t a l , 1973). O f f - s i t e dynamic d i l u t i o n (OSDD) and o f f - s i t e s t a t i c d i l u t i o n , (O'SSD) were compared t o the o n - s i t e dynamic d i l u t i o n method (OSDD) and i t was found t h a t OSSD gave v a l u e s up t o 300% lower than OSDD. I t was assumed t h a t OSDD was the b e s t measure and was, t h e r e f o r e , used as a comparative standard. These authors have suggested t h a t the b e s t p r a c t i c a l method f o r determining odor t h r e s h o l d s i s dynamic d i l u t i o n by mixing measured flows of sample and non-odorous a i r . Even w i t h i n the realm of dynamic d i l u t i o n t here e x i s t s d i v e r s i t y between methods. These v a r i o u s methods are d e s c r i b e d by Schroeder (1975) and the e s s e n t i a l d i f f e r e n c e s between systems v/hich were brought t o l i g h t i n c l u d e d flow r a t e of a i r , i n i t i a l d i l u t i o n gas used and method of presen-t a t i o n to the p a n e l i s t . Some systems employed a hig h flow r a t e and presented the sample t o the p a n e l i s t i n an odor room, a hood or mask which allowed f r e e r e s p i r a t i o n . Other methods employed low flov; r a t e s r e q u i r i n g t h a t the p a n e l i s t e v a l u a t e the odor by s n i f f i n g gases from a p o r t or a s e r i e s of p o r t s . F u r t h e r , some systems employed n i t r o g e n as the d i l u t i o n gas f o r the i n i t i a l d i l u t i o n i n o r d e r t o a v o i d o x i d a t i o n o f odorous components i n the odor sample. 19. A l l of the systems d e s c r i b e d have t h e i r own advan-tages and disadvantages. A l s o i t must be r e a l i z e d t h a t each method w i l l r e s u l t i n d i f f e r e n t t h r e s h o l d l e v e l s f o r the same sample depending on choice of p a n e l i s t s , mode of sample presen-t a t i o n and s t a t i s t i c a l design of experiment. From t h i s l i t e r a t u r e some i d e a can be gained as t o what c o n s t i t u t e s a good d i l u t i o n system. F i r s t , s u r f a c e t o volume r a t i o s w i t h i n the system must be kept t o a minimum. Flow r a t e should be h i g h enough so t h a t dead spots are minimized and m a t e r i a l s of an i n e r t nature should be used on a l l s u r f a c e s t h a t c o n t a c t the gases to be e v a l u a t e d . A l s o , p r e s e n t a t i o n t o the p a n e l i s t must e i t h e r allow f r e e r e s p i r a t i o n o r , i f a s n i f f i n g p o r t i s used, a v o i d p a n e l i s t d i s c o m f o r t and unknown d i l u t i o n . L i n d v a l l (19 70) reviewed dynamic d i l u t i o n systems and i n d e s c r i b i n g h i s own d i l u t i o n equipment design i l l u s t r a t e d the important f a c e t s of an odor d i l u t i o n system. The system maintains r e l a t i v e l y h i g h flow r a t e s through an odor hood ( T e f l o n coated). I n i t i a l d i l u t i o n s of odorant are c a r r i e d out i n n i t r o g e n (avoids o x i d a t i o n ) and f i n a l d i l u t i o n s i n cleaned a i r . His system, although l a r g e and expensive has i n c o r p o r a t e d the best m a t e r i a l s with low odor a b s o r p t i v e p r o p e r t i e s and knowledge of p s y c h o - p h y s i c a l measurement and human p h y s i o l o g y . I t i s probably the best a l l round system the author has found r e p o r t e d . 20. Hemeon's system (196 8) i s a two-stage d i l u t i o n system u s i n g room a i r as a d i l u t i o n medium. Flow r a t e s are 35 cfm presented through a p o r t at face l e v e l . H is technique of category s c a l i n g and e x t r a p o l a t i o n back t o zero, to determine the t h r e s h o l d l e v e l , i s q u i t e d i f f e r e n t from the more u s u a l t h r e s h o l d method which r e q u i r e s the p a n e l i s t to respond t o a s l i g h t odor stimulus near the t h r e s h o l d . Dynamic d i l u t i o n methods which put some r e s t r i c -t i o n s on f l o w o f sample t o the nose i n c l u d e a dynamic f o r c e d -choice t r i a n g l e o l f a c t o m e t e r (Dravnieks and Prokop, 1975) and the scentometer (Huey e t a l . , 1960). Dravniek's system i s a two-stage d i l u t i o n system but flow r a t e s are q u i t e low (0.5 1/min) r e l a t i v e t o the human r e s t i n g i n h a l a t i o n r a t e (about 12 1/min). S n i f f i n g p o r t s are arranged i n a c i r c u l a r s y m e t r i c a l p a t t e r n , one p o r t d e l i v e r i n g odorous and the o t h e r two non-odorous a i r . S i x of these arrangements d e l i v e r s i x d i l u t i o n l e v e l s s i m u l t a n e o u s l y which are e v a l u a t e d i n sequence by p a n e l i s t s choosing one of the t h r e e p o r t s as the odorous one. I t has been shown t h a t the low flow r a t e r e s u l t s i n p a n e l c o n f u s i o n at low odor l e v e l s due t o background involvements (Wade e t a l . , 19 74). The scentometer, u n l i k e the o t h e r dynamic d i l u t i o n methods d e s c r i b e d , r e q u i r e s t h a t the motive f o r c e f o r a i r flow be p r o v i d e d by the human lungs. Therefore the r e s t r i c t i o n on 21. a i r flow i s only the resistance that the i n d i v i d u a l doing the sampling might sense. B a s i c a l l y i t i s hand held and d i l u t i o n a i r i s drawn through the nasal i n s e r t s . The d i l u t i o n a i r comes i n the top and bottom of the box, passing through activated charcoal beds. Odorous a i r i s brought i n t o the instrument through cali b r a t e d holes i n the end of the instrument which are stopped or opened depending on the d i l u t i o n desired. The design and use of t h i s instrument has been described (Huey, 1960). The order and time of stimulus presentation and inclusions of blanks have been shown to a f f e c t the response of panelists (Johansson e t al;-;1973; -Lindva.il19 70).. Adaptation effects are important when working at threshold l e v e l s , or above. Berglund e t a l (1973) found that adaptation to an odor stimulus near threshold, with a t e s t stimulus near threshold was rapid (20 seconds) and persisted longer as the adaptation stimulus increased i n strength. On the other hand, i t has been shown (Berglund, 19 74; Ekman et a l . , 1967) that adaptation to a constant supra-threshold stimulus caused an exponential decrease i n perceived i n t e n s i t y . To avoid adaptation e f f e c t s , a minimum of 30-60 seconds should be allowed between odor presentations (Berglund, 19 74). L i n d v a l l (1970) tested various orders of presen-tation that had been used previously i n sensory t e s t i n g . He concluded that the most p r a c t i c a l technique for measuring odorous a i r p o l l u t a i n t s , was the ascending method of l i m i t s . T h i s r e q u i r e s t h a t odor p r e s e n t a t i o n s begin at a l e v e l below t h r e s h o l d and i n c r e a s e i n steps w i t h a p e r i o d o f recover y allowed between each l e v e l . The p r e s e n t a t i o n s stop when the p a n e l i s t has responded c o r r e c t l y or some other predetermined c r i t e r i o n i s reached. Response C r i t e r i a and I n d i c a t i o n o f Response. Those conducting t e s t s must be very c l e a r on what c r i t e r i a the p a n e l i s t i s t o base a response. One must q u e s t i o n what a t h r e s h o l d i s so t h a t p a n e l i s t s can t e l l when t o respond. Questions i n c l u d e : 1) Is the s u b j e c t t o respond t o a d e t e c t i o n o f any p e r c e i v e d change i n st i m u l u s from the c o n t r o l gas? 2) Is the p a n e l i s t t o respond on p e r c e i v i n g a malodor? 3) Is the p a n e l i s t t o respond on a c t u a l r e c o g n i t i o n o f the odor? Another f a c t o r of importance to the p s y c h o - p h y s i c a l method i s the i n d i c a t i o n o f response. Methods i n c l u d e yes-no responses which depend on honesty and m o t i v a t i o n of p a n e l i s t s , a f o r c e d c h o i c e between two or more c a t e g o r i e s o r s e m i - f o r c e d choice between p a i r e d comparisons ( e i t h e r both are the same or one or the other i s d i f f e r e n t ) . L i n d v a l l i n d i c a t e s , a f t e r c a r r y i n g out v a r i o u s experiments, t h a t there i s l i t t l e d i f f e r e n c e i n r e s u l t s between the completely f o r c e d c h o i c e with f o u r a l t e r n a t i v e s and the semi - f o r c e d with two a l t e r n a t i v e s ( L i n d v a l l , 1970). H i s f i n a l c h o i c e f o r f i e l d type measurement of odor t h r e s h o l d s i s an ascending method o f l i m i t s with semi-forced c h o i c e p a i r e d comparisons although t h i s r e s u l t s i n a tendancy to put the t h r e s h o l d s l i g h t l y too h i g h . S i g n a l d e t e c t i o n theory which i s r e p o r t e d to c o r r e c t f o r response b i a s on the p a r t of the p a n e l i s t i s a l s o used (Berglund e t a l , 1971; L i n d v a l l , 1970). T h i s system i s l i m i t e d i n t h a t i t only works i n c l o s e p r o x i m i t y to the t h r e s h o l d and i t r e q u i r e s e x t e n s i v e t e s t i n g and p r e l i m i n a r y experiment-a t i o n to f i n d the proper range f o r each p a n e l i s t . I n d i c a t i o n of response i s a l s o important when conduct ing s u p r a - t h r e s h o l d i n v e s t i g a t i o n s . Responses i n c l u d e choosing a category or e s t i m a t i n g a r e l a t i v e change from a p r e v i o u s s t i m u l u s . These responses are g e n e r a l l y used to produce s u b j e c t i v e s c a l e s and are d i s c u s s e d i n d e t a i l by Cain and Moskowitz (19 74). I n t e r p r e t a t i o n of Responses. The l a s t step i s a l s o the most ;important step. Once a group of people have been coaxed to respond to'odors a t t h r e s h o l d or above t h r e s h o l d , t o make p a i r e d comparisons or f o r c e d choice t r i a n g l e s , and to gi v e responses t h a t a good a n a l y t i c a l instrument should g i v e , what do you do with the numbers? T h r e s h o l d methods r e s u l t i n data g i v i n g the number of d i l u t i o n s an odorous sample must undergo to reach a non-odorous s t a t e . T h i s data must be a c q u i r e d from a group of people and i n t e r p r e t a t i o n of the data i s a f f e c t e d by both the s i z e and composition of the group. The s i z e of the panel depends p a r t l y on the group r e p r e s e n t e d . A reasonable panel s i z e i s 5 to 8 people, below which i n d i v i d u a l v a r i a b i l i t y becomes much more e v i d e n t (Wade e t a l , 1974). The composition of the panel depends again on the p o p u l a t i o n i t isv/ibolEepresent. I f " t h e /panel i s merely f o r comparative purposes then p a i n s should be taken to screen the panel i n order to achieve as much u n i f o r m i t y as p o s s i b l e thereby i n c r e a s i n g p r e c i s i o n . S u p r a - t h r e s h o l d r e s u l t s are more complex and harder to i n t e r p r e t whereas t h r e s h o l d r e s u l t s d e a l with simple d i l u t i o n s to t h r e s h o l d . S u p r a - t h r e s h o l d e v a l u a t i o n s r e s u l t i n a s c a l e r e l a t i n g p e r c e i v e d i n t e n s i t y to e i t h e r a b s o l u t e c o n c e n t r a t i o n or d i l u t i o n s from a g i v e n l e v e l . I f p l o t t e d i n l o g - l o g c o o r d i n a t e s , a s t r a i g h t l i n e u s u a l l y r e s u l t s . T h i s k i n d of data r e f l e c t s the amount t h a t p e r c e p t i o n w i l l change with a g i v e n change i n the amount of odorant. S i m i l a r care with regard to panel s i z e and composition must be given to the i n t e r p r e t a t i o n of s u p r a - t h r e s h o l d r e s u l t s as was given to a n a l y s i s of t h r e s h o l d . ODOR MEASUREMENT - AGRICULTURE T h i s d i s c u s s i o n w i l l be l i m i t e d t o sensory odor measurement systems and w i l l i n c l u d e some which measure odor i n t e n s i t y u s i n g , i n most cases, category s c a l e s and odor d e t e c t a b i l i t y as measured by d i l u t i o n s to t h r e s h o l d . The v a r i o u s methods which have been used i n a g r i c u l t u r a l odor r e s e a r c h can be grouped on the b a s i s o f a number o f c r i t e r i a . The author has chosen the odor dimension being measured and the d i l u t i o n method employed as the most important. Odor I n t e n s i t y . Odor i n t e n s i t y i s g e n e r a l l y measured u s i n g e i t h e r vapour or l i q u i d d i l u t i o n systems. L i q u i d d i l u t i o n systems have been employed t o a much g r e a t e r extent than vapour d i l u t i o n systems, f o r a g r i c u l t u r a l odor measurement. There i s q u i t e a wide v a r i a t i o n i n the l i q u i d d i l u t i o n procedures used by d i f f e r e n t r e s e a r c h e r s but they are a l l s i m i l a r i n some r e s p e c t s . Most methods employ a category s c a l e o f judgements i n c l u d i n g from f o u r to eleve n p o i n t s on the s c a l e . Most a l s o i n c l u d e word d e s c r i p t i o n s at each p o i n t on the s c a l e such as f a i n t , d e f i n i t e , s t r o n g , very s t r o n g e t c . T h i s approach has been adopted from the food i n d u s t r y where e x t e n s i v e work has i n v o l v e d food and f l a v o r e v a l u a t i o n . Sobel (1972) was one of the f i r s t to. employ these category e s t i m a t i o n techniques i n a g r i c u l t u r a l odor e v a l u a t i o n . He used a s c a l e of 0-10 w i t h a p p r o p r i a t e d e s c r i p t o r s f o r r a t i n g i n t e n s i t y and o f f e n s i v e n e s s . J a r s o f manure, having r e c e i v e d v a r i o u s treatments, were presented to a pa n e l o f people and judgements made. The numbers generated were then t r e a t e d s t a t i s t i c a l l y and used t o make q u a n t i t a t i v e compari-sons among treatments as t o t h e i r e f f e c t i v e n e s s a t red u c i n g odors. Sobel's g e n e r a l technique was used by U l i c h (1975) t o assess the e f f e c t i v e n e s s o f v a r i o u s chemicals i n the con-t r o l o f odors from manure samples o b t a i n e d at a beef c a t t l e f e e d l o t . A p p l i c a t i o n r a t e s f o r the v a r i o u s treatments were not s t a t e d c l e a r l y . U l i c h r e p o r t s the q u a n t i t y o f d i f f e r e n t chemicals r e q u i r e d f o r t o t a l odor s u p p r e s s i o n although none of the pane l data given i n d i c a t e s any measured valu e s below the t h i r d l e v e l of the s c a l e ( f a i n t ) f o r e i t h e r presence o r o f f e n s i v e n e s s . T h i s i n d i c a t e s some c o n f u s i o n as t o how the panel data can be v a l i d l y used on inadequate r e p o r t i n g procedures. Cole e t a l . (1976) has' a l s o used Sobel's method to compare v a r i o u s chemical treatments f o r the c o n t r o l o f odors from l i q u i d swine manure. A p a n e l o f 5-10 members was used and p a n e l means were generated. The odor data were not s t a t i s t i c a l l y analyzed but simple o b s e r v a t i o n s were made a f t e r p l o t t i n g the means. 27. Others have used altered versions of Sobel 1s method. Ogilvie and Dale (197T) used an 8 point scale in evaluation of aerated c a t t l e manure. He also used what he terms "a less elaborate sampling arrangement" than Sobel. E s s e n t i a l l y no information i s given describing sampling procedures or panel presentation techniques although the number of panelists used i s given . Overcash et a l (1976) considered the relationship between lagoon management and odor generation. I n i t i a l odor work consisted of opinions from students and researchers in the v i c i n i t y of the lagoons being tested. He then took samples from lagoons at d i f f e r e n t loading rates and had a panel assign values from a four point category scale of t h i s s i z e . Burnetts and Dondero (1970) used a 10 point category scale, but with a difference. He studied the e f f e c t of chemical additives on odor emitted from poultry manure. Using an untreated v i a l of manure as a standard,panelists assigned numbers indicating the degree of s i m i l a r i t y between a sample and the standard. Large amounts of data were gathered with with well controlled experimental conditions. The problem i s that by generating values which simply give an indication 0 28. of d i s s i m i l a r i t y from u n t r e a t e d manure no knowledge i s gained concerning the a c c e p t a b i l i t y of the r e s u l t a n t odor. T h i s work does not d i f f e r e n t i a t e between odor c o n t r o l m a t e r i a l s on the b a s i s of which w i l l do th.e>best job, but merely i n d i c a t e s divergence from a standard odor. In a study by McGrath (1977), p a n e l i s t s standing downwind from an u n t r e a t e d manure spreading o p e r a t i o n assessed the r e s u l t a n t odors. They then compared three t r e a t e d loads to the i n i t i a l u n t r e a t e d l o a d . U n f o r t u n a t e l y , no attempt was made to a l l o w p a n e l i s t s time f o r t h e i r o l f a c t o r y sense to r e c o v e r between t r i a l s . D i r e c t v i s u a l c o n t a c t and knowledge of treatments may a l s o havee s e v e r e l y b i a s e d the r e s u l t s . Hashimoto (19 74) used Sobel's method to e v a l u a t e a e r a t i o n of p o u l t r y wastes f o r odor c o n t r o l . In t h i s study, b e s i d e s the b a s i c drawbacks of category e s t i m a t i o n s , there were problems with the methods of sampling and panel p r e s e n t a t i o n . A i r from two r e a c t i o n v e s s e l s was p i p e d to two g l a s s f u n n e l s i n a booth. The p a n e l i s t e n t e r e d the booth, opened the flow v a l v e f o r each v e s s e l and determined the odor i n t e n s i t y by category e s t i m a t i o n . A f t e r the f i r s t sampling the p a n e l i s t would then know which sample was which, s e v e r e l y b i a s i n g h i s judgement i n subsequent t e s t s . Sobel's work and the work of others who have used h i s measurement method have c o n t r i b u t e d some u s e f u l informa-t i o n about odor c o n t r o l techniques and systems. There i s a l i m i t , however, to the amount of i n f o r m a t i o n forthcoming from t h i s technique. Stevens-(19 71) examined a v a r i e t y of category s c a l e s i n a number of d i f f e r e n t c o n t i n u a and concluded t h a t t h e i r use i n q u a n t i t a t i v e s t u d i e s was q u e s t i o n a b l e . Data generated by category e s t i m a t i o n are supposed to be of an equal i n t e r v a l n a t u r e , e.g. the d i f f e r e n c e between s t r o n g and very s t r o n g should be the same as the d i f f e r e n c e between f a i n t and moderate. Since i t i s u n l i k e l y t h a t the s i z e of these i n t e r v a l s w i l l be equal (Stevens, 1971), a r i t h m e t i c averages and o t h e r s a t i s t i c a l o p e r a t i o n s assuming equal iafcexvaldata have l i m i t e d v a l i d i t y . T h e r e f o r e , category s c a l i n g i s more v a l i d l y used f o r r a n k i n g odor c o n t r o l chemicals or methods and does not allow v a l i d q u a n t i t a t i v e c o n c l u s i o n s . Vapour D i l u t i o n The author has found o n l y one r e p o r t a p p l y i n g vapour d i l u t i o n techniques and s u p r a t h r e s h o l d a n a l y s i s to the measurement of odors from a g r i c u l t u r a l sources. L i n d v a l l e t a l (1974) i n v e s t i g a t e d chemical treatment and b u r i a l by 30. measuring t h r e s h o l d and s u p r a t h r e s h o l d i n t e n s i t y l e v e l s o f odorous gases emanating from t r e a t e d and u n t r e a t e d manure d u r i n g and a f t e r l a n d s preading. Magnitude matching ( r a t i o s c a l i n g technique) was used t o produce p s y c h o - p h y s i c a l f u n c t i o n s r e l a t i n g p e r c e i v e d odor i n t e n s i t y t o manure gas d i l u t i o n . L i n d v a l l p o i n t e d out that these measurements d i d not g i v e p r o o f of d i f f e r e n c e s between the f u n c t i o n s f o r the v a r i o u s treatments beyond what c o u l d be determined from t h r e s h o l d measurements. Th r e s h o l d Measurement L i n d v a l l e t a l . (1974) has p u b l i s h e d data from measurements o f odorous emissions from animal wastes, They were concerned w i t h comparisons of odor c o n t r o l f o r v a r i o u s waste treatments and land a p p l i c a t i o n methods. A comparison was made of odors r e l e a s e d from l a n d r e c e i v i n g e i t h e r a e r o b i c a l l y or a n a e r o b i c a l l y s t o r e d swine manure. The e f f e c t of plowing a f t e r manure a p p l i c a t i o n as w e l l as subsurface i n j e c t i o n on odor p r o d u c t i o n was-also s t u d i e d . The method 2 used was to p l a c e a 1.5m hood over the area t o be t e s t e d , move a i r through the hood at a low (2.2 mph) r a t e and determine d e t e c t i o n t h r e s h o l d s w i t h an o n - s i t e o l f a c t o r y l a b o r a t o r y . T h i s dynamic odor measurement system i s e x t e n s i v e l y d e s c r i b e d by L i n d v a l l (1970) and was developed i n i t i a l l y to make detec-t i o n t h r e s h o l d odor measurements of pulp and paper e m i s s i o n s . Data presented i s of the type necessary t o b u i l d up an under-s t a n d i n g of q u a n t i t a t i v e d i f f e r e n c e s between odor c o n t r o l techniques. S p e c i f i c a l l y , i t was found t h a t b u r i a l techniques r e s u l t e d i n r e d u c t i o n of odor s t r e n g t h (as measured by d i l u t i o n s to threshold) by one or two powers o f ten. T h i s i s q u i t e an advance over many papers which r e p o r t o n l y r e l a -t i v e d i f f e r e n c e s between a l i m i t e d number of te c h n i q u e s , u s u a l l y based on an i n d i v i d u a l ' s s u b j e c t i v e n o n - q u a n t i t a t i v e e v a l u a t i o n . Another instrument used t o measure odor t h r e s h o l d i s the p o r t a b l e , hand h e l d scentometer. T h i s instrument has been used e x t e n s i v e l y i n the Un i t e d S t a t e s f o r measuring ambient odor t h r e s h o l d s around l i v e s t o c k r a i s i n g o p e r a t i o n s . I t i s even b e i n g c o n s i d e r e d i n many s t a t e s as an instrument f o r making r e g u l a t o r y d e c i s i o n s . I t was developed i n i t i a l l y f o r f i e l d a n a l y s i s o f ambient odors from i n d u s t r i a l sources (Huey, 1960). I t c o n s i s t s of two h o r i z o n t a l f l a t - p l a t e carbon f i l t e r s w i t h a r e c t a n g u l a r mixing chamber between. Odorous a i r i s admitted a t the end of the box through c a l i -b r a t e d holes which are opened or c l o s e d depending on the d i l u t i o n d e s i r e d . The motive f o r c e f o r d i l u t i o n i s p r o v i d e d by the observer who breathes through the instrument w i t h the a i d of n a s a l i n s e r t s . Sweeten e t a l . (1977), Sweeten and -Redell (1976) and R e d e l l and Sweeten (1975) have a l l r e p o r t e d on the use of 32. t h i s instrument to e v a l u a t e ambient odors a t c a t t l e f e e d l o t s . G e n e r a l l y , only one observer was used at any one time which c a s t s some doubt on the r e s u l t s , due t o person t o person v a r i a b i l i t y . R e d d e l l and Sweeten (1975) took scentometer readings over a f a i r l y long p e r i o d at a swine o p e r a t i o n and s e v e r a l beef c a t t l e f e e d l o t s . In a c t u a l f a c t the bulk o f the paper d i s c u s s e d r e s u l t s from l i q u i d d i l u t i o n o f manure and l i t t l e i s s a i d about the scentometer. The c o n c l u s i o n s were t h a t d i f f e r e n t observers get d i f f e r e n t r e s u l t s from the scentometer and t h a t the scentometer i s an i m p r e c i s e measuring instrument. Sweeten and R e d d e l l (1976) d i s c u s s management aspects of odor c o n t r o l i n f e e d l o t s and p r e s e n t a t a b l e of scentometer readings from f e e d l o t s c o v e r i n g a two year p e r i o d (19 73-75). The most observers used f o r any one e v a l u a t i o n was two and more o f t e n only one. Sweeten and R e d d e l l e t a l . (19 77) used the scentometer to evaluate g e n e r a l f e e d l o t odors, t o determine the e f f e c t s on odor of a p p l i c a t i o n s of b a c t e r i a l c u l t u r e s t o f e e d l o t s u r f a c e s and to determine the e f f e c t on manure odor of f e e d i n g c a l c i u m b e n t o n i t e to c a t t l e . Again, too few observers were used to get meaningful r e s u l t s . Miner and Stroh, (1976) researched the e f f e c t s of a v a r i e t y of s u r f a c e a p p l i e d m a t e r i a l s on odor i n t e n s i t y a t a l a r g e c a t t l e f e e d l o t . Odor analyses f o r the v a r i o u s t r e a t -ments were c a r r e d out on two separate o c c a s i o n s u s i n g a d i f f e r e n t observer on each o c c a s i o n . Again, t h i s i s too few o b s e r v a t i o n s to o b t a i n u s e f u l r e s u l t s . A l s o manure samples were t r a n s p o r t e d elsewhere i n p l a s t i c bags f o r a n a l y s i s and changes might have occ u r r e d d u r i n g t r a n s p o r t . I t i s i n t e r e s t i n g t o note here t h a t none of the above authors f e e l the scent-ometer to be a u s e f u l r e s e a r c h t o o l . Lack of f a i t h i n the scentometer i s strengthened by Dravnieks e t a l (1978) who s t a t e s t h a t use of t h i s instrument l e a d to b i a s i n judgement by obs e r v e r s . Other problems with the scentometer i n c l u d e b i a s through v i s u a l c o n t a c t with the odor source, d e s e n s i t i z a t i o n of the nose as the observer approaches the odor source, unknown time to r e s t o r e s e n s i t i v i t y by b r e a t h i n g through the scentometer, and l a c k of s u f f i c i e n t number of p a n e l i s t s . Prokop (19 74) and L i c h t and Miner (19 78) have p o i n t e d out s i m i l a r drawbacks t o the use of the instrument. Another completely p o r t a b l e o l f a c t o m e t e r was d e s c r i b e d by Mannebeck (19 741. T h i s device made use of o d o r l e s s compressed a i r as a d i l u t i n g stream and a j e t pump to draw i n odorous a i r . A l s o i n c l u d e d was a face mask f o r p r e s e n t a t i o n of odor to the a n a l y s t . Flow r a t e s were measured by rotometers and the pressure of the odorkess a i r e n t e r i n g the j e t pump. The d i l u t i o n range was up to 3,000 times. The system seems reasonable but no measurement data was presented i n the paper. A l s o , as with the scentometer, observer judgement may be b i a s e d by being exposed v i s u a l l y to the odor source. L i q u i d D i l u t i o n . Determination of odor t h r e s h o l d by l i q u i d d i l u t i o n of animal waste has been c a r r i e d out by R e d d e l l and Sweeten (1975) who used the method d e s c r i b e d and used by Burnett and Dondero (1969). Samples of waste were d i l u t e d with d i s t i l l e d water and p a n e l i s t s e v a l u a t e d whether an odor was p r e s e n t by s n i f f i n g the f l a s k s . U n f o r t u n a t e l y d i l u t i o n i n water has an unknown e f f e c t on changing gas e v o l u t i o n r a t i o s and r a t e s of the v a r i o u s odorous components of the waste. LITERATURE CONCLUSIONS I t i s w e l l e s t a b l i s h e d t h a t the c o n t r o l o f a g r i c u l t u r a l odors r e l i e s t o a l a r g e extent on the use of a p r a c t i c a l odor measurement technique f o r e v a l u a t i o n of v a r i o u s odor c o n t r o l methods. There are many approaches t o the pro-blem o f odor measurement i n c l u d i n g o b j e c t i v e chemical and p h y s i c a l techniques and s u b j e c t i v e sensory methods. O b j e c t i v e chemical methods w i l l e v e n t u a l l y p l a y a very important r o l e i n a g r i c u l t u r a l odor measurement when the s e n s i t i v i t y of the v a r i o u s techniques i s i n c r e a s e d . The eve n t u a l g o a l i s a qu i c k in e x p e n s i v e method r e l y i n g on q u a n t i t a t i v e , o b j e c t i v e measurements which have been success-f u l l y c o r r e l a t e d w i t h the s u b j e c t i v e sensory dimensions o f odor (Dravnieks, 197.7; D o r l i n g , 1977; E l l i o t e t a l . (1978). U n t i l t h i s g o a l i s r e a l i z e d , l e s s r e l i a b l e but s t i l l u s e f u l sensory methods must s u f f i c e . When odors o f a h i g h l y u n d e s i r a b l e nature are bein g e v a l u a t e d hedonic ( l i k i n g o r d i s l i k i n g ) approaches are of l i m i t e d v a l u e . A l s o s u p r a t h r e s h o l d i n t e n s i t y determina-t i o n s as normally c a r r i e d out i n animal waste odor measurement onl y p r o v i d e enough i n f o r m a t i o n t o rank odor c o n t r o l methods on a " w i t h i n experiment" b a s i s . They do not allow q u a n t i t a -t i v e comparison from one study t o another. Although dynamic vapor d i l u t i o n and odor t h r e s h o l d d e t e r m i n a t i o n has l i m i t a -t i o n s and many u n c o n t r o l l a b l e v a r i a b l e s i t i s the b e s t 36. p r a c t i c a b l e method a t t h i s time f o r the a n a l y s i s o f animal waste odors i f some k i n d o f q u a n t i t a t i v e measure of the odor presence i s d e s i r e d ( D o r l i n g , 1977; L i n d v a l l , 1970; Dravnieks, 19 77). MATERIALS AND METHODS The Olfactometer Sensory analyses were accomplished u s i n g a dynamic d i l u t i o n o l f a c t o m e r , (MISCO)* and a pane l o f f i v e o b s e r v e r s . The system as d e l i v e r e d r e q u i r e d e x t e n s i v e a l t e r a t i o n s and the method of instrument a p p l i c a t i o n was not the same as suggested by the manufacturer. I t i s a two stage d i l u t i o n system (Figure .4)i and i s shown i n F i g u r e 5'. The b a s i c components and d i r e c t i o n s o f flow can be d i s c e r n e d from the schematic (Figure 4). The d i l u t i o n a i r i s compressed and passes through a carbon f i l t e r (A) and a surge chamber (B) and then e n t e r s a mixing chamber (C). The odorous sample i s i n t r o d u c e d by a p e r i s t a l t i c pump or a l a r g e p r e s s u r e v e s s e l (D) i n t o the same mixing chamber v i a a rotometer (FM1). This c o n s t i t u t e s the f i r s t d i l u t i o n step. The second d i l u t i o n i s c a r r i e d out by s p l i t t i n g the flow o f the p a r t i a l l y d i l u t e d sample from the f i r s t mixing chamber, p a s s i n g a p o r t i o n through a carbon f i l t e r (E), thereby d e o d o r i z i n g i t . The r e s u l t i n g odorous and non-odorous streams are again mixed i n another mixing chamber (F). The d i l u t i o n achieved i s c o n t r o l l e d by the v a l v e (G) which d i r e c t s l a r g e r o r s m a l l e r p o r t i o n s o f odorous a i r d i r e c t l y t o the f i n a l mixing chamber. Only one of the flowmeters 2, 3 or 4 i s used depending on the s p l i t r a t i o . The equation which determines the number o f d i l u t i o n s achieved i s : •* AAE Environmental Products. D 38, FM1 CROSS-OVER VALVE 4 k k f \ FACE MASKS FIGURE 4. Olfactometer dynamic d i l u t i o n system schematic diagram. 39. FIGURE 5. F r o n t p a n e l o f d y n a m i c d i l u t i o n o l f a c t o m e t e r w i t h f l o w m e t e r s (A) and c o n t r o l v a l v e s ( B ) . 40. # of d i l u t i o n s = FM C + FM X FM r + FM 5 x 5 x FM, FM 1 x where FM,- = f l o w r a t e (1/s) o f rotometer #5 FM^ = fl o w r a t e (1/s) of rotometer #1 (odorous sample) FM = f l o w r a t e (1/s) of rotometer #2,3 or 4 depending on f l o w r a t e The instrument has a d i l u t i o n range from approximately 5 0 t o 100,000 times. The b a s i c d i l u t i o n system d e s c r i b e d above was not a l t e r e d d u r i n g the course o f t h i s study. However, the methods used f o r i n t r o d u c t i o n of odorous sample, the compressed a i r source and the pa n e l p r e s e n t a t i o n techniques were changed. In i n i t i a l experiments a compressor w i t h i n the ol f a c t o m e t e r p r o v i d e d motive f o r c e f o r d i l u t i o n a i r and i n t e r n a l carbon f i l t e r s c a r r i e d out i n i t i a l and secondary d e o d o r i z a t i o n s t e p s . Odorous samples were i n t r o d u c e d u s i n g a v a r i a b l e speed p e r i s t a l t i c pump and o n l y one sample a i r stream was conducted t o the p a n e l i s t f o r sensory e v a l u a t i o n . Due t o n o i s e problems and l a c k o f c a p a c i t y the i n t e r n a l compressor was l a t e r r e p l a c e d by u s i n g a i r from the b u i l d i n g a i r supply and the i n i t i a l d e o d o r i z a t i o n o f the a i r was accomplished u s i n g a l a r g e r e x t e r n a l carbon f i l t e r ( Figure 6 ) , f a b r i c a t e d by the author. When the e x t e r n a l a i r source was i n c l u d e d i n the system i t p r o v i d e d enough volume to supply a i r t o three masks i n the pa n e l booth i n s t e a d of FIGURE 6. E x t e r n a l c a r b o n f i l t e r s h o w i n g t h e t u b e s h a p e d f i l t e r i n a f r a m e ( A ) , t h e two way c r o s s o v e r v a l v e ( B ) , a n d t h e f l o w e q u a l i z a t i o n f l o w m e t e r s one. One a i r - s t r e a m was taken d i r e c t l y t o a mask through t e f l o n t u b i n g . One went through the o l f a c t o m e t e r t o a c r o s s o v e r valve and then to a mask. The t h i r d went d i r e c t l y t o the same .crossover v a l v e and again to a mask. This allowed one non-odorous a i r s t r e a m and the a i r s t r e a m from the o l f a c t o m e t e r to be i n t e r c h a n g e d between two masks. With t h i s o r g a n i z a t i o n the odor can be randomly a s s i g n e d to one mask or the other, a v o i d i n g a s y s t e m a t i c e r r o r when p a n e l i s t s attempt t o decide which mask i s odorous. The o n l y other a l t e r a t i o n made was i n the method of odorous sample i n j e c t i o n . Because of the p o s s i b i l i t y of odor l o s s e s from low odor samples i n the tygon t u b i n g of the p e r i s t a l t i c pump, a method of sample i n j e c t i o n a v o i d i n g i n t i m a t e c o n t a c t of sample w i t h tygon i n the sample pump was developed. A l a r g e p r e s s u r e v e s s e l was c o n s t r u c t e d which c o n t a i n e d the sample bag (Figure 7) . The v e s s e l was p r e s s u r i z e d t o 10 P s i (69 kPa) to overcome back pr e s s u r e and f o r c e sample i n t o the o l f a c t o -meter. A simple booth was a l s o c o n s t r u c t e d where the p a n e l i s t s a t t o e v a l u a t e odors from the sample p r e s e n t a t i o n masks. The booth and masks are shown (Figure 8) and the mask and b r e a t h i n g bag assembly are shown i n a c l o s e up s c h e m a t i c a l l y diagrammed (Figure 9). In i n i t i a l t e s t i n g only one mask was p r e s e n t while l a t e r three masks were pre s e n t e d to the p a n e l i s t . The P a n e l i s t s . P a n e l i s t s c o n s i s t e d of p r o f e s s o r s and students from the Department of Bio-Resource E n g i n e e r i n g at the U n i v e r s i t y 43. FIGURE 7. P r e s s u r e v e s s e l (A) t h e d i l u t i o n s y s t e m b a g e n c l o s e d . u s e d t o i n j e c t s a m p l e i n t o shown c l o s e d w i t h s a m p l e FIGURE 8. P a n e l b o o t h s h o w i n g s a m p l e masks ( A ) . The c e n t e r mask c a r r i e s c a r b o n f i l t e r e d a i r o n l y . FIGURE 9. C l o s e u p o f mask w i t h b r e a t h i n g b a g ( A ) , s h o w i n g t h e n o n - r e b r e a t h i n g v a l v e ( B ) , on t h e mask-bag a s s e m b l y . of B r i t i s h Columbia. G e n e r a l l y there were no s p e c i a l panel s e l e c t i o n procedures f o l l o w e d , except f o r the h i g h odor l e v e l , sample storage t e s t . The number of p a n e l i s t s used to e v a l u a t e any one sample was f i v e which has been found by o t h e r s to be adequate, (Wade, 19 74). Sensory A n a l y s i s Procedures. During the f i r s t experiment ( f i e l d e v a l u a t i o n of a s u r f a c e a e r a t o r ) a very simple but e f f e c t i v e a n a l y s i s pro-cedure was used. A t i m e t a b l e was designed f o r p a n e l i s t s which randomly a l l o t t e d t e s t times. T e s t s were c a r r i e d out i n a booth which c o n t a i n e d a mask through which odorous or non-odorous a i r c o u l d be d i r e c t e d by the o p e r a t o r . The p a n e l i s t was i n i t i a l l y p r o v i d e d with o d o r l e s s a i r . A f t e r 2-3 minutes a c c l i m a t i z a t i o n the o p e r a t o r i n d i c a t e d v e r b a l l y t h a t a stimulus was to be e v a l u a t e d . Odorous d i l u t i o n s were presented i n i n c r e a s i n g c o n c e n t r a t i o n s i n t e r s p e r s e d with blanks to a v o i d a d a p t a t i o n . For each d i l u t i o n the p a n e l i s t responded e i t h e r p o s i t i v e l y or n e g a t i v e l y , the t e s t being complete a f t e r two c o r r e c t p o s i t i v e responses. In l a t e r experiments, as a r e s u l t of n e g a t i v e feedback from p a n e l i s t s , the author decided to a l t e r the sensory a n a l y s i s procedure s l i g h t l y to a l l o w a semi-forced c h o i c e response from the p a n e l i s t . Instead of one a i r stream three were generated and fed to three masks l i n e d up s i d e by s i d e . The c e n t e r mask d e l i v e r e d cleaned a i r f o r r e a c c l i m a t i -z a t i o n o f the o l f a c t o r y sense and was breathed through at a l l times except d u r i n g an e v a l u a t i o n . The two masks t o the r i g h t and l e f t c o u l d have odorous and non-odorous a i r i n t e r c h a n g e d between them at the o p e r a t o r ' s d i s c r e t i o n . The p a n e l i s t began by b r e a t h i n g deodorized a i r f o r 2-3 minutes. The mask through which the odorous a i r was d i r e c t e d was chosen a t random and the f i r s t mask the p a n e l i s t s n i f f e d was a l s o chosen at random. The p a n e l i s t had three c h o i c e s o f response; l e f t mask odorous, r i g h t mask odorous, n e i t h e r mask odorous. The t e s t - was complete a f t e r two c o r r e c t p o s i t i v e responses and p r e s e n t a t i o n s were made i n i n c r e a s i n g c o n c e n t r a t i o n s a l l o w i n g one minute between p r e s e n t a t i o n s t o a v o i d p a n e l i s t o l f a c t o r y a d a p t a t i o n . The odds of p a n e l i s t s guessing the c o r r e c t mask were 1:9 o r 11%. The i n d i v i d u a l t h r e s h o l d s were determined by t a k i n g the geometric mean between the d i l u t i o n l e v e l d e t e c t e d and the one p r e c e d i n g i t , on the assumption t h a t . t h e t h r e s h o l d l i e s between these two v a l u e s . The d i s t a n c e between the two d i l u t i o n l e v e l s was s e t a t 10°• 2 5(Lindvall, 1970). The EDrn value o r the d i l u t i o n l e v e l a t which 50% D U of a p o p u l a t i o n - c o u l d d e t e c t a sample, was determined by c a l c u l a t i n g the geometric mean f o r the log-normal d i s t r i b u t i o n of t h r e s h o l d values from i n d i v i d u a l p a n e l i s t s . T h i s was 48. accomplished by determining the a r i t h m e t i c average of the logs of the i n d i v i d u a l t h r e s h o l d v a l u e s f o r a sample and then t a k i n g the a n t i l o g ( L i n d v a l l , 1970). 49. THE EXPERIMENTS I. Olfactometer D i l u t i o n Test T h i s was a simple t e s t u sing c a l i b r a t e d CO^ standards and n i t r o g e n d i l u t i o n gas to t e s t whether the d i l u t i o n as determined by rotometer r e a d i n g were acc u r a t e . The carbon i n the f i l t e r used i n the d i l u t i o n system to f a c i l i t a t e the second stage d i l u t i o n step was r e p l a c e d by NaOH p e l l e t s which absorb and n i t r o g e n r e p l a c e d d e o d o r i -zed a i r as the d i l u t i o n medium. An i n f r a - r e d a b s o r p t i o n spectrometer (Beckman IRGA Model No. 215) was used t o measure the o u t l e t c o n c e n t r a t i o n of C O 2 • By a l t e r i n g the s t a r t i n g c o n c e n t r a t i o n of C O 2 i n the standard s e v e r a l d i l u t i o n l e v e l s were checked. A 200 ppm standard was used to c a l i b r a t e the spectrometer and h i g h e r c o n c e n t r a t i o n s were used to t e s t the o l f a c t o m e t e r . I I . Odor Storage Experiment (High Odor Level) This experiment was c a r r i e d out to determine the e f f e c t of storage time on the odor t h r e s h o l d of swine manure odor samples s t o r e d i n p r e f l u s h e d T e d l a r (Poly V i n y l F l u o r i d e ) sample bags. Samples f o r the t e s t s were generated from 100 ml f r o z e n swine manure supernatant samples. To produce gaseous samples a b o t t l e of f r o z e n swine manure was thawed f o r 16 hours at 20°C. The l i q u i d i n the b o t t l e was then 50. sparged w i t h non-odorous a i r i n t o a sample bag at a f l o w r a t e of approximately one l i t e r per minute f o r 30 minutes. A sample produced i n t h i s f a s h i o n was c o n s i d e r e d the odor source. Samples f o r storage were produced by p r e f l u s h i n g and then f i l l i n g a sample bag from a f r e s h l y produced source sample. P a n e l i s t s were screened f o r t h i s t e s t by having a group of 11 people e v a l u a t e standard samples on t h r e e s u c c e s s i v e days. The c r i t e r i a f o r choosing p a n e l i s t s were c o n s i s t e n c y and d e v i a t i o n from an o v e r a l l mean. The f i v e p a n e l i s t s c l o s e s t to the mean and showing the most c o n s i s t e n c y were chosen . -•- The experimental design was a 3 x 2 x 3 f a c t o r i a l . F a c t o r one was TIME a t three l e v e l s ; immediately a f t e r s t o r a g e . One day a f t e r storage and two days a f t e r s t o r a g e . F a c t o r 2 was SAMPLE of which there were two and f a c t o r 3 was REPLICATION i n the" form o f three separate experimental t r i a l s . P a n e l i s t times were chosen randomly and the a n a l y s i s i n v o l v e d the use of three masks and a semi-forced choice d e t e c t i o n t h r e s h o l d response from the p a n e l i s t s . I I I . Odor Storage Experiment (Low Odor L e v e l ) . Experiment I I was repeated u s i n g a i r samples of lower odor i n t e n s i t y . I t was f e l t t h a t at low odor l e v e l s , the tygon i n the sample pump was e l i m i n a t i n g some of the odor from the sample r e s u l t i n g i n a r e d u c t i o n i n odor l e v e l . T h i s was not observed a t the h i g h e r i n t e n s i t i e s because the amount absorbed was not s i g n i f i c a n t compared to the t o t a l odorant present. A pressure vessel was used to force the sample into the olfactometer i n place of the p e r i s t a l t i c pump used previously. The odor sample was produced by passing a i r over one l i t e r of swine manure supernatant which had been diluted 1:10 with d i s t i l l e d water. The airflow rate was approximately 1 S,/min through a container 30 cm long, 15 cm wide and 15 cm high with approximately 2.5 cm. of manure i n the bottom. A sample bag was flushed with t h i s odorous a i r twice and then f i l l e d a t h i r d time to produce the sample. A preliminary analysis was made on this sample by three panelists using the semi-forced choice response technique. The remaining portion of the sample was then used to flush another sample bag once (normal f i e l d sampling pro-cedure) and was then transferred to the second bag. This second sample was analyzed by fi v e panelists immediately, three hours and 24 hours aft e r sampling. The t r i a l was carried out twice. IV. Short Term Aeration of Swine Manure for Odor Reduction: F i e l d Odor Measurements at the Tank '~• •~r~~'- - -x  T h e S i t e : This work was carried out on a swine farm in Chilliwack, B r i t i s h Columbia. The swine unit con-s i s t e d of a farrowing and a f i n i s h i n g barn, both with s l a t t e d floors and underfloor trenches where the waste ( manure, u r i n e and wash water) c o u l d be s t o r e d f o r up to three months. Two manure tanks were l o c a t e d between the two barns t o allow l o n g e r term storage of the waste. One tank has a l a r g e c a p a c i t y ' covered tank w i t h a g r a v i t y i n l e t t r e n c h from the f i n i s h i n g u n i t . The other tank i s 5m x 12m x 2m and was i n s t a l l e d f o r the purpose of odor c o n t r o l . A 5 h.p.(3.75Kw) s i n g l e phase f l o a t i n g s u r f a c e a e r a t o r i s i n s t a l l e d i n the tank. The a e r a t o r f u n c t i o n s by an i m p e l l o r drawing l i q u i d up a draught tube and onto a d e f l e c t i o n f l a n g e . The l i q u i d i s then d i r e c t e d a t r i g h t angles across the pond s u r f a c e (Figure 10 ). The i n c r e a s e d a i r to l i q u i d c o n t a c t area allows a g r e a t e r i n f l u x o f oxygen t o the l i q u i d and at the same time r e s u l t s i n a hi g h r a t e o f v o l a t a l i z a t i o n o f odorous compounds from the l i q u i d phase and more i m p o r t a n t l y allows v o l a -t i l e odorous compounds to leave the l i q u i d phase at a hi g h e r r a t e . The manure used i n the t r i a l s came p r i m a r i l y from the l a r g e covered tank and was pumped over to the open tank and allowed t o s i t f o r at l e a s t two days b e f o r e another t r i a l . The manure i n the covered tank came, i n t u r n , from the f i n i s h i n g barn f ) troughs where i t had been s i t t i n g f o r approximately three months. Sampling Devices. There were t h r e e components t o the gas sampling system used: the f i e l d sampling apparatus, the storage sample bag, and the system used t o i n j e c t sample i n t p the o l f a c t o m e t e r . The f i e l d sampling apparatus c o n s i s t e d o f a r e c t a n g u l a r V plywood box t o c o n t a i n the sample bag, a 12V motor w i t h rechangeable power source w i t h c e n t r i f u g a l fan f o r gas sampling, and t u b i n g to t r a n s m i t sample i n t o the bags (Figure 11) . The sample bags used were 30" x 30" formed by heat s e a l i n g two f l a t sheets o f T e d l a r (PVF) p l a s t i c . A t e f l o n tube f i t t i n g was l o c a t e d i n the ce n t e r o f the bag f o r f i l l i n g and f l u s h i n g purposes. Before b e i n g used the bags were f l u s h e d t h r e e times w i t h carbon f x l t e re d ;'_ai r.;, , The o l f a c t o m e t e r sample pump used was a v a r i a b l e speed p e r i s t a l t i c pump wit h tygon t u b i n g used i n the pumping element. Bags were connected d i r e c t l y t o the pump v i a V O.D. T e f l o n t u b i n g . In a l a t e r experiment, a p r e s s u r e v e s s e l r e p l a c e d the p e r i s t a l t i c pump f o r i n t r o d u c t i o n of odor sample i n t o the d i l u t i o n system. FIGURE 11. F i e l d g a s s a m p l i n g b a g ( A ) , t h e power s a m p l i n g f a n ( C ) . u n i t s h o w i n g t h e s a m p l e s o u r c e ( B ) , a n d t h e s m a l l In o r d e r t o c o l l e c t odor samples a t the tank the sampler was attached to the c e n t e r o f the tank fence on the downwind s i d e . The fan i n l e t was approximately 2.5 f e e t above the tank edge. Samples were c o l l e c t e d over approximately a s i x minute i n t e r v a l s i n c e i t took approximately s i x minutes to f i l l each sample bag. For the sampling of odors e m i t t e d from the tank the f i r s t sample was taken b e f o r e a e r a t o r s t a r t - u p and represented the background odor l e v e l . The next sample was taken w i t h i n 10 minutes a f t e r a e r a t o r s t a r t - u p . The times o f sampling a f t e r t h a t p o i n t v a r i e d f o r the three t r i a l s conducted and are shown i n Table IV. A l l odor p a n e l analyses were c a r r i e d out w i t h i n 4 8 hours of sampling. RESULTS AND DISCUSSION 58. OLFACTOMETER DILUTION TEST This test was conducted to quickly check the accuracy of the olfactometer d i l u t i o n system. Carbon dioxide was substituted for the odorant i n these tests and nitrogen replaced the d i l u t i o n a i r . D i l u t i o n changes i n carbon dioxide concentration were measured using an i n f r a - r e d absorption spectrometer and an i n i t i a l carbon dioxide concentration of 100,000 parts per m i l l i o n i n nitrogen. This mixture was further d i l u t e d with nitrogen from 178 to 5620 times. At each d i l u t i o n l e v e l tested the gases were allowed to flow at a constant rate u n t i l the spectrometer needle was stable. The needle did not fluctuate more than one d i v i s i o n on the scale and a reading was taken over a period of a few minutes. The results of this t e s t were s a t i s f a c t o r y , showing that the d i l u t i o n s predicted by the d i l u t i o n equation were very close to those measured (Table i ) . The values at the extreme ends of the spectrometer scale were .Lmiprecise but this was more l i k e l y a function of the measuring device than the d i l u t i o n system. Further, the actual value measured at 5620 times d i l u t i o n may- have been higher due" to- i n e f f i c i e n c y of the NaOH p e l l e t s i n the scrubber to remove high concentrations of carbon dioxide. Due to the i n a b i l i t y of the scrubbers to handle 100 percent carbon dioxide, in the secondary d i l u t i o n Step, TABLE I. Values from olfactometer d i l u t i o n test showing predicted* and actual values. C0 2 (ppm) #Dilutions 100,000 ppm 5620 1000 562 316 178 Predicted' Reading 6.0 27.0 43.5 67.5 96.0 Actual Reading 8.5 27.0 43.0 67.0 100.0 * Value from c a l i b r a t i o n curve c h a r a c t e r i s t i c of the Beckman I.R. Absorption meter for CO-. 60. h i g h e r d i l u t i o n l e v e l s c o u l d not be measured u s i n g t h i s system. However, s i n c e the flowmeters have been c a l i b r a t e d t o g e t h e r over a wide flow range and produce c o r r e c t d i l u t i o n s at low l e v e l s , t h i s can be e x t r a p o l a t e d t o h i g h e r d i l u t i o n l e v e l s . A l s o , any v a r i a b i l i t y a t t r i b u t a b l e t o the r e a d i n g of the flowmeter i s much s m a l l e r than t h a t e x h i b i t e d by p a n e l i s t s i n t h e i r responses. ODOR STORAGE EXPERIMENT - HIGH ODOR LEVEL ; Th i s experiment was c a r r i e d out i n order to de t e r -mine whether the sensory t h r e s h o l d of odor samples from swine manure would remain s t a b l e over a 48 hour p e r i o d , i f s t o r e d i n T e d l a r sample bags. The author c a r r i e d out three experimental runs w i t h two d u p l i c a t e odor samples and used f i v e • p a n e l i s t s i n each run. The p a n e l i s t s were p r e s e l e c t e d as d e s c r i b e d i n methods s e c t i o n . The p a n e l data from the s t o r e d sample bags and the ED<-0 v a l u e s are presented i n Table I I . A f a c t o r i a l a n a l y s i s of v a r i a n c e was c a r r i e d out to determine whether there were any s i g n i f i c a n t d i f f e r e n c e s between the length o f time samples were s t o r e d , experimental runs (blocks) or d u p l i c a t e samples. The d e t a i l s of t h i s a n a l y s i s are con t a i n e d i n Appendix 1. The r e s u l t s showed no s i g n i f i c a n t d i f f e r e n c e between times, or between sample d u p l i c a t e s (Figure 12). There were s i g n i f i c a n t d i f f e r e n c e s between experimental runs (blocks) but t h i s was expected s i n c e the d i f f e r e n t experimental runs were c a r r i e d out at separate p o i n t s of time. E s s e n t i a l l y , these r e s u l t s show that odorous gases c o l l e c t e d from swine manure can be s t o r e d i n T e d l a r p l a s t i c bags f o r up t o 4 8 hrs w i t h no s i g n i f i c a n t change i n the measured sensory odor t h r e s h o l d . 63. TABLE I I . Odor Storage T e s t ; Log D i l u t i o n s and EDe-v a l u e s For St o r e d High L e v e l Swine Manure Odor Samples Sample 1 Time , Days 1 PANELIST 2 3 4 5 Log Aver-age E D50 E x p e r i mental Run • 0 3. 88 3.62 . 3.62 3.62 3.62 3.67 4700 1 1 3. 62 3.62 4.12 3.62 3.62 3. 72 5248 2 3.62 3. 37 3. 60 3. 37 3. 37 3. 47 2951 .0 3.62 3.12 3. 88 3.62 3.37 3.52 3327 2 1 3. 62 3.37 3.62 3. 12 2. 88 3.32 2100 . 2 3.62 3.12 3. 62 3. 37 3. 43 2707 .0 3. 88 3.62 3.62 3. 37 3.88 3.67 4721 3 1 3. 88 3. 37 3. 62 3.62 3. 37 S. 57 3722 2 3.62 3. 37 3. 88 3.37 3. 88 3.62 4207 0 3. 88 3. 62 4. 12 3. 62 3. 62 3. 77 5915 1 3. 62 3. 88 4. 12 3. 62 3. 62 3. 77 5916 2 3. 62 3. 62 3. 62 3. 62 3. 88 3. 67 4699 0 4. 12 3. 37 3. 62 3. 62 3. 62 3. 67 4677 1 3. 88 3. 62 3. 62 3. 62 3. 12 3. 57 3733 2 3. 62 3. 62 3. 62 3. 37 3. 56 3609 '0 3. 62 3. 62 3. 37 3. 12 3. 62 3. 47 2951 1 3. 88 3. 62 3. 62 3. 37 3. 37 3. 57 3722 2 3. 62 3. 12 3. 62 3. 37 3. 88 3. 52 3327 E D J - Q i s the geometric mean o f the t h r e s h o l d values generated by the pane l f o r one sample. A number of workers have ca r r i e d out Miis kind of determination using odor samples from other sources. 3 Hemeon (1968) reported that 3-5 f t polyethylene bags caused odor deterioration after 2-3 hours. On the other hand Dravnieks and Prokop (19 75) found that a valeraldehyde mixture was stable for 48 hrs, and e f f l u e n t from two rendering plants was stable up to 96 hrs, after sampling in thickwall polyethylene bags. Kenson et a l . (19 75) also did some work in t h i s area which has been mentioned e a r l i e r in t h i s paper. They e s s e n t i a l l y showed that storage of rendering plant odors in Tedl bags was fea s i b l e up to 24 hr i f the bags were preflushed with the odorant to be measured. Cormack et a l . (1974) also found Tedlar p l a s t i c bags to be suitable for sampling and short-term storage of odorous gases. These conclusions are important since use of these sample containers allows samples to be transported from the f i e l d to the laboratory where testing conditions are better controlled. 65. ODOR STORAGE EXPERIMENT - LOW ODOR LEVEL •'• ' During f i e l d odor experimentation, problems were encountered while attempting to measure the sensory t h r e s h o l d f o r low c o n c e n t r a t i o n odors. I t was found that some odor was be i n g absorbed by the tygon t u b i n g used i n the p e r i s t a l t i c pump employed f o r odor sample i n j e c t i o n i n t o the o l f a c t o m e t e r . I t was f e l t t h a t s i g n i f i c a n t odor a d s o r p t i o n may a l s o occur i n the sample bag f o r low c o n c e n t r a t i o n odor samples. Whereas the a d s o r p t i o n o f some odorant from a concentrated sample would have l i t t l e o r no s i g n i f i c a n t e f f e c t on the t h r e s h o l d odor l e v e l , the amount adsorbed may be s i g n i f i c a n t i n a weaker sample where t h e r e i s much l e s s t o t a l odorant pre s e n t . Although time was l i m i t e d and p a n e l i s t s s c a r c e two s h o r t experimental runs were c a r r i e d out. In t h i s experiment, s i n c e low odor c o n c e n t r a t i o n s were d e s i r e d , only the headspace above a d i l u t e s o l u t i o n of swine manure super-natant was purged with non-odorous a i r and used as an odor source. An odor source sample was produced by f l u s h i n g a T e d l a r bag three times w i t h the headspace d e r i v e d odorous a i r and then f i l l i n g the bag. T h i s sample was p r e s s u r i z e d and analyzed by three p a n e l i s t s t o get a t h r e s h o l d value b e f o r e sampling. No more p a n e l i s t s c o u l d be used because sample was l i m i t e d . T h i s source sample was then used to f l u s h and f i l l 66. another Tedlar bag which was then analyzed sequentially by five panelists at 0.5 hours, 3 hours and 24 hours aft e r sampling. Results from t h i s experiment were in t e r e s t i n g and i n some ways quite s i m i l a r to results of an experiment carried out by Dravnieks et a l . (1978). There was not enough data to j u s t i f y s t a t i s t i c a l analysis but the trend can be determined from Table XII and Figure 13. E s s e n t i a l l y there was no d r a s t i c change after 24 hours of storage. The experiment by Dravnieks was carried out using ambient odors from the v i c i n i t y of a meat rendering plant i n Teflon p l a s t i c bags. A panel of 11 people were used to determine the thres-hold of the odor source before sampling and at i n t e r v a l s a f t e r sampling. His results also showed no s i g n i f i c a n t change i n odor threshold over the 24 hour period tested. I t i s i n t e r e s t i n g to note that i n Dravniek's tests and one of the authors ythe d i l u t i o n s to odor threshold increased after sampling rather than decreasing kAlthough no explanation for this i s put forward by Dravnieks•it i s possible that s e l e c t i v e adsorption of an odor masking agent present i n i t i a l l y , i n the odor sample i s the cause. The removal of the masking agent could a l t e r the sensory odor threshold. TABLE I I I . Odor Storage Test: Low Odor Concentrations: Panelist D i l u t i o n to Threshold and E D ^ Q Values are shown for two experimental t r i a l s . SAMPLE STORAGE TIME T r i a l Panelist Before Sampling 0.5 hr, 3 hr 2 4 hr 1 1333 4216 750 2 750 750 1333 2371 1 3 1333 4216 1333 1333 4 421 750 2371 750 5 2371 1333 2371 E D50 749 1496 1883 1333 1 75 75 75 75 2 133 237 237 2 3 1333 750 750 1333 4 750 237 421 237 5 421 421 1333 E D 5 0 422 237 298 377 SHORT TERM AERATION OF SWINE MANURE FOR ODOR REDUCTION: FIELD ODOR MEASUREMENTS, AT THE AERATION BASIN. This experiment was made p o s s i b l e by The B r i t i s h Columbia M i n i s t r y of A g r i c u l t u r e who i n s t a l l e d a s u r f a c e f l o a t i n g a e r a t o r on a B.C. farm as a demonstration p r o j e c t . The author was giv e n access t o the a e r a t o r and manure tank to study the e f f e c t o f r e l a t i v e l y s h o r t term a e r a t i o n f o r gas s t r i p p i n g on the t h r e s h o l d odor l e v e l downwind from the a e r a t i o n b a s i n . The data c o l l e c t e d from t h r e e experimental runs i s presented i n Table IV. This data represents ED^g values from a p a n e l of f i v e people. These values were c a l c u -l a t e d i n the same f a s h i o n as those i n the bag t e s t experiment. When p l o t t e d on semi-log graph paper (Figure 14), a l l three t r i a l s show a d e c r e a s i n g t r e n d i n odor t h r e s h o l d with time. From the curves i t can be seen t h a t a e r a t i o n s t r i p p i n g reaches i t s f u l l e f f e c t i v e n e s s a f t e r approximately 3.5 hr. A f t e r t h i s time the curves begin t o l e v e l out i n the range o f the background odor measurements. F u r t h e r a e r a t i o n beyond t h i s p o i n t f o r the purpose of gas s t r i p p i n g would not l i k e l y reduce odor l e v e l s s i g n i f i c a n t l y . To change the manure t o an aer o b i c s t a t e would r e q u i r e a e r a t i o n f o r an extended p e r i o d of time. The quick i n i t i a l drop i n odor l e v e l measured on the farm i s a l s o supported by a sm a l l a e r a t i o n experiment c a r r i e d out on U.B.C. campus. A 200 g a l l o n manure sample was c o l l e c t e d 7 0. TABLE IV. Evaluation of Odor Thresholds During Aeration of Wastes at the Tank; Panelist Dilution to Threshold and ED_„ Values. SAMPLE TIME AFTER AERATOR STARTUP Panelist Background before Aerator start-up 5 Minutes after s t a r t up 1.25 hr 8 hr 24 hr 1 534 1266 158 400 400 2 225 4000 170 158 225 3 467 '. : 16856 400 534 534 4 225 9482 534 170 5 225 2250 300 15 8 E D 5 0 310 4488 238 366 264 Before Start-up 5 min .5 hr 1 hr 2. hr " 1 400 53273 3000 5333 1266 2 830 39955 3000 6222 1688 3 712 94706 9482 8297 3000 4 225 39955 1688 712 400 5 949 94706 12642 4000 949 E D50 550 59770 4488 3790 1195 Before Start-up . 5 miri after .5 hr 2 hr 8 hr 1 158 29966 9482 534 225 2 554 22475 1688 300 300 3 170 71030 53273 225 170 4 15 8 39955 9482 225 225 5 712 71030 39955 1266 1266 276 42321 12643 400 318 100,000 o r-§ 10,000 o z 1/1 —H o —I X 33 m X o I— o 1000 h T I M E , HRS FIGURE 14. Odor t h r e s h o l d changes f o r samples c o l l e c t e d downwind of the ae r a t e d b a s i n on three separate o c c a s i o n s . from the same tank which housed the surface 'aerator i n the on-farm evaluation. The sample was mixed and aerated simultaneously i n a 200 gallon tank. Small manure samples were taken at time, 0, 5 minutes, 10 minutes, 15 minutes and 30 minutes after the aerator was started. M. F a t t o r i , a graduate student, analyzed the headspace above these samples using a gas chromatograph (Perkin Elmer, Sigma 2). It i s i n t e r e s t i n g to note that i n the f i r s t two samples (t = 0 min and t = 5 min), two large peaks with low retention times are present (Figure 15). These indicate the presence of highly v o l a t i l e compounds. At the 15 minute mark the f i r s t of these peaks has almost disappeared and afte r 30 minutes both peaks are almost non-existant. This rapid reduction i n highly v o l a t i l e materials i s i n agreement with the rapid decline i n odor threshold followed by a l e v e l i n g out of the curves found for the f i e l d experiments. The .., i n i t i a l high odor lev e l s are l i k e l y related to the removal of the highly v o l a t i l e compounds present i n the i n i t i a l l y undisturbed manure. After the odor threshold vs. time curve levels out, i t i s l i k e l y that compounds with a lower v o l a t i l i t y contribute to the odor and these would not be removed by normal gas st r i p p i n g . The greater time required to s t r i p the v o l a t i l e s i n the large aeration basin i s probably a function of the longer turnover time of the l i q u i d material i n the larger basin as FIGURE 15. Gas chromatographic a n a l y s i s of the headspace o f m a t e r i a l c o l l e c t e d from a s m a l l s c a l e manure a e r a t i o n experiment. The valve temperature was 50°C, the Fl". d e t e c t o r 200°C and the temperature program was i s o t h e r m a l (2 5°C) •74. w e l l as a d i f f e r e n c e i n a e r a t i o n methods used and o v e r a l l s c a l e . I t should be noted t h a t a d i r e c t comparison of these experiments i s not being made here. In order t o determine the e f f e c t s o f gas s t r i p p i n g on the r e s u l t i n g odor l e v e l s f o r manure spread on l a n d , s e v e r a l attempts were made at c o l l e c t i n g gas samples from grass covered f i e l d s which had been f r e s h l y manured. U n f o r t u n a t e l y although much e f f o r t was put i n t o a s p e c i a l f i e l d sampling d e v i c e , s u i t a b l e samples c o u l d not be c o l l e c -ted. The problems encountered i n t h i s phase o f experimentation l e d to the r e a l i z a t i o n t h a t a t low odor t h r e s h o l d s , the p e r i s t a l t i c t r a n s f e r pump was a l t e r i n g the odor t h r e s h o l d of samples. This l e d the odor experiments and the development of the new sample device f o r the o l f a c t o m e t e r . Again, time c o n s t r a i n t s have not allowed f u r t h e r work on t h i s aspect of the f i e l d measuring program. The author f e e l s t h a t i n the f u t u r e these types o f measurements should be made as the i n f o r m a t i o n p r o v i d e d would be of great value. Short-term a e r a t i o n has been shown t o e f f e c t a measurable change i n the odor t h r e s h o l d downwind from the a e r a t i o n b a s i n . T h i s r e s u l t , i n i t s e l f , i s not h i g h l y s i g n i f i c a n t but the f a c t t h a t an attempt was made to q u a n t i f y the e f f e c t s o f an a g r i c u l t u r a l odor c o n t r o l d e v i c e , i s . There are a s i g n i f i c a n t number o f p r o j e c t s t h a t have used a e r a t i o n as a method f o r c o n t r o l l i n g odor from anaerobic swine manure. However, without a comprehensive odor measure-ment program i n t e g r a t e d w i t h these p r o j e c t s the r e s u l t s forthcoming are of l i m i t e d value from the p o i n t of view of odor c o n t r o l . 76-THE ODOR MEASUREMENT SYSTEM A l l of the author's work has centered around the use of an o l f a c t o m e t e r and groups of people, to p r o v i d e a means t o measure the t h r e s h o l d of odor samples. Although t h i s t h e s i s was not embarked upon to develop an odor measurement method, these techniques had.'not been developed to the p o i n t where a s t a n d a r d i z e d approach c o u l d be taken. Because of t h i s , the olfactometer system and the method by which i t was employed changed as work progressed. These changes are covered i n the Methods s e c t i o n but some o b s e r v a t i o n s concerning the measurement system are important t o d i s c u s s . As p o i n t e d out by L i n d v a l l (1970) the author found t h a t p r o v i d i n g s u f f i c i e n t flow r a t e o f a i r i s very important f o r p a n e l i s t comfort. T h i s , a l s o avoids the problem o f unknown d i l u t i o n s o c c u r r i n g . The author a l s o noted t h a t a v a r i e t y o f problems developed as a r e s u l t o f u s i n g masks and b r e a t h i n g bag assemblies. Increased background odors from the b r e a t h i n g bag o c c u r r e d causing p a n e l i s t , c o n f u s i o n a t times. Other background odor problems o c c u r r e d as a r e s u l t o f the i n a b i l i t y o f carbon f i l t e r s t o completely deodorize the compressed d i l u t i o n a i r source. For t h i s k i n d of measurement technique i t would be a d v i s a b l e t o e l i m i n a t e these background odors. I t was found t h a t p a n e l i s t s were much more c o n f i d e n t u s i n g a semi-forced c h o i c e comparison technique to make t h r e s h o l d d e c i s i o n s as compared to a simple yes-no response. This i s supported by work c a r r i e d out by L i n d v a l l (1970, 1974) when he used semi-forced choice p a i r e d comparison and Dravnieks (1975) who' used a 3-way f o r c e d choice com-p a r i s o n method. Both of these workers f e l t t h a t a simple yes-no response was not adequate t o make such a s u b j e c t i v e measurement and the author agrees. Another important f a c t i s t h a t at l e a s t one minute o f deodorized a i r should be i n c l u d e d between each odor p r e s e n t a t i o n t o p a n e l i s t s t o avoid problems of s a t u r a t i o n . A l s o , because o f the h i g h degree o f v a r i a b i l i t y among p a n e l i s t s , panels should c o n t a i n f i v e o r more members to reduce the v a r i a b i l i t y to acceptable l e v e l s . The f u t u r e of t h i s type o f odor measurement i s unknown to the author. However, i t should have become obvious to the reader t h a t odor measurement i s not a simple p r o c e s s , but a complex one fr a u g h t with d i f f i c u l t i e s . I t i s l i k e l y t h a t the s i m p l e r more c o n t r o l l e d o b j e c t i v e odor measurement techniques w i l l be the most l i k e l y to be pursued i n the f u t u r e . U n f o r t u n a t e l y though, the s u b j e c t i v e measurement system with a l l i t s problems w i l l have t o remain with us i f c o r r e l a t i o n i s to e x i s t between o b j e c t i v e measurements and the human sensory system. 78. CONCLUSIONS T e d l a r sample bags can be used to s t o r e r e l a t i v e l y s t r o n g swine manure odor samples up to 48 hr with no s i g n i f i c a n t change i n the odor t h r e s h o l d . Data i n d i c a t e s t h a t T e d l a r bags can a l s o be used to s t o r e low l e v e l swine manure odor samples, although more work i s r e q u i r e d t o e s t a b l i s h t h i s w i t h a h i g h e r degree of c e r t a i n t y . Gas s t r i p p i n g of anaerobic swine manure, u s i n g a s u r f a c e f l o a t i n g a e r a t o r r e s u l t e d i n a r a p i d r e d u c t i o n of odor l e v e l s , f o r gases emitted from the manure tank. The major r e d u c t i o n i n odor l e v e l , f o r t h i s a e r a t o r -manure tank system, took three to f o u r hours a f t e r which odor l e v e l s had been reduced two orders of magnitude and remained r e l a t i v e l y constant. Gas s t r i p p i n g l i k e l y removes the h i g h l y v o l a t i l e component o f swine manure, the remaining odor being a t t r i b u t a b l e to l e s s v o l a t i l e components. When employing dynamic d i l u t i o n odor t h r e s h o l d measurement techniques, p a n e l i s t s should be allowed, a t l e a s t , one minute betv/een p r e s e n t a t i o n s t o avoid a d a p t a t i o n and s a t u r a t i o n phenomena. Semi-forced response i n dynamic d i l u t i o n odor t h r e s h o l d measurement i s p r e f e r r e d over a yes-no response. P a n e l i s t s found i t much e a s i e r t o d i s t i n g u i s h between odorous and non-odorous samples u s i n g the former technique. 80. BIBLIOGRAPHY AMOORE, J.E. , J.W. Johnston and M. Rubin. 1964. The stereochemical theory of odor. S c i e n t i f i c American, February. BERGLUND, B., U. Berglund, T. Engen and T. L i n d v a l l , The e f f e c t of adaptation oh odor detection, Perception and Psychophysics 9: 435-438. 1971 BERGLUND, U. 19 74. Dynamic properties of the olfactory N.Y. Acad. S c i . , Vol. 237: 17-27. system. Ann BURNETT, W.E. andN.C. Dondero. 1969. Microbiological and chemical changes i n poultry manure associated with decomposition and odor generation. Presented at the Cornell Animal Waste Management Conference, Syracuse, N.Y., January 13-15. CAIN, William S. and Howard R. Moskowitz. 1974. Psychophysical Scaling of Odor. In: (Human Responses to Environmental Odors. Ed. Amos Turk, James W. Johnston, J r . , and David G. Moulton, Academic Press: New York and London). COLE, C.A., H.D. B a r t i e t t , D.H. Buckner and D.E. Younkin. 1976. E f f i c i e n c y of cert a i n chemical and b i o l o g i c a l com-pounds for control of odor from anaerobic l i q u i d swine manure. Journal of Animal Science, Vol. 4 , No. 1, 2-7. CORMACK, D., T.A. Dorling, and B.W.J. Lynch. 1974. 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Status of regulations for source emission and ambient odors. Ann N.Y. Acad. S c i . Vol. 237: 288-308. 83. REDDELL, D.L. and J.M. Sweeten. 19 75. Evaluation of odor i n t e n s i t i e s at livestock feeding operations i n Texas. In: Managing Livestock Wastes, ASAE Proc. 275, p. 358-361. SCHROEDER, W.H. 19 75. A i r p o l l u t i o n aspects of odorous substances. A l i t e r a t u r e Survey. Environmental Protection Service Report EPS 3-AP-75-1. SOBEL, A.T. . .1969. Removal of water from animal manure. Animal Waste Management Proceedings at the 1969 Cornell A g r i c u l t u r a l Waste Mangement Conference, Syracuse, N.Y. SOBEL, A.T. ; 19 72. Olfactory Measurement of animal manure odor. Trans. ASAE 15: 696-699, 703. STEVENS, S.S. 19 71. Issues in Psycholophysical Measurement. Psychological Review, Vol. 78, No. 5, 426-450. SWEETEN, J.M., D.L. Reddell, Lowell Schake, B. Garner. 19 77. Odor i n t e n s i t i e s at c a t t l e feedlots. Trans. ASAE Vol. 20, No. 3: 502-508. SWEETEN, J.M., D.L. Reddell. 19 76. Managing feedlots for odor contr o l . Presented ASAE Annual Meeting, University of Nebraska, Lincoln, Nebraska, June 27-30. WADE, W.A.,|K.C. Tower and S. Cha. 19 74. Evaluation of four odor measurement systems. Technical report to the I l l i n o i s Environmental Protection Agency by the Research Corporation of New England, Wethersfield, Connecticut. WRIGHT, R.H'. 1957. In: Molecular Structure and Organoleptic Quality. S.C.I. Monography No. 1, Soc. Chem. Ind., London, pp'. 91-102. WRIGHT, R.H. 1977. Odor and molecular v i b r a t i o n : Neural Coding of Olfactory Information. J. Theor. Bio. 64, 473-502. 84, APPENDIX I. 3 x 3 F a c t o r i a l A n a l y s i s o f Variance w i t h Block R e p l i c a t i o n s Source; DF SS MS F Comparison Blocks 2 2 7678900 3839450 4.)96* S amp l e 1 1 1364148 1364148 1. 76 Time 2 1944914 972457 1.26 Sample x Time 2 198616 99308 0. 13 E r r o r 10 8512468 773861 T o t a l 17 19699046 

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