P.J. Hobbs

Reduction of Odorous Compounds in Fresh Pig Slurry by Dietary Control of Crude Protein

Two diets containing reduced levels of crude protein for both growing (35-65 kg) and finishing (65-95 kg) pigs were tested against standard commercial diets to determine changes in the odorants produced in fresh slurry. The experimental diets were formulated on a least cost basis using either a full commercial database or with restriction mainly to home-grown (UK) cereals and pulses. Synthetic essential amino acids were included in both formulations to obtain essential amino acids in an ideal protein ratio, with the crude protein being as low as possible. Nitrogen excretion by both growing and finishing pigs offered the low crude protein diets was significantly lower (P < 0.001) than that of pigs offered the commercial diets. Major odorants responsible for pig odour from slurries were identified and their concentrations determined using gas chromatography-mass spectrometry. Five out of 10 odorants from slurries produced by growing pigs were significantly lower (P < 0.05) in concentration for each of the low crude protein diets compared with the commercial diet. For the finishing pigs, nine out of ten odorants from slurries for the least cost and four odorants for the home grown diets were significantly lower (P < 0.05) than slurry produced from the commercial diet. Reducing dietary nitrogen and providing essential amino acids in an ideal protein ratio not only decreases the nitrogen excreted by the pig, but also reduces odorants produced in the resultant slurries.

Characterisation of odorous compounds and emissions from slurries produced from weaner pigs fed dry feed and liquid diets

Changes in odorous emissions were recorded from slurries produced by weaner pigs fed dry feed and feed with water added in the respective ratios of 3:1 and 4:1. Slurries were placed in an environmentally controlled emissions chamber, periodic air sampling was performed to determine the olfactometric response as odour concentration, and the air was analysed to identify volatile organic compounds present. Distinctive odours were produced by each slurry. However, four major groups of odorants were identified as sulphides, volatile fatty acids, phenols and indoles. The odour concentration from the slurry of the 4:1 diet was significantly less (P<0·05) than the odour concentration from the dry feed and 3:1 slurry samples. Decay of the sulphide component of the odours was investigated and the role of methanogenesis in reducing odour production is discussed. While monitoring the emissions in the chamber the slurry odorant concentrations increased by up to 50 ppm h-1.

Development of a relationship between olfactory response and major odorants from organic wastes

Hobbs, P. J., Misselbrook, T. H., Dhanoa, M. S., Persaud, K. C. (2001). Development of a relationship between olfactory response and major odorants from organic wastes. Journal of the Science of Food and Agriculture, 81, (2), 188-193

Emission rates of odorous compounds from pig slurries

Techniques to identify odorous compounds and to determine their emission rates from liquid wastes are described. Odorous compounds, or odorants, were analysed by GC-MS and odour concentration was measured by olfactometry after being emitted from slurry under controlled environmental conditions using a specially designed odour emission chamber. The slurries were obtained from pigs fed commercial and reduced crude protein diets and stored for 6 weeks, the effects of age and sex upon the odours produced in the headspace of the chamber were evaluated. The major odorous compounds were identified as belonging to the sulphide, volatile fatty acid, phenolic and indolic chemical groups. The mean emission rates from 200 litres of stirred slurry samples with a surface area of 1 m(2) using a wind speed of 4 m s(-1) were 1.35 million Odour Units min(-1) for odour and 214, 2.15, 0.21, 0.44, 0.068 and 0.02 mg min(-1) for hydrogen sulphide, ammonia, phenol, 4-methyl phenol, 4-ethyl phenol and indole respectively. Sex and sex/diet interaction effects were demonstrated for emission rates

Application of unsupervised clustering methods to the assessment of malodour in agriculture using an array of conducting polymer odour sensors

Abstract Odour sensing instrumentation based on arrays of sensors that display broad specificity and high sensitivity to odorous chemicals have been developed. Methods of unsupervised reduction of complex multidimensional data were examined, and useful algorithms were adapted for the use with broad specificity sensor arrays. As a result, a simple interface that would allow the human observer to decide easily whether a particular odour pattern could be distinguished from another on the basis of Euclidean distances between patterns, and calculation of 95% confidence limits around individual clusters of data was developed. The best performance was obtained from a combination of principal components analysis used as a starting point for Sammon mapping. This combined the invariance of the eigenvector calculation with the Euclidean distance mapping of the Sammon procedure, without the disadvantages of rotation of clusters when the order of patterns in a database was changed. The methods were applied to the assessment of odour differences of fresh pig slurry from pigs fed with different diets. The results show that the transformation of multidimensional data into two-dimensional clusters allowed easy visualisation of the difference in odour between slurries from the pigs fed with different diets.

A novel technique to determine organic processes in pig wastes

Complex processes concerning declining concentration of organic matter within pig wastes have been investigated using deuterated phenol (d(5)) and acetic acid (d(4)) over a ten day period. Decomposition rates of products responsible for odours and pollution were also quantified. These products included the volatile fatty acids, phenols and indoles as well as gaseous methane and carbon dioxide. The last two were quantified in the headspace flow to assess methanogenesis and the activity of bacteria. The relative rates of emission, production and bio-decay were calculated as exponential curves showing that acetic acid was lost through emission and bio-decay with half lives of 158 h and 95 h, respectively. Bio-production of acetic acid was very low. The emission rate of methane was 4.0 g m(-3) d(-1). The ratio of methane generated to the bio-decay of acetic acid concentration was 1:66. The decline of acetic acid in slurry was shown to be a concentration-dependent process. Other volatile fatty acids demonstrated similar declining concentration characteristics but at a lesser rate. This was also the case for 4-methyl phenol with a half life of 495 h. However phenol demonstrated different declining concentration and production characteristics with a maximum concentration of 85 mg l(-1) at 175 h. Carbon dioxide was produced at a greater rate than acetic acid was lost from the slurry (a ratio of 1.88:1.0). Ammonia was emitted at a rate of 4.7 g m(-2) d(-1)