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Title: Microbiological studies of farm animal wastes, their treatment and disposal on land
Author: Evans, M. R.
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1973
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The possibility that changes in agricultural practice, away from the production of farmyard manure to a hydraulic system of handling animal excreta, may promote the dissemination of viable intestinal pathogenic bacteria in the environment and lead to an increased incidence of animal and human infections, are discussed, investigations concerning the probability of salmonellae survival in pig excrement on the farm and the factors influencing the passage of enteric bacteria through soil into drainage water, are described. In a series of experiments it was shown that some cells of Salmonella Dublin can survive in pig excrement stored as a semi-liquid slurry, for at least 12 months. The rate of decline of viable cells was not affected by the suspended solids concentration of the slurry within the range expected in a storage reservoir on a farm. However the rate of decline of viable cells was affected by the anaerobic metabolic activity of micro-organisms in the environment during storage. The rate of decline of viable S. Dublin in the flocculent sludge during aerobic treatment of pig excrement was similar to that of Escherichia coli. However it was considerably higher than its rate of decline during storage when anaerobic conditions developed. Few cells of S. Dublin remained viable in the liquid phase of the mixed liquor of the treatment unit, but more survived in the residual sludge which, it is argued, is the main product of aerobic treatment of animal exreta. High numbers of enteric bacteria are shown to appear in sub-surface drainage water for short periods following the application to land of large volumes of semi-liquid animal excrement. At other times the main factors which affect the numbers of bacteria in sub-surface drainage water are (i) the rate passage of water through soil which is largely determined by the drainage characteristics of the soil; (ii) the amount of precipitation and evapotranspiration; and (iii) the numbers of bacteria in or on the soil and vegetation. The numbers of bacteria in or on the soil and vegetation are also affected by the time since the last application of excrement to the land. The application of these findings to better control of land treatment of animal excreta and/or the siting of new intensive animal production units is discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available