Behavior and Transport of Microbial Pathogens and Indicator Organisms in Soils Treated with Organic Wastes1
- K. R. Reddy,
- R. Khaleel and
- M. R. Overcash2
In a critical review of pathogen and indicator-organism transformations and transport from land areas receiving organic wastes, microbial die-off was described assuming first-order kinetics. First-order die-off rate constants (k) were calculated from the literature data for various pathogens and indicator organisms. For indicator organisms average die-off rates were 1.14 day−1 (0.08–9.1) for fecal coliforms, and 0.41 day−1 (0.05–3.87 day−1) for fecal streptococci. For pathogens, the average die-off rates were 1.33 day−1 (0.21–6.93) for Salmonella, 0.68 day−1 (0.62–0.74 day–1) for Shigella sp., and 1.45 day−1 (0.04–3.69 day−1) for viruses, respectively. Die-off rates increased approximately two times with a 10°C rise in temperature (5–30°C). Microbial die-off increased with decrease in soil moisture and was minimum in a pH range of 6–7. Correction factors were presented to adjust the k values for the changes in temperature, moisture, and pH. Retention of pathogens and indicator organisms by soil particles was described assuming a linear isotherm. Retention of microorganisms increased with an increase in clay content of the soil.
Major transport processes reviewed were leaching and surface runoff for land areas receiving animal wastes, and pastures and rangeland watersheds where animals distribute waste directly on the land. Some of the important research needs identified include (i) mechanisms involved in the retention of bacteria and viruses by the soil; (ii) measurement of retention coefficients for some important pathogens and indicator organisms, as a function of physico-chemical properties of soil; (iii) processes involved in the transport of bacteria and viruses along with the percolating water or in runoff water; and (iv) extensive testing of available models.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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