Bacterial inactivation and dispersion in cold ocean waters

Thoms, Joseph I. (2000) Bacterial inactivation and dispersion in cold ocean waters. Masters thesis, Memorial University of Newfoundland.

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Abstract

For discharge of sewage into the ocean, two parameters need to be estimated, namely the T₉₀ time and the diffusion coefficient (K). The T₉₀ time is a measure of the rate of decay of the bacterial contained in the sewage, representing a 90% reduction from the initial value. The diffusion coefficient (K) is a measure of how fast a plume of sewage will grow or disperse once released into the ocean. -- Both the T₉₀ value and the diffusion coefficient (K) depend upon local conditions, such as latitude and sea conditions. Published values are based upon tests that generally have been carried out in lower latitudes and/or in temperate waters, and may not accurately predict sewage dispersion and bacterial decay in local waters. It was therefore important to determine acceptable values that can be used for sewage outfalls in Newfoundland. -- It was the goal of this study to determine acceptable ranges for both bacterial decay and dispersion that accurately depict conditions encountered in Newfoundland, and to determine generally if water temperature appears to have a important effect on the T₉₀ value. -- For the T₉₀ study, a clear lexan container was filled with sewage and allowed to float around in the ocean, thus simulating natural conditions as much as possible. Samples of the sewage were taken every half hour and analyzed for total coliform count. The results gave an average T₉₀ time of 4 hours in the summer (July to September) and 6.5 hours in winter (September to March). These values agree with current literature. -- For the dispersion study, several floats were released into the ocean and tracked over a period of time. Using analysis methods proposed by other authors, the rate of plume growth was determined. The values that were obtained estimated the rate of dispersion to be greater than anticipated. Weather and conditions of the test may have contributed to this. In addition, no significant difference was found between dispersion rates for both inshore and open ocean tests.

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