Theme:
Biosolids
cryofront City of Dawson wastewater treatment – biosolids management Ken Johnson, NTWWA Director Once commissioned in 2012, the Dawson City, Yukon, wastewater treatment plant will produce primary washed screenings and biosolids. Both the screening, and biosolids will be periodically hauled to the municipal landfill referred to as the ‘Quigley Landfill,’ which is nine kilometres east of the town, for disposal. In the summer, volumes may require one trip to the landfill every two-to-three days using a truck or trailer system. In the winter, little to no sludge will be removed from the plant. Remediation and neutralization of the biosolids will take place in excavated trenches over a number of years, and ultimately the material may be used as cover material. The proposed management system combines the process technologies of air drying, freezing/thawing, anaerobic digestion and long retention times. The biosolids disposal configuration at the landfill is the narrow trench method, and the biosolids will be disposed in the trench year
Trench excavation for Dawson City biosolids management system.
round. Water loss by trench disposal occurs by air drying (especially in the snow-free months), desiccation and draining over time once covered. Drying and reduction of pathogenic microorganisms will be promoted within the portion of biosolids exposed to freeze-thaw action. Four trenches will be developed over four years, and on the fifth year, the first trench, which has been covered for about three full years, will be excavated to provide a new
disposal trench. The excavated digested biosolids from the trench will be mixed with intermediate cover material and used for topsoil amendment in the final cover on closed areas of the landfill. The trench method can be considered final disposal, if the solids are left in the trenches. However, by excavating the stabilized biosolids from the trenches on a rotational basis, the amount of landfill area required to manage biosolids will be significantly reduced. Precipitation falling into the trench and water leaving the biosolids will infiltrate into the surrounding soil matrix. This water will be treated within the soil matrix system by natural biological and physical processes. This simple sludge management system will be welcomed by the Dawson City staff since they are readying themselves for the operation of what will be a complex mechanical wastewater treatment facility.
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40 | Western Canada Water | Summer 2012
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