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Wastewater
Treatment Articles Index
Many wastewater lagoons now need to be sealed with a composite liner. A composite liner often consists of a plastic membrane placed on top of an impervious clay base. This may more readily result in air or gas accumulating under the plastic liner. This situation may not have occurred when the plastic membrane is placed on top of a more porous soil such as sand.
Plastic membrane liners may include vents above the maximum water level. These vents are holes in the liner designed to allow the release of any air or gas that may collect under the liner. These vents are sometimes recommended when the underlying soil contains organic matter that can decay and release gas in the process. If these gases collect, they can create a huge bubble under the liner. This reduces the storage capacity of the lagoon.
For gases to be released through the vents in the liner, those gases need to migrate across the flat bottom, up the sloped sides, and out the vent holes. A sand cushion under the liner on the lagoon bottom may allow the gases to more easily travel across the lagoon bottom. The situation is further improved if the lagoon bottom is concave up.
Wastewater Treatment Articles Index
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