Sewers may be open or closed. In urban areas in developing countries and some developed countries, sewer
systems may consist of networks of open canals, gutters, and ditches, which are referred to as open sewers. In
most developed countries and in high-income urban areas in other countries, sewers are usually closed and
underground. Wastewater in closed underground sewers is not believed to be a significant source of CH4. The
situation is different for wastewater in open sewers, because it is subject to heating from the sun and the sewers
may be stagnant allowing for anaerobic conditions to emit CH4.
Sewers may be open or closed. In urban areas in developing countries and some developed countries, sewersystems may consist of networks of open canals, gutters, and ditches, which are referred to as open sewers. Inmost developed countries and in high-income urban areas in other countries, sewers are usually closed andunderground. Wastewater in closed underground sewers is not believed to be a significant source of CH4. Thesituation is different for wastewater in open sewers, because it is subject to heating from the sun and the sewersmay be stagnant allowing for anaerobic conditions to emit CH4.
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