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[[File:SE DD Bildergalerie Klaerwerk Kaditz Faulung.jpg|thumb|Large sewage works in Germany]]
'''Sewage treatment''' is the process of dealing with [[sewage]] so that is does not cause harm to people or to rivers. Sewage flows in [[sewer]]s from houses and [[factory|factories]]. When it arrives at a sewage treatment works it passes through many stages. Larger works often have more stages than a smaller works.
Large objects are removed using [[screen]]s. The sewage then flows through a [[tank]] so [[sand]] can fall out. Large objects and sand might damage [[machine]]s in later stages.
[[Fat]]s and solids are removed in the most important stage. Sewage stays in a ''first'' tank until solids fall to the bottom. Fat also floats to the top. Fat and solids stay when the water leaves.
Water leaving the most important stage may be cleaned by [[bacteria]] and other very small animals and plants in the ''second'' important stage. These bacteria use [[oxygen]] from the air to eat [[chemical]]s from the sewage.
Cleaning bacteria may live in a small pond in simple works with enough land to build a pond. Larger works use machines to help the bacteria find the chemicals. Some works have [[Rock (geology)|rocks]] or pieces of [[plastic]] for the bacteria to grow on. Water is pumped over the rocks or plastic.
Clumps of bacteria grow while eating the chemicals from the water. The cleaned water stays in a ''second'' tank until these clumps of bacteria fall to the bottom. The clumps of bacteria stay when the cleaned water leaves.
Other works don't have rocks and plastics for the bacteria to live on. These works blow [[air]] through the water to mix it with clumps of bacteria. Some of the bacteria falling to the bottom of the ''second'' tank are pumped back to the mixing tank so there are enough bacteria to create a thick brown mixture.
Clean water on the top of the ''second'' tank or pond can then flow to a river or the sea but it may also need further treatment to make it cleaner. Some works try to kill bacteria that might make people sick. Some works use chemical [[poison]]s to kill these bacteria. Other works use the kind of light that causes a [[sunburn]].
[[Solid]]s from the ''first'' and ''second'' tanks can be used to make [[methane]] gas and fertiliser for farmers fields.
{{Commons category}}
{{science-stub}}
[[Category:Waste management]]
'''Sewage treatment''' is the process of dealing with [[sewage]] so that is does not cause harm to people or to rivers. Sewage flows in [[sewer]]s from houses and [[factory|factories]]. When it arrives at a sewage treatment works it passes through many stages. Larger works often have more stages than a smaller works.
Large objects are removed using [[screen]]s. The sewage then flows through a [[tank]] so [[sand]] can fall out. Large objects and sand might damage [[machine]]s in later stages.
[[Fat]]s and solids are removed in the most important stage. Sewage stays in a ''first'' tank until solids fall to the bottom. Fat also floats to the top. Fat and solids stay when the water leaves.
Water leaving the most important stage may be cleaned by [[bacteria]] and other very small animals and plants in the ''second'' important stage. These bacteria use [[oxygen]] from the air to eat [[chemical]]s from the sewage.
Cleaning bacteria may live in a small pond in simple works with enough land to build a pond. Larger works use machines to help the bacteria find the chemicals. Some works have [[Rock (geology)|rocks]] or pieces of [[plastic]] for the bacteria to grow on. Water is pumped over the rocks or plastic.
Clumps of bacteria grow while eating the chemicals from the water. The cleaned water stays in a ''second'' tank until these clumps of bacteria fall to the bottom. The clumps of bacteria stay when the cleaned water leaves.
Other works don't have rocks and plastics for the bacteria to live on. These works blow [[air]] through the water to mix it with clumps of bacteria. Some of the bacteria falling to the bottom of the ''second'' tank are pumped back to the mixing tank so there are enough bacteria to create a thick brown mixture.
Clean water on the top of the ''second'' tank or pond can then flow to a river or the sea but it may also need further treatment to make it cleaner. Some works try to kill bacteria that might make people sick. Some works use chemical [[poison]]s to kill these bacteria. Other works use the kind of light that causes a [[sunburn]].
[[Solid]]s from the ''first'' and ''second'' tanks can be used to make [[methane]] gas and fertiliser for farmers fields.
{{Commons category}}
{{science-stub}}
[[Category:Waste management]]