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[[File:SE DD Bildergalerie Klaerwerk Kaditz Faulung.jpg|thumb|Large sewage works in Germany]]

[[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 it  does not cause harm to people or to rivers. Sewage flows in [[sewer]] pipes from houses and [[factory|factories]]. When it arrives at a sewage treatment plant it passes through many stages. Larger treatment plants often have more stages than smaller ones.  

'''Sewage treatment''' is the process of dealing with [[sewage]] so that it  does not cause harm to people or to rivers. Sewage flows in [[sewer]] pipes from houses and [[factory|factories]]. When it arrives at a sewage treatment plant it passes through many stages. Larger treatment plants often have more stages than smaller ones.  

Large objects and rags are removed using [[screen]]s. The sewage then flows through a [[wikt:tank|tank]] so [[sand]] and grit can fall out.  This protects the [[machine]]s in later stages.  

Large objects and rags are removed using [[screen]]s. The sewage then flows through a [[wikt:tank|tank]] so [[sand]] and grit can fall out.  This protects the [[machine]]s in later stages.  

[[Fat]]s and solids are removed in the first treatment stage.  Sewage enters a tank where solids fall to the bottom and fat floats to the top.  Fats and solids stay in the tank and the water continues to the next stage. This is called [[Primary Treatment]].

[[Fat]]s and solids are removed in the first treatment stage.  Sewage enters a tank where solids fall to the bottom and fat floats to the top.  Fats and solids stay in the tank and the water continues to the next stage. This is called primary treatment.

Water leaving the first treatment stage may be cleaned by [[bacteria]] and other very small animals and plants in the [[Secondary Treatment]] stage. These bacteria use [[oxygen]] from the air to eat pollution and [[chemical]]s from the sewage. Clumps of bacteria grow while eating the pollution from the water.  These clumps of bacteria eventually fall to the bottom of the tank.  The clumps of bacteria stay in the tank and the  cleaner water leaves.Some of the bacteria falling to the bottom of the ''secondary'' tank are pumped back to the mixing tank so there are enough bacteria to create a thick brown mixture.

Modern sewage treatment started in [[London]] about 1850. The first treatment plants for sewage were designed by Sir [[Joseph Bazalgette]].

Small treatment plants may use a small pond, called a lagoon, to hold the sewage while bacteria eat the pollution.  Larger treatment plants use machines to help the bacteria process the sewage.  Some treatment works have [[Rock (geology)|rocks]] or pieces of [[plastic]] for the bacteria to grow on.  Water is pumped over the rocks or plastic.

Bacteria and [[amoebae]] in the [[gut]] and [[bowel]]s are totally [[anaerobic]]. [[Oxygen]] kills them. A key aspect of the treatment is not just to remove solids, but to ''run the sewage through oxygenated water''.  It is this which is the most important part of treatment after solids are removed. The use of chemicals is only done exceptionally. Dumping sewage into the sea is disgusting, but has been done at times when the treatment plants are not adequate.

Other works don't have rocks and plastics for the bacteria to live on. These works may blow [[air]] through the water to mix it with clumps of bacteria.   

Small treatment plants may use a small pond, called a lagoon, to hold the sewage while oxygen destroys the bacteria.  Larger treatment plants use machines to help process the sewage. Some treatment works have [[Rock (geology)|rocks]] or pieces of [[plastic]] for the bacteria to grow on.  Water is pumped over the rocks or plastic.

Clean water on the top of the ''secondary'' tank or pond can then flow to a river or the sea but it may also need further treatment to make it cleaner.  Some treatment works kill bacteria that might make people sick.  Some works use chemical [[poison]]s, like bleach, to kill these bacteria. Other works use [[ultraviolet]] light, the kind of light that causes a [[sunburn]]. This is called [[Tertiary treatment]].

[[Solid]]s from the first and second treatment  tanks can be used to make [[methane]] gas and fertilizer for farmers fields or may be dried and sent to a landfill.<ref>Water and Environmental Health at London and Loughborough 1999. Waste water Treatment Options. Technical brief no. 64. London School of Hygiene & Tropical Medicine and Loughborough University. [https://web.archive.org/web/20110717210830/http://www.lut.ac.uk/well/resources/technical-briefs/64-wastewater-treatment-options.pdf]</ref><ref>Primer for Municipal Wastewater Treatment Systems [https://www.epa.gov/sites/production/files/2015-09/documents/primer.pdf]</ref>

{{Commons category}}

{{Commons category}}

[[Category:Waste management]]

[[Category:Waste management]]