Sewage treatment facts for kids
Sewage treatment is the process of dealing with sewage so that is does not cause harm to people or to rivers. Sewage flows in sewers from houses and 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 screens. The sewage then flows through a tank so sand can fall out. Large objects and sand might damage machines in later stages.
Fats 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 chemicals 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 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 poisons to kill these bacteria. Other works use the kind of light that causes a sunburn.
Solids from the first and second tanks can be used to make methane gas and fertiliser for farmers fields.
Images for kids
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Activated sludge sewage treatment plant in Massachusetts, US
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Constructed wetland (vertical flow) at Center for Research and Training in Sanitation, Belo Horizonte, Brazil
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Trickling filter sewage treatment plant at Onça Treatment Plant, Belo Horizonte, Brazil.
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Aeration tank of activated sludge sewage treatment plant (fine-bubble diffusers) near Adelaide, Australia
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Upflow anaerobic sludge blanket (UASB) reactor in Brazil (picture from a small-sized treatment plant), Center for Research and Training in Sanitation, Belo Horizonte, Brazil
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A poorly maintained anaerobic treatment pond in Kariba, Zimbabwe (sludge needs to be removed)
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Preliminary treatment arrangement at small and medium-sized sewage treatment plants: Manually-cleaned screens and grit chamber (Jales Treatment Plant, São Paulo, Brazil)
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Preliminary treatment: Horizontal flow grit chambers at a sewage treatment plant in Juiz de Fora, Minas Gerais, Brazil
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Rectangular primary settling tanks at a sewage treatment plant in Oregon, USA
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Simplified process flow diagram for a typical large-scale treatment plant using the activated sludge process.
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Overall setup for a micro filtration system
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Nitrification process tank at an activated sludge plant in the United States.
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Constructed wetlands (vertical flow) for sewage treatment near Shanghai, China.
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View of a belt filter press at the Blue Plains Advanced Wastewater Treatment Plant, Washington, D.C.
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Mechanical dewatering of sewage sludge with a centrifuge at a large sewage treatment plant (Arrudas Treatment Plant, Belo Horizonte, Brazil)
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Treated effluent from sewage treatment plant in Děčín, Czech Republic is discharged to surface waters.
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Sludge drying beds for sewage sludge treatment at a small treatment plant at the Center for Research and Training in Sanitation, Belo Horizonte, Brazil.
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Circular secondary sedimentation tank at activated sludge sewage treatment plant at Arrudas Treatment Plant, Belo Horizonte, Brazil.
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See also
In Spanish: Tratamiento de aguas residuales para niños
