1. Subject: Environmental Studies
Chapter: 07-Environment pollution-Water pollution
Topic: Control of water pollution
Department Mechanical Engineering
Name of the Student : Dhyey P. Shukla
Enrollment No: 170990119016
1st Year Mechanical Engineering
Name of Subject Teacher
Mr. Ruchit Shoemaker
Mr. Virdattsinh Solanki
(Assistant Professor, MED)
2. NAME : DHYEY P. SHUKLA
ROLL NUMBER : 7
ENROLLMENT NUMBER : 170990119016
12/3/2017
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3. Wastewater Treatment Plants
•Specially designed plants that accept municipal sewage from
homes, businesses and industrial sites.
•Delivered to plant by network of pipes.
•Following treatment, they discharged into surface water.
• Main purpose is to breakdown and reduce BOD and kill bacteria.
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4. Methods usually divided into three categories:
•Primary treatment
•Secondary treatment
•Advanced wastewater treatment
• Primary and secondary required by law.
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5. Primary Treatment
•Incoming raw sewage enters plant.
•Passes through series of screens.
• Remove large floating organic material.
•Next enters a grit chamber.
• Sand, small stones and grit removed.
•Then enters sedimentation tank.
• Particulate matter settles out to form a sludge.
•Sludge is removed and transported to a digester.
•Primary treatment removes ~35% of BOD.12/3/2017 5
6. Secondary Treatment
•Most common treatment, activated sludge.
•Wastewater from primary sedimentation tank enters the tank.
•Then enters the final sedimentation tank.
• Sludge settles out.
• Some activated sludge used again in aeration.
•Most of the sludge transported to digester.
•Wastewater from final tank is disinfected and discharged.
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7. Secondary Treatment
• Secondary treatment removes ~90% of BOD.
• Sludge from the digester is dried and disposed of in a landfill
or applied to improve soil.
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9. Advanced Wastewater Treatment
• Additional pollutants can be removed by adding more
treatment steps.
• Sand filters, carbon filters and chemicals applied to assist
removal process.
• Treated water can then be used for agricultural or
municipal irrigation (referred to as “Grey Water” –
most of this is currently discharged to sea.
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10. Chlorine Treatment
• Chlorine is very effective in killing the pathogens that
historically caused outbreaks.
• Chlorine treatment byproducts may pose hazard to fish
and cancer risk to humans.
• (This is a HUGE risk and benefit issue).
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12. • Sewage treatment is the process of dealing with sewage so that it does not cause harm to
people or to rivers.
• 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.
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13. • 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.12/3/2017 13
14. • 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.
• Wikimedia Commons has media related to Sewage treatment.
• Large sewage works in Germany.
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Figure 20.A
Water quality as measured by dissolved oxygen (DO) content in parts per million (ppm) at 20 °C (68 °F). Only a few fish species can survive in water with less than 4 ppm of dissolved oxygen at this temperature. Some warmer water species have evolved ways to tolerate low DO levels better than cold water species can. Question: Would you expect the dissolved oxygen content of polluted water to increase or decrease if the water is heated? Explain.
