The Main Stages of WasteWater Treatment

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The reason for me doing this report is because I could not attendclass enough to grasp the concept of Wastewater Treatment. This report is an overview of each stage of the treatment of sewage. I have included a diagram of a typical sewage plant. The wastewater that enters a treatment plant contains debris that might clog or damage the pumps and machinery. The material is removed by screens, and is burned or buried. The wastewater then passes through a comminutor (grinder), where all the organic material such as leaves are mushed smaller so that they can be removed later. The digested sludge is place on sand beds for air drying. Air drying needs dry, warm weather for it to work. Some plants have shelters over the sand beds. Dried sludge in most cases is used as a fertilizer because of the 2 percent nitrogen and 1 percent phosphorus content. After removing 40 to 60 percent of the suspended solids and 20 to 40 percent of the BOD5 in the primary stage by physical resources, the secondary treatment biologically reduces the organic material that stayed in the liquid stream. Secondary treatment contains keeping and speeding up nature’s process of waste disposal. Aerobic bacteria in the oxygen change the organic matter to stable forms such as CO2 , water, nitrates, and phosphates. The new organic material that is made is an indirect result of biological treatment processes, and is removed before the wastewater is dumped into the streams.

In this process, a waste stream is sent over a bed or column of some type of porous medium. A sticky film of microorganisms coats the medium and acts as the removal agent. The organic matter in the waste stream is absorbed by the film and changed to carbon dioxide and water. If the trickling filter step comes before the sedimentation stage it can remove about 85 percent of the BOD entering the plant. This stage is an aerobic process that adds sticky sludge particles that have millions of of actively growing bacteria stuck together by a gelatinous slime. Organic matter is assimilated by the floc and changed to aerobic output. The reduction of BOD varies between 60 to 85 percent. Another way of biological treatment is the the stabilization pond or lagoon. Facultative lagoons are the most common, being 2 to 5 ft deep, with a surface area of several acres. Anaerobic conditions succeed in the bottom area, where the solids are decomposed. The area near the surface is aerobic, allowing the oxidation of dissolved and homogenous mixture of organic matter. A decrease in BOD of 75 to 85 percent can be There are many other ways and stages of wastewater treatment but these are the basic processes. I learned alot about wastewater treatment and the it is a good thing we have it so the lakes and streams.

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  1. Waterlink Industries. 2000. “Wastewater Treatment.” Science (Refreshed Daily): 6pp.Online. Internet. May 01, 2000. Available
  2. Microsoft Encarta Encyclopedia 99 (1999). [Cd Rom computer program]. Redmond, WA: Microsoft Corporation.

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