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Biological Sewage Treatment Plant

Updated on April 23, 2010

Raw sewage is passed to an aeration chamber and air is supplied through diffusers. This promotes the action of aerobic bacteria which break down the sewage into carbon di oxide, water and inorganic waste. Figure below shows a typical biological sewage treatment plant. 

Sewage then passes into the clarification or settling chamber. Any solids that settle out are returned via an air lift to the aeration chamber which ensures that they are fully broken down. The sample applies to any surface scum. A small vane type air compressor supplies the air for air diffusers and air lift.

The clear liquid then passes through the chlorinator where the liquid is disinfected, into the chlorination chamber. The chamber has float switches, which control the discharge pump, and a high level alarm.

Although the sewage treatment plant runs automatically, without regular maintenance the unit will not function properly and anaerobic bacteria may promote the formation of hydrogen sulphide and methane, both of which are hazardous.

The chambers need to be cleaned out occasionally to remove any accumulated matter. The aeration diffusers should be checked to ensure they are clear and that air is bubbling from them. The air lift returns should also be checked to make sure they function correctly. These usually have a clear plastic pipe so that the sludge can be seen returning to the aeration chamber.

The internal tank coating should be inspected for any signs of cracking or blistering.

When cleaning out a sewage unit rubber gloves and a mask should be worn. After overhaul the external surfaces of the unit and surroundings are to be washed down with disinfectant. Hands should also be thoroughly scrubbed and overalls washed.


"Operation and Maintenance of Machinery in Motor Ships" by N.E. Chell

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    • jabelufiroz profile image

      Firoz 4 years ago from India

      Yes, since the direct discharge of sewage is prohibited, water and wastes from toilets to be treated properly with treatment plants.

    • tamarawilhite profile image

      Tamara Wilhite 4 years ago from Fort Worth, Texas

      Where are these systems used? Onboard ships?

    • epbooks profile image

      Elizabeth Parker 4 years ago from Las Vegas, NV

      Interesting hub. Well-written and explained.

    • profile image

      plumbing 6 years ago

      Sewage treatment plants nowadays must be carefully checked because sewage treatment plants can be easily clogged and can really damage the flow of water on the pipes.

    • mrali2010 profile image

      mrali2010 6 years ago

      Nice work

    • thevoice profile image

      thevoice 7 years ago from carthage ill

      terrific terrific detail thanks