Biological Sewage Treatment Plant

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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Comments 6 comments

thevoice profile image

thevoice 6 years ago from carthage ill

terrific terrific detail thanks

mrali2010 profile image

mrali2010 5 years ago

Nice work

plumbing 5 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.

epbooks profile image

epbooks 3 years ago from Las Vegas, NV

Interesting hub. Well-written and explained.

tamarawilhite profile image

tamarawilhite 3 years ago from Fort Worth, Texas

Where are these systems used? Onboard ships?

jabelufiroz profile image

jabelufiroz 3 years ago from India Author

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

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