sewage treatment

Sewage Treatment

Contents of Entire Course

Methods of treating sewage
Sources of Household sewage
Composition of Household Wastewater
Septic Tank System

adapted to HTML from lecture notes of Prof. Stephen A. Nelson Tulane University

Methods of treating sewage

Household sewage is comes from a variety of sources. 

Sources of Household sewage

Toilets  40% 
Bathing  30% 
Laundry  15% 
Kitchen  10% 
Miscellaneous  5% 

Excluding about 1% solids, household sewage is 99.9% water. 

Composition of Household Wastewater

Constituent Materials  Concentrations (ppm) 
Dissolved Solids  500 
Suspended Solids  200 
Settleable Solids  (1%) 
Biochemical Oxygen Demand
(BOD) material 
Chemical Oxygen Demand
(COD) material 
Nitrogen 40
Organic 15 
Free Amonia  25 
Phophorus 10
Chloride  50 
Alkalines  100 
Grease  100 

Septic Tank System
In many areas the main type of sewage disposal is a septic tank system.


  • In the diagram,  sewage travels to a leaching field after it goes through the septic tank. This is needed in places where they do not have good drainage.
  • Sandy sediments are necessary in order to oxidize the sewage water, and filter out the bacteria from it.

    Ammonium that travels through the unsaturated zone is oxidized and converted to nitrate by the time it reaches the water table. Thus, areas with high populations that rely on septic tank systems have to be concerned about the possibility of the groundwater achieving  high nitrate concentrations.

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