Waste Water


The water which gets contaminated after various works; like washing, bathing, mopping, etc. is called wastewater.

Sewage Treatment: The process of removing impurities from waste water before it can be reused or sent to the water bodies is called sewage treatment or cleaning of water.

Sewage: The liquid waste which has water as its largest component; along with various types of impurities is called sewage.

Composition of Sewage

Type of impurities Examples
Organic impurities Human faeces, animal waste, oil, urea (urine), pesticides, herbicides, fruits and vegetables
Inorganic impurities Nitrates, phosphates, metals
Nutrients Phosphorus, nitrogen
Bacteria Various types; such as those causing cholera, typhoid, etc.
Other microbes Various types; such as those causing diarrhea, jaundice, etc.

Sewers: The pipes which carry wastewater.

Sewerage: The network of sewers.

Manhole: These are the holes made in sewers at frequent intervals, so that timely inspections and cleaning of sewers can be done through them. The manhole is covered with a hard lid so that people and traffic can easily move over it.

Wastewater treatment plant or Sewage treatment plant:

These are large plants where wastewater is cleaned before being sent to the nearest water bodies or being reused. The sewage treatment involves physical, chemical and biological processes to remove impurities from the wastewater.

Physical Process

  1. Filtration : The wastewater is passed through the bar screen. Large objects; like rags, sticks, plastic bags, cans, etc. are removed in this process.
  2. Grit and Sand Removal : The wastewater is slowly passed through the sedimentation tank. Grit, sand and pebbles settle down at the bottom.
  3. Sedimentation : Water is then sent to the sedimentation tank. Solids; like faeces settle at the bottom. Floatable impurities; like oil and grease float on the surface. A scraper removes the faeces from the water. The impurity thus collected is called sludge; which is sent to the sludge tank. The sludge can be used to produce biogas or to produce manure. A skimmer removes the floatable impurities. Now, the water is called clarified water.

Biological process

  1. Aeration: Air is pumped into clarified water so that bacteria can proliferate. Bacteria consume the human waste. It leaves food waste, soap and other unwanted materials in the water. The microbes settle down at the bottom after several hours. Water is then removed from the top. This water is fit for irrigation and can be used for that purpose.

Chemical process

  1. Chlorination: Water purified through aeration is not fit for human consumption. It needs to be treated with chlorine. For this, bleaching powder is added to the water. The chlorine kills whatever germs may be left in the water. After chlorination, the water is fit for drinking.