Question

What are the three major kinds of impurities in domestic wastewater?

Answer 1

Components of domestic wastewater

Domestic wastewater or sewage contains 99.9$\%$ water and 0.01$\%$ impurities. The impurities in wastewater can be categorised as follows:-

• Colloids
• Dissolved solids
• Suspended solids

Colloids

Colloids are small particles that impart turbidity and colour to the waste water. Coagulation-flocculation processes are used to remove colloids during water treatment. Examples include bacteria, faecal matter etc.

Dissolved solids

Dissolved solids include inorganic solids like ions, minerals, salt as well as organic matter.

Suspended solids

Suspended solids are the fine particles present in the waste water. These particles are removed easily by sedimentation and filtration. Examples include silt, clay and sand.