Question

Read the following statements (A-D) related to the composition of domestic wastewater and select the correct option stating true (T) and false (F).

A. Wastewater contains 0.3 % of impurities.
B. Suspended solids in wastewater include sand, silt and clay.
C. Colloidal materials like fecal matter, bacteria, cloth and paper fibres are present in wastewater.
D. Dissolved materials in waste water include nutrients like starch, nitrates and ammonia.

• A. A - F, B - F, C - T, D - F
• B. A - F, B - T, C - T, D - F
• C. A - T, B - F, C - T, D - F
• D. A - T, B - F, C - F, D - T

Answer 1

The correct option is B A - F, B - T, C - T, D - F

Wastewater is the polluted form of water generated from rainwater runoff and human activities.

Domestic wastewater contains 0.1 % of impurities and 99.9 % of water. Hence, statement A is false.

The 0.1% of impurities present in the domestic wastewater include:

• Suspended solids: These materials do not dissolve but remain suspended in the water. The suspended solids include sand, silt and clay.
  • Sand is composed of finely divided rock and mineral particles of size ranging from 0.05 mm to 2 mm.
  • Silt is a dust-like sediment of size ranging from 0.002 mm to 0.05 mm transported by water, ice, and wind and deposited in water.
  • Clay is a soft, loose, earthy material containing particles with size less than 0.002mm. Hence, statement B is true.
• Colloidal materials: They are microscopically dispersed insoluble particles with a size ranging from 10^-7 to 10^-3 cm suspended in water. These include fecal matter, bacteria, cloth and paper fibres. Hence statement C is true.
• Dissolved materials: These are the particles that are dissolved in the water which includes nutrients like nitrates, ammonia, phosphate, sodium, calcium etc. Starch, being a polysaccharide (macromolecule) will not dissolve in water. Hence statement D is false.

Figure: Composition of wastewater