Question

Explain the process of Sewage Treatment.​

Answer 1

Answer:

Sewage treatment consists of three treatment stages:

(i) Primary Treatment – It consists of following steps:

• Screening - The wastewater is first passed through bar screens which remove large objects like plastic bottles, napkins, rags, cans etc. from the sewage.

• Grit and sand removal - The wastewater is then passed through a grit and sand removal tank. The speed of the water is decreased at this step which allows the sand, dirt and pebbles to settle down.

• Primary Sedimentation - The sewage is then passed into primary sedimentationtank called clarifier and allowed to stand for 10-12 hours. Most of the solids like faeces to settle at the bottom in the form primary sludge. The primary sludge is then removed with the help of a Scrapper and shifted to a large closed tank called digester tank where anaerobic bacteria decompose the organic matter to produce biogas which can be used as a fuel. Substances like oil and grease are removed with the help of a skimmer as they float above the water. In this step clarified water is obtained.

(ii) Secondary Treatment

• Aeration - The clarified water is then passed into aeration tank. Compressed air is bubbled to provide oxygen which helps aerobic bacteria to grow rapidly in water. The aerobic bacteria decompose most of the organic matter.

• Secondary Sedimentation - The clarified water is allowed to settle for several hours and then aerobic bacteria settle down at the bottom of the tank as ‘activated sludge’.

(iii) Tertiary Treatment

Now, the water is disinfected with chemicals like chlorine and ozone before it is discharged into a sea, river or into the ground.

Answer 2

Answer:

Sewage treatment consists of three treatment stages:

(i) Primary Treatment – It consists of following steps:

Screening - The wastewater is first passed through bar screens which remove large objects like plastic bottles, napkins, rags, cans etc. from the sewage.

Grit and sand removal - The wastewater is then passed through a grit and sand removal tank. The speed of the water is decreased at this step which allows the sand, dirt and pebbles to settle down.

Primary Sedimentation - The sewage is then passed into primary sedimentation tank called clarifier and allowed to stand for 10-12 hours. Most of the solids like faeces to settle at the bottom in the form primary sludge. The primary sludge is then removed with the help of a Scrapper and shifted to a large closed tank called digester tank where anaerobic bacteria decompose the organic matter to produce biogas which can be used as a fuel. Substances like oil and grease are removed with the help of a skimmer as they float above the water. In this step clarified water is obtained.

(ii) Secondary Treatment

Aeration - The clarified water is then passed into aeration tank. Compressed air is bubbled to provide oxygen which helps aerobic bacteria to grow rapidly in water. The aerobic bacteria decompose most of the organic matter.

Secondary Sedimentation - The clarified water is allowed to settle for several hours and then aerobic bacteria settle down at the bottom of the tank as ‘activated sludge’.

(iii) Tertiary Treatment

Now, the water is disinfected with chemicals like chlorine and ozone before it is

discharged into a sea, river or into the ground.

Explanation: