In primary treatment, all solids that settle during sedimentation form the:

[Microbes-in-Human-Welfare] [class-xii ]

• Activated sludge
• Flocs
• Grit
• Primary sludge
Correct Option: D  [ Primary sludge ]

Remark: All solids that settle form the primary sludge, and the supernatant forms the effluent.

The secondary treatment of sewage is also known as:

[Microbes-in-Human-Welfare] [class-xii ]

• Chemical treatment
• Physical treatment
• Biological treatment
• Tertiary treatment
Correct Option: C  [ Biological treatment ]

Remark: Secondary treatment is also called Biological treatment.

During secondary treatment in aeration tanks, vigorous growth of useful aerobic microbes form mesh-like structures called:

[Microbes-in-Human-Welfare] [class-xii ]

• Primary sludge
• Grit
• Biogas precursors
• Flocs
Correct Option: D  [ Flocs ]

Remark: Aerobic microbes grow into flocs (masses of bacteria associated with fungal filaments to form mesh like structures).

The growth of flocs in the aeration tank significantly reduces the BOD of the effluent. What does BOD stand for?

[Microbes-in-Human-Welfare] [class-xii ]

• Biomass Oxygen Demand
• Biological Organic Decomposition
• Biochemical Oxygen Demand
• Bacterial Oxidation Deterioration
Correct Option: C  [ Biochemical Oxygen Demand ]

Remark: The growth of microbes significantly reduces the BOD (biochemical oxygen demand) of the effluent.

The greater the BOD of waste water, the greater is its:

[Microbes-in-Human-Welfare] [class-xii ]

• Water purity
• Polluting potential
• Mineral content
• Aerobic microbial count
Correct Option: B  [ Polluting potential ]

Remark: The greater the BOD of waste water, more is its polluting potential.

In the settling tank after aeration, the bacterial flocs sediment to form:

[Microbes-in-Human-Welfare] [class-xii ]

• Primary effluent
• Activated sludge
• Grit
• Biogas mixture
Correct Option: B  [ Activated sludge ]

Remark: The bacterial ‘flocs’ are allowed to sediment in a settling tank, forming the activated sludge.

A small part of the activated sludge is pumped back into the aeration tank to function as the:

[Microbes-in-Human-Welfare] [class-xii ]

• Fertilizer
• Filter medium
• Inoculum
• Biogas source
Correct Option: C  [ Inoculum ]

Remark: A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum.

The remaining major part of the activated sludge is pumped into large tanks for anaerobic digestion, called:

[Microbes-in-Human-Welfare] [class-xii ]

• Aeration tanks
• Primary settling tanks
• Digester flocs
• Anaerobic sludge digesters
Correct Option: D  [ Anaerobic sludge digesters ]

Remark: The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters.

The digestion of bacteria and fungi in the anaerobic sludge digesters produces a mixture of gases including:

[Microbes-in-Human-Welfare] [class-xii ]

• Oxygen, Nitrogen, and Methane
• Methane, Hydrogen sulphide, and Carbon dioxide
• Carbon monoxide, Hydrogen, and Oxygen
• Sulphur dioxide, Methane, and Ammonia
Correct Option: B  [ Methane, Hydrogen sulphide, and Carbon dioxide ]

Remark: During digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide.

Which ministry initiated the Ganga Action Plan and Yamuna Action Plan to save major rivers from pollution?

[Microbes-in-Human-Welfare] [class-xii ]

• Ministry of Agriculture
• Ministry of Health and Family Welfare
• Ministry of Environment and Forests
• Ministry of Rural Development
Correct Option: C  [ Ministry of Environment and Forests ]

Remark: The Ministry of Environment and Forests has initiated Ganga Action Plan and Yamuna Action Plan.