# NPTEL Water and waste water treatment Week 4 Assignment Answers 2024

## NPTEL Water and waste water treatment Week 4 Assignment Answers 2024

1. Which of the following are attached type treatment systems:

• Activated sludge process
• Trickling filter
• Oxidation pond
• Rotating biological filter
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2. A certain type of bacteria multiplies by dividing into two cells every 10 minutes. If you start with 2 × 105 bacterial cells in a Petri dish, how many cells will there be after 40 minutes?

• 3.2 × 10^5
• 6.8 × 10^5
• 6.8 × 10^6
• 3.2 × 10^6
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3. A wastewater treatment plant has influent MLSS as 5500 mg/L. After a settling period, the volume of sludge in the settling tank is measured to be 450 mL/L of mixed liquor. Calculate the Sludge Volume Index (SVI) for the given mixed liquor in mL/g.

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4. In biological nutrient removal, what is the purpose of using anoxic zones in biological treatment processes?

• To promote the growth of aerobic bacteria
• To facilitate denitrification
• To enhance phosphorus precipitation
• To optimize ammonia oxidation
`Answer :- `

5. Calculate the specific growth rate of microorganisms (per hour) in an activated sludge wastewater treatment system, where
Maximum specific growth rate = 0.4/hr,
Half-saturation constant = 12 mg/L
Substrate concentration = 6 mg/L.

• 0.09/hr
• 0.18/hr
• 0.13/hr
• 0.17/hr
`Answer :- `

6. In a wastewater treatment plant utilizing facultative ponds, what is the unexpected challenge that might arise during the winter season in northern regions?

• Enhanced microbial activity
• Reduced treatment efficiency
• Increased pathogen removal
• Improved settling of solids
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7. A completely mixed flow reactor is designed with the following data: Qo = 20000 m3/d, BOD after PST = 180 mg/I, BOD of the effluent of = 10 mg/l, Y = 0.5 kg/kg, Kd = 0.05 per day, MLSS = 4000 mg/l. Underflow concentration (Xu) = 10000 mg/I for secondary sedimentation tank and mean residence time (Ɵc) = 8 days. The reactor volume is __.

`Answer :- `

8. Statement A: Heterotrophs are organisms that cannot produce organic compounds from inorganic sources and, therefore, rely on obtaining pre-formed organic molecules from external sources.
Statement B: Autotrophs are organisms capable of synthesizing organic molecules from simple inorganic substances like carbon dioxide.

• Statement A is true.
• Statement B is true.
• Statement A and Statement B both are true.
• Statement A is false, and Statement B is true.
`Answer :- `
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