ACTIVATED SLUDGE AND NUTRIENT REMOVAL

Question

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A wastewater treatment plant based on activated sludge with biological phosphate and nitrogen removal via pre-denitrification. The influent flow (dwf) is 30,000 m3/day and the influent BOD concentration is
300 mg BOD/l. The suspended solid concentration in the influent is 150 mg/l of which 40% is removed in the primary clarifier. The sludge recycle flow ratio (fr) is 0.5, the sludge yield (Y) is 0.6 kgX/kgBODremoved and the SVI is 130 mL/g.
The treatment plant consists of different process units, namely:

Final clarifier
Screen
Aerobic tank
Primary sedimentation
Anoxic tank
Grit chamber
Anaerobic tank
Sludge dewatering
After dewatering the sludge will be directly transported to the sludge incineration plant.

Additional information

The wastewater treatment plant is extended with the Nereda technology.

Q1:What is correct for the aerobic granules of a Nereda system.

a//Nitrification takes place inside the granule
b//Denitrification takes place inside the granule
c//Due to reduction of oxygen in the outer layer, anoxic conditions will exist inside the granule
d// Due to diffusion limitation the substrate can only reach the outer layer of the granule
e//Aerobic granules make settling tanks superfluous
f//Screening is not needed due to the characteristics of the aerobic granular sludge

Q2:QUESTION 3G (5 points possible)
The waste sludge of the Nereda installation is added to the conventional wastewater treatment plant, which will lead to a decreased SVI of the activated sludge plant. What is the main advantage of a lower SVI?

a/The maximum sludge concentration in the return flow will increase, reducing biomass storage in the final clarifier during rwf, decreasing the chance for biomass wash out.
b/The biomass concentration in the aeration tank can increase, which could lead to higher conversion capacity.
c/The size of the final clarifier can be reduced due to the increased settling velocity of the aerobic granules in the sludge.
d/ The oxygenation capacity will increase due to a higher alpha factor of the sludge water mixture.

Answer 1

Q1: b- Denitrification takes place inside the granule , c- Due to reduction of oxygen in the outer layer, anoxic conditions will exist inside the granule , e- Aerobic granules make settling tanks superfluous.

Answer 2

Q2: The maximum sludge concentration in the return flow will increase, reducing biomass storage in the final clarifier during rwf, decreasing the chance for biomass wash out. The biomass concentration in the aeration tank can increase, which could lead to higher conversion capacity.