Lecture notes of Environmental Engineering-II as per Solapur university syllabus of TE CIVIL. Prepared by Prof S S Jahagirdar, Associate Professor, N K Orchid college of Engg and Technology, Solapur

1. L-27
Activated Sludge process
Part-III
Environmental Engineering - II

2. Modifications in ASP
• In conventional ASP many
modifications can be made both with
respect to basin configuration, asrespect to basin configuration, as
well as aeration techniques.

3. Conventional ASP

4. Tapered Aeration
• The tapered aeration system is similar to
the conventional activated sludge process.
The major difference is in the
arrangement of the diffusers.
• The diffusers are close together at the• The diffusers are close together at the
influent end where more oxygen is
needed.
• Toward the other end of the aeration
basin, the spacing of the diffusers is
increased.

6. Step Aeration
• In step aeration, the returned sludge is
applied at several points in the aeration
basin.
• Generally, the tank is subdivided into
three or more parallel channels with
around-the-end baffles, and the sludge is
applied at separate channels or steps.
• The oxygen demand is uniformly
distributed.

7. Q1 Q2 Q3 Q4 Q5 Q6

8. Contact Stabilization
• In contact stabilization, primary treatment
is not required. The activated sludge is
mixed with influent in the contact tank
where the organics are absorbed by
microorganisms.microorganisms.
• The MLSS is settled in the clarifier. The
returned sludge is aerated in the
reaeration basin to stabilize the organics.
• The process requires approximately 50%
less tank volume.

9. Sludge rearation tank

10. Extended Aeration Activated Sludge
• Extended aeration does not require primary
treatment. It utilizes a large aeration basin
where a high population of microorganisms is
maintained. It is used for small flows from
subdivisions, schools, etc.
• It has a channel in the shape of a race track,• It has a channel in the shape of a race track,
with rotors being used to supply oxygen and
maintain circulation.
• Typically the process produces high-quality
effluent and less activated sludge. (Oxidation
ditch is a variation of extended aeration
process).

12. Completely mixed process
• Incoming waste and the return sludge are
dispersed uniformly throughout the basin,
• Organic load and oxygen demand are
uniform over the aeration tank length.
• Efficiency is maximum
• Dilution of wastewater in aeration tank.
• Good stabilization of waste solids.
• Due to above reasons it is best ASP

14. Sludge bulking
• Foam formation and poorly settling
sludges are the two most common
problems of ASP
• Sludge that exibits poor settling
characteristics is known as bulking ofcharacteristics is known as bulking of
sludge
• Filamentous microorganisms are
responsible for a bulked sludge.

15. • Other factors responsible are
- Low pH
- Inadequate air supply
- Prolonged aeration
- Sludge accumulation at bottom of aeration- Sludge accumulation at bottom of aeration
tank.
- Presence of industrial waste containing
toxic contaminants.

16. Control of sludge bulking
1. Sludge age less than 6 days
2. Chlorination of return activated sludge
3. Rearation of return sludge.3. Rearation of return sludge.
4. Addition of lime to raise pH to 8 or
more.
5. Application of Hydrogen Peroxide to
control growth of filamentous
microorganisms

17. Theory questions
Write Short notes on
1. Modifications in ASP
2. Step aeration ASP2. Step aeration ASP
3. Tapered aeration ASP
4. Sludge bulking