Activated sludge

1. WASTE WATERS
ACTIVATED SLUDGE
CPI-I

2. MUNICIPAL WASTE WATERS
• Efficient sewage disposal is important to the
health.
• The impurity in a particular sewage or the
amount of treatment required is usually
measured on:
1. The amount of suspended solids
2. The biological oxygen demand (BOD), which is
the amount of molecular oxygen required by a
microbial population to stabilize biodegradable
organic material.

3. • SEWAGE TREATMENT ARE DIVIDED INTO:
1. Primary or Physical treatment
2. Secondary or biochemical treatment
3. Tertiary treatment

4. PRIMARY TREATMENT
• Is designed to remove from the sewage 30-60%
of the suspended solids and reduce the BOD by
the same amount.
• The effluent is usually chlorinated to destroy
bacteria and viruses.
• In the primary plant the influent is screened to
allow the passage of solids not larger than 2.5-5
cm.
• Primary treatment then removes the “settleable”
solids.

5. • Fine particles may be agglomerated to
increase their size and permit settling so that
coagulation of fine, so that coagulation of fine
particles makes larger ones by flocculation,
and these are then removed by
sedimentation.
• The total process is a clarification operation.
• Coagulants are added to assist in this
operation.
• The chemical additives and polyelectrolytes
are also used to form hydrated colloidal flocs.

6. • Primary treatment alone is inadequate, and
with secondary treatment dissolved organic
materials are oxidized to reduce the BOD by
85-90%.
• This imitates nature’s conversion by animal
microorganisms which feed on them.
• An ACTIVATED SLUDGE or a Trickling filter are
used to accelerate the biochemical oxidation
in the secondary treatment.

7. ACTIVATED SLUDGE TRICKLING FILTERS

8. ACTIVATED SLUDGE
• One of the most effective processes to remove both
suspended and dissolved substances from sewage.
• Activated sludge contains aerobic microorganisms that digest
raw sewage.
• Some activated sludge from the previous run is introduced
into the raw sewage, and air is blown in, not in excess but only
the amount needed.
• The solids are burned, buried or sold as a fertilizer after
filtering and drying.
• The liquids remaining after the removal of the solids are
usually chlorinated to destroy harmful microorganisms and
then discharged into nearby streams.