Wastewater treatment is a process used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environment or is reused for various purposes (called water reclamation).

1. Wastewater
Engineering
SECONDARY TREATMENT OF SEWAGE –
TRICKLING FILTERS
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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2. Biological Treatment
Objective
◦ Remove organic matter from the wastewater which is present in soluble and
colloidal
◦ Remove nutrients such as nitrogen and phosphorous from the wastewater.
Process
The microorganisms (principally bacteria) are used to convert the colloidal and
dissolved carbonaceous organic matter into various gases and into cell tissue.
Cell tissue having high specific gravity than water can be removed in settling tank.
Biological removal of degradable organics involves a sequence of steps including
mass transfer, adsorption, absorption and biochemical enzymatic reactions.
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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3. Batch Process
During fresh commissioning of the reactor if the
microorganisms inoculated in the reactor are not
adapted (acclimatized) to the type of wastewater
being treated, there may be some lag phase.
During this phase there will be some lag time
before the substrate is being accepted by the
microbes, hence to reflect in substrate depletion
and microbial growth.
Log growth phase: Substrate is adequate in this
phase and rate of metabolism is only dependent
on the ability of microorganism to utilize the
substrate.
Declining growth phase: The rate of metabolism
and hence growth rate of microorganisms
decreases due to limitations of substrate supply.
This is referred as substrate limited growth
condition where substrate available is not enough
to support maximum growth rate of
microorganisms.
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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4. Batch Process
Stationary phase: When the bacterial growth
rate and decay rate are same there will be no
net increase or decrease in mass of
microorganism. This phase is referred as
stationary phase.
Endogenous growth phase: The
microorganisms oxidize their own protoplasm
for energy (endogenous respiration) and
thereby decrease in number and mass.
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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5. Aerobic Treatment of Sewage
1. Attached growth process(Fixed film process).
2. Suspended growth process.
3. Combined process.
Attached Growth - micro organisms are responsible for conversion of organic matter
present in waste water to gases and cell tissues are attached to some inert medium
such as rock, slag, ceramic or plastic material.
This process include: 1.Intermittent sand filters 2.Trickling filters 3.Rotating
biological contactors 4.Packed bed reactors
Suspended Growth - micro organisms are responsible for conversion of organic
matter present in waste water to gases and cell tissues are maintained in suspension
within the liquid in the reactor by employing either natural or mechanical mixing.
This process include: 1.Activated sludge process. 2.Aerated lagoons. 3.Sludge
digestion system. 4.Suspended growth nitrification & denitrification
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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6. Trickling Filters
Percolating filters or Sprinkling Filters
Water trickles down with the help of
spray nozzles or rotary distributors
Collected from the underdrainage
systems
Sloughing is common.
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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7. Construction
and Operation
- TF
Above ground (Rectangular &
Circular)
Rectangular – Network of
pipes
Circular – Rotary Distributors
( Electric Motor – Rotor Arms (
0.5 to 2 RPM)
Dosage – 3 to 5 mins and
resting 5 – 10 mins.
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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8. Construction and Operation
Filtering Media
 Coarser Material (stones or slag also free from dust)
 Size 25 mm – 75 mm
 Should not change weight when exposed to Acidic and
Basic Conditions
 Total depth – 2 to 3 m
 Honeycombed walls for free circulation
 Sometimes compressed gas is blown for cleaning
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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9. Working of a Trickling Filter
• The sewage is allowed to sprinkle over
filter media through nozzles or rotary
distributors.
• The biological purification is mainly
done by aerobic bacteria which form a
bacterial film known as biofilm or slime
layer around filter media.
• This biofilm layer is aerobic only upto
a depth of 0.1 to 0.2mm and remaining
part is anaerobic.
• The organic matter is degraded by
aerobic micro organisms on the outer
portion of biofilm.
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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10. Classification of Trickling Filters
Conventional trickling filter or ordinary trickling filter or standard rate or low
rates trickling filter
• The settled sewage is applied to the filter bed and after trickling through it,
passes through the final sedimentation tank for removal of most of the stabilized
solids.
High Rate Filters
• the settled sewage is applied at much higher rate than for the low rate filter.
• the difference is that provision is made in them for recirculation of sewage
through the filter by pumping a part of the trickling filter effluent to the primary
settling tank (or the dosing tank of trickling filter) and re-passing it through filter.
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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11. Recirculation
of High Rate
Trickling
Filters
•
To increase the load rate of
trickling filter the sewage is an
essential and important feature
of high rate filters.
The recirculation consists in
returning portion of the treated
or partly treated sewage to the
treatment process (i.e. filter).
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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12. Comparison of
Standard Rate
Trickling
Filter SRTF and
High Rate
Trickling
Filter HRTF
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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13. Operation and Maintenance
Problems
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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14. Operation and Maintenance
Problems
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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15. Advantages and Disadvantages of
Trickling Filter
ADVANTAGES OF TRICKLING
FILTER
• Rate of Filter loading is high as required
less land areas and smaller quantities of
filter media for their installations.
• Effluent obtained from the trickling
filter is sufficient stabilized.
• Working of Trickling filter is simple and
does not require any skilled supervision.
• They are flexible in operation.
• They are self cleaning
• Mechanical wear and tear is small as
they contain less mechanical equipment.
DISADVANTAGES OF TRICKLING
FILTER
The beds loss through these filters is
high.
• Construction cost is high
• These filters cannot treat raw sewage
and primary sedimentation is must.
• Fly nuisance and odor nuisance may
prevail.
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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16. Design of Trickling Filters
REFERENCE – SEWAGE TREATMENT DISPOSAL & WASTE WATER
ENGINEERING – P.N MODI
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