3. Trickling Filter
3
Trickling filter is an attached-growth aerobic type
of process in which microorganisms attached to a
medium are used for removing organic matter
from wastewater.
These reactors are also called as non-submerged
fixed film biological reactors.
These are also called percolating filters or
sprinkling filters
A trickling filter, is a tank of media such as gravel,
Stone Ballast or plastic material.
Wastewater is distributed over the top of the
media and flows downward across the media
surface in a thin film.
It then exits the bottom of the tank and flows into
5. Tricking Filter- Filter media
5
Trickling filter uses packing medium composed of
crushed stone, slag, rock or plastic over which
wastewater is distributed continuously
The ideal medium should have the following
properties: high specific surface area, high void
space, light weight, biological inertness, chemical
resistance, mechanical durability, and low cost.
Coarser materials broken stone, blast furnace slag
Size vary from 25-75mm
Should be washed before placing
Required hardness -12 in brinell’s hardness testing
machine and should have a minimum crushing
strength of 100N/mm2
Media placed in layers
Depth of filter 1.8-3m
6. Filter media
6
Can use plastic media
lighter - can get deeper beds (up to 12 m)
reduced space requirement
larger surface area for growth
greater void ratios (better air flow)
less prone to plugging by accumulating slime
7. Typical Modular and Random Packed Plastic Media
Schematic diagrams of modular and random packed media used
in fixed-film treatment systems (Source: Bordacs and Young, 1998)
7
10. Rotating Arms
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Rotate around central support by force of reaction
on sprays/electric motor
Rate of revolution 2 RPM for small distributors
½ RPM for large distributors
More than 2 arms
Advantages for the rotation action
Hepls in reduction of shock loads
2 arms only working during low flow
Rotary arms are kept 15-20 cm above the top
filtering surface
11. Dosing of sewage
11
Rotary arms dose continues
Spray nozzles are present in which the sewage is
dosed for 3-5 min and then rest for 5-10min
Dosing tank for filter with distributors designed for
1-3 min detention time for smaller capacity
5-10 min detention time for higher capacity
12. Under drains
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Taking the effluent to
the effluent pipe
Sloped
Only filled 50% so
that helps in aeration
13. Trickling Filter-Working
The wastewater in trickling filter is distributed over the
top area of a vessel containing non-submerged packing
material.
Air circulation in the void space, is either natural draft or
blowers, provides oxygen for the microorganisms
growing as an attached biofilm.
During operation, the organic material present in the
wastewater is metabolised by the biomass attached to
the medium.
The biological slime grows in thickness as the organic
matter abstracted from the flowing wastewater is
synthesized into new cellular material.
The thickness of the aerobic layer is limited by the depth
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14. Trickling Filter-Working
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The micro-organisms near the medium face loose
their ability to cling to the media surface due to the
increase in thickness.
The liquid then washes the slime off the medium
and a new slime layer starts to grow.
This phenomenon of losing the slime layer is called
sloughing.
The sloughed off film and treated wastewater are
collected by an under drainage which also allows
circulation of air through filter.
The collected liquid is passed to a settling tank
used for solid- liquid separation.
Some water is recycled to the filter, to maintain
moist conditions
17. Biological Process of Trickling
Filter
Biofilm
a biological slime layer
bacteria in biofilm
degrade organics
biofilm will develop
on almost anything
20. Performance
Power Required is less per unit BOD removal
Suspended solids reduced by 90%
BOD reduced to about 80-90 %
BOD less than 20 ppm
20
21. Advantages and disadvantages
Advantages Disadvantages
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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 nitrified and
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
The head loss through
these filters is high.
Construction cost is high
These filters cannot treat
raw sewage and primary
sedimentation is must.
Operational troubles like
fly nuisance and odour
nuisance may prevail.
22. Operational Troubles in TF
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Filter Ponding
Filter Flies
Odour
Icing for Filter Surface
23. Operational Troubles in TF
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Filter Ponding
If the voids in the media get plugged, flow can collect
on the surface in ponds.
Excessive sloughing, excessive organic loading, non-
uniformity in size of media and improper functioning of
primary treatment units are its chief causes.
Remedies
Wash the filter surface with a stream of water under high
pressure.
Dose the filter with heavy applications of chlorine.
Take the filter out of service for a period of one day or
longer to allow it to dry out.
24. Operational Troubles in TF
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Filter Flies
primary nuisance insect- tiny, gnat-size filter fly,
or Psychoda. Filter flies develop most frequently
in an alternately wet and dry environment.
Remedies:
Dose filter continuously, not intermittently.
keep orifice openings clear
apply insecticides to filter walls
dose filter with chlorine
keep weeds and tall grass cut around filter
25. Operational Troubles in TF
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Odour Problem
The presence of “rotten egg” odour is an indication of
anaerobic condition.
Remedies
Maintain aerobic conditions in all units, including settling tanks
and waste water system.
Recirculate to filters.
Icing for Filter Surface
Cold weather not only reduces the efficiency of trickling
filters by decreasing the activity of the microorganisms, but
in severe cases actually can cause the wastewater to
freeze on the medium surface.
Remedies
decrease recirculation to the filter (influent is usually warmer
than recycled flows)
construct wind screens
operate two-stage filters in parallel rather than in series
26. Types of Trickling Filter
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Conventional Trickling Filter/Low Rate TF
single stage rock media units
loading rates of 1-4 m3 wastewater/m2 filter cross-
sectional area-day
large area required
High Rate Trickling Filter
single stage or two-stage rock media units
loading rates of 10-40 m3 wastewater/m2 filter
cross-sectional area-day
re-circulation ratio 1-3
27. Types of Trickling Filter
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Super rate/ Biotower
Synthetic plastic media units
Modules or random packed
Specific surface areas 2-5 times greater than rock
Much lighter than rocks
Can be stacked higher than rocks
Loading rates of 40-200 m3 wastewater/m2 filter
cross-sectional area-day
Plastic media depths of 5-10 m
