A biofilter uses biological degradation by microorganisms attached to filter media to remove pollutants from wastewater. Microorganisms colonize on the media's surface through transportation, adhesion, and attachment processes. As the biofilm grows, dissolved organics and suspended particles are degraded but oxygen diffusion limits aerobic zones to shallow depths. The biofiltration process is influenced by wastewater flow rate, organic loading, and substrate and oxygen diffusion rates. Common biofilters used for wastewater treatment include contact beds, intermittent sand filters, and trickling filters.

2. Any type of
filter with attached biomass on the filter-media can
be defined as a
Biofilter.
The filtration process in which the pollutants are
removed due to
Biological degradation rather than physical straining
as is the case in
normal filter,
is called Biofiltration.

3. 3.Decay and detachment of microorganisms
2. Growth of microorganism
1. Attachment of microorganism

4. Organisms attached to medium and grow into dense films of
viscous, jellylike nature.
Mechanisms by which microorganisms can attach and
colonize on the surface of the filter media of a biofilter are:
(i) Transportation,((a) diffusion (Brownian motion), (b)
convection,(c) sedimentation due to gravity, and (d) active
mobility of the microorganisms)
(ii) Initial adhesion, (depending upon the total interaction
energy)
(iii) Firm attachment (depend on influent characteristics
(such as organic type and concentration) and surface
properties of the filter media)
(iv) Colonization (depend on influent characteristics (such as
organic type and concentration) and surface properties of the
filter media)

5. *Dissolved organics passes into biofilm due to
concentration gradients within film.
*Suspended particles and colloids retain on sticky
surface and decomposed into soluble products.
*Oxygen for aerobic reactions , provided by dissolved
oxygen in WW and from void spaces of medium.
*Waste products diffuse outwards and carried away by
water currents.
*The factors that influence the rate of substrate
utilization within a biofilm are
(i) substrate mass transport to the biofilm,
(ii) diffusion of the substrate into the biofilm, and
(iii) utilization kinetics within the biofilm.

6. *As the film grows thicker, both anaerobic and
endogenous mechanisms occur at biofilm-medium
surface interface.
*Attachment mechanism weakened.
*Shearing action of WW washes it away. This Process is
called “sloughing”.
*Sloughing is function of hydraulic and organic loading
rate.
*Limiting factor is oxygen diffusivity. Aerobic zones are
limited to 0.1-0.2 mm thickness.

7. Biofiltration Process

8. WW flow Rate
Organic loading rate
Rate of diffusivity of substrate
Rate of diffusivity into oxygen
Temperature

9. Biofilters used in Waste
Water Treatment
Contact Beds
Intermittent
Sand Filters
Trickling
Filters

10. 1.Works in
cycles(alternate
contact of sewage and
air).
2.One cycle lengh=8-12
hrs
3. 80% SS and 60-75%
BOD removal.
4.Rate of loading should
not exceed 110 litres
per day per sqm.
5. Have become almost
obsolete these days.Source: Environmental engineering, S.K.

11. 1.Sewage is applied for
24hrs on one bed then
to another bed.
2.D10 =0.2-0.5 mm &
Cu= 2to5 .
3.Excellent
performance effluent
SS<10ppm,BOD<5ppm.
4.Large area
requirement.
5. Not used these days.
Source: Environmental engineering, S.K.
Garg

12. A TF consists of a permeable media made of a bed
of rock, slag, or more recently, plastic over which
wastewater is distributed and trickles through.
Single Stage TF
• Carbon oxidation & nitrification take
place in a single TF unit
Two- stage TF
• The first-stage filter and intermediate
clarifier reduce carbonaceous BOD, and
nitrification takes place in the second stage

15. Source: Water Environment Federation (1996),

17. Source: Environmental engineering, Metcalf & Eddy

18. Dosing characteristics of the
distribution system
Choosing the right packing / media
Configuration of the underdrain system
Provision for adequate ventilation

19. Consists of distributor arms mounted on a pivot
in the center,
These are hollow through which water is
discharged over the filter bed
For uniform distribution the flowrate per unit of
length should be proportional to the radius from
the center
Head loss is in the range of (0.6 –1.5 m)
Dosing tanks must ensure that minimum flow is
sufficient to rotate the distributor & discharge
all wates from nozzles

20.  A material having high surface area per
unit volume , does not clog easily
Media can be rock , plastic , pvc etc.
Stones less than 25mm not be used as they
do not provide sufficient pore space

21. Source: Environmental engineering, Metcalf & Eddy

22. These are waste water collection systems that collects the
filtered waste water & solids discharged from the filter
packing
They ventilate the filter by providing air for the micro-
organisms by being open at least to a circumferential
channel
Should be designed such that forced air vibrations can be
added later
Air flow:
Natural draft
Forced air ventilator

23. Source: Environmental engineering, S.K. Garg

24. Because of their large air-water interface can
remove CO2,H2S, N2 & other gases
A portion of liquid in underdrain system is
recycled:
It improves the treatment efficiency
To dilute strength of incoming wastewater
To maintain enough wetting of slime layer
Prevents ponding in filter
Suitable for shock loads
Low running cost

25. Additional treatment may be needed to meet
more stringent discharge standards
Generates sludge that must be treated and
disposed of
Regular operator attention needed
 Relatively high incidence of clogging
 Relatively low loadings required depending on
the media
Limited flexibility and control in comparison with
activated sludge processes
Potential for vector and odour problems

26. Trickling filters running at low organic loading
are found to have nitrification(Stequist et al. 1974;
Parker and Richards, 1986)
Heterotrophic bacteria have high yield coefficient
and high growth rate are competitive than
nitrifying bacteria
Significant nitrification occurs when BOD is
appreciably reduced. BOD had to be less than 30
mg/L to initiate nitrification and less than 15 mg/L
for complete nitrification(Bruce et al., 1975)

27. Fly nuisance
Odor nuisance
Ponding trouble
Icing