wastewater

1. TRICKLING FILTERS
Trickling filter is an aerobic attached growth biological system.
The major components of the trickling filter are:
1. The tank
2. Rotary distributor
3. Filter media
4. Under drain system
5. Ventilation

2.  As rotary distributors are more reliable & easy to maintain and operate.
So circular shape is most commonly used.
 The walls are either masonry or concrete walls. The walls are constructed such
that they should withstand the pressure exerted by sewage from inside.
- The walls are made water tight.
 The tank is either rectangular or square if fixed nozzles are used and circular
in shape if rotary distributors are used.

3. The under drain system is supported by a floor which slopes to a collection
channel.
 It also consists a filter media which should have high specific surface area,
high percent void space, resistance to abrasion & insoluble in sewage
water.
 (crushed stones, gravel, plastic)

4. • The bacteria is attached to the filter media forming a biological layer called
also bio-film.
• Sprinkled wastewater over the filter media forms liquid film including food
and dissolved oxygen.
• The bacteria (bio-film) absorbs the organic matter and oxidized it producing
CO2, H2O, NH3 and new cell
• The biological layer consists of aerobic and anaerobic partitions.
• When the mass of the bio-film increase the lower layer will be anaerobic with
lower food supply which will lead to the decrease of the attaching force
between the bio-film and the filter media. In this case the bio-film is sloughed
out (disconnected) and flows out with the wastewater to the final
sedimentation tank where it settles.
Biological process

5. Types of Filters
Trickling filters are classified as
Low Rate Trickling Filter High Rate Trickling Filter
based on the
Organic loading Hydraulic loading

6. Low Rate Trickling Filter

7. High Rate Trickling Filter
Recycle is used to increase the efficiency of treatment.
Different ways of recycle are used.

8. Recirculation (R) is the return of a portion of treated or partly
treated sewage to the treatment process.
Recirculation of High Rate Trickling Filter

9. (1) Recirculation keeps the self pushed distributors running at the
time of reduced flows (i.e. during night hours).
(2) The thickness of biological film, on contact media is reduced by
forced film sloughing.
(3) The filter influent is freshened due to which foul odour is
prevented.
(4) The filter influent is diluted and weakened so that filter works at a
constant efficiency and the quality of filter effluent is improved.
(5) The applied sewage is seeded with active organisms and enzymes
of effluent, due to which the efficiency of filter is increased.
(6) Recirculation loads deeper portions of the filters more effectively.
Advantages of recirculation:

11. BASIC DESIGN EQUATIONS
 National Research Council Equation (NRC-Equation)
• For a low rate or single-stage TF
• For a high rate or two-stage TF
• Modified National Research Council Equation
 Eckenfelder Equation
• Without circulation
• With circulation
 Rankins equation

12. Design of Trickling filters
• Organic loading rate
• Recirculation ratio Filter Volume
• Depth
• Surface area
Hydraulic loading

13. Eckenfilder equation:
Without circulation

15. BOD5 =?
35m
1.5m
Q =1,900 m3/d
BOD5 =150

17. Rankins equation:
This equation also known as Tentative Method of Ten States USA
has been successfully used over wide range of temperature.
It requires following conditions to be observed for single stage
filters:
Raw settled domestic sewage BOD applied
to filters should not exceed
1.2 kg BOD5/day/ m3 filter volume.
Hydraulic load (including recirculation) should
not exceed
30 m3/m2 filter surface-day.
Recirculation ratio (R/Q) should be such that
BOD entering filter (including recirculation) is
not more than
three times the BOD expected in
effluent.
This implies that as long as the above conditions are satisfied
efficiency is only a function of recirculation and is given by:

18. NRC Equations:
These equations are valid to both low-rate as well as high-rate filters.
The efficiency of single stage filter or first stage of two stage filters is
given by-

19. u = W/VF
Where
W = Total BOD in Kg.
V = Volume in ha-m.
F = Recirculation factor.

20. Recirculation factor:
The number of effective passes through the filter is known as
recirculation factor (F) and is given by the equation:

22. Example
The sewage flows from a primary settling tank to a standard rate filter at a
rate of 5 million liters per day having a 5- day BOD of 150 mg/l. Determine
the depth and the volume of the filter, adopting a surface loading of 2500
l/m2/day and an organic loading of 165 g/m3/day. Also, determine the
efficiency of the filter unit, using NRC formula.

23. surface loading of 2500 l/m2/day
Total BOD = Q X BOD
V=
𝑇𝑜𝑡𝑎𝑙 𝐵𝑂𝐷
𝑂𝑟𝑔𝑎𝑛𝑖𝑐 𝑙𝑜𝑎𝑑𝑖𝑛𝑔
A=
𝑇𝑜𝑡𝑎𝑙 𝐵𝑂𝐷
𝑠𝑢𝑟𝑓𝑎𝑐𝑒 𝑙𝑜𝑎𝑑𝑖𝑛𝑔
Depth=V/A
Diameter

26. Rock filter diameters may range up to 60 m.

27. 3
m
Volume
Kg/d
BOD
Total
U
loading,
Organic 

28. Example:
Determine the size of a high rate trickling filter for
the following data :
 Sewage flow = 5mld
 Recirculation ratio = 1.5
 BOD of raw sewage = 230 mg/l
 BOD removal in primary tank = 30%
 Final effluent BOD desired = 25 mg/l

29. Total BOD = Q X BOD
BOD removal in primary tank = 30%
BOD entering the filter = 70%
Total BOD entering the filter = Q X BOD
BOD entering the filter Effluent BOD
Removal BOD
Total removal BOD
Total Effluent BOD
depth Area Diameter