trickling filter design model

1. A FUNDAMENTAL MODEL FOR
TRICKLING FILTER PROCESS
DESIGN
Represented by: Ubedullah lolai
16EE36
Submited to: Sir Abdul Razzaque

2. Introduction
A trickling filter is a type of
wastewater treatment system.
which consists of fixed bed of
filtering media over which
sewage or other wastewater
flows downward and causes a
layer of biofilm to grow.
The removal of pollutants from the
waste water involves both
absorption and adsorption of
organic compounds and some
inorganic species such as nitrite
and nitrate ions by the layer of
microbial bio film.
Filter may have a variety of types of
filter media used to support the
biofilm. Types of media
commonly used include coke,
plastic matrix material, rocks,
gravel, sand and geotextiles.

3. Model for process design
Eckenfelder (1970) has developed performance equation based on the specific rate of substrate
removal for a pseudo-first-order reaction.
−
1
𝑥
𝑑𝑠
𝑑𝑡
= 𝑘𝑠
Where ,
1
𝑥
𝑑𝑥
𝑑𝑡
= Specific rate of substrate utilization,
K = rate constant,
S = Substrate concentration.
Rearranging the above equation:
1
𝑠
ds = −k. x. dt
Integrating s from s0 to st and t from 0 to t:
𝑠0
𝑠𝑡
1
𝑠
𝑑𝑠 = − 𝑘. 𝑥
0
𝑡
𝑑𝑡

4. Continued..
𝑙𝑛 𝑆𝑡 − 𝑠0 = −𝑘. 𝑥. 𝑡 − 0
ln
𝑆𝑡
𝑆0
= −𝑘. 𝑥. 𝑡
By applying exponent to both sides
𝑙𝑛𝑒[
𝑆𝑡
𝑆0]
= 𝑒−𝑘𝑥𝑡
𝑆𝑡
𝑆0
= 𝑒−𝑘𝑥𝑡
X is proportional to surface area of packing media (As) i.e.,
.:X≈A
Where, A is the specific area of the packing media
And The mean contact time ‘t’for a filter is given by Howland (1950) (Reynolds & Richard, 1996).
𝑡 =
𝐶. 𝐷
𝑄 𝑛
Where, t = mean contact time
D = Depth of filter bed
Q = Surface loading
C and n = constant.
By replacing t we get:
𝑆𝑡
𝑆0
= 𝑒
−𝑘.𝐴.
𝐶.𝐷
𝑄 𝑛

5. 𝑆𝑡
𝑆0
= 𝑒
−𝑘.𝐴.𝐶.𝐷
𝑄 𝑛
(Elimination of constant C as it is taken into account in K),
The value of ‘n’ depends on flow characteristics through packing and usually about 0.5 to 0.67. For wastewater
n=0.5.
filter media equation may be simplified by combining 𝑘. 𝐴. 𝐶 give :
𝑆𝑡
𝑆0
= 𝑒
−𝑘.𝐷
𝑄 𝑛
𝑆𝑡 = 𝑆0𝑒
−𝑘.𝐷
𝑄 𝑛
S t = BOD5 of effluent, mg/L
So = BOD5 of influent, mg/L
D = filter depth, ft (or m)
Q = surface loading (m3/m2-d)
n= 0.5 specified for domestic waste water

6. Design a super rate trickling filter for the following data:
Average wastewater flow = 500 m3/d,
Influent BOD = 160 mg/L
Effluent BOD required = 20 mg/L
Filter depth = 5.0 m
Pilot plant studies using synthetic packing have shown a removal rate constant K = 1.903 at 20 C, and n = 0.5 (Reynolds
& Richard, 1996).
SOLOUTION:
𝑆𝑡
𝑆0
= 𝑒
−𝑘.𝐷
𝑄 𝑛
Substituting values in the equation,
20
160
= 𝑒
(−1.903∗5)
𝑄0.5
0.125 = 𝑒
(−9.515)
𝑄0.5
𝑄0.5
= (−9.515)/ln(0.125)
𝑄0.5 = 2.496
𝑄 = (2.496)2
= 6.23𝑚3/𝑚2. 𝑑
Average waste water flow is 500m3/d, therefore area for trickling filter
𝐴 =
500𝑚3
/𝑑
6.23𝑚3/𝑚2. 𝑑
= 80.25m2
The diameter of trickling filter by using equation,𝐴 =
𝜋
4
𝑑2
⇒ 𝑑 = 10.09𝑚

7. 0
10
20
30
40
50
60
70
80
0 2 4 6 8 10 12
BOD(St)mg/l
depth(m)
graph
depth(m) BOD(St)
1 73
2 67
3 61
4 56
5 52
6 47
7 43
8 40
9 36
10 33
Q^0.5 BOD(St)
2.5 52
3.5 37
4.5 29
5.5 23
6.5 20
7.5 17
8.5 15
9.5 14
10.5 12
12.5 10
0
10
20
30
40
50
60
0 2 4 6 8 10 12 14
BOD(ST)MG/L
Q^0.5
graph

8. ‫خير‬ ُ‫هللا‬ ‫جزاك‬