55 Gangesh 200-207
55 Gangesh 200-207
55 Gangesh 200-207
s
=surface BOD loading (kg BOD/ha/d)
Design value of s:
s = 350 (1.107 - 0.002 T)
(T-25)
- (2.11)
Where T is mean temperature in the coldest
month (C).
The organic removal efficiency can be calculated
as follows:
r =0.725 s+10.75 - (2.12)
r =0.79 s +2 -(2.13)
r =0.83679s -0.486 -(2.14)
r= 0.956 s -1.31 -(2.15)
Retention time (t) was calculated from:
t =A
f
H/Q -(2.16)
Where:
H = pond depth (usually 1.5m)
Q = average flow, (m
3
/.d)
A
f =
Area of facultative pond (m
2
)
Coliform removal:
N
e
/N
o
=1/ (1+k
b
t) -(2.17)
Where:
N
o
= coliform conc. in influent (org/100ml)
N
e
= coliform conc. in effluent (org/100ml)
t =hydraulic retention time of facultative pond
K
b
=coliform dieoff coefficient
K
bt
=K
b20
(t-20)
-(2.18)
Where:
K
b20
=coliform die-off coefficient at 20C, taken
as 2.6 (Marais, 1974)
T = Temperature (C)
= Temperature coefficient, taken as 1.19
(Marais, 1974)
Table 3: Recommended volumetric organic loading range for UASB reactors.
Category of
waste water
COD(mg/l)
OLR,
Kg
COD/m
3
.d
SLR,Kg
COD/kg
VSS.d
HRT,
hours
Liquid upflow
velocity, m/h
Expected
efficiency
Low
Strength
Up to 750 1.0-3.0 0.1-0.3 6-18 0.2-0.7 70-75
Medium
Strength
750 -3000 2.0 -5.0 0.2 -0.5 6 -24 0.25 -0.7 80 -90
High
Strength
3000 -
10000
5.0 -10.0 0.2 -0.6 6 -24 0.15 -0.7 75 -85
Very high
Strength
>10000 5.0-15 0.2 -1.0 >24 - - 75 -80
Source:http://www.waterandwastewater.com/www_services/ask_tom_archive/toc.htm
Biolife | 2013 | Vol 1 | Issue 4 204
Gangesh Kumar Kasaudhan et al Copyright@2013
Ammonical nitrogen removal:
Equation used when temperature is below 20C.
C
e
=C
o
/1+[(A/Q)(0.0038+0.000134.T).6(1.041+0
014 T) (pH -6.6)] - (2.19)
When temperature is more than 20C
C
e
=C
o
/1+[5.03510
-3
(A/Q)(1.540(pH-6.6) -
(2.20)
Where:
C
e
= ammonical nitrogen concentration in pond
effluent, (mg N/L)
C
o
=ammonical nitrogen concentration in pond
influent, (mg N/L)
A = pond surface area, (m
2
)
T = temperature, (C)
pH = 7.3exp (0.0005A) [where A = influent
alkalinity (mg CaCO3/L)
Total nitrogen removal:
Equation used in case of facultative and
maturation ponds (Reed, 1995):
C
e
=C
o
exp
{-[0.0064(1.039)
T-20
] [t+60.6
(pH-6.6)]} -(2.21)
Where:
C
e
= total nitrogen concentration in the pond
effluent, (mg N/L)
Co=total nitrogen concentration in the pond
influent, (mg N/L)
T = temperature, (C; range: 1-28C)
t = retention time, (days; range: 5-231days)
pH = 7.3exp (0.0005A) [where A = influent
alkalinity (mg CaCO
3
/L).
RESULTS AND DISCUSSIONS
Design Analysis Outcome
Average ambient air temperature for the coldest
winter month of the year for Bharwara, Lucknow
is 17C. Design capacity of the STP is 345
MLD. Both ambient air temperature and
wastewater temperature, and flow rates of the
sewage were recorded at the time of sampling.
Grab sampling was practiced and the samples
were mostly collected between 10:30 AM and
11:20 AM from March till June 2013.
UASB reactor:
Volume and area of the UASB reactor are
123,648 m
3
and its designed is HRT 8.6 hrs.
Volume of the digestion zone is 87879.6 m
3
and
design HRT of the digestion zone is 6.1 hours.
Design volumetric loading rate according to the
equation 2.1 was calculated as 3.9 m
3
/ m
3
.d.
Typical organic loading rate (kg COD/ m
3
.day)
for Low strength of waste water is 1.96 kg/ m
3
.d
(table 3). Upflow velocity in the UASB reactor
for the design flow is 0.54 m/hour. Methane
production per kg of COD removed, according
to the equation 2.7 is 0.052 m
3
and biogas
production is 0.080 m
3
(assuming 65% methane
in the biogas). Treatment efficiencies of the
UASB reactor, according to the empirical
equations 2.4 and 2.5, expected are 66% for
COD and 74% for BOD. Nutrient removals in
the UASB are usually insignificant and can be
equated to the nutrients assimilated by the
microbial biomass synthesized. For nutrient
assimilation removal calculations, net biomass
yield coefficient was taken as 0.1 of the COD
removed and the microbial biomass was
assumed to have 12.3% nitrogen and 2.3%
phosphorus. For pathogen removal calculations
the equation used for anaerobic ponds of the
waste stabilization pond system was used.
The design analysis calculations which included
volumetric loading are presented in the table 5
and 6. Volumetric loading rates were highly
variable and ranged between 3.45 and 4.09
m
3
/m
3
.day and as a consequence the upflow
velocity was also highly varying from 0.47 to
0.55 m/hour. This must be resulting in
operational instability and reduced efficiency of
working. Despite this, the treatment efficiencies
were observed to be higher than the expected.
Observed efficiencies were 59.3-67.7% for COD
and 66.6-77.1% for BOD while expected
efficiencies calculated according to the
equations 3.4 to3.6 are 63.35-65.75% and 71.88 -
74.48% respectively. This indicates that the
equations used were underestimating the
efficiency, and this may be because of the
differences in the characteristics of the sewage
being treated. The equations used may require
calibration. The STP was frequently overloading
instead of 345 MLD the STP was loaded with as
high as 360 MLD
Biolife | 2013 | Vol 1 | Issue 4 205
Gangesh Kumar Kasaudhan et al Copyright@2013
sewage. Biogas production rates were not being
monitored. However expected biogas
production rates have been estimated on the
basis of the amount of COD actually being
converted into methane or biogas. Amount of
COD removed in the UASB minus the amount
used up in the synthesis of active anaerobic
microbial biomass was taken as the COD
converted into methane. The amount of COD
utilized in the biomass synthesis was taken
14.2%. Further, methane content of the biogas
generated was taken as 65%. It appears that
with increasing organic loading amount of
biogas generated per unit COD removal also
increases. And the organic loading rates were
also highly variable from 0.81 to 1.21 kg/
m
3
.day.
Design of Final Polishing Pond:
Area of the polishing pond is 77000 m
2
and its
designed HRT is 1days. Designed surface
loading rate according to the equation 2.18 at
17C was calculated as 200 kg/ha.d. Designed
organic matter removal efficiency for winter
coldest month, according to the equation 2.11 is
Table 4: Design analysis calculations for UASB reactor
Months
Volumetric
hydraulic loading
rate (m
3
/m
3
.d)
Volumetric organic
loading rate
(kgCOD/m
3
.d)
Upflow
velocity
(m/hr)
HRT
(hr)
Estimated CH
4
production rate
(m3)
March 3.34 1.03 0.45 7.1 592
April 4.09 1.21 0.55 5.85 567
May 3.52 0.87 0.48 6.8 390
June 3.45 0.81 0.47 6.9 349.7
Table 5: Efficiencies calculation for the UASB reactor
Month
COD removal efficiency (%) BOD removal efficiency (%)
Expected Observed Expected Observed
March 65.75 67.7 74.48 74.1
April 63.35 59.4 71.88 71.5
May 65.23 61.2 73.92 77.1
June 65.46 59.3 74.16 66.6
Table 6: Design calculation for final polishing pond
Parameter March April May June
HRT (days) 1.17 0.96 1.11 1.13
Surface loading rate
(Kg/ha/d)
Design value at 17C 200 200 200 200
Maximum allowed
sewage
330.50 423.80 423.80 440.35
Temperature C 24 29 29 30
Organic matter removal efficiency
(%)
Actual value 47.8 51.9 62.5 46.6
Efficiency expected 95.20 95.29 95.29 95.30
Pathogen removal (%)
Actual value 67.9 40.5 95.6 47.6
Efficiency expected 87.2 74.7 98.15 78.4
Nutrient removal (%)
Actual value -58 13 -25 8
Efficiency expected 32 44 35 38
Biolife | 2013 | Vol 1 | Issue 4 206
Gangesh Kumar Kasaudhan et al Copyright@2013
expected as 94%. Expected designed pathogen
removal efficiency calculated according to the
equation 2.17 is 65%. Expected designed total
nitrogen removal efficiency calculated from
equation 2.21 is 25%.
Calculations related to the design analysis of the
final polishing pond are given in table 7. In the
design analysis, though the design equations are
actually based on average ambient air
temperature of the coldest month of the year,
actual temperature of the wastewater was used
for estimating maximum surface loadings
allowed, and expected efficiency of organic
matter removal and pathogen removal. As a
consequence error in calculations was
introduced. Further, the fact that the winter
sewage temperature is usually higher than that of
the ambient air, and that in summers the water
temperature is lower than that of the ambient air
was not taken into account in these calculations.
Actual surface loading rate of the organic matter
(BOD) was higher than the design surface
loading rate during the four months of the study.
The reason for this could be the variation in the
hydraulic loading rate. Actual removal
efficiencies were lower than expected removals
(around 52% removal was observed against
expected 95%). This is due to algal cell
concentration in treated effluent is 46 mg/l
which is around the prescribed limit 50 mg/l.
Thus, proper attention should be given towards
the growth of algal cell
CONCLUSION
In the present work, the study has focused on the
design analysis indicates that the design of the
sewage treatment plant is adequate and
appropriate. According to the standard design
considerations the design criteria has been found
complying. The hydraulic loading rates have
been found frequently going beyond the
designed capacity. This indicates that the design
is well suited and efficient. But proper attention
should be given towards reduction of algal cell.
Algaecide could be used taking into
consideration that it should not affect the water
quality of the river when treated effluent is
discharge into it.
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13. www.waterandwastewater.com
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