Transcript Wastewater Stabilization Ponds

Summer School on
Wastewater Treatment Plants and Management
STABILIZATION PONDS
Eng. Dr. Erich Kellner
Lector of Civil Engeneering Department of São Carlos
Federal University (UFSCar)
November, 7th – 2012
São Carlos - Brazil
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Stabilization ponds:
Figure 1: Stabilization ponds – Lins (SP) - Brazil
Stabilization ponds are biological treatment systems in which
stabilization of organic material is carried out by bacterial oxidation
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and/or photosynthetic reduction of algae.
Basic Configurations of
Wastewater Treatment Systems by Stabilization Ponds:
Figure 2: Configurations of wastewater treatment systems by stabilizations ponds
Source: adapted from von Sperling (2000)
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Pros and Cons of using stabilization ponds:
PROS
•Simplicity to built, operate and
maintain;
CONS
• Need large areas;
•Low operational cost;
• Limited and dependent on
weather;
•Good quality on effluent;
• Quality of effluent varies;
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Anaerobic Ponds:
•Basins of 3m to 5m (10 feet to 17
feet) depth receiving continuous
organic load of wastewater so that
anaerobic conditions are met.
•Sedimentation pond.
•High waste water loading –
depletes all O2.
Figure 3: Anaerobic Pond– São Carlos (SP) - Brazil
•Solids settle at bottom of the to
pond.
•Anaerobic digestion of sludge
occurs at the bottom of the pond.
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Anaerobic Ponds:
Hydrolysis - Complex organics
(proteins and fats broken down
to simpler compounds by various
bacteria
Acidogenesis (Fermentation) –
Fatty acids and alcohols oxidized
,amino acids and carbohydrates
fermented, produce volatile fatty
acids and hydrogen
Acetogenesis – conversion of
complex fatty acids to acetic acid
Methanogenesis - conversion of
acetic acid to methane and CO2
and CO2 ,H2 to methane
Figure 4: Metabolic process in anaerobic digestion
Source: adapted from Pescod (1995)
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Anaerobic Ponds - Design Criteria:
Design is highly empirical – based on volumetric load (g BOD/m3/day) and
Hydraulic Detention Time (day)
•Time of Hydraulic Detention (q) = between 4 to 6 days for the final plan
•Liquid depth = between 4 to 5m
•Volumetric organic load (lv) = 0.08 and 0.4 kgDBO/m3pond.day
•Superficial organic load(ls) > 1000 kgDBO/ha.day
•Sludge accumulation = 0.01 to 0.03 m3/inhab.year
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Anaerobic Ponds - Design Criteria:
Table: Expected efficiency to reduce DBO due to average air
temperature in the coldest month
Average Air Temperature
Coldest Month
(oC)
Removed DBO
(%)
<10
40
10-25
2.T + 20
>25
70
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Facultative Ponds:
•Basins of 1.5m to 2m depth.
•To have clear water, light
penetration and photosynthetic
production of oxygen to
decompose organic material
take place easier
•Part of the solids present in
the wastewater settle and are
biodegradable in an anaerobic
process
Figure 5: Facultative ponds – Barretos (SP) - Brazil
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Facultative Ponds:
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Facultative Pond Interactions:
Figure 6: Definition of interactions occurring in a facultative pond
Source: Tchobanoglous and Schroeder (1985)
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Facultative Ponds - Design Criteria:
PRIMARY FACULTATIVE PONDS:
•Superficial application rate limit* (lS) = 20.T – 60 kgDBO/ha.day**
•Expected efficiency to reduce DBO (Empirical equation based on complete mixture
model)*:
let e be the efficiency (%); ls superficial application rate (kgDBO/ha.day)
Notes:
• Refers to half depth in the area
• Average air temperature in the coldest month (oC).
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Facultative Ponds - Design Criteria:
SECONDARY FACULTATIVE POND:
14.T – 40 < 200 kgDBO/ha.day** p/T >17oC
•Superficial application rate limit* (lS) =
350. (1,107-0,002.T)T-25 kgDBO/ha.day** p/T
<17oC
•Expected efficiency to reduce DBO (Empirical equation based on complete mixture model)*:
let e be the efficiency(%); ls superficial application rate (kgDBO/ha.day)
Notes:
* Refers to half depth in the area.
** Average air temperature in the coldest month (oC).
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Maturation Ponds:
•Basins of between 0.8m and
1.5m depth. Normally, 1.0 m
depth is used.
•The main objective of maturation
ponds is to remove pathogenic
microrganisms present in the
wastewater, which occur mainly
due to sunlight in the water
column.
Figure 7: Maturation ponds – Barretos (SP) - Brazil
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Maturation Ponds - Design Criteria:
•Superficial organic load (ls) < 50 kgDBO/ha.day
•HDT for each pond (qm) > 7 days, with at least 3 maturation ponds in sequence.
•Decrease of pathogenic microrganisms:
Ne 
No
(1  KT  qm )
n
Continuously
Stirred Tank
Reactor (CSTR)
KT  2,6  (1,19 )
T  20
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But what kind of reactor do
we have here?
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Hydrodynamic Test:
FP2
FP1
AP
Figure 8: Stabilization Ponds in Novo
Horizonte (SP)
Source: Moreira (2006)
Figure 9: Rodamina B injection in FP1
Source: Moreira (2006)
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Hydrodynamic Test:
7,00
6,00
C/Co
5,00
4,00
3,00
2,00
1,00
0,00
0,0
0,5
1,0
1,5
2,0
2,5
t/tm
Figure 10: Non-dimensional concentration curve of Rodamina B in function of measured
time in FP1 exit
Source: Kellner, Moreira & Pires (2009).
•Theoretical hydraulic Detention Time teórico was 164 hours.
•Real hydraulic Detention Time resulted in 55 hours, with dispersion number(d) equal to
11.034.853.603 !!!.
•Active volume of 33.6% (3.5h) and recuperation of dye mass of 95.6%.
Source: (Kellner, Moreira & Pires, 2009).
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Influence of Thermal Stratification in the Distribution of
Rodamina B in the Water Column of FP1o
Depth (m)
Temperature ( C)
Concentration (mg/l)
[Animation done from results presented by Kellner, Moreira & Pires (2009).]
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Thermal Stratification of a stabilization pond
affects…
…the useful volume,
…the dispersion number,
…the HDT, etc.
According to Kellner & Pires (2000), temperature gradient
0.6oC/m, in stabilization ponds with temperature of 25oC,
can lead to a thermal stratification state.
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Design and Operational Problems:
Figure 11: Facultative Pond built in shaded area
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Design and Operational Problems:
Figure 12: Infiltration problem in anaerobic pond
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Design and Operational problems:
Facultative Pond with red brown colour
Possible causes:
• Organic material overload
• Presence of photosynthetic bacteria
that oxidates sulphyte and does not
produce oxygen does not contribute
to reducing BOD
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Design and Operational Problems:
Facultative Pond withmilky
green colour
Possible causes:
• The pond is in an
autofloculation
process
due to increase in pH and
temperature
• Precipitation of hydroxide
magnesium or calcium
dragging algae and other
microrganisms with it 24
Design and Operational Problems:
Facultative Pond with yellow green
colour
Possible causes:
• Growth of rotifers, protozoas or
crustaceans which feed on algae;
• There could be a significant
decrease in the DO and possibly a
bad odor from the anaerobic
decomposition of OM.
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Design and Operational Problems:
Facultative Pond with green
blue colour
Possible causes:
• Significant
growth
of
cianobacteria;
• Appearance of native certain
species which decompose
easily, causing bad odors,
reducing the penetration of
sunlight and diminishing
oxygen production.
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Design and operational problems:
Facultative pond with
grey colour
Possible causes:
• Overload of organic
material and/or short
detention time
• Fermentation in sludge
layer incomplete.
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Design and operational problems::
Absence of Grit Removal System
Not
having
desanders
can
cause silting in the
ponds
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Design and operational problems::
Absence of Grit Removal System
…is able to change
the
flow
and
wastewater in the
ponds
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Anaerobic pond – Problems of bad odor
Free surface makesexchange
of gases easier (CH4, H2S,…)
for the atmosphere
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Anaerobicpond - Problems with bad odor (possibility of
using methane)
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Sludge:
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Sludge conditioning (Solution or Environmental passivity?)
Sludge
conditioning in
materia lsacks
can make it
passive.
Figure: Sludge conditioning
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Thank You!
E-mail: [email protected]
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