STABILIZATION PONDSSTABILIZATION PONDS

Eng. Dr. Erich Kellner

November, 7th – 2012São Carlos - Brazil

Summer School onWastewater Treatment Plants and Management

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Lector of Civil Engeneering Department of São Carlos Federal University (UFSCar)

Stabilization ponds are biological treatment systems in which stabilization of organic material is carried out by bacterial oxidation and/or photosynthetic reduction of algae.

Figure 1: Stabilization ponds – Lins (SP) - Brazil

Stabilization ponds:

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Figure 2: Configurations of wastewater treatment systems by stabilizations pondsSource: adapted from von Sperling (2000)

Basic Configurations ofWastewater Treatment Systems by Stabilization Ponds:

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Pros and Cons of using stabilization ponds:

•Simplicity to built, operate and maintain;

•Low operational cost;

•Good quality on effluent;

• Need large areas;

• Limited and dependent on weather;

• Quality of effluent varies;

PROS CONS

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Figure 3: Anaerobic Pond– São Carlos (SP) - Brazil

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.

•Solids settle at bottom of the to pond.

•Anaerobic digestion of sludge occurs at the bottom of the pond.5

Figure 4: Metabolic process in anaerobic digestionSource: adapted from Pescod (1995)

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

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Anaerobic Ponds - Design Criteria:

•Time of Hydraulic Detention = between 4 to 6 days for the final plan

•Liquid depth = between 4 to 5m

•Volumetric organic load (v) = 0.08 and 0.4 kgDBO/m3pond.day

•Superficial organic load(s) > 1000 kgDBO/ha.day

•Sludge accumulation = 0.01 to 0.03 m3/inhab.year

Design is highly empirical – based on volumetric load (g BOD/m3/day) and Hydraulic Detention Time (day)

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Anaerobic Ponds - Design Criteria:

Average Air TemperatureColdest Month

(oC)

Removed DBO (%)

<10 40

10-25 2.T + 20

>25 70

Table: Expected efficiency to reduce DBO due to average air temperature in the coldest month

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Figure 5: Facultative ponds – Barretos (SP) - Brazil

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

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Facultative Ponds:

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Facultative Pond Interactions:

Figure 6: Definition of interactions occurring in a facultative pondSource: Tchobanoglous and Schroeder (1985)

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Facultative Ponds - Design Criteria:

PRIMARY FACULTATIVE PONDS:

•Superficial application rate limit* (S) = 20.T – 60 kgDBO/ha.day**

•Expected efficiency to reduce DBO (Empirical equation based on complete mixture model)*:

Notes:•Refers to half depth in the area•Average air temperature in the coldest month (oC).

let be the efficiency (%); s superficial application rate (kgDBO/ha.day)

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SECONDARY FACULTATIVE POND:

14.T – 40 < 200 kgDBO/ha.day** p/T >17oC

•Superficial application rate limit* (S) =

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)*:

Facultative Ponds - Design Criteria:

let be the efficiency(%); s 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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Figure 7: Maturation ponds – Barretos (SP) - Brazil

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.

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Maturation Ponds - Design Criteria:

•Superficial organic load (s) < 50 kgDBO/ha.day

•HDT for each pond (m) > 7 days, with at least 3 maturation ponds in sequence.

•Decrease of pathogenic microrganisms:

nmTKNoNe

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202,6 1,19 TTK

Continuously Stirred Tank Reactor (CSTR)

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But what kind of reactor do we have here?

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AP

FP1FP2

Figure 9: Rodamina B injection in FP1 Source: Moreira (2006)

Figure 8: Stabilization Ponds in Novo Horizonte (SP)

Source: Moreira (2006)

Hydrodynamic Test:

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0,00

1,00

2,00

3,00

4,00

5,00

6,00

7,00

0,0 0,5 1,0 1,5 2,0 2,5

t/tm

C/Co

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•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).

Figure 10: Non-dimensional concentration curve of Rodamina B in function of measured time in FP1 exit

Source: Kellner, Moreira & Pires (2009).

Hydrodynamic Test:

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Temperature (oC)

Dept

h (m

)

Concentration (g/l)[Animation done from results presented by Kellner, Moreira & Pires (2009).]

Influence of Thermal Stratification in the Distribution of Rodamina B in the Water Column of FP1

According to Kellner & Pires (2000), temperature gradient 0.6oC/m, in stabilization ponds with temperature of 25oC, can lead to a thermal stratification state.

Thermal Stratification of a stabilization pond affects……the useful volume,…the dispersion number,…the HDT, etc.

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Design and Operational Problems:

Figure 11: Facultative Pond built in shaded area 21

Figure 12: Infiltration problem in anaerobic pond

Design and Operational Problems:

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Facultative Pond with red brown colourPossible causes:• Organic material overload• Presence of photosynthetic bacteria

that oxidates sulphyte and does not produce oxygen does not contribute to reducing BOD

Design and Operational problems:

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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

Design and Operational Problems:

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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.

Design and Operational Problems:

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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.

Design and Operational Problems:

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Facultative pond with grey colour

Possible causes:• Overload of organic

material and/or short detention time

• Fermentation in sludge layer incomplete.

Design and operational problems:

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Design and operational problems::

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Not having desanders can cause silting in the ponds

Absence of Grit Removal System

Design and operational problems::

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Absence of Grit Removal System

…is able to change the flow and wastewater in the ponds

Anaerobic pond – Problems of bad odor

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Free surface makesexchange of gases easier (CH4, H2S,…) for the atmosphere

Anaerobicpond - Problems with bad odor (possibility of using methane)

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Sludge:

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Sludge conditioning (Solution or Environmental passivity?)

33Figure: Sludge conditioning

Sludge conditioning in materia lsacks can make it passive.

Thank You!E-mail: erich.kellner@ufscar.br

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