manoj pandey
TRANSCRIPT
2111 2005
Ponds Manoj Pandey
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Decentralized wastewater treatment
Constructed wetland
Infiltration
Package treeatment
Pond systems
STEP/STEG
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Waste Stabilization Ponds Waste stabilisation ponds
(WSP) are typically man-made basins surrounded by an earthen embankment.
The first recorded construction of a WSP in the US was at San Antonio, Texas, in 1901.
The oldest WSP in Europe are probably the ‘Fischteiche’, built around 1920 in Munich (Germany).
Anaerobic pond in Colombia (Ginebra) (IHE, 2003)
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Types of Pond
Anaerobic
Facultative
Maturation (aerobic)
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Anaerobic Ponds
Pond depth is usually between 3 to 5 meters and the HRT for ponds treating municipal sewage is between 1-3 days (for municipal sewage).
3-5 m
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Anaerobic Ponds -Treatment Mechanism
Sedimentation
– Sedimentation of non-degraded and degraded suspended particles
Biological degradation
– Biological degradation is due to the anaerobic degradation of complex organic material
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Anaerobic ponds- degradation process
Acetic acid
Complex organic matter: proteins, carbohydrates, lipids
Amino acids, sugars and fatty acids
Volatile Fatty Acids: propionic acid, butyric acid. Alcohols
Hydrogen
Methane
Hydrolysis
acidogenesis
acetogenesis
methanogenesis
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Anaerobic Ponds -Treatment Process
The rate of anaerobic processes depends highly on temperature, in particular the methanogenic bacteria accelerate their metabolic activity with temperature.
At higher temperatures BOD is therefore more effectively removed, especially the BOD-dissolved.
In cold climates anaerobic ponds mainly act as settling ponds
In case the influent contains sulphate or nitrate, also sulphate reduction and denitrification is occurring.
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Anaerobic Pond –Pollutant removal
BOD removed by sedimentation and anaerobic decomposition
Ammonia nitrogen removal by volatilization, algal uptake
Nitrite reach infleunt may get denitrified
Phosphorus removal is minimal
Removal of bacterial pathogens in anaerobic ponds is poor (1 log unit faecal coliform reduction)
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Anaerobic Ponds - Odor
Odour formation from anaerobic ponds is frequently reported.
One of the main odorous compounds is H2S, the product of sulphate reduction.
In a well designed and operated anaerobic pond the pH is kept in a range around 7.5. In this range most of the sulphide is present as the bisulphide ion, which has no odour.
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Anaerobic Ponds -Odor
Odor Reduced By
– Raising the pH to around 8 by lime addition to prevent the formation of odorous H2S.
– Recirculation of final maturation pond effluent to the anaerobic pond. This measure will result in an aerobic top layer, in which sulphide is oxidised to sulphate.
– Reducing the applied organic loading rate by providing extra anaerobic ponds in parallel or by increasing the depth
– Stimulating the establishment of a scum layer on top of the anaerobic pond, for instance by spreading a thin layer of straw on the surface.
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Anaerobic ponds- Design
Anaerobic ponds are designed on the basis of volumetric organic loading (kgCOD/m3/day).
– Van = Pond volume (m3)
– A = Surface are (m2)
– D = Average pond depth (m)
– BODin = Influent concentration (kgBOD/m3)
– Q = Flow rate (m3/day)
– = volumetric organic loading rate (kgBOD/m3/day)
It is quite common to use pond systems in series of two or three modules for a full scale treatment.
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Anaerobic ponds- Design
Volumetric organic loading λv (kg BOD/m3/day) based on minimum month-averaged air temperature (0C)
Temp < 10 0.10 (40 % removal)
Temp 10-20 0.02 * Temperature – 0.10 (then % remvola is -2* Temperature +20 )
Temp >20 0.30 (60 % removal)
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Operation and maintenance
Regular desludging
– The performance of anaerobic ponds may deteriorate when ponds are getting full with sludge.
– The accumulated sludge causes the HRT to decrease and this may prevent complete settling and digestion of particulate matter
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Facultative Pond
Facultative ponds are the second treatment step in a pond system.
Depth of pond -1.5 – 2.5 m deep earthen basin with an embankment slope of 1:3.
Detention time 5 – 10 days.
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Aerobic layer
Anaerobic Layer
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Facultative Pond-Treatment mechanism
sedimentation and anaerobic digestion.
Sludge BOD removed -while desludging and anaerobically transformed into methan gas
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Facultative Pond-Treatment mechanism
The oxygen produced by algal photosynthesis in the top layer is used for the decomposition of organic matter in deeper layers by heterotrophs.
Symbiotic interrelationship referred to as ‘Algae-Bacteria Symbiosis’ .
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Facultative Pond –Pollutant removal
BOD removed by sedimentation and aerobic and anaerobic decomposition
Ammonia nitrogen removal by volatilization (during day time when pH is increase due to production of CO2), algal uptake , ammonification
Nitrate -denitrified
Phosphorus removal is minimal
Removal of bacterial pathogens in anaerobic ponds is poor (1-2 log unit faecal coliform reduction)
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Facultative Ponds- Design
Design based on organic surface loading rate load λo (Kg BOD/ha/day)
– λo = 10 * T (10<T<20 0C) (WHO, 1987 )
– T = Temperature (o C)
Area of Facultative Pond
– Where, AF = area of Pond
– Q = Wastewater flow
– Li = Influent BOD
L/W ratio = 3:1
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Maturation Pond
Maturation ponds are the final treatment step in a pond system.
Depth of pond -1 – 1.5 m deep earthen basin with an embankment slope of 1:3.
Detention time minimum 3 days., max 20 days
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Maturation Pond – Treatment mechanism
Introduced to polish or upgrade facultative pond effluents and achieve substantial microbial reductions
Active algal biomass is maintained throughout the entire depth of the system so that during daytime large amounts of oxygen are produced.
Further stabilisation of organic matter and nutrient removal is accomplished mainly through aerobic bacteria
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Maturation Ponds –Treatment mechanism
Filtered effluent BOD values range from 20 to 60 mg/l, while TSS levels vary from 30 to 150 mg/l.
Faecal coliform and virus die-off rates may reach over 3 to 4 log units.
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Ponds- Removal mechanisms of Faecal coliforms
Adsorption to particles and subsequent sedimentation
Grazing by other micro-organisms (protozoa)
(Natural) decay
– FC deprive of food
– affected by adverse environmental conditions.
– UV radiation absorbed by the DNA molecules thus damaging the DNA molecule and causing cell death
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Maturation Pond - Design
Designed to remove pathogens. Equation for completely mixed pond
= No. Of FC in the influent, No./100 ml
= No. Of FC in the effluent, No./100 ml
= First order decay coefficient, day-1
n = maturation pond in series, number
= retention time, days
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Maturation Pond - Design
Kd is taken as 2.6 day-1 200C
Value of Kd can be corrected for other prevailing sewage temperatures.
Retention time (t) usually 3-20 days
Depth 1-1.5m
L/W ratio = 3-10
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Pond Layout
The basic units in WSP systems are anaerobic, facultative and maturation ponds.
Anaerobic ponds are put in parallel to provide operational flexibility for sludge removal and distribution of settled solids
Facultative or maturation ponds are put in series to achieve a better overall performance with respect to BOD and faecal coliform reduction.
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The pond/wetland system at Vidaråsen Camphill
Enhanced facultative pond
Ponds Constructed wetlands
Pretreatment -planted sandfilter
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The pond/reedbed system at
Vidaråsen Camphill
Enhanced facultative pond Enhanced facultative pond