stabilization ponds
TRANSCRIPT
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APresentation
on
Stabilization Ponds
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Definition It is a shallow basin used to treat raw
water by natural processes
Where rate of waste oxidation is slower
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Three categoriesAnaerobic ponds removes BOD by
sedimentation, sludge is then digested
in bottom layer
Facultative ponds bacteria degradewaste ,uses O2 and generates CO2,
algae use CO2 and generate O2 Maturation ponds Disinfection is used
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Arrangement
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Anaerobic pond Sedimentation pond
High waste water loading depletes allO2
Solids settles to pond
Anaerobic digestion of sludge occurs inpond bottom
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Anaerobic digestion process Hydrolysis - Complex organics (proteins
and fats broken down to simpler
compounds by various bacteria
Acidogenesis (Fermentation) Fattyacids and alcohols oxidized ,amino acids
and carbohydrates fermented ,formsvolatile fatty acids and hydrogen
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Anaerobic digestion processActeogenesis conversion of complex
fatty acids to acetic acid
Methnogenesis - conversion of aceticacid to methane and CO2 and CO2 ,H2to methane
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Process When temperature rises above 15
degree centigrade digestion generates
enough biomass which causes pondsurface to bubble biogas (70% CH4and 30% CO2)
Digested solids accumulate cleanoutin 1 to 3 years
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Pond Characteristics Hydraulic detention time is short 1 day Depth 2 to 5 m (usually 3m)
Design is highly empirical based onvolumetric load (gm BOD/m3/day)
for e.g. 100gm BOD/m3.day to 3 m deep pond=3000kg/ha/day
For air temp.(Degree centigrade)
10 Loading(gm BOD/m3/day)
100
20 300
25 350
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Role of pH pH= 7.5 (S HS-)
Below pH 7- H2S forms and causesodor
Below ph 6.2conditions are toxic
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Facultative ponds Much lower aerial loading rates- 100 to 400
Kg/ha/day (vs. 3000+ for anaerobic ponds of
BOD) Pond water is aerobic and supports and
supports very high density algal population
Beneath water is an anaerobic bottom layer(sludge) in which sludge is digested
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.Algae generate O2 by photosynthesis
during the day ,which is useful for
oxidation of waste by bacteria
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. It may operate as a primary pond (with
no anaerobic pond for pretreatment) or
secondary ponds (after anaerobicponds)
Performance depends upon
1)time(diurnal )2)vertical space
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Vertical variations Algae requires light but depth of photic zone
(light penetration) may be limited in pondwith heavy algae growth and turbid water
Light penetrates about 30 cm(1 foot) Pond algae tend to be motile species which
swim to optimum level Non-motile species requires wind mixing to
circulate through photic zone Wind mixes O2 from photic zone to pond
depth
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In tropics , ponds go through diurnalstratification pattern
Morning wind mixing ,uniform temperaturethrough depth
Mid-day- warming of surface water, onset ofstratification, thermocline forms (hot water
above ,cold water below and no mixing)Late afternoon or evening-top layer cools,
mixing occurs during wind mixing
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..
Motile algae optimum depth-not very upperwater (too hot) ,not too deep (very dark)-30
to 50cm below surface Ponds have oxypause (depth at which DO
goes to zero), moves up and own during day
Besides generating O2,bacteria consume CO2to the point that depleted CO2 alterscarbonate equilibrium. This raises pH andkills fecal bacteria
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Diurnal pattern
Leads to diurnal treatment performance
Rise in DO ,pH during day
Decrease in coliform
Rise in BOD,TSS and chlorophyll-a
BOD is high but it is algae and notorganic waste-chlorophyll-a=500 to1000 micro gm /l
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Effect on H (Depth)
H 1.8 m- oxypause is too shallow relativeto overall depth (pond is more anaerobicthan aerobic)
Optimal H=1.5 m (1m
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Maturation ponds
Used to remove pathogenic bacteriaand viruses(99.9997%)- e-Coli removal
of 6 log units using three maturationponds in series in brazil
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Mechanism
Solar disinfection using UV light
Raising pH
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Design
1 m deep
Total detention time of the order of 10
days
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THANK YOU