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Wastewater Treatment
Processes
CEL212 Environmental Engineering
(2nd Semester 2010-2011)
Dr. Arun Kumar Dr. Arun Kumar (arunku@civil.iitd.ac.in)
Department of Civil Engineering
Indian Institute of Technology (Delhi)
Courtesy: Dr. Irene Xagoraraki (USA) and Dr. Arvind K. Nema (India)
Wastewater Treatment Wastewater Treatment
April 6, 2011 2arunku@civil.iitd.ac.in
Wastewater Management
www.oconomowocusa.com/ wastewater.gif
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Municipal Wastewater
Treatment Systems
• Preliminary treatment (removes materials that can cause operational problems, equalization basins are optional)
• Primary treatment (remove ~60% of • Primary treatment (remove ~60% of solids and ~35% of BOD)
• Secondary treatment (remove ~85% of BOD and solids)
• Advanced treatment (varies: 95+ % of BOD and solids, N, P)
• Final Treatment (disinfection)
• Solids Processing (sludge management)
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• Industrial wastewaters must be pretreated prior to being discharged to municipal sewer system
• Pretreatment requirements set by regulatory bodies
• Why: remove materials that will not be treated
Pre-Treatment of Industrial
Wastewaters
• Why: remove materials that will not be treated by municipal system, remove materials that inhibit the biological processes in secondary treatment
April 6, 2011 5arunku@civil.iitd.ac.in
3 stages of water treatment3 stages of water treatment
• Primary
– solids are separated
• Secondary
– dissolved biological matter is converted into a solid – dissolved biological matter is converted into a solid
mass by using water-borne bacteria
– 95% of the suspended molecules should be removed
• Tertiary
– biological solids are neutralized then disposed, and
treated water may be disinfected chemically or
physically
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Bar racks• Purpose: remove
larger objects
• Solid material stored • Solid material stored
in hopper and sent to
landfill
• Mechanically or
manually cleaned
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Grit Chambers
• Purpose: remove inert
dense material, such
as sand, broken
glass, silt and pebbles
• Avoid abrasion of • Avoid abrasion of
pumps and other
mechanical devices
• Material is called “grit”
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– Wastewater flow has daily fluctuations
– Purpose: To dampen the variation in wastewater flow into a WWTP
– Flow equalization is not a treatment process
– Improves effectiveness of primary & secondary treatment
Equalization
Basins
& secondary treatment
– Usually achieved by large basins to collect wastewater and pumped to treatment plant at a constant rate
– Adequate aeration and mixing need to be provided to prevent odors and deposition of solids
Source: Davis and Cornwall, Introduction to Environmental Engineering, 2008April 6, 2011 9arunku@civil.iitd.ac.in
Treatment stages Treatment stages -- Primary Primary
treatmenttreatment
• typical materials that are removed during primary treatment include– fats, oils, and greases (aka FOG)
– sand, gravels and rocks (aka grit)– sand, gravels and rocks (aka grit)
– larger settleable solids including human waste, and
– floating materials
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Settling/Sedimentation• Solid liquid separation process in which a
suspension is separated into two phases –– Clarified supernatant leaving the top of the
sedimentation tank (overflow).
– Concentrated sludge leaving the bottom of the sedimentation tank (underflow).sedimentation tank (underflow).
• Purpose of Settling– To remove coarse dispersed phase.
– To remove coagulated and flocculated impurities.
– To remove precipitated impurities after chemical treatment.
– To settle the sludge (biomass) after activated sludge process / tricking filters
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Some basic definitions
• Sedimentation, also known as settling, may be defined as the removal of solid particles from a suspension by settling under gravity.
• Clarification is a similar term, which usually refers specifically to the function of a sedimentation tank in removing suspended matter from the water to give a clarified effluent. In a broader sense, clarification the water to give a clarified effluent. In a broader sense, clarification could include flotation and filtration.
• Thickening in sedimentation tanks is the process whereby the settled impurities are concentrated and compacted on the floor of the tank and in the sludge-collecting hoppers.
• Concentrated impurities withdrawn from the bottom of sedimentation tanks are called sludge, while material that floats to the top of the tank is called scum.
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• Primary
Sedimentation Tank
– Remove grease, oil
– Fecal solid settle,
floating material rise to
the surface
– Produce a
homologous liquid for
later biological
treatment
– Fecal sludge are
pumped to sludge
treatment plant
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Primary Settling
Basins
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Secondary Treatment (Biological)(Biological)
Secondary Treatment
• Secondary treatment is a biological treatment process that removes dissolved organic matter from wastewater.
• Sewage microorganisms are cultivated and added to the wastewater. The microorganisms use organic matter from sewage as their food use organic matter from sewage as their food supply. This process leads to decomposition or biodegradation of organic wastes.
• Two approaches are used to accomplish secondary treatment; fixed film, and suspended film systems.
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Secondary Treatment
• Basic approach is to use aerobic biological degradation:
microorganisms
organic carbon + O2 CO2 + new cells
• Objective is to allow the BOD to be exerted in the treatment plant rather than in the stream
microorganisms
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How is this accomplished?Create a very rich environment for growth of a diverse microbial community
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Basic Ingredients
• High density of microorganisms (keep organisms in system)
• Good contact between organisms and wastes (provide mixing)(provide mixing)
• Provide high levels of oxygen (aeration)
• Favorable temperature, pH, nutrients (design and operation)
• No toxic chemicals present (control industrial inputs)
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Activated sludgeActivated sludge
• mixed community of microorganisms
• Both aerobic and anaerobic bacteria may exist
• Biological floc is formed• Biological floc is formed
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Activated Sludge• Process in which a mixture of wastewater and
microorganisms is agitated and aerated
• Leads to oxidation of dissolved organics
• After oxidation, separate sludge (mostly microbial cells, • After oxidation, separate sludge (mostly microbial cells,
water, and other contaminants) from wastewater
• Induce microbial growth
– Need food, oxygen
– Want Mixed Liquor Suspended Solids (MLSS) of
3,000 to 6,000 mg/L
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MixedLiquor Ai
raw
wastewater
Return Activated Sludge(RAS)
Air
Activated Sludge Process
Liquor Air
Secondaryclarifier
Waste Activated Sludge
(WAS)
treated
wastewater
Discharge to
River or Land
Application
Air
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Biological Treatment
Gra
vity
Microorganism
Gra
vity
For further treatment
Soluble and colloidal organics
+ =
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Physical Physical components of activated components of activated
sludge processsludge process
• aeration tank
– oxygen is introduced into the system
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• aeration source
– ensure that adequate oxygen is fed into the tank
– provided pure oxygen or compressed air
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• secondary clarifiers
– activated-sludge solids separate from the surrounding wastewater
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• Activated sludge
outflow line
– Pump activated sludge
back to the aeration
tank tank
• Effluent outflow line
– discharged effluent
into bay or tertiary
treatment plant
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April 6, 2011 28arunku@civil.iitd.ac.in
• Lagoon Systems– hold the waste-water for several months
– natural degradation of sewage
– Usually reeds are preferred
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Dispersed Growth vs Fixed Growth
SystemsDispersed growth (suspended film) systems
stir and suspend microorganisms in wastewater. As the microorganisms absorb organic matter and nutrients from the wastewater they grow in size and number. After the microorganisms have been suspended in the wastewater for several hours, suspended in the wastewater for several hours, they are settled out as a sludge. Some of the sludge is pumped back into the incoming wastewater to provide "seed" microorganisms. The remainder is wasted and sent on to a sludge treatment process.
April 6, 2011 30arunku@civil.iitd.ac.in
Dispersed Growth vs Fixed Growth
SystemsFixed film systems grow
microorganisms on substrates such as rocks,sand or plastic. The wastewater is spreadover the substrate, allowing the wastewaterto flow past the film of microorganisms fixedto flow past the film of microorganisms fixedto the substrate. As organic matter andnutrients are absorbed from the wastewater,the film of microorganisms grows andthickens.
April 6, 2011 31arunku@civil.iitd.ac.in
Dispersed (suspended) growth
vs Fixed growth
• Dispersed Growth (suspended organisms)
– Activated sludge– Activated sludge
– Oxidation ditches/ponds
– Aerated lagoons, stabilization ponds
• Fixed Growth (attached organisms)
– Trickling filters
– Rotating Biological Contactors
April 6, 2011 32arunku@civil.iitd.ac.in
Advanced Wastewater TreatmentTreatment
Nutrients RemovalNutrients Removal
• Nitrogen removal– Ammonia (NH3) → nitrite (NO2-)→ nitrate (NO3-)
• Phosphorous removal• Phosphorous removal– Precipitation with iron or aluminums salt
• Lead to eutrophication
• May cause algae bloom
April 6, 2011 34arunku@civil.iitd.ac.in
Disinfection Processes (refer Disinfection Processes (refer
Notes from Water Treatment)Notes from Water Treatment)
• remove disease-causing organisms from wastewater
• 3 different disinfection process
– Chlorination– Chlorination
– UV light radiation
– Ozonation
April 6, 2011 35arunku@civil.iitd.ac.in
What can effluent use for?What can effluent use for?
• discharged into a stream, river, bay, lagoon or wetland
• used for the irrigation of a golf course, green way or parkgreen way or park
• If it’s sufficiently clean, it can be used for groundwater recharge
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SummarySummary
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April 6, 2011 arunku@civil.iitd.ac.in 38
Sludge Treatment
and Disposal
CEL212 Environmental Engineering
(2nd Semester 2010-2011)
Dr. Arun Kumar Dr. Arun Kumar (arunku@civil.iitd.ac.in)
Department of Civil Engineering
Indian Institute of Technology (Delhi)
Courtesy: Dr. Irene Xagoraraki (USA) and Dr. Arvind K. Nema (India)
Sludge Treatment and Disposal
April 6, 2011 40arunku@civil.iitd.ac.in
Sludge Types
• Primary sludge– 3 to 8% solids– About 70% organic material– odor
• Secondary sludge
Bar screens
Grit chambers
Not true sludge, not a fluid.Since it can be drained easilyand is relatively stable, it can be disposed of directly in a municipal landfill.
• Secondary sludge– Consists of wasted microorganisms and inert materials– About 90% organic material– WAS: 0.5 to 2% solids– Trickling filter sludge: 2-5% solids
• Tertiary sludge– If secondary clarifier is used to remove phosphate, this sludge will also contain chemical precipitates (more difficult to treat)
– Denitrification sludges - similar to WAS sludge
April 6, 2011 41arunku@civil.iitd.ac.in
Goals of Sludge Goals of Sludge treatmenttreatment
• Goals of treatments are:– Reduce odors
– Remove water reduce volume
– Decompose organic matter – Decompose organic matter
April 6, 2011 42arunku@civil.iitd.ac.in
Treatment processes include:
– Thickening – separates water from solids by gravity or flotation
– Stabilization – converts organic solids to more refractory forms through digestion
Sludge Treatment
refractory forms through digestion
– Conditioning – treats sludge with chemicals or heat so that the water can be readily separated
– Dewatering – separates water by vacuum, pressure or drying
– Reduction – decreases the volume of sludge by incineration
April 6, 2011 43arunku@civil.iitd.ac.in
Sludge Treatment: 1) Thickening
• Flotation– Especially effective on activated sludge
• Gravity thickening– Best with primary sludge
– Increases solids content from 0.5 -1% to 3-6%
– Increases solids content from 1-3% to 10%
PrimarySludge
Gravity Thickening
SecondarySludge
Flotation
Further processing
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Thickening
Gravity Belt Thickener
Gravity Thickener(From: http://www.thomasregister.com/olc/dorroliver/sedi.htm)Flotation
April 6, 2011 45arunku@civil.iitd.ac.in
Sludge Treatment: 2) Stabilization
• Aerobic Digestion
– Extension of activated sludge
– Accomplished by aeration of sludge then followed by
• Anaerobic Digestion
– 2 stage: acid fermentation followed by methane production
– Advantages:– Accomplished by aeration of sludge then followed by sedimentation
– Supernatant goes back to head of plant (high in BOD, TKN, total-P)
– Treated sludge is 3% solids
– Advantages:
• produce methane
• do not add oxygen
– As with aerobic digestion, supernatant goes to headworks
April 6, 2011 46arunku@civil.iitd.ac.in
Stabilization
Anaerobic DigestionAnaerobic DigestionAerobic DigestionAerobic DigestionApril 6, 2011 47arunku@civil.iitd.ac.in
Composting Composting
• aerobic process
• requires the correct
mix of carbon,
nitrogen, oxygen nitrogen, oxygen
and water with
sludge
• Generate large
amount of heat
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Sludge Treatment: 3) Conditioning
• Chemical Conditioning
– Add lime, ferric chloride, or alum
– Can also add polymers
• Heat Treatment
– High temperatures (175-230 oC)
– High pressure (10 to 20 atmospheres)
– Can also add polymers
– Chemicals are added just prior to de-watering stage
– High pressure (10 to 20 atmospheres)
– Advantages
• bound water is released and sludge is easily dewatered
– Disadvantages
• complex process
• highly concentrated liquid stream
April 6, 2011 49arunku@civil.iitd.ac.in
Sludge Treatment: 4) De-watering
• Sludge Drying Beds
• Filtration– Apply vacuum to pull out water– Most popular
method
– Simple
– Low maintenance
– Effected by climate
– Apply vacuum to pull out water
– Force out water by essentially squeezing water between two moving filter belts
April 6, 2011 50arunku@civil.iitd.ac.in
De-watering
Sludge Drying Beds Vacuum Filtration(From: http://www.infilcodegremont.com/) (From: http://www.thomasregister.com/olc/dorroliver)April 6, 2011 51arunku@civil.iitd.ac.in
De-watering: Belt Filter Press
East Lansing, MIFairhaven, MA
(From: http://www.environline.com/fhwpcf.htm)
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Sludge Treatment: 6) Volume Reduction
• Incineration– Complete evaporation of water from sludge
• Wet Oxidation– Treated sludge is wetof water from sludge
– Requires fuel
– Solid material is inert
– Exhaust air must be treated prior to discharge
wet
– Requires energy
– Solid material is inert
– Exhaust air must be treated prior to discharge
April 6, 2011 53arunku@civil.iitd.ac.in
Volume Reduction: High Temperature Fluidized Bed Incineration
(From: http://www.infilcodegremont.com/)(From: http://www.unep.or.jp/CTT_DATA/WATER/WATER_4/html/Water-173.html
April 6, 2011 54arunku@civil.iitd.ac.in
Sludge Disposal
• Method depends on regulations – Land Spreading• lawns, gardens
• agricultural land• agricultural land
• forest land
• golf courses and other public recreational areas
– Municipal Solid Waste Landfill
– Utilization in other materials
April 6, 2011 55arunku@civil.iitd.ac.in
SummarySummary
April 6, 2011 56arunku@civil.iitd.ac.in
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