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Wastewater Treatment

Processes

CEL212 Environmental Engineering

(2nd Semester 2010-2011)

Dr. Arun Kumar Dr. Arun Kumar ([email protected])

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 [email protected]

Wastewater Management

www.oconomowocusa.com/ wastewater.gif


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)


• 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


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


Bar racks• Purpose: remove

larger objects

• Solid material stored • Solid material stored

in hopper and sent to

landfill

• Mechanically or

manually cleaned


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”


– 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 [email protected]

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


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


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.


• 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


Primary Settling

Basins


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.


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


How is this accomplished?Create a very rich environment for growth of a diverse microbial community


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)


Activated sludgeActivated sludge

• mixed community of microorganisms

• Both aerobic and anaerobic bacteria may exist

• Biological floc is formed• Biological floc is formed


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


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


Biological Treatment

Gra

vity

Microorganism

Gra

vity

For further treatment

Soluble and colloidal organics

+ =


Physical Physical components of activated components of activated

sludge processsludge process

• aeration tank

– oxygen is introduced into the system


• aeration source

– ensure that adequate oxygen is fed into the tank

– provided pure oxygen or compressed air


• secondary clarifiers

– activated-sludge solids separate from the surrounding wastewater


• Activated sludge

outflow line

– Pump activated sludge

back to the aeration

tank tank

• Effluent outflow line

– discharged effluent

into bay or tertiary

treatment plant


• Lagoon Systems– hold the waste-water for several months

– natural degradation of sewage

– Usually reeds are preferred


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.


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.


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


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


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


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


SummarySummary


April 6, 2011 [email protected] 38

Sludge Treatment

and Disposal

CEL212 Environmental Engineering

(2nd Semester 2010-2011)

Dr. Arun Kumar Dr. Arun Kumar ([email protected])

Department of Civil Engineering

Indian Institute of Technology (Delhi)

Courtesy: Dr. Irene Xagoraraki (USA) and Dr. Arvind K. Nema (India)

Sludge Treatment and Disposal


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


Goals of Sludge Goals of Sludge treatmenttreatment

• Goals of treatments are:– Reduce odors

– Remove water reduce volume

– Decompose organic matter – Decompose organic matter


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


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


Thickening

Gravity Belt Thickener

Gravity Thickener(From: http://www.thomasregister.com/olc/dorroliver/sedi.htm)Flotation


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


Stabilization

Anaerobic DigestionAnaerobic DigestionAerobic DigestionAerobic DigestionApril 6, 2011 [email protected]

Composting Composting

• aerobic process

• requires the correct

mix of carbon,

nitrogen, oxygen nitrogen, oxygen

and water with

sludge

• Generate large

amount of heat


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


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


De-watering

Sludge Drying Beds Vacuum Filtration(From: http://www.infilcodegremont.com/) (From: http://www.thomasregister.com/olc/dorroliver)April 6, 2011 [email protected]

De-watering: Belt Filter Press

East Lansing, MIFairhaven, MA

(From: http://www.environline.com/fhwpcf.htm)


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


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


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


SummarySummary


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