wastewater treatment processesweb.iitd.ac.in/~arunku/files/cvl100_y16/lecsep2728.pdf · big picture...

September 29, 2016 Arun Kumar ([email protected])

1

(Sep 27th and 28th, 2016)

by Dr. Arun Kumar ([email protected])

Wastewater Treatment Processes

Objective: To learn about processes used in tertiarytreatment

Courtesy: Dr. Irene Xagoraraki, MSU, USA

Sludge Disposal

• Method depends on RCRA regulations

– Land Spreading

• lawns, gardens

• agricultural land

• forest land

• golf courses and other public recreational areas

– Municipal Solid Waste Landfill

– Utilization in other materials

Q0,C0

(Q0-Qw); Ceff

Qw,XwQ0,=flow rate

C0,=initial concentration

X=biomass concentrationQw=sludge withdrawal rate

Xw= biomass concentration in secondary settling tank


3

Biological Treatment

Gra

vity

For further treatment

Microorganism

Soluble and colloidal organics

+ =

September 29, 2016 [email protected]

Municipal Wastewater

Treatment Systems

• Preliminary treatment (removes materials that can cause operational problems, equalization basins are optional)

• 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)

Secondary Wastewater Treatment

• High treatment efficiency– BOD to ~ 20 - 50 mg/L

– SS to ~ 20 mg/L

• Low treatment efficiency– Nitrogen

– Phosphorus

– Heavy Metals

– Poorly-biodegradable organic chemicals

– Small particles

– Resistant organisms

Some pollutants are not

removed by the

conventional secondary

wastewater treatment

Problem: Particles

• Presence of small particles that are too small to be removed by settling.

• Attached to these particles can be organic chemicals and metals.

• Particles may eventually settle in river or stream (longer detention time).

• Particles can also be bacteria, protozoans, etc.

1. Particles

Methods for removing particles

• Methods: (1)Sedimentation with and without addition of

coagulants (example: secondary sedimentation tank

(SST)with addition of ferric chloride or alum), (2)sand

filtration after SST to remove remaining particles from

supernatant

• Solids are called secondary solids

• Solids are settled at the bottom of tank and thickened.

• Mixed liquor suspended solids =10000mg/L

• Qw=solid wastage rate per day

September 29, 2016 7

Problem: Trace Organics• Organic

compounds, pesticides, endocrine disruptors, homores, pharmaceuticals

2. Organics

Methods for removing organics

• Ozonation: organic compounds are oxidized

• Chlorination: organic compounds are oxidized

• Adsorption: organic compounds are adsorbed on

materials (i.e., adsorbent surface)


• Carbon is heated to about 1500 oC to “activate” surfaces

• High surface area of particles with vast pore spaces

– Capable of absorbing high quantity of organics

– Surface area > 1,000 m2/g

• Wastewater effluent is passed through filter under pressure

• Carbon becomes exhausted

– replace carbon in system

– regenerate carbon (on-site or off-site)

Carbon Adsorption

2. Organics

Problem: Phosphorus

• increase in nutrients and organic substances, sediments

• overstimulation in growth of algae and aquatic plants

• create conditions that interfere with recreational uses of lakes, and the health and diversity of indigenous life

• eutrophication

3. Phosphorus

Phosphorus Removal

• Most phosphate in the form of (HPO42-)

• Usually removal accomplished with chemical precipitation (salts)

– Ferric chloride: FeCl3– Alum: Al2(SO4)3

•14H2O

– Lime: CaO or Ca(OH)2

3. Phosphorus

Phosphorus Removal: Chemical

methodFeCl3 + HPO4

2- = FePO4 (s) + HCl

Al2(SO4)3·14H2O + 2 HPO42- = 2AlPO4 (s) + 2H+ + 3SO4

2-

• Effective range for alum or ferric chloride is pH 5.5 to 7.0

• If insufficient alkalinity - must add lime to neutralize H+

There is another option: Biological Phosphorus Removal

3. Phosphorus

Nitrogen

• Excess nutrients: nitrogeneous BOD exerts oxygen demand

• Anaerobic conditions in stream

4. Nitrogen

Solution: Nitrogen Removal (chemical)• Ammonia stripping

– Raise pH to convert ammonium ions to ammonia

NH4+ + OH- = NH3 + H2O

– Ammonia purged from water in process similar to

aeration

Tray-type Air Stripper Packed Column Air Stripper(From: http://www.mittelhauser.com/airstrip.html) (From: http://www.carbonair.com/OS.htm)

4. Nitrogen

Solution: Nitrogen Removal (biological)

• Forms: NH3, NH4+, NO2

-, NO3-

• Nitrification/ De-nitrification

– Occurs

• in activated sludge process - by increasing the

detention time in activated sludge basin

• in separate reactor

– Nitrification:

NH4+ + 2O2 = NO3

- + H2O + 2H+ (2 steps)

– De-nitrification:

2NO3- + organic matter = N2+ CO2 + H2O

4. Nitrogen

Wastewater Treatment

• Preliminary Treatment (screening)

• Primary Treatment (primary settling)

• Secondary Treatment (e.g. activated sludge)

• Advanced Treatment (e.g. P removal)


• Solids Processing (sludge treatment)

Final Treatment (disinfecting)

1. Final treatment focuses on removal of disease-

causing organisms from wastewater. Treated

wastewater can be disinfected by adding

chlorine or by using ultraviolet light.

2. High levels of chlorine may be harmful to

aquatic life in receiving streams. Treatment

systems often add a chlorine-neutralizing

chemical to the treated wastewater before

stream discharge.

Disinfection

Disinfectants:

NaOCl

Ca(OCl)2

Cl2 gas

Chloramines

OzoneUV irradiation

Disinfection

• Water is often disinfected before it enters thedistribution system to ensure that potentiallydangerous microbes are killed.

• Chlorine, chloramines, or chlorine dioxide are mostoften used because they are very effectivedisinfectants, not only at the treatment plant butalso in the pipes that distribute water to our homesand businesses.

• Ozone and ultraviolet radiation are effectivedisinfectants for relatively clean source waters, butneither of these are effective in controlling

biological contaminants in the distribution pipes.

September 29, 2016 (C) Arun Kumar, IIT Delhi 21

Disinfection (chlorination)

Full-scale

Courtesy: Dr. Irene Xagoraraki (MSU, USA)

Bench-scale

UV Disinfection

Wastewater Treatment

• Preliminary Treatment (screening)

• Primary Treatment (primary settling)

• Secondary Treatment (e.g. activated sludge)

• Advanced Treatment (e.g. P removal)


• Solids Processing (sludge treatment)

Sludge Types• Primary sludge

– 3 to 8% solids

– About 70% organic material

• 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

Treatment processes include:

– Thickening – separates water from solids by gravity or

flotation

– Stabilization – converts organic solids to more 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

Big Picture


BP_Ex 1_Exposures of nanoparticles from contaminated edible Plants

Singh and Kumar (2013)

BCF=bioconcentration

Factor

Csoil = concentration in soil

C0

Chuman

• See how contaminants from different products

finally end up in compartments where human

exposure is possible.

• See how much material is lost in different

compartments and how much is transferred to

next compartment

• For every compartment, write down names of

parameters required for calculating fate of

contaminants

• Determine relationship between C0; Cwater; Csoil;

Cplant; Chuman



Raw Wastewater

Raw Drinking WaterWastewater

Treatment

Drinking Water Treatment

Potential human exposurevia drinking water

Natural waters

Removal and/or transformation

Animal Manure

Land Application

Removal and/or transformation

Solid Waste

Runoff, Infiltration, Sorption, Microbial activity, other transformations

Runoff, Infiltration,Sorption,Microbial activity, other transformations

Landfills

Biosolids

ECs present in human urine and feces

BP_Ex2_Fate of Nanoparticles in Environment

[email protected]

C0 C1

C2

C3

C4

• See how contaminants from different products

finally end up in compartments where human

exposure is possible.

• See how much material is lost in different

compartments and how much is transferred to

next compartment

• For every compartment, write down names of

parameters required for calculating fate of

contaminants

• Determine relationship between C0 and C4



31

� Water solubility –

32-40 mg/L

� Weakly volatile

� Low sorption to soil

LOW ADSORPTION HENCE MOVES FROM SOIL TO WATER

INCINERATION DUST

LOW WATER SOLUBILITY

MOVES SLOWLY IN

WATER

BP_Ex4_Environmental Fate

Occurrence

&

Exposure

Assessment

Risk

Assessment

Physical

Properties

&

Environmental

Fate

Detection

Methods

Treatment

Methods

Regulation

Source: Layton D. et al., 1987

• Write down different processes shown in this

figure

• Describe fate of organic compounds in soil,

plant, air and water

• Which processes are involved in soil; in water; in

air

• What is the role of Sun in these processes


wastewater treatment processesweb.iitd.ac.in/~arunku/files/cvl100_y16/lecsep2728.pdf · big picture...

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