Wastewater Treatment Processesweb.iitd.ac.in/~arunku/files/CVL100_Y16/LecSep2728.pdf · Big Picture...
Transcript of Wastewater Treatment Processesweb.iitd.ac.in/~arunku/files/CVL100_Y16/LecSep2728.pdf · Big Picture...
September 29, 2016 Arun Kumar ([email protected])
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(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
September 29, 2016 Arun Kumar ([email protected])
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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
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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)
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• 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)
• Final Treatment (disinfection)
• 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.
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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)
• Final Treatment (disinfection)
• 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
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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
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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
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
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September 29, 2016 Arun Kumar ([email protected])
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� 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
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