physical & chemical treatment chapter 9. chemistry review chapter 3
TRANSCRIPT
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Physical & Chemical Treatment
Chapter 9
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Chemistry Review
Chapter 3
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Activity - Individual
Is it organic or inorganic?
– PCBs– Methane– Carbon dioxide– Ammonia– Lead– Pesticides
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Organics
Hydrocarbons
Aliphatic Aromatic
AlkanesCnH2n+2
AlkenesCnH2n
AlkynesCnH2n-2
Cycloaliphatics
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In-Class Activity
• Solubility• Vapor pressure• Diffusion coefficient• Henry’s constant• Organic-carbon partition
coefficient• Octanol-water partition
coefficient• Freundlich constant• Bioconcentration factor• Biomagnification• Volatility
1. Amount of chemical passing through an area
2. Sorption of an organic to another organic
3. Increased concentration in an organism
4. Amount of solute dissolved in a solvent
5. Tendency to adsorb to a solid6. Solubility of a gas in a liquid7. Tendency to move from solution to
gas phase8. Pressure exerted by a vapor on a
liquid at equilibrium9. Sorption of an organic to the
organic portion of soil or sediment10.Increased concentration through
the food chain
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Physical/Chemical Treatment Methods
• Stripping
• Carbon adsorption
• Neutralization
• Precipitation
• Reduction/oxidation
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Physical Treatment
Carbon Adsorption
(Section 9-2)
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Activated Carbon
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Typical Column
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Flow Patterns
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Design Parameters
• Contaminant properties– Solubility– Molecular structure– Molecular weight– Hydrocarbon saturation
• Contact time
• Carbon exhaustion
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Adsorption Evaluation: Batch Test
• Grind GAC to pass 325-mesh screen
• Evaluate contact time to reach equilibrium– Mix 500 mg/L GAC with waste over 24 h – Determine degree of adsorption at various
time intervals – Choose time to achieve 90% removal
• Evaluate GAC dosage– Mix various C with waste for 90% chosen
time
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Adsorption Isotherm
• Plot of contaminant adsorbed per unit mass of carbon (X/M) vs. equilibrium contaminant concentration in bulk fluid
• Mathematical forms– Langmuir: X/M = (aCe)/(1+bCe)
– Freundlich: X/M = kCe 1/n
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Example: Adsorption Isotherm
Each jar receives activated carbon and 100 mL of a 600-mg/L solution of xylenes and is then shaken for 48 h.
Jar 1 2 3 4 5
Carbon (mg) 60 40 30 20 5
Ce (mg/L) 25 99 212 310 510
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Example continued
Freundlich Isotherm
y = 0.1875x + 2.7121
R2 = 0.9219
2.95
3
3.05
3.1
3.15
3.2
3.25
3.3
0 0.5 1 1.5 2 2.5 3
log (Ce) (mg/L)
log
(X
/M)
(mg
/g)
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Example: Adsorption Isotherm
Test 1 2 3 4
P (kPa) 0.027 0.067 0.133 0.266
X/M (kg/kg) 0.129 0.170 0.204 0.240
Benzene
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Example continued
Langmuir Isotherm
y = 3.7159x + 0.0035
R2 = 0.9967
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.000 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008
Ce
Ce
/(X
/M)
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Activity – Team
Each jar receives activated carbon and 100 mL of a solution with 0.5% TOC and is then shaken for 48 h.
Jar 1 2 3 4 5
Carbon (g) 10 8 6 4 2
Ce (mg/L) 42 53 85 129 267
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Example: Using Reference Data
Estimate the daily carbon utilization to remove chlorobenzene from 43.8 L/s of wastewater saturated with chlorobenzene. Assume a chlorobenzene concentration of 5 mg/L is acceptable for discharge to the sewer.
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Freundlich Isotherms
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Comparing Different Carbons
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Batch vs. Column Capacity
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Adsorption Zone
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Bed Depth Service Time Design
Bohart-Adams equation
1ln2
1
out
in
in
in
C
C
KC
Fb
VC
NFa
baXt
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Modified Bohart-Adams Eq.
1ln
1ln
''
'':
''
':
'
'
''
out
in
out
in
in
in
in
in
C
C
CC
C
Cbb
C
Caa
bXationConcentrat
Q
Qaa
bXatrateFlow
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Modified Bohart-Adams Eq.
f
aa
bXatbedmovingorcolumnsMultiple
'
':
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BDST Design
• Determine height of adsorption zone (AZ)– Small diameter columns in series run to breakthrough – Plot breakthrough for 10% and 90% vs. cumulative
depth – AZ = horizontal distance between 10% & 90% lines
• Determine number of columns– n = [(AZ)/d] +1, where d = depth of column– Round up to next whole number
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BDST Design Continued
• Determine diameter of columns– Use same loading rate in full-scale units as lab units
[L = Qw/As from lab operation]
– As = Qw/L with Qw for full-scale operation
– Round up to nearest size available– Typically, d:D = 3:1 - 10:1
• Determine carbon usage rate– CUR = (As)(1/a)(CUW)
• a = slope of 10% line = velocity of AZ• CUW = carbon unit weight
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Example: BDST Design
A waste stream at a flow rate of 0.145 m3/min requires treatment to reduce the organic concentration from 89 mg/L to 8.9 mg/L (90% removal). Lab studies are run in columns 2.3 m high by 0.051 m diameter at a flow rate of 0.5 L/min. Assume a unit weight of carbon of 481 kg/m3.
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Example: BDST Design
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Example: BDST Design
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Example: BDST Design
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Activity – Team
A petrochemical washwater with a flow of 322 m3/d and concentration of 630 mg/L has to be treated to an effluent standard of 50 mg/L. A four-column pilot plant was operated with a carbon that had a density of 481 kg/m3. The columns were 3 m long and loaded at a hydraulic rate of 0.20 m3/min/m2. The pilot plant was operated in series. Determine the required number of columns, the time required to exhaust a column, the column diameter, the daily carbon use, and the carbon adsorption loading.
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Empty Bed Contact Time
EBCT
WusageCarbon
V
WdosageCarbon
v
QA
v
H
Q
VEBCT
carbon
ghbreakthrouatwaste
carbon
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Example: Single Column Data
Limited data has been obtained to evaluate whether carbon adsorption is a viable alternative to treat 1 MGD of secondary effluent containing 50 mg/L organics to a level of 5 mg/L. Carbon density is 23 lb/ft3. Is adsorption a viable treatment option? Is the data adequate?
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Example cont.
0
200
400
600
800
1000
1200
1400
1600
1800
0 2 4 6 8 10
Loading Rate (gpm/sq ft)
Ser
vice
Tim
e (h
)
5' Bed
10' Bed
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Other Design Considerations
• Pretreatment
• Fluctuations in contaminant concentration
• Head loss
• Short circuiting
• Air binding
• Regeneration and/or disposal
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Carbon Regeneration
• Heat
• Steam
• Solvent
• Acid/base
• Oxidant
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Regeneration Effects
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Common Design Deficiencies
• Poor effluent quality due to poor carbon adsorption – Adsorption not applicable to waste– Poor regeneration – pH out of proper range– Operating temperature wrong
• BDST too short due to high loadings or under-designed system
• Head loss too high for available gravity head or pump capacity
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Deficiencies continued
• High & ineffective backwash volume due to high influent solids content
• No method to determine breakthrough
• Carbon transfer piping plugging and no means provided to disconnect & flush lines
• Incorrect pumps for carbon slurries
• Incorrect valves for carbon slurries
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Adsorber Selection
0
5
10
15
20
25
30
35
0 2 4 6 8 10
Years of Operation
Tota
l C
ost
($)
2,000-lb vessel5 vessel exchanges/yearMonthly monitoring
10,000-lb vessel1 vessel exchange/yearQuarterly monitoring