Transcript Chemistry Review

Physical & Chemical
Treatment
Chapter 9
Chemistry Review
Chapter 3
Activity - Individual
Is it organic or inorganic?
– PCBs
– Methane
– Carbon dioxide
– Ammonia
– Lead
– Pesticides
Organics
Hydrocarbons
Aliphatic
Alkanes
CnH2n+2
Alkenes
CnH2n
Aromatic
Alkynes
CnH2n-2
Cycloaliphatics
In-Class Activity
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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 solid
6. Solubility of a gas in a liquid
7. Tendency to move from solution to
gas phase
8. Pressure exerted by a vapor on a
liquid at equilibrium
9. Sorption of an organic to the
organic portion of soil or sediment
10.Increased concentration through
the food chain
Physical/Chemical Treatment
Methods
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Stripping
Carbon adsorption
Neutralization
Precipitation
Reduction/oxidation
Physical Treatment
Carbon Adsorption
(Section 9-2)
Activated Carbon
Typical Column
Flow Patterns
Design Parameters
• Contaminant properties
– Solubility
– Molecular structure
– Molecular weight
– Hydrocarbon saturation
• Contact time
• Carbon exhaustion
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
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
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
Carbon (mg)
60
40
30
20
Ce (mg/L)
25
99
212 310
5
5
510
Example continued
Freundlich Isotherm
log (X/M) (mg/g)
3.3
3.25
y = 0.1875x + 2.7121
3.2
R2 = 0.9219
3.15
3.1
3.05
3
2.95
0
0.5
1
1.5
log (Ce) (mg/L)
2
2.5
3
Example: Adsorption Isotherm
Benzene
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
Example continued
Langmuir Isotherm
0.035
y = 3.7159x + 0.0035
R2 = 0.9967
Ce/(X/M)
0.030
0.025
0.020
0.015
0.010
0.005
0.000
0.000
0.001
0.002
0.003
0.004
Ce
0.005
0.006
0.007
0.008
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)
53
85
129
267
42
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.
Freundlich Isotherms
Comparing Different Carbons
Batch vs. Column Capacity
Adsorption Zone
Bed Depth Service Time Design
t  aX  b
F1 N
a
CinV
Bohart-Adams equation
 F2   Cin

 ln
b  
 1
 KCin   Cout

Modified Bohart-Adams Eq.
Flow rate : t  a' X  b
Q
a'  a
Q'
Concentration : t  a' X  b'
Cin
a'  a '
Cin
C

ln
 1
Cin  C

b'  b '
Cin  Cin

ln
 1
 Cout

'
in
'
out
Modified Bohart-Adams Eq.
Multiple colum nsor m ovingbed : t  a' X  b
a
a' 
f
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
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
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.
Example: BDST Design
Example: BDST Design
Example: BDST Design
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.
Empty Bed Contact Time
V H
EBCT  
Q v
Q
A
v
Carbon dosage
Wcarbon
Vwaste at breakthrou gh
Wcarbon
Carbon usage 
EBCT
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?
Service Time (h)
Example cont.
1800
1600
1400
1200
1000
800
600
400
200
0
5' Bed
10' Bed
0
2
4
6
Loading Rate (gpm/sq ft)
8
10
Other Design Considerations
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Pretreatment
Fluctuations in contaminant concentration
Head loss
Short circuiting
Air binding
Regeneration and/or disposal
Carbon Regeneration
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Heat
Steam
Solvent
Acid/base
Oxidant
Regeneration Effects
Common Design Deficiencies
• Poor effluent quality due to poor carbon
adsorption
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Adsorption not applicable to waste
Poor regeneration
pH out of proper range
Operating temperature wrong
• BDST too short due to high loadings or underdesigned system
• Head loss too high for available gravity head
or pump capacity
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
Adsorber Selection
Total Cost ($)
35
30
25
10,000-lb vessel
1 vessel exchange/year
Quarterly monitoring
20
15
10
2,000-lb vessel
5 vessel exchanges/year
Monthly monitoring
5
0
0
2
4
6
Years of Operation
8
10