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 Aromatic

AlkanesCnH2n+2

AlkenesCnH2n

AlkynesCnH2n-2

Cycloaliphatics

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

Physical/Chemical Treatment Methods

• 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 5

Carbon (mg) 60 40 30 20 5

Ce (mg/L) 25 99 212 310 510

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)

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

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)

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

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

Bohart-Adams equation

1ln2

1

out

in

in

in

C

C

KC

Fb

VC

NFa

baXt

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

Modified Bohart-Adams Eq.

f

aa

bXatbedmovingorcolumnsMultiple

'

':

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

EBCT

WusageCarbon

V

WdosageCarbon

v

QA

v

H

Q

VEBCT

carbon

ghbreakthrouatwaste

carbon

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?

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

Other Design Considerations

• Pretreatment

• Fluctuations in contaminant concentration

• Head loss

• Short circuiting

• Air binding

• Regeneration and/or disposal

Carbon Regeneration

• Heat

• Steam

• Solvent

• Acid/base

• Oxidant

Regeneration Effects

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

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

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