In-situ Dechlorination of Polychlorinated Biphenyls in Sediments

In-situ Dechlorination of Polychlorinated Biphenyls in Sediments Using ZeroValent Iron

Kevin H. Gardner Deana Aulisio, Jean M. Spear Center for Contaminated Sediments Research University of New Hampshire RTDF Sediments meeting, Feb. 18-19, 2004

Overview • In situ remediation or dredging

accompanied with offsite treatment. • Introduction of zero-valent iron (ZVI) – various sizes and manufacturing techniques • Dechlorination of PCBs in PCBcontaminated sediments • Relatively fast reaction and an economically viable process

RTDF Sediments meeting, Feb. 18-19, 2004

PCB Dechlorination Kinetics with ZVI in Housatonic Sediment 90 80

Conc of PCBs, ppm

70 60 50 40 30 20

y = 23.535x -0.1088 R2 = 0.8306

10

84.1% Removed

0 0.0

5000.0

10000.0

15000.0

20000.0

25000.0

Time (min) RTDF Sediments meeting, Feb. 18-19, 2004

New Bedford Harbor typical results

Conc of PCBs, pp m

300

250

200

y = 183.33x -0.0415 R2 = 0.8221

150

56.4% Removed 100 0.0

5000.0

10000.0 15000.0 Time, min

20000.0

25000.0


Different Types of ZVI Evaluated UNH ZVI

RNIP

RNIP/Pd

Cerac

Mallinkrodt

Source

lab

Toda America

Toda America

Milwaukee, WI

St. Louis, MO

Cost

$N/A

$9/lb

$9/lb

$4.3/lb

$2.39/lb

Size

1-100 nm

30 nm

30nm

50 um

50 um

Water Content

79.9% water

52.5% water

52.5% water

25.0% water

25.5% water

Surface Area

33.5 m2/g

23.6 m2/g

23.6 m2/g

N/A

N/A

Characteristic suspension suspension suspension dry powder dry powder


Scanning Electron Micrographs Micro-scale ZVI

Nanoscale ZVI-the diameter of each particle ~ 50 nm


50-um iron materials


PCB dechlorination with different iron types Percent Removal of Total PCBs (%)

80

Nanoscale irons 60

Microscale irons 40

20

0 CERAC

Mallinkrodt

Toda Kogyo Toda Kogyo Method of Wang Fe/Pd and Zhang (1996)

Iron Source RTDF Sediments meeting, Feb. 18-19, 2004

Why does degradation level off? • Iron degradation faster than PCBs • Passivation of iron surface • Desorption of “slow” PCB fraction


ORP over time Oxidation-Reduction Potential (mV)

-100 -200 Control CERAC Mallinkrodt Toda Kogyo

-300 -400 -500 -600 -700 -800 0

10

20

30

40

50

Time (days) RTDF Sediments meeting, Feb. 18-19, 2004

Sequential Fe additions Static experiment – initial mixing only 1 0.9 0.8

C/Co

0.7 0.6 ZVI add

0.5

ZVI add

0.4 3 Additions of Fe - 52% Removed

0.3

1 Addition of Fe - 37% Removed 0.2 0

500

1000

1500

2000

2500

3000

3500

4000

4500

Tim e (m in)


Percent Removal of Total PCBs (%)

PCB desorption and dechlorination kinetics - NBH sediments desorption with Tenax dechlorination with zero valent iron

100 80 60 40 20 0 0

2

4

6

8


What are the Breakdown Products?? 7 Day Breakdown of Congener 207 Internal Standard Congener 204

Internal Standard Congener 30

Congener 207

170+190 Noise 5+8

46

56+60

135+118


Homolog Concentration / Total PCB Concentration

Transient behavior of 1-CB, 2-CB 0.07 Monochlorobiphenyl Dichlorobiphenyl

0.06 0.05 0.04 0.03 0.02 0.01 0.00 0

2

4

6

8

10

12

14

16


Ortho dechlorination

Concentration (mg/kg)

40 Ortho only congeners Non-ortho congeners

30

20

10

0

0.0

1.0

1.5

2.0

2.5

3.0

3.5


Positional analysis 220 Congeners with ortho chlorines Congeners with meta chlorines Congeners with para chlorines

Concentration (mg/kg)

200 180 160 140 120 100 80 60 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5


Specificity of degradation 0.9 initial final

0.8

fraction of concentration

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 ortho

meta

para

o,m

o,p

m,p

o,m,p

isomer


Mass Balance Balance

0.7

Concentration (mmole/kg)

0.6 0.5 0.4

PCB

Biphenyl

0.3 0.2 0.1 0


In-Situ Treatment Technology: Reagent Delivery

• Deliver reagent(s) to contaminated subsurface

strata • Provide adequate mixing of reagent in strata • Maximize yield – minimize reagent dispersion • Minimize dispersion of contaminated sediment


Seaway Systems - Field Examples Contaminated Sediment Excavator À Pressure-controlled housing

provides a dry environment around the mechanical bucket or mixing in-situ treatment zone o Sediments are prevented from mixing with the water o Pressure-control subsurface technology permits mixing in dry environment for in-situ treatment


Seaway Systems - Field Examples Contaminated Sediment Remediation Vessel Water Treatment (Membrane Filtration)

Excavator Vessel

Contaminated Sediment Remediation Vessel (CSRV)

À CSRV establishes a containment area within the river o Prevents migration of contaminants o Operator can work quickly and efficiently o Progress can be easily monitored

À Low pressure within containment area prevents water from escaping À CSRV applicable for in-situ treatment technology RTDF Sediments meeting, Feb. 18-19, 2004

Deploying shrouds


Conclusions • Cost? ~ $50/cubic yard in materials (for ~2-3% • •

• •

iron addition) 50 micrometer size iron works well and may be more cost-effective, easier and safer to handle Remediation endpoint – high organic carbon results in slow desorption kinetics (addition of surfactant/cosolvent to enhance PCB availability is currently being investigated) Implementation − Reactive cap or mixed into sediment Why does this study show results so different from others? − Catalysis (by Ti, Mn oxides, Pd, Pt?) RTDF Sediments meeting, Feb. 18-19, 2004

End
