In-situ Dechlorination of Polychlorinated Biphenyls in Sediments Using Zero- Valent Iron

Transcription

1 In-situ Dechlorination of Polychlorinated Biphenyls in Sediments Using Zero- Valent Iron Kevin Gardner, Emese Hadnagy Deana Aulisio, Jean Spear Center for Contaminated Sediments Research University of New Hampshire

2 Overview In situ remediation or dredging / offsite treatment. Introduction of zero-valent iron (ZVI) various sizes and manufacturing techniques Dechlorination of PCBs in PCB- contaminated sediments Relatively fast reaction and an economically viable process

3 PCB Dechlorination Kinetics with ZVI in Housatonic River Sediment Conc of PCBs, ppm y = x R 2 = % Removed Time (min)

4 New Bedford Harbor results 300 Conc of PCBs, ppm y = x R 2 = % Removed Time, min

5 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? $4.3/lb $2.39/lb Size 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 * Wang and Zhang, 1996

6 50-um iron materials ground iron oxide powder reduced with hydrogen or carbon monoxide at very high temperatures precipitation of aqueous iron on the anode of an electrochemical cell

7 PCB dechlorination with different iron types 80 Percent Removal of Total PCBs (%) Microscale irons Nanoscale irons 0 CERAC Mallinkrodt Toda Kogyo Method of Wang Toda Kogyo and Zhang (1996) Fe/Pd Iron Source

8 Why does degradation level off? Iron degradation faster than PCBs Passivation of iron surface Desorption of slow PCB fraction (unavailable PCBs)

9 ORP over time -100 Oxidation-Reduction Potential (mv) Control CERAC Mallinkrodt Toda Kogyo Time (days)

10 PCB desorption and dechlorination kinetics - NBH sediments Percent Removal of Total PCBs (%) desorption with Tenax dechlorination with zero valent iron Time (days)

11 What are the Breakdown Products?? 7 Day Breakdown of Congener 207 Internal Standard Congener 30 Internal Standard Congener 204 Congener Noise

12 Ortho dechlorination 40 Concentration (mg/kg) Ortho only congeners Non-ortho congeners Time (days)

13 Positional analysis Concentration (mg/kg) Congeners with ortho chlorines Congeners with meta chlorines Congeners with para chlorines Time (days)

14 Homolog-specific dechlorination 120 Homolog Concentration (mg/kg) initial 1 min 60 min 1 day 3 day 0 Homolog

15 Mass Balance Concentration (mmole/kg) PCB Biphenyl 0.1 0

16 Reagent Delivery Seaway Environmental Technologies Deliver reagent(s) ) to contaminated subaqueous strata Provide adequate mixing of reagent in strata Maximize yield minimize reagent dispersion Minimize dispersion of contaminated sediment

17 Seaway Systems - Field Examples Contaminated Sediment Excavator 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-controlled subsurface technology permits mixing in dry environment for in-situ treatment Vision: barge-mounted, hollowstem auger encased in pressure-controlled housing

18 Seaway Systems - Field Examples Contaminated Sediment Remediation Vessel Water Treatment (Membrane Filtration) Excavator Vessel Contaminated Sediment Remediation Vessel (CSRV) 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 Low pressure within containment area prevents water from escaping CSRV applicable for in-situ treatment technology

19 Patent Drawing: In-Situ Treatment of Contaminated Sediments A A FIG Section A-A FIG FIG. 19

20 Deploying shrouds

21 Current initiatives Use of biodegradable, food-grade surfactants to increase availability of PCBs to iron Minimization, optimization of iron added Use of iron filings Influence of iron on microbial consortia Large-scale lab. experiments using prototype mixing/delivery device - summer Bioavailability/chronic toxicity of treated sediments - summer Fundamental investigation of catalysis / reduction mechanisms Reactivity of dioxins/furans/pcns (proposed)

22 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 Implementation mixed into sediment or reactive cap Delivery/mixing a key issue for full scale deployment

23 End