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
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
PCB Dechlorination Kinetics with ZVI in Housatonic River Sediment 90 80 70 Conc of PCBs, ppm 60 50 40 30 20 10 y = 23.535x -0.1088 R 2 = 0.8306 84.1% Removed 0 0.0 5000.0 10000.0 15000.0 20000.0 25000.0 Time (min)
New Bedford Harbor results 300 Conc of PCBs, ppm 250 200 150 y = 183.33x -0.0415 R 2 = 0.8221 100 56.4% Removed 0.0 5000.0 10000.0 15000.0 20000.0 25000.0 Time, min
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 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 * Wang and Zhang, 1996
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
PCB dechlorination with different iron types 80 Percent Removal of Total PCBs (%) 60 40 20 Microscale irons Nanoscale irons 0 CERAC Mallinkrodt Toda Kogyo Method of Wang Toda Kogyo and Zhang (1996) Fe/Pd Iron Source
Why does degradation level off? Iron degradation faster than PCBs Passivation of iron surface Desorption of slow PCB fraction (unavailable PCBs)
ORP over time -100 Oxidation-Reduction Potential (mv) -200-300 -400-500 -600-700 Control CERAC Mallinkrodt Toda Kogyo -800 0 10 20 30 40 50 Time (days)
PCB desorption and dechlorination kinetics - NBH sediments Percent Removal of Total PCBs (%) 100 80 60 40 20 0 desorption with Tenax dechlorination with zero valent iron 0 2 4 6 8 Time (days)
What are the Breakdown Products?? 7 Day Breakdown of Congener 207 Internal Standard Congener 30 Internal Standard Congener 204 Congener 207 170+190 Noise 5+8 46 56+60 135+118
Ortho dechlorination 40 Concentration (mg/kg) 30 20 10 0 Ortho only congeners Non-ortho congeners 0.0 1.0 1.5 2.0 2.5 3.0 3.5 Time (days)
Positional analysis Concentration (mg/kg) 220 200 180 160 140 120 100 Congeners with ortho chlorines Congeners with meta chlorines Congeners with para chlorines 80 60 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Time (days)
Homolog-specific dechlorination 120 Homolog Concentration (mg/kg) 100 80 60 40 20 initial 1 min 60 min 1 day 3 day 0 Homolog
Mass Balance 0.7 0.6 Concentration (mmole/kg) 0.5 0.4 0.3 0.2 PCB Biphenyl 0.1 0
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
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
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
Patent Drawing: In-Situ Treatment of Contaminated Sediments 191 102 101 151 194 193 A A 195 197 192 194 193 195 FIG. 18 192 103 197 151 196 Section A-A FIG. 20 145 191 FIG. 19
Deploying shrouds
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)
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
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