Phytoremediation of Persistent Organic Pollutants John H. Pardue Louisiana State University
Outline Technology description Laboratory and greenhouse evidence for mechanism Applications of technology Pilot and proposed full-scale systems Observations Future Directions
Technology Description Rapid contaminant attenuation for certain chlorinated organics is observed in vegetated sediments (i.e., wetlands). In these sediments, enhanced biological processes (aerobic and anaerobic biodegradation and plant uptake) have been observed in the root zone that drives rapid natural recovery. By vegetating sediments contaminated with chlorinated compounds, root matter and exudates will serve as a source of hydrogen for halopiring organisms that can biodegrade the target compounds.
CONFINED DISPOSAL FACILITY WATER DETRITUS RHIZOSPHERE REDUCED CONTAMINANT FLUX
Proposed mechanisms Reductive dechlorination is enhanced in vegetated sediments because the root surface serves as a location of enhanced activities of dehalopiring and other degrading microbial populations By vegetating sediment contaminated with chlorinated organic compounds, belowground root matter will serve as source of H 2, overcoming redox potential limitations in sediments.
I II III Rapid dechlorination observed in rhizosphere Root matter stimulates dechlorination rate IV Halopiring organisms identified Root sorption is key mechanism for desorption-istant, weathered compounds
I 60 50 cis-1,2-dce VC Ethene Chloroethenes (µm) 40 30 20 10 0 50 0 25 50 75 100 125 150 175 200 225 1600 40 1400 1200 Hydrogen (nm) 30 20 1000 800 600 Methane (µm) 10 400 0 Hydrogen Methane 200 0 0 25 50 75 100 125 150 175 200 225 Elapsed time (Hours) Rapid dechlorination of chlorinated solvents observed in rhizosphere
II. Root matter stimulates dechlorination rate Root Experiment River Sediment with 5g Roots (RCLR) 1000 600 1000 1,2,3,4-TECB, mm /kg dry weight 800 600 400 200 Time vs RCNR Time vs RCSR Time vs RCMR Time vs RCLR Daughter product, mm/kg dry soil 500 400 300 200 100 Time vs 1234TCB Time vs 123TCB Time vs 124TCB Time vs 12DCB Time vs 14DCB Time vs 13DCB 800 600 400 200 Parent 1,2,3,4-TCB, mm/kg dry soil 0 0 0 0 10 20 30 40 50 0 10 20 30 40 50 Time (days) Time (day)
II T3-2 T2-1 T2-2 Core dissection approach
II Typha, Chlorobenzene Typha, Benzene 25 1.2 20 1.0 Chlorobenzene (Aqeuous), ppm 15 10 5 Benzene (Aqeuous), ppm 0.8 0.6 0.4 0.2 0 0.0-0.2-5 0 10 20 30 40 50 Time (days) 0 10 20 30 40 50 Time (days) Time vs Typha top far away from root Time vs Typha medium far away from root Time vs Typha bottom far away from root Time vs Typha top near root Time vs Typha medium near root Time vs Typha bottom near root Time vs Typha top far away from root Time vs Typha medium far away from root Time vs Typha bottom far away from root Time vs Typha top near root Time vs Typha medium near root Time vs Typha bottom near root
III. Halopiring organisms identified Detection of Dehalococcoides 16S rdna sequences in constructed wetland mesocosms. Lane L Ladder; Lane 1 microcosm derived from bottom section of constructed wetland; Lane 2 microcosm derived from middle section of constructed wetland; Lane 3 microcosm derived from top section of constructed wetland.
Example ults for Archae RT probes Depth Soil 12-15 Soil 15-18 Soil 18-21 Root 12-15 Root 15-18 Root 18-21 C T 34.5 31.7 33.4 ND ND 36.5 1:100 dilutions of DNA extracts
IV 0.08 Observed chlorobenzene uptake 0.06 0.04 0.02 m = 0.631 r ² = 0.627 Plant uptake K oc q OC q r m t1 t 2 2 max K q = TSCF Trans max f f q r K 2 OC K oc OC q ( t1 t 2) (( K ) / 2) + OC q 2 max q f max q oc f q OC q K OC 1 max q f max 1 f q OC K oc + OC 0.00 0.00 0.02 0.04 0.06 0.08 0.10 Salix n. Scirpus o. Predicted chlorobenzene uptake Root sorption the major uptake mechanism for wetland plant uptake of desorption-istant chlorobenzene
Repartitioning of desorption-istant organics to the root surface, predictable from simple equilibrium relationships Plant uptake Desorption istant soil fraction Plant root Contaminant Desorption irr K d Root uptake RCF Bulk solution is RCF > irr K d?
Application: Treatment Wetland Concept for VOCs A constructed wetland to treat both chlorinated and non-chlorinated VOCs maximizing biodegradation, minimizing volatilization while operating year-round Wetland is constructed as an alternative discharge point for the groundwater plume within the site boundary either passively intercepting the plume or serving as a component of a pump and treat system
METHANOTROPHIC BIODEGRADATION PLANT UPTAKE ATMOSPHERE WATER DETRITUS RHIZOSPHERE SUB-RHIZOSPHERE SORPTION REDUCTIVE DECHLORINATION
Example sites where wetland systems proposed or piloted RESOLVE (CERCLA), North Dartmouth, MA SRSNE (CERCLA), Southington, CT Aberdeen Proving Ground (CERCLA), Edgewood, Md (3 sites) Landfill site in central North Carolina Industrial facility in Louisiana (RCRA)
ReSolve CERCLA site Chemical recycling and process facility in North Dartmouth, MA NPL listed in 1983 PCBs, and chlorinated solvents including TCE, methylene chloride, toluene and others (DNAPL) Two-tiered groundwater pumping, containment and treatment system in place since 1998 Motivation-reduce annual O&M costs on mechanical system
Resolve CERCLA site North Dartmouth, MA
BFP Cross-section
10 8 cis-1,2-dce Trench B 800 Concentration (um) 6 4 2 600 400 200 Concentration (ug/l) Trench B inlet/outlet ults 0 outlet inlet 0 0 50 100 150 200 250 300 350 Concentration (um) 6 5 4 3 2 1 Vinyl chloride 300 200 100 Concentration (ug/l) Solid line indicates the time when the water levels were raised in the system. Dashed line indicates time of microbial inoculation. 0 outlet inlet Trench B 0 0 50 100 150 200 250 300 350 Days
22 nd Street Landfill
Offshore Groundwater VOC Plume Legend Characterization DPT Locations Characterization well Locations RI Monitoring Well FFS Monitoring Well Phase I FFS DPT Phase II FFS DPT Total VOC (ppb) 1-99 100-999 1,000-4,999 5,000-9,999 >10,000 Bush River
Remedial options for 22 nd Street Landfill Passive barrier treatment an option for multiple sources (several plumes, landfill leachate, shoreline erosion of landfill) Treatment wetland one type of passive barrier built similar to existing natural marshes in other areas of the site. Wetland is constructed as an alternative discharge point for the groundwater plumes within the site boundary, to intercept landfill leachate and prevent erosion
22 nd Street Landfill Characterization Sampling Locations Legend Dialysis Sampler Locations Pore Water Leachate Sample Geotechnical Boring DPT Locations Surface Water Samples RI Monitoring Well FFS Monitoring Well Phase I FFS DPT Phase II FFS DPT 22 nd Street Landfill Rad Yard Bush River
Field Observations Halopiring populations can be maintained in the plant rhizosphere when appropriate redox conditions are maintained. This has ulted in very efficient removal of chlorinated solvents in groundwater over short travel distances To date, vegetation type is a consideration only in that high root biomass is desired. Temperature is important consideration as well as a ensuring that there is a source of halopiring microorganisms Strong regulatory acceptance of technology to date
Applications to dioxin/furans/pcbs Halopiring microorganisms important for dechlorination of dioxins (Ballerstedt et al., 2004; Bunge et al., 2003); PCBs (Wu et al., 2002) and chlorobenzenes (Jayachandra et al., 2003; Holscher et al., 2003). Floodplain sediments amenable to wetland creation with vegetation (up to a meter of water depth). Deeper river sediments would require CDFs. A significant body of knowledge on wetland creation and toration. This expertise can be exploited to assist in application of a plant-based remediation concept for sediments.
Future needs Pilot/greenhouse studies are needed to apply plant-based remedial approaches to specific dioxin/pcb/furan contaminated sediments Bioavailability issues: Can we screen for good and bad candidate sediments by evaluating relative roles of organic carbon, soot and oil/grease as sorptive phases? Microbial community structure analysis: need to screen sediments for starting halopiring populations
Questions?