Challenges in subsurface in situ remediation of chlorinated solvents Chemical degradation focus

Transcription

1 Challenges in subsurface in situ remediation of chlorinated solvents Chemical degradation focus Mette M. Broholm 1, Annika S. Fjordbøge 1, Camilla M. Christiansen 1, Jirij Hønning 1, Bente H. Hansen 1, Lærke W. Nedergaard 1, Kristina Kern 1, Basil Uthuppu 2, Mogens H. Jakobsen 2, Peter Kjeldsen 1, Poul L. Bjerg 1, Lisbeth Ottosen 3 1 DTU Environment, 2 DTU Nanotech, 3 DTU Civil Engineering

2 Motivation and scope Conceptual models for DNAPL source zones DNAPL source zones Target DNAPL Low metabolites Heterogeneous geologic settings Secondary source zones Fractured media Target matrix contamination Scope In Situ remediation alternatives Challenges Shortly after release Later Later again

3 ISCO permanganate clay till In Situ contact sport Diffusion limited Contaminant reactant contact challenge PCE diffused into matrix Curtecy of: Tom Heron, NIRAS

4 PCE and MnO 2 profiles in non-weathered (reduced) clayey till PCE (µg/kg) PCE Distance (m) MNO MnO (g/kgts) 2 Diffusion limited, retardation by TOC and Fe(II) as well as PCE oxidation

5 ZVI-Clay Soil Mixing Targeting heterogeneous geologic media and DNAPL The importance of contact CCH, CSU Soil mixing for delivery and contact Less sensitive to geologic heterogeneity and contaminant distribution ZVI addition for degradation (mzvi or granular ZVI) Clay addition for containment/stabilization Still stabilized when reactivity depleted Contaminant mass discharge reduced by both processes

6 ZVI-Clay Soil Mixing - Skuldelev PCE DNAPL observed in source zone PCE depleted below soil quality criteria (5 mg/kg) High mobilization costs (soil mixing) Log(Concentration in mg/kg) Time [d] Down-gradient contaminant concentrations and mass discharge significantly reduced Application limitations Site infrastructure Post-treatment land use Soil structure significantly altered by soil mixing Post-treatment soil strength varies

7 Enhanced injection technologies Pneumatic fracturing Hydraulic fracturing Direct push injection Pilot-tests of 3 enhancement technologies in a clayey till Tracers: brilliant blue, fluorescein and rhodamine WT Direct documentation (coring and excavation) Fracture spacing Fracture thickness Fracture ROI Tracer distribution

8 Pneumatic fracturing Expectation Dense network of closely spaced fractures Observations 2-4 m bgs: spacing 5-10 cm 4-8 m bgs: large spacing (> 1 m) Most tracer mass within 2 m ROI Transport in subvertical fractures Technology development High mobilization costs

9 Hydraulic fracturing Strategies: Source treatment - multifracture Barrier deep fracture Observations: 3 m: cm thick fracture, ROI 3 m 6-7 m: few observations, partly successful, mm thick Multi: merged fractures 9 m: surfaced, subvertical fracture Not recommended for site High cost

10 Direct push injections Expectation Distribution in natural fractures etc. Risk of vertical transport along probe Observations Single and 3 point cluster, injections at cm spacing in 3 depth intervals Tracer distributed in natural and induced fractures at same or closer spacing for all depths ROI m, individual > 2 m Flexible and at reasonable cost Variable success High pressure and other enhancements

11 Electrokinetic enhancement Potentially enhanced reactant contaminant contact Electrokinetically induced transport processes Overcome diffusion limitations in double porous media Challenging due to electrolysis: Anode: H + Cathode: OH -

12 EK-BIO in limestone EK transported lactate and bacteria into the contaminated limestone core Chemical oxidants and reductants may also be transported EOF (neutral species migration) was not observed in limestone

13 Targeting DNAPL with nzvi Stability Mobility Reactivity Field application Affinity Sustainability Each characteristic should be optimized without significantly compromising the other characteristics Approach Block copolymer coated nzvi Fe 0 Water DNAPL

14 Coated nau-tracer affinity and mobility PVP-COOH PVP-VA Coated nau Affinity for DNAPL Emulsion Dissolved coating Non-coated nau not mobile aglomerates Coated nau PVA-COOH nau:pva-cooh ratio PVP-VA Pre- versus post-grafted Coating types CMC versus block copolymers

15 Organo Green Rust Affinity for DNAPL CH 4 CCl 4 CO HCOO - 70% CCl 4 DNAPL removal

16 Summary - Continued challenges Though ZVI-clay is a proven technology also at field scale, it is far from applicable at all sites Even for successfull injections of reactants in the subsurface, the time frames for in-situ remediation in low permeability geologic media are expected to be long Electrokinetically enhanced delivery is a promising but yet unproven technology Mobile and reactive nanoparticles surgically targeting DNAPL source zones are very novel and have not yet progressed beyond bench scale The development and upscaling of these pose significant challenges Continued need for research and development Need for well documented pilot and full scale field tests

17 Acknowledgements The presented results were financed by REMTEC, Danish Research Counsil The Region of Southern Denmark The Capitol Region of Denmark The Danish Minestry of Environment INWAT, DTU-KAIST collaboration project IronX, Danish Research Counsil Technicians at DTU Environment have assisted with field and laboratory work Consulting engineers from NIRAS, Orbicon, COWI and Geosyntec for collaboration on remediation projects

18 References Christiansen, C.M., Damgaard, I., Broholm, M.M., Kessler, T., Klint, K.E., Nilsson, B., Bjerg, P.L., (2010). Comparison of Delivery Methods for Enhanced In Situ Remediation in Clay Till. Ground Water Monitoring and Remediation, 30, (4), Fjordbøge, A.S., Riis, C., Christensen, A.G., Kjeldsen, P ZVI-Clay remediation of a chlorinated solvent source zone, Skuldelev, Denmark: 1. Site description and contaminant source mass reduction. Journal of Contaminant Hydrology, , Fjordbøge, A.S., Uthuppu, B., Caspersen, E., Fischer, S.V., Jakobsen, M.H., Broholm, M.M., Towards Coated Nano-Gold Particles as Non-Reactive Tracers in Coated nzvi for In-Situ Remediation. Abstract in The proceedings of The ninth international conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, California, USA, May 19-23, Hansen, B.H., L.WNedergaard,. (2014). Experimental design and assessment of electrokinetically enhanced bioremediation of chlorinated solvents in limestone. MSc Thesis. DTU Environment. Hønning, J., Broholm, M., and Bjerg, P. (2007). Role of diffusion in chemical oxidation of PCE in a dual permeability system. Environ. Sci. Technol. 41, Kern, K., Luis, K.A., Cooper, N.G.A., Hansen, H.C.B,. Jakobsen, R., Broholm, M.M. (2012). DNAPL Remediation Potential by Organo-Green Rust Reductive Degradation of Chlorinated Solvents. Abstract in Proceedings of The eights international conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, California, USA, May 21-24, 2012.