A Novel & Sustainable Combined Oxidant In-Situ Remediation Approach for Brownfield Redevelopment

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1 A Novel & Sustainable Combined Oxidant In-Situ Remediation Approach for Brownfield Redevelopment RE3 Conference Will Moody November 14, 2012

2 4+ Acre DNAPL Site Carbon Tetrachloride + Chloroform DNAPL Complex mix: Reducible: Carbon tetrachloride Chloroform Methylene chloride Oxidizable: Carbon disulfide Chlorobenzene Ethylbenzene Methoxychlor Anisole

3 Chloromethanes cannot be oxidized Cl Cl C Cl Carbon tetrachloride Cl Cl No double carbon bonds Cl C H Chloroform Cl

4 Chemical Reduction during ISCO Catalyzed peroxide reactions: H 2 O 2 + Fe +2 OH + OH - + Fe +3 OH + Fe +2 OH - + Fe +3 Fe +3 + H 2 O 2 H + + HO 2 + Fe +2 Fe +2 + HO 2 Fe +3 + HO 2 - Fe +3 + HO 2 Fe +2 + O 2 + H + OH + H 2 O 2 H 2 O + O H + HO 2 H + + O 2 - Superoxide (reductant)

5 Manganese-Catalyzed Peroxide Watts and coworkers: Under acidic conditions: H 2 O 2 + Mn +2 OH + OH - + Mn +3 As ph approaches 6.8: Mn H 2 O MnO 2 (s) + 2e - + 4H + Hydroxyl radical production less efficient At ph >6.8: Mn +4 + H 2 O 2 Mn H + + O 2 - Only superoxide; no hydroxyl radicals

6 Cannot distribute Mn +4 Inject MnSO 4 (precipitate Mn +4 ) Very acidic Require large ph shifts MnO 2 is solid Fracture emplace? Chelated Mn Mn +2 valence state

7 What about permanganate? MnO H 2 O + 3e - MnO 2 (s) + 4OH - Mn +7 Mn +4 Permanganate is already widely used in ISCO Permanganate solutions have a near-neutral ph Permanganate will oxidize certain COCs Preferential permanganate reduction in zones with highest concentration of organics MnO 2 catalyst is fixed as solid and not displaced by injection of additional liquids

8 Biggest Challenge: Stabilization H 2 O 2 + MnO 2 +2H + Mn H 2 O + O 2 Mn H 2 O Mn(OH) 2 + 2H + Mn(OH) 2 + H 2 O 2 MnO 2 + 2H 2 O Net reaction: 2H 2 O 2 2H 2 O + O 2 Permanganate-MnO 2 amorphous, very fine Extremely fast H 2 O 2 degraded in minutes

9 Phosphate Buffer ph = 6.80 ph = 6.84 ph = 6.97 ph = ml volume 500 mg MnO 2 Peroxide = 1.9%

10 Bench Test Set-Up Batch reactor / soil slurry tests 500 g composited soil 1,500 ml homogenized groundwater 20 g MnO 2 (precipitated from TCE/KMnO 4 ) 200 ml 1.0 M phosphate buffer ph = 6.8 Soil, groundwater, volatilization VOST tube (Tenax/Anasorb)

11 Bench Test Water Results

12 Contaminant Mass Results Groundwater, Soil and DNAPL

13 Bench Test Conclusions Phosphate buffer controls ph and stabilizes reaction All of the COCs are readily destroyed: Chloromethanes by superoxide reduction. Aromatics by hydroxyl radical oxidation. DNAPL was destroyed. Superoxide degradation pathway not fully resolved. Phosgene not detected.

14 4+ Acre DNAPL Site Carbon Tetrachloride + Chloroform DNAPL Field Pilot Test 50 ft x 50 ft area 4,800 gal NaMnO 4 4% 2,800 gal 1M buffer 26,000 gal 11% H 2 O 2

15 Conceptual Cross Section Shallow Deep 3 ft F-M Sand 8 ft DNAPL 2 ft Meadow Mat (Organic Silt) 3 ft

16 Design Modifications Add barrier sand to deep injection wells to block lower screen interval Add barrier sand to shallow injection wells to target shallower portion of the saturated zone Install new injection wells to base of sand and gravel layer with 1-ft screens Implement a more traditional Fenton s approach due to the high chlorobenzene concentrations Install vent wells to allow controlled offgas venting

17 Pilot Results Eight soil samples obtained; total VOC reductions were reduced by an average of 99.6% DNAPL not observed PID readings significantly reduced Odors not detected Both MWs showed an additional decrease in total VOC concentrations

18 Full-Scale Design Evaluate smaller portions of the site for geochemical conditions and VOCs Conduct traditional Fenton s in areas with low ph conditions and chlorobenzene and methoxychlor present Conduct new approach in areas where neutral ph exists and relatively higher chloromethanes are present

19 Full-Scale Implementation Approximately 500 injection wells and 100 vent wells installed All vent wells cored and sampled for VOCs Soil tested in field with a dye tracer tests Total treatment area divided into small sections for better site management Site conditions vary throughout the 4 acre area Injection currently underway.

20 Conclusions Mn +4 catalyzes peroxide to produce reductant Use permanganate to distribute Mn Organic matter reduces Mn +7 Mn +4 (MnO 2 ) Phosphate buffer stabilizer, ph control Peroxide reductant and oxidant Natural soils: Fe to catalyze peroxide

21 Questions? Will Moody Dan Bryant