Andrew Hart Golder Associates (NZ) Limited. Assessment of ISCO for Remediation of PCP Impacted Soil

Transcription

1 Andrew Hart Golder Associates (NZ) Limited Assessment of ISCO for Remediation of PCP Impacted Soil

2 Overview Introduction to In-Situ Chemical Oxidation (ISCO) Case Study PCP contamination at a timber treatment site Bench trials to assess efficacy of oxidants for PCP degradation Experimental design Analytical results Key findings October 14,

3 Oxidation and Reduction Chemistry ISCO (& ISCR) involves electron transfer Objective is to create conditions to support the break down of contaminant(s) of interest (COI) via electron transfer Oxidation Loss of Electrons Reduction Gain of Electrons Oxidant acts as electron acceptor Reductant acts as electron donor October 14,

4 Oxidation and Reduction Chemistry Oxidation H 2 O 2 + Fe 2+ Fe 3+ + OH - + OH + 1e - Reduction MnO H + + 3e - MnO 2 + 2H 2 O October 14,

5 How Oxidants Work Contaminants can be oxidised directly by the oxidant or indirectly by free radicals Provide additional energy in reaction H 2 O 2 has a direct oxidation potential of 1.78 ev but in presence of catalyst (e.g. ferrous iron), peroxide forms OH which has an oxidation potential of 2.78 ev October 14,

6 Redox Reactions Successful oxidation requires balance of stoichiometry, thermodynamics and kinetics Redox Reaction Kinetics Can oxidant provide sufficient energy to break chemical bonds? Bond Chemical ev C-C PAHs, PCBs & PCPs +2.5 C-C BTEX +2.0 C-C PCE, TCE, DCE & VC +1.5 C-H Alkanes +1.0 October 14,

7 Oxidants and Reductants Available Permanganate (MnO 4- ) Peroxide (H 2 O 2 ) Fenton s Reagent (H 2 O 2 Fe 2+ ) Persulfate (S 2 O 2-8 ) Sulfides (S 2- ) Ozone (O 3 ) Perozone (OH + O 3 ) Active Carbonates (CO 2-3 ) Zero Valent iron and other metals Commercial proprietary products, e.g. Regenesis, Adventus October 14,

8 Oxidation Potential Vs Persistence Oxidant Potential Persistence Fenton s Reagent 2.80 V Low <10 days Perozone 2.80 V Low <5 days Activated Persulfate 2.60 V Average <4 months Ozone 2.42 V Low <5 days Persulfate 2.01 V Average <4 months Hydrogen Peroxide 1.78 V Low <10 days Permanganate 1.68 V Average-High >1 month Chlorine 1.4 V Average <1 month Oxygen 1.2 V Average-High >1 month October 14,

9 Feasibility of ISCO/ISCR Contaminants of Interest Conceptual Site Model geology, mineralogy, structure, diagenesis Aquifer Characteristics hydraulically active structures, porosity, effective porosity from drainage and pressure perspective Geochemistry ph, redox/eh/couples, low ionic strength solutions, rock/wall/soil/fluids, precipitation Natural oxidant/reductant demand often greater than contaminant demand Competing reactions Preferential pathways CONTACT IS KEY October 14,

10 Case Study PCP Impacted Soil Former timber treatment site Pentachlorophenol (PCP) based anti-sapstain timber treatment (trade name Santa-brite) Spray tunnel application with capture and re-use of excess solution Spray tunnel located undercover in south-west corner of building Ground below spray tunnel not sealed Ground level raised following completion of treatment October 14,

11 Site Layout Spray Tunnel October 14,

12 Hydrogeology Stratigraphy: Granular FILL Clay SILT SILT Silt CLAY CLAY 0.6 m bgl 1.2 m bgl 1.4 m bgl 1.8 m bgl >1.8 m bgl Moist to wet Confining CLAY layer Deeper aquifer not assessed Former drainage channel along southern edge of mill October 14,

13 Contamination Summary 41 samples between 0.05 m and 2 m bgl PCP 6,000 mg/kg max TCP 160 mg/kg max 7 samples >570 mg/kg between 0.3 m and 1.8 m 5 samples >1,000 mg/kg October 14,

14 Remedial Works Preliminary excavation of soils for off-site disposal to 0.4 m Issues with this option: Excavation of soils beneath roofline of mill High water content of soils Perched building foundations on edge of excavation October 14,

15 Pentachlorophenol Chemical Formula - C 6 Cl 5 OH Molar mass g/mol Solubility C Antisapstain solutions Sodium pentachlorophenate October 14,

16 Oxidation Oxidation is Process of reducing electron density around central atom to break a bond (or form a new bond) In case of PCP treatment looking to break C-C and C-Cl bonds to form simpler less persistent and less toxic compounds. Limited evidence of chemical oxidation of PCP impacted soils Steam stripping trials successful but management of waste liquid required Successful chemical oxidation of PCP impacted groundwater October 14,

17 Microbubble Perozone Batch Trial Time PCP TCP Chloride TOC ph Total Alkalinity (Hours) g/m3 g/m3 g/m3 g/m3 ph units g/m3 as CaCO < PCP below 1 g/m 3 after 12 hours PCP below 0.1 g/m 3 after 24 hours Literature (lab studies) suggested that below 1 g/m 3 should be achieved in 1 hour Chloride results inconclusive TOC results indicate reaction not going to completion October 14,

18 Ideal Situation Chemical Oxidation of PCP PCP + oxidant 6CO 2 + 5Cl - Stoichometric increase in Cl - Stochiometric decrease in total organic carbon Real World PCP + oxidant intermediates + byproducts + Cl - May not observe predicted changes in Cl - and total organic carbon Intermediates and byproducts less toxic than PCP e.g. oxalic acid October 14,

19 Potassium Permanganate Can be used in-situ Long lived to allow for transport and reaction with target Highly soluble Introduction of manganese to ground water Accumulation of solid MnO 2 may reduce permeability To our knowledge no field data for PCP removal October 14,

20 Persulfate Strong oxidant (but kinetically slow in destroying organics) Long lived to allow for transport and reaction with target Lower solubility (K 2 S 2 O 8-6% at 25ºC, Na 2 S 2 O 8-40% at 25ºC) Heat or ferrous iron salt (Fe 2+ ) increases oxidative strength generation of sulfate free radicals Sulfate free radicals also activated under alkaline conditions (ph 12-13) Lower NOD than KMnO 4 Potential for clogging of pathways due to swelling October 14,

21 ISCO Bench Trials Objective to assess whether ISCO represents a feasible option for managing PCP soil contamination Trials using commercially available chemical oxidants Potassium Permanganate (KMnO 4 ) Potassium Persulfate (K 2 S 2 O 8 ) Sodium Persulfate (Na 2 S 2 O 8 ) Hydrogen Peroxide (H 2 O 2 ) Proprietary oxidant products Regenesis - RegenOx Adventus - Daramend VeruTek - S-ISCO October 14,

22 ISCO Bench Trials Design Potassium Permanganate (KMnO 4 ) Purple, flowing-grade crystals (need to mix into solution) 3-4% solution (63 20 C) Bulk unit cost CDN$6/kg Potassium Persulfate (K 2 S 2 O 8 ) White, flowing-grade crystals 40% solution (529 20ºC) Sodium Persulfate (Na 2 S 2 O 8 ) White, flowing-grade crystals 40% solution ( C) October 14,

23 ISCO Bench Trials Design Potassium Permanganate 75g impacted soil 3% stock solution Dosing rates 3% 15% 30% NOD ~10% Hydrogen Peroxide Not run at lab scale due to strong potential for violent reaction based on NOD October 14,

24 ISCO Bench Trials Design Potassium persulfate - 40% stock solution Dosing rates 5% 10% 15% Sodium persulfate - 40% stock solution Dosing rates 5% 10% 15% Both persulfate solutions ph activated NaOH solution (0.1 mol/l) used in make up water (ph 13) Heat activated persulfate final temperature of 60ºC October 14,

25 ISCO Bench Trials KMnO 4 Pentachlorophenol (PCP) Chloride Commercial/Industrial Criteria Total Organic Carbon 2, , , , , , Control 0 3% 15% 30% 0 October 14,

26 ISCO Bench Trials Na 2 S 2 O 8 Pentachlorophenol (PCP) Chloride Commercial/Industrial Criteria Total Organic Carbon 2, , , , , , Control 0% 5% 10% 15% 0 October 14,

27 ISCO Bench Trials K 2 S 2 O 8 Pentachlorophenol (PCP) Chloride Commercial/Industrial Criteria Total Organic Carbon 2, , , , , , Control 0% 5% 10% 15% 0 October 14,

28 ISCO Bench Trials Key Findings Evidence of PCP degradation with decrease in PCP and TOC and increase in chloride Potassium permanganate appears effective NOD ~10% Dosing rate between 15% and 30% Effectiveness of persulfate unclear Comparative PCP concentrations between dosing rates Evidence of increased chloride and decrease TOC Partial degradation aromatic ring not broken? Key questions? Natural variability in PCP concentrations Matrix interference ability to achieve contact in fine grained matrix October 14,

29 Further Research Up-scale treatment trials Improved mixing to increase contact Increased dosing? Field trials? Regulatory approval October 14,