New Uses for Old Chemistry Chemical Methods of Environmental Remediation

Presented by Cindy G. Schreier, Ph.D.

El Dorado Hills, California www.primaenvironmental.com

KMnO4

Iron

Na2S2O8

Ozone

About PRIMA Independent

laboratory Founded in 1998 Specializing in ◦ Treatability testing ◦ Innovative remediation

technologies ◦ Custom laboratory work

Woman-owned small business

Contamination of Groundwater

Common Contaminants Petroleum hydrocarbons ◦ Gasoline ◦ Diesel

BTEX ◦ Benzene ◦ Toluene ◦ Ethylbenzene ◦ Xylenes

Fuel Oxygenates ◦ Methyl t-butyl ether (MTBE) ◦ t-Butyl alcohol (TBA)

Common Contaminants Chlorinated solvents ◦ Tetrachloroethene, C2Cl4

◦ Trichloroethene, C2HCl3

1,4-Dioxane Hexavalent chromium, Cr(VI)

Solubilities and MCLs Contaminant Solubility in

Water, mg/L MCL, mg/L MCL, µmol/L

Benzene Toluene Ethylbenzene Xylenes

1,880 470 150

~ 150

0.001 0.15 0.3

1.78

0.013 1.6 2.8 17

MTBE TBA

26,000 Miscible

0.013 0.012**

0.15 0.12

PCE TCE

150 1,280

0.005 0.005

0.030 0.038

1,4-Dioxane Miscible 0.001** 0.011 Cr(VI) ~ 50,000 0.050* 0.96 MCL = Maximum Contaminant Level; values listed are for CA as of Nov 2008 * Total chromium ** Notification level

Common Remediation Options

In Situ Chemical Oxidation ◦ Catalyzed hydrogen peroxide (aka

Fenton’s Reagent) ◦ Ozone ◦ Permanganate ◦ Persulfate

In Situ Chemical Reduction ◦ Zero-valent iron (ZVI) ◦ Calcium polysulfide

Oxidation Potential Hydroxyl radical, •OH 2.7V Sulfate radical, SO4• 2.6V Ozone, O3 2.2V Persulfate, S2O8

2- 2.1V Hydrogen peroxide H2O2 1.8V Permanganate, MnO4

- 1.7V

Permanganate 3C2Cl4 + 4KMnO4 + 4H2O→ 6CO2 + 4KCl + 4MnO2(s) + 8HCl

COC Theoretical Demand (g KMnO4/g COC)

Tetrachloroethene (PCE, C2Cl4) 1.3 Trichloroethene (TCE, C2HCl3) 2.4 Dichloroethene (DCE, C2H2Cl3) 4.3 Vinyl chloride (VC, C2H3Cl) 8.4

C2HCl3 + 2KMnO4 → 2CO2 + 2KCl + 2MnO2(s) + HCl

Permanganate Limited to chlorinated

ethenes and some pesticides

Reacts relatively slowly with soil

Secondary Effects ◦ Oxidation of soil Cr to

Cr(VI) is common ◦ Pink water if

permanganate doesn’t decompose

Permanganate Decomposition of KMnO4 does not tell

you if COCs can be destroyed!

Soil treated with 38 g/L (76 g/kg) permanganate

All permanganate consumed within 1.5 hrs.

NO EFFECT on DDT or toxaphene.

Catalyzed Hydrogen Peroxide

Developed by HJH Fenton in 1890s as an analytical reagent

Generates hydroxyl and other radicals, which oxidize a wide range of organic compounds

Iron is a catalyst

Classical Fenton’s Reagent

Fe2+ + H2O2, pH < 4

Fe2+ + H2O2 +H+ → Fe3+ + HO• + H2O Fe3+ + H2O2 → Fe2+ + HOO• + H+

Catalyzed Hydrogen Peroxide

Common catalysts are iron EDTA or VTX (proprietary catalyst)

Similar effectiveness as classical Fenton’s Preferred in the field because pH adjustment not

needed

Modified Fenton’s Reagent

Catalyst + H2O2, near-neutral pH

Catalyzed Hydrogen Peroxide Reaction is exothermic Decomposition generates about

3.3L O2/L of 1%H2O2 ◦ Decomposition is rapid, may get

stripping of VOCs rather than destruction. This is addressed in lab testing.

◦ Off-gases may need to be managed.

Secondary effects ◦ pH changes/increase in sulfate ◦ Mobilization of metals ◦ Cr(VI) formation

Ozone

Used in water treatment for disinfection since early 1900s.

Reacts with broad range of contaminants including GRO, BTEX, PCE

Effective in saturated zone as well as unsaturated zone

Most likely/significant secondary effects ◦ Formation of Cr(VI) from soil Cr ◦ Formation of bromate from bromide

Ozone C2Cl4 + 2O3 + 2H2O → 2CO2 + 2O2 + 4HCl

COC Theoretical Demand (g Ozone/g COC)

Tetrachloroethene (PCE, C2Cl4) 0.6 Trichloroethene (TCE, C2HCl3) 1.1 Benzene (C6H6) 9.2 n-octane (surrogate for gasoline) 10 MTBE 8.2

C6H6 + 15O3 → 6CO2 + 15O2 + 3H2O

Ozone Column Tests Test O3 Applied

(g) O3 Consumed

(g) GRO

(mg/kg) DRO

(mg/kg) Control 0 0 483 5600 Nitrogen 0 0 43 5200 O3 – low 33 13 33 3600 O3 – med 67 32 9.9 170 O3 - high 108 33 31 340

Notes • 1 inch diameter x 6 inch long columns • 150 g soil per column • Flowrate ~ 125 mL/min • O3 concentration ~ 45 mg O3/L O2 • Test duration ~ 15 days

Ozone column test

Persulfate – S2O82-

Widely used in industry since at least 1940s ◦ Initiator of polymerization reactions ◦ Etchant and cleaning of circuit boards ◦ Booster in hair bleaching formulations ◦ Dye removal ◦ Secondary oil recovery as polymerization initiator and gel

breaker Environmental use began about 2005 ◦ May be activated or unactivated ◦ Activated has broader range of reactivity than unactivated ◦ Activators include heat, iron EDTA, H2O2, high pH (heat

and high pH used in TOC analysis)

Persulfate – S2O82-

S2O82- + activator → 2SO4

- • persulfate sulfate radical

Persulfate Activation

SO4- • + e- → SO4

2- sulfate

S2O8

2- + H2O → 2HSO4- + ½ O2

sulfuric acid oxygen

Persulfate Decomposition

Persulfate Reactivity and oxidant persistence depend upon

activator ◦ Alkaline activation (pH >10.5) and heat are most versatile ◦ Oxidation reactions relatively slow – days to weeks ◦ FeEDTA activated persulfate rapidly decomposes if pH <

~5 ◦ If H2O2 activation, usually either H2O2 or persulfate

decomposes quickly. Secondary Effects ◦ Changes in pH ◦ Increase in sulfate , sodium ◦ Increase in ORP, TDS ◦ Changes in dissolved metals ◦ Cr(VI) formation

Oxidation by Persulfate Analyte Units Control AP-HP AP-pH

Trichloroethene

µg/L 110,000 250 4,900

1,4-dioxane µg/L 20,000 2,300 2,000 Chloride mg/L 18 220 290 Cr(VI) mg/L < 0.001 < 0.001 0.19 Sodium persulfate g/L 0 0.4 9.8 Notes • Initial TCE = 210,000 ug/L; dioxane = 28,000 ug/L • AP-HP: 16 g/L sodium persulfate + 1% H2O2 • AP-pH: 24 g/L sodium persulfate, pH > 10.5 • Samples collected at 21 days • Off-gases collected from AP-HP test; 3.4% TCE volatilized

Zero-valent Iron (ZVI) Known in the corrosion industry since early

1900s “Discovered” by environmental industry in

1990 by Bob Gilham, University of Waterloo Removes wide variety of compounds ◦ Organics: chlorinated ethylenes and some

ethanes, chlorinated pesticides (DBCP, Dieldrin) ◦ Inorganics: Cr(VI), arsenic, nitrate, nitrite,

cyanide, metals Removal mechanisms include reduction,

adsorption, complexation, precipitation

Zero-valent Iron – PCE Removal

Reductive dehalogenation Ethene, ethane are primary end-products Lesser halogenated intermediates may

build up.

C2Cl4 + 2e + H+ → C2HCl3 Fe0 → Fe2+ + 2e C2Cl4 + Fe0 + H+ → C2HCl3 + Fe2+

ZVI Permeable Reactive Barrier

Direction of flow

Source

Contaminated water Impermeable barrier

Iron wall

Treated water

Zero Valent Iron Test

ZVI Column Results

Analyte Units Port

Influent Port #1 Port #2 Port #3 Effluent Contact Time min 0 44 87 130 170

VC µg/L < 40 < 20 < 5.0 < 1.0 < 1.0 1,1-DCE µg/L < 40 < 20 < 5.0 < 1.0 < 1.0 cis-DCE µg/L < 40 < 20 < 5.0 3.2 1.1 trans-DCE µg/L < 40 < 20 < 5.0 < 1.0 < 1.0 TCE µg/L < 40 37 34 1.5 < 1.0 PCE µg/L 4900 2300 640 < 1.0 < 1.0

Hexavalent Chromium, Cr(VI) Used extensively in plating May be naturally occurring (< 0.01 mg/L) Remediate by converting to Cr(III) Cr6+ + 3e Cr3+ Electron sources: ◦ Ferrous iron (Fe2+) ◦ Ascorbic acid (Vitamin C) ◦ Calcium polysulfide (CaSx) ◦ ORGANIC MATTER

Remediation of Cr(VI) in Soil

Injection Wells

Source Plume Liquid barrier

Initial soil Cr(VI): ~ 50 mg/kg Final soil Cr(VI): ~ 0.2-5 mg/kg

Treatment of Cr(VI) Impacted Soil

Chemistry in Environmental Science Analysis – many parameters must be

measured in soil, water and gas matrices Risk Assessment – understanding chemical

behavior aids understanding of risk Regulation – understanding of chemistry is

necessary to make rational, fair decisions regarding management of impacted sites

Remediation – chemistry needed to develop site conceptual model and identify potential remediation options and side effects

Summary / Conclusions Many chemical treatment options exist

to clean up the environment Most are well-known to chemists, but

new to environmental scientists Many opportunities for chemists in

environmental science

THANK YOU

Cindy G. Schreier, Ph.D.

El Dorado Hills, California www.primaenvironmental.com

KMnO4

Iron

Na2S2O8

Ozone