General Overview of Remediation of the Oxygenates

Patricia Ellis Delaware Department of Natural Resources and Environmental Control Tank Management Branch

October 2002 ASTSWMO Conference Arlington, Virginia

Presentation Overview • Chemical Properties of the Oxygenates • Implications for Fate and Transport • Implications for Remedial Options

Physical Behavior of MTBE, Ethanol, ETBE and Benzene B – Benzene M – MTBE E – ETBE Et - Ethanol Et E E Et E Et Et E E Et E Jans

en, Moyer, Woodward, and Sloan, 2002

Et

Remediation Strategies • The starting point for evaluating a remediation strategy is to develop an understanding of the fate and transport characteristics relative to other petroleum hydrocarbons.

• Comparing the physical and chemical characteristics to BTEX compounds can elucidate the fate and transport of oxygenates relative to other gasoline hydrocarbons.

Other Oxygenates….

• Little literature available for remediation of the other ethers • Allow physical and chemical properties to guide choice of remediation technology

Criteria for Selection and Evaluation of Alternative Technologies • Ability to consistently meet cleanup goal • Cost-effectiveness • No formation of unwanted by-products • Operability (e.g. ability to run unattended) • Compatibility with existing technologies • Robustness (e.g. ability to deal with high and low flows and concentrations) • Simplicity of operation

Initial Decisions • Initial concentrations – VOCs such as BTEX constituents – Oxygenate type and concentration – Other chemical parameters • Cleanup goals – Contaminant reduction – Drinking water standards – Source removal vs. plume remediation • Plume size and treatment flow rates – Large volume water at low concentrations – High volume water at low concentrations • Multiple Technologies?

Chemicals for Comparison • Alcohols – Ethanol – Methanol – TBA • Ethers – MTBE – TAME – DIPE – ETBE • Others – Benzene – Toluene – Ethylbenzene – Xylenes – Naphthalene – Benzo(a) pyrene

Solubility • Solubility: The degree to which a contaminant dissolves in groundwater and unsaturated zone pore water • Concentrations of individual constituents observed in groundwater depend on the composition of the fuel as well as the chemical properties of the individual constituents • Solubility of each compound in a mixture like gasoline is a function of Raoult’s Law

Pure Phase Solubility

100000 80000 60000 40000 20000 0 + + +

Solubility

+ + + 1000000 100000 10000 1000 100 10 1 0.1

0.01

0.001

Gasoline constituent MTBE Benzene Toluene Ethylbenzene Xylenes (mixed) Approximate % by volume Solubility of constituent (mg/l) 11% 1% 11% 2% 11% 4700-6000 18 59 3 19

Solubility from Gasoline into Water

60000 50000 40000 30000 20000 10000 0 ?

Groundwater Pump and Treat • MTBE relatively soluble and relatively non adsorptive, so pump and treat very effective • Aboveground water treated by: – GAC/resin adsorption – Bioreactor – Air stripping (need air to water ratio of  200:1); vapor-phase treatment by: • Catalytic oxidation (economical for high concs.) • Activated carbon (economical for low concs.) • Biofilters

Groundwater Pump and Treat • Groundwater extraction followed by ex-situ treatment is successful in removing MTBE from groundwater • The enhanced solubility of MTBE relative to BTEX compounds indicated that MTBE subsurface concentrations can be significantly reduced with fewer pore volumes of extracted groundwater • Furthermore, due to the relatively low sorption potential of MTBE, dissolved phase MTBE concentrations are less likely to rebound than BTEX concentrations following cessation of pumping activity

Adsorption • Soil adsorption coefficient K d = C S concentration sorbed on soil surfaces C W concentration in water K d = f oc K oc fraction of organic carbon in soil times the soil/sediment organic carbon to water coefficient • Adsorption retards contaminant migration in groundwater

7 6 5 4 3 2 1 0

Log K oc

Remediation Strategies • MTBE’s low sorption potential suggests that ex-situ adsorption technologies (i.e. granular activated carbon, resins) are likely less efficient for removing MTBE from water relative to BTEX compounds • Low sorption of the alcohols is even more problematic for remediation

Sorption (Retardation) • Sorption causes compounds to migrate slower than the groundwater. The lower the retardation factor, the faster the chemical will migrate. • Retardation factor for: – Advective/Dispersive Front R = 1 – MTBE R = 1.1

– Benzene R = 1.8

Retardation Factor

100 80 60 40 20 0 f oc = 0.001 mg/mg, bulk density = 1.75 kg/L, porosity = 0.25

f oc = 0.004 mg/mg, bulk density = 1.75 kg/L, porosity = 0.25

+ +

Adsorption Coefficient: Implications for Remediation • Because the alcohols and ethers have low adsorption coefficients, sorption technologies for remediation such as granular activated carbon work less well than for the BTEX compounds • Because the ethers and alcohols don’t sorb well to soils, pump-and-treat is more effective than for the BTEX compounds

Liquid-Phase Sorption Processes - GAC • The theoretical loading rate of MTBE on GAC is approximately 10% of the loading rate of benzene. Therefore removal of MTBE generally requires substantially larger quantities of GAC than removal of a comparable amount of carbon

Liquid-Phase Sorption Processes - Resins • Synthetic resins may have sufficiently better sorption capacities for TBA comparable to GAC, and therefore may present a practical alternative treatment for TBA-contaminated sites.

• Resins can be regenerated on-site.

• Resins do not produce oxidation byproducts • Resins less prone to bacterial fouling • Technology still in development

Henry’s Law Constant • Partitioning between the liquid phase and the gaseous phase governed by Henry’s law • Determines tendency of contaminant to volatize from groundwater or pore water into the soil gas • Ratio of partial pressure of a compound in vapor phase to concentration of compound in liquid phase is Henry’s Law Constant of the compound • Henry’s Law Constant is an indication as to how easy it will be to air-strip a compound

Henry’s Law Constant (H) • H = C G /C w • Henry’s constant > 0.05

– Volatilization likely – Off-gassing likely • Henry’s constant < 0.05

– Volatilization unlikely

0.4

0.35

0.3

0.25

0.2

0.15

0.1

0.05

0

Henry's Law Constant (Dimensionless)

Remediation Strategies • MTBE has a lower Henry’s constant than BTEX compounds suggesting that air stripping is likely to require a greater air to water ratio to achieve MTBE removal efficiencies similar to those of BTEX . ETBE easier to strip than MTBE.

• Alcohols have extremely low H, therefore not good potential for stripping.

Air Strippers

Henry’s Law Constant: Implications for Remediation • Because of the low Henry’s Law Constant of the ethers, they are more difficult to airstrip than the BTEX compounds • The Henry’s Law Constants of the alcohols are even lower, making air stripping even more difficult that for the ethers

Air Strippers Removal efficiency is a function of the volatility of the contaminant • Water temperature • Air/water flow ratio • Contact time • Number of trays or tower size

Air Sparging • Strips VOCs, and oxygenates soil and groundwater to enhance bioremediation in situ • Often accompanied by SVE to manage vapors • Treats saturated and unsaturated zones • Relatively inexpensive and widely used • High solubility and low H keep MTBE in water phase • May need exceptionally high air-to-water ratio compared to many other VOCs

Air Sparging/SVE

Vapor Pressure • Vapor pressure is a measure of ease of volatilization from NAPL to the vapor phase, either from free product on the water table or from residual contamination in soils • Higher vapor pressures are an indication of greater expectation of success of soil vapor extraction for a compound

Vapor Pressure (mm Hg) If vapor pressure > 100 mm Hg • Volatilization from free phase (NAPL) • Vaporization of residual product from dry soil

Vapor Pressure

300 250 200 150 100 50 0

Vapor Pressure (mm Hg) Constituent Approximate % by volume P i (mm Hg) MTBE Benzene Toluene Ethylbenzene Xylenes (mixed) 11% 1% 10% 2% 27-28 0.8-0.9

2.8

0.2

0.7-0.8

Remediation Strategies • MTBE has a much higher vapor pressure than BTEX compound. This suggests that vapor extraction technologies will be effective for removing MTBE from dry soils relative to BTEX compounds • ETBE and DIPE have lower vapor pressures than MTBE, and TAME is lower still, therefore will be harder to remove by SVE

Soil Vapor Extraction • MTBE has high vapor pressure so SVE effective • High air flow rates in extraction mode to strip VOCs • Treats upper portion of unsaturated zone • Control water level • Aboveground gas treatment by – Granular activated carbon – Catalytic oxidation – Thermal oxidation – Biofilters

Vapor Pressure: Implications for Remediation Removal from free product or soils: • Of the ethers, MTBE is easily removed from dry soil by SVE. ETBE and DIPE are somewhat more difficult, but TAME is less easy to remove by SVE than benzene.

• Ethanol and TBA have lower vapor pressures than benzene.

Multi-Phase Extraction • The combination of SVE and pump-and treat, designated as multi-phase extraction (MPE), allows for the remediation of both soil and groundwater with higher efficiencies than the separate application of each of these technologies

Emerging Reactive Barrier Technologies • Biostimulation by oxygen release • Bioaugmentation and sparging • Chemical permeable reactive barrier

Passive In-Situ Treatment Wall Groundwater flow direction Plume Optional funnel and gate (sheet piles) or slurry wall (clay)

Passive In-Situ Treatment Wall Treatment media may include adsorbents such as: • Granular activated carbon • Granular organic polymers • Synthetic resins Subsurface chemistry can be augmented with: • Organic acid catalysts • Chemically treated iron particles for Fenton’s chemistry Passive bioremediation treatment media may include, but are not limited to products that release oxygen, nutrients, or other products

MTBE Bio-Barriers Waterloo Permeable Release Panel Pilot Test Oxygen Emitter Diffusive Barrier Diffusive Oxygen Release Systems

Port Hueneme MTBE Bio-Barrier

Bioventing • Low air flow rates in injection or extraction mode • Aerates unsaturated to enhance bioremediation in situ • Aboveground vapor treatment usually not required • Passive systems - barometric pressure, wind turbine ventilation

Bioremediation • Capable indigenous organisms are ubiquitous in some areas • Aerobic rate correlated with O 2 conc. • Contaminants degraded as sole carbon/energy source or co-metabolically • Complete mineralization – With or without intermediates – Aerobic/anaerobic environments

In Situ Groundwater Bioremediation of Ethers • Preliminary results from field studies using in situ bioaugmentation and/or oxygen injection at Port Hueneme and Vandenberg AFB suggest that aerobic bioremediation strategies have a strong potential for success at MTBE-impacted sites.

• These may include applications involving direct metabolism, cometabolism, bioaugmentation, or some combination thereof.

• Additional studies are necessary to determine the relative biodegradability of the other ethers.

In Situ Groundwater Bioremediation of Ethers • MTBE is biodegradable, although more slowly than BTEX compounds • Less information available about other ethers • Indigenous organisms or bioaugmentation • Optimize electron acceptors, nutrients, pH and other factors • Several approaches: – Direct injection of amendments to subsurface – Membrane diffusion of amendments into groundwater – Extraction/reinjection of water with amendments

Biodegradation of Alcohols • Ethanol and methanol readily biodegradable in aerobic or anaerobic environments • Increased oxygen consumption due to alcohol biodegradation likely to drive aquifer to be anaerobic • Biodegradation of BTEX compounds in the presence of an ethanol or methanol release likely will occur more slowly due to the consumption of oxygen and other electron acceptors by the more easily biodegradable alcohols • TBA????

BTEX and Ethanol Biodegradation • Depletion of electron acceptors by ethanol degrading organisms will reduce their availability to BTEX degraders • Competition for electron acceptors could lead to a decrease in the BTEX intrinsic biodegradation rate and potentially result in longer BTEX plumes

Remediation Strategies • MTBE is more difficult to biodegrade than BTEX compounds due to the high energy required to cleave ether bonds, and the resistance of the branched carbon structure to microbial attack • ETBE generally thought to be relatively easy to biodegrade

Port Hueneme Benzene and MTBE Plume

Plume Control and Containment System (Pump & treat trench, artificial gradient) (18 gpm 24/7 to sanitary sewer, >1 ppm to GAC)

2500 ft.

Envirogen Propane & O 2 Enhancement UC Davis Culture Injection PM-1 Equilon Culture In-Situ Bioremediation Feb 2002 Approximate Locations MTBE 15 ug/L Benzene 1000 ug/L LNAPL Source Zone In-Situ Bioremediation Culture Injection Sites 1500 ft.

NFESC/Equilon/ASU In Situ Bio-Barrier for source control 800 ft.

NEX Gas Station Site

Port Hueneme Test Plots

Port Hueneme BioBarrier Envirogen Air Sparge Phyto remediation Long-Term Monitoring

Port Hueneme - Biobarriers

In-Situ Bioremediation Pressure-swing adsorption oxygen generator is capable of achieving high levels of dissolved oxygen in groundwater Used for biostimulation or with bioaugmentation

Bioremediation • Use of indigenous microorganisms or bioaugmentation with cultures of microorganisms • Optimization of electron acceptors, nutrients, pH and other factors • Breakdown products – Cautions!

Iso-Gen Technology • Iso-Gen Technology from H2O Technologies, Inc. uses electrolysis to disassociate water into hydrogen and oxygen and generate a stable-in solution form of dissolved oxygen • The stable DO is available for microbes to utilize and degrade MTBE and other petroleum hydrocarbons and additives • The technology uses vertical recirculation mechanisms to distribute the DO laden groundwater throughout the aquifer without pumping any water to the surface

Iso-Gen

Downhole unit Wall-mounted controller

Iso-Gen O 2 O 2 O 2 O 2 O 2 O 2 O 2 O 2 O 2 H 2 O + Energy  2H 2 + O 2 O 2 O 2

Iso-Gen

iSOC - In-situ Submerged Oxygen Curtain

iSOC - In-situ Submerged Oxygen Curtain

Microbial Metabolism of Organic Matter Respiration process Aerobic respiration Dinitrification Iron Reduction Sulfate Reduction Methanogenesis Electron acceptor O 2 NO 3 Fe 3 + SO 4 -2 CO 2 Metabolic products CO 2 , H 2 O CO 2 , N 2 CO 2 , Fe 2 + CO 2 , H 2 S Relative potential energy High CH 4 Low Suflita and Sewell (1991)

Intrinsic Biodegradation Processes

Organics CO 2 Metabolic Products Fe(II) H 2 S CH 4 N 2 Aerobic Respiration Denitrification Iron (III) Reduction +10 0 0 -100 O 2 NO 3

-

Fe(III) Sulfate Reduction Methanogenesis Dominant Electron Acceptors SO 4 2 2 CO Source Plume Migration/ Groundwater Flow

In Situ Chemical Oxidation Treatment Considerations • Destructive process • Non-target organics and inorganics • Choice of oxidant is site-specific • Impact of pH, pre-/during/post-treatment • Delivery of oxidants • Residual oxidation state • Monitored in-situ bioremediation/natural attenuation

Relative Oxidizing Power of Chemical Oxidants Reactive Species Fluorine Hydroxyl Radical (Fenton’s Reagent) Ozone Hydrogen Peroxide Permanganate Chlorine Dioxide Chlorine Bromine Iodine Relative Oxidizing Power (Cl 2 2.23

= 1.0) 2.06

1.77

1.31

1.24

1.15

1.0

0.80

0.54

In-situ Chemical Oxidation Injection ports Groundwater flow direction Plume In-situ injection of chemical oxidants such as hydrogen peroxide, potassium permanganate, etc. to oxidize contaminants

In-situ Chemical Oxidation Fenton’s Reaction following Pressure injection DRIS Oxidant delivery

KVA C-Sparger System KVA Spargepoints Palletized Unit C-Sparger unit pumps air/ozone mixture Mobile Unit

Ex-situ Chemical Oxidation Technologies Advanced Oxidation Processes • O 3 / H 2 O 2 • O 3 / UV • H 2 O 2 / UV • High Energy Electron Beam Irradiation (E Beam) • TiO 2 -catalyzed UV • Sonication / Hydrodynamic Cavitation • Fenton’s Reaction

Ex-situ Chemical Oxidation Technologies • Advanced Oxidation Processes (AOPs) have been shown to achieve MTBE removal rates exceeding 99% • Contaminants are destroyed • Cautions: – Need to monitor for sufficient destruction of breakdown products – Need to avoid bromate generation

Traditional Ex-Situ AOP

Ex-Situ AOP (HiPox System) Organic Contaminants 2O 3 + H 2 O 2  2•OH + 3O 2 O 2 OH• Intermediates O 2 OH• CO 2 + H 2 O

Ex-Situ AOP

AOP Cautions: • Hydroxyl radicals tend to react preferentially with aromatic compounds such as BTEX. However, if sufficient OH• radical is present, hydroxyl radicals react with MTBE as well as other intermediates until total mineralization is achieved.

• Ideally, OH• attack on organics results in complete mineralization to bicarbonate ion or carbon dioxide. However, suboptimal OH• generation has been shown to result in formation of products of incomplete oxidation, including TBA, TBF, acetone, formaldehyde, formate, acetate, and methanol.

Hollow Fiber Membrane Technology Water containing volatile and semivolatile organic compounds is passed through the inside of the hollow fibers while a vacuum is applied to the outside of the fibers. The organic compounds are transferred to the gas phase outside of the fiber and then are destroyed using an internal combustion unit The hollow fibers are made of materials that retain the flowing water, yet allow for gaseous exchange

Phytoremediation • Gradient control/evapotranspiration • Rhizosphere biodegradation • Native species perform best – Low maintenance conditions • Species selection influenced by water balance – Modeling, plant transpiration rate, stand density • Irrigation required to establish stand – Deep watering stimulates deeper root growth • Water/soil quality affects plant establishment/survival – Salt concentration, pH

Natural Attenuation Processes • Destructive (mass reduction) – Intrinsic biodegradation – Abiotic chemical reactions • Non-destructive (mass conservative) – Adsorption (K d =K oc f oc ) to organic fraction – Dispersion – Advection – Diffusion – Volatilization (vapor pressure, Henry’s Law) – Dilution

Natural Attenuation • Natural attenuation as remediation strategy less effective for MTBE removal relative to BTEX compounds due to MTBE’s low retardation factor, and slower rate of biodegradation especially under anaerobic conditions.

• In certain hydrologic settings (flat gradients, groundwater flow rates less than 0.1 foot/day), natural attenuation may be a feasible alternative for MTBE remediation • Greater retardation, lower solubility of other ethers may make natural attenuation a feasible option in more situations.

• TBA may be a problem due to toxicity

Monitored Natural Attenuation • Begins when active treatment yields diminishing returns and monitoring efforts are reasonable • Characterized by reduction of contaminant concentration, mass, toxicity or mobility • Monitor/model: – Decreasing contaminant concentrations – Physical, chemical, biological processes

Conclusions • With the right technologies, the ether and alcohol oxygenates can be remediated • Not much information available on remediation of oxygenates other than MTBE, but you can chose potential remedial technology based on physical and chemical properties of the contaminants

Technology Sequencing Often 4 major phases — minimize costs by optimizing level of effort of each: 1) Protect receptors 2) Control sources 3) Remediate residual and dissolved contamination 4) Monitored natural attenuation

Oxygenate Remediation References • EPA-OUST Guidance document (in preparation) on MTBE Remediation Technologies • ITRC Technology Overview document (in preparation) on MTBE and TBA remediation • California MTBE Research Partnership reports (Air Stripping, Advanced Oxidation Processes, Granular Activated Carbon, Synthetic Resin Sorbents) • MTBE Treatment Profiles at http://clu-in.org/products/mtbe