Bioremediation Technologies: Background

• Three main classes

- Engineered in situ

- Intrinsic in situ

- Engineered ex situ• Different purposes

- Engineered bioremediation: to increase the biotransformation rates significantly

- Intrinsic bioremediation: to prevent the migration of contamination away from its source.

Bioremediation Technologies:Contents

• Scope and characteristics of contaminants• Contaminant availability for biodegradation• Treatability studies• Engineering strategies for bioremediation• Evaluating bioremediation

Treatability studies

Level Goals Approach

1 Determine if biodegradation is option

•Thermodynamics•Simple lab microcosms

2 Evaluate biodegradation nonidealities (kinetics, multiphasic transport, mixed substrates etc.)

•Laboratory microcosms of all types (batch, column, slurry etc.)•Stoichiometry, thermodynamics, and kinetics

3 Evaluate site-specific issues, such as hydrogeologic conditions and heterogeneity

•Field pilot scale

Intrinsic bioremediation

• Essentially in situ bioremediation without human intervention.

• Removal of contamination source may be necessary prior to intrinsic bioremediation.

• Although intrinsic bioremediation does not involve active site manipulation, it requires construction and maintenance of a monitoring system.

• Need to monitor the plume distribution, indicator parameters of biodegradation, and possibility of contamination in previously non-contaminated areas.

• Need to evaluate the possibility and extent of intrinsic bioremediation in order to examine the effectiveness of “active” groundwater-soil remediation methods (no-treatment control

experiment).

Anaerobic Core

Aerobic Margin

Source

Anaerobic Core

Aerobic Margin

GW flow

Intrinsic bioremediation

Application

• Diverse microbial populations indigenous to subsurface environments can degrade important classes of organic contaminants.

• The extent of intrinsic bioremediation depends on the biodegradability of the contaminant and on the site’s hydrogeologic and chemical characteristics.

• Four types of hydro-geologic and geochemical characteristics determine the successfulness of intrinsic biodegradation instead of an engineered cleanup system.

- Predictability of groundwater flow.

- Sufficient amount of electron acceptors.

- Adequate capacity to buffer against pH changes that may occur with the increased microbial activity.

- The site must have a natural supply of the elemental nutrients.

Limitations.

• Involves somewhat greater risk of failure than engineered bioremediation because active measures (thorough monitoring) are not used to control plume migration.

• Pollutant producers may like this approach while regulators, environmental groups, and the public may be unwilling to accept this approach.

• Plume is mobile.

Advantages.

• Minimizes treatment costs by requiring little or no energy input.

• Eliminates the chance of remobilizing contaminants or causing additional contamination by pumping.

Intrinsic bioremediation

In Situ Bioremediation

Contaminant plume

Nutrients

E-acceptor

(Biostimulation)

Surface Soil/Cap

Unsaturated Zone

Saturated Zone

Biostimulation: addition of nutrients and electron-acceptor into groundwater in order to stimulate subsurface microorganisms (mainly bacteria) to degrade contaminants.

Bioaugmentation: addition of efficiently degrading bacteria into contaminated groundwater with nutrients/electron acceptor to enhance biodegradation of contaminant.

*Bioaugmentation

Method to add degrading bacteria

In Situ Bioremediation - Hydrocarbons

Application

•Successful method for treating soil and groundwater contaminated with certain types of hydrocarbons (mainly petroleum products and derivatives and others such as refinery wastes, crude oil, fuels, phenols, cresols, acetone and celluloisic wastes.)

•A specific microbial enhancement feasibility study and a general hydrogeologic site investigation are essential.

In Situ Bioremediation - Hydrocarbons

Limitation

•Geological heterogeneity inhibits the supply of nutrient/e-acceptor or microbes into the contaminated groundwater area.

•In the cases of slow NAPL dissolution or/and slow desorption, the availability of contaminant to biodegradative microbes is limited.

•Requirement of a minimal contaminant concentration to remain the population size and to induce the biodegradative pathway (never be complete zero concentration!)

•Oxygen limitation.

In Situ Bioremediation – Hydrocarbons (continued)

Advantage over conventional pump-and-treat approach

•Completely degrading into non-toxic end products.

•Less pumping requirement than conventional pump-and-treat.

•Faster

•Bacteria move to contaminated zone (chemotaxis)

Air Sparging

Contaminant plume

Air

Vapor Extraction

Well

Surface Soil/Cap

Unsaturated Zone

Saturated Zone

• Inject air either directly into the aquifer formation or into specially designed extraction wells.

• Then, it displaces pore water and rises through the saturated zone into the vadose zone)

• The air stream must be captured by a properly designed SVE system.

Vapor Treatment

Air Sparging

Application

• Successful laboratory- and pilot-scale evaluations for volatile and biodegradable contaminants.

•Permeability of air > 10-3 cm/s

• the size of the porous medium > 1 mm

• Henry’s law constant > 10-5 atm-m3/mole

• Water solubility < 20,000 mg/liter

• Vapor pressure < 1 mmHg

Air Sparging

Limitation

•Problematic when the depth of air sparing > 10 m.

•Diffusion limited process will slow cleanup.

•Clogging problem when ion is oxidized by provided oxygen.

•Possibly move the residual NAPLs into another locations.

Different Configuration of Air Sparging

Contaminated Zone

Surface Soil/Cap

Unsaturated Zone

Saturated Zone

Injection point for flushing gas

Extraction of contaminant gas

Better control of gas (air) flow in subsurface

Bioventing

Residual LNAPL

Air injection well with periodic

nutrient flooding Vapor Recovery

Well

Surface Soil/Cap

Unsaturated Zone

Saturated Zone

In situ Bioremediation of the unsaturated zone.

Main purpose is to provide oxygen to soil microbes.

*Bioaugmentation

Method to add degrading bacteria

Microorganisms

Vapor Recovery

Well

Bioventing

Application

• Successful method for treating petroleum hydrocarbons and some chlorinated solvents.

• Applicable in permeable soils (sand aquifers).

Limitation

• Possible limitation of nutrient.

• Change in soil moisture can affect the load-bearing capacity.

• Significant masses of contaminants in low permeability zone.

Advantage over conventional pump-and-treat approach

• A greater ease of circulating air compared to circulating water.

• Easy transport of oxygen in air than in water.

Solubility (μM)

Vap

or

Pre

ssu

re (

atm

)1

10-3

10-9

102

103

10-5

10-3

KH=102 KH=100 KH=10-2

KH=10-4

KH=10-6

(atm*m3/mole)

Diesel

JP-4 Jet Fuel

Gasoline

Vapor Pressure Too High to Biovent

Vapor Pressure Amenable to Bioventing or Volatilization

Vapor Pressure Too Low to Volatilize

10-7

In situ Bioremediation – Chlorinated Solvents

Application

•Aerobic cometabolism of chlorinated hydrocarbons. (aerobic TCE degradation by methanotrophs or aromatic degraders)

•In 1998, a successful case of in-situ aerobic TCE bioremediation by stimulating the cometabolism of TCE by toluene oxidizing bacteria in groundwater.

• Anaerobic dechlorination (Chlorinated hydrocarbons are electron acceptors)

Limitation

•Toxic intermediates

•Limitation of food (primary substrate) into the contaminated zone

•Limitation of biodegradative microorganisms

•Threshold concentration for biodegradation

In situ Bioremediation - Metals

Application

•Manipulating bacteria to either dissolve the metals (cleanup) or immobilize the metals (containment).

•Potential mechanisms in anaerobic microorganisms: (1) enzyme reduction of metal, (2) biochemical alteration of red-ox conditions, (3) biogenic chelate, (4) metal sequestration, (5) metal bioaccumulation.

•Dissolution of metals (Fe2O3, MnO2, CdO, CuO, PbO and ZnO)

•Immobilization of uranium (VI => IV)

Limitation

•Similar to those for In Situ Bioremediation-Chlorinated solvents.

•Needs to control the mobilized metals through groundwater.

•Uncertainties in immobilized metals.

Bio-degradabilities under different respiration conditions

Type of bacteria

benzene toluene naphthalene Dichloro-benzene

TCE Methyl-phenols

Penta-chloro-phenol

•Aerobic•De-nitrifying•Iron-reducing•Sulfate-reducing•Methano-genic

++

+

-

+

+

++

++

++

++

++

++

+

-

-

-

++

-

-

-

-

+

+

-

+

+

++

++

++

++

++

+

-

-

-

+

Treat the contaminant plume as it passes through permeable reactive zones or walls within the aquifer.

In situ Reactive Barriers

Contamination in saturated zone

ImpermeableBarrier wall

Permeable Reaction Wall

GW Flow

In situ Reactive Barriers

Application

1) A trench with reactive materials (shallow depth)

2) Slurry well (deeper and larger)

3) Modules to enable periodic replacement.

Reactive materials.

1) Activated carbons or biological activated carbons.

2) Redox controls (zero iron).

3) Microbial filters.

In situ Reactive Barriers

Limitations

1) Has not been demonstrated in field scale.

2) Difficulties in installing the reactive materials.

3) Difficulties in providing suitable amounts of these reactive materials.

Advantages

1) Like in situ bioremediation, it lowers costs of pumping once installed.

2) Safer and more reliable than intrinsic bioremediation.

3) Small and defined zone of reactions: easy to design, monitor and control.

• Isolating contaminant.

• Physical isolation with low-permeability barriers such as caps, liners, and cutoff walls.

• Solidifying it in place with either chemical fixatives or extreme heating (a process known as vitrification).

Containment Technologies

Application

• Barriers: lower permeability than the aquifer (compacted clay, synthetic plastics, soil and bentonite mixtures, cement and bentonite mixtures, and sheet piling).

• Solidification in place

-Mixing with cementing agents (lime-flyash pozzolan, and asphalt)

-Heating (1600-2000 oC) it into a molten mass that solidifies upon cooling, a process known as in situ vitrification.

Containment Technologies

Limitations

• The long-term performance of physical barriers is uncertain.

• Construction difficulties are common.

• The long-term stability and leaching characteristics of contaminated materials that have been solidified or vitrified are unknown.

• Vitrification may cause volatilization, mobilization, and migration of contaminants.

Containment Technologies

Soil Flushing

NAPL residualIn Saturated Zone

Surfactants

Surface Soil/Cap

Unsaturated Zone

Saturated Zone

•Enhances contaminant recovery in conventional pump-and-treat systems by injecting chemical agents that mobilize the contaminant residuals in saturated zone.

NAPLs and Recovered

Groundwater to Treatment

Separator

Soil FlushingApplication

• Chemical agents to improve dissolution of NAPL into groudwater and/or to reduce the viscosity of water.

• Co-solvents:

- when mixed with water, they enhance the solubility of some organic compounds (e.g. alcohols).

- also function as either stimulators or repressors for biodegrading microbes in groundwater.

- at least 20% of co-solvent is needed to cause efficient mobilization.

Soil Flushing

Application (continued)

• Surfactants:

- one end with a hydrophilic portion; the other end with a hydrophobic portion.

-Micelle formation.

- reducing the interfacial tension bet. NAPLs and water.=> Enhancement of dissolution of contaminant from NAPLs.

- also enhance recovery of sorbed contaminants.

- feasible to remove PAHs, PCBs, PCE/TCE, petroleum hydrocarbons etc.

- can function as biodegradation stimulator or inhibitor.

Soil Flushing

Micelle Formation and Enhanced Dissolution of NAPL by Surfactant

HydrophobicContaminant(solute)

Hydrophobictail of a surfactant monomer (anionic-, cationic-, non-ionic)

Hydrophobictail of a surfactant monomer

NAPL Phase

Surfactant monomers

Soil Flushing

Limitations

• Geological conditions can limit the performance of soil flushing systems.

• Complicating the prediction of transport behavior.

- Use of large amount of cosolvent =>changes in density, viscosity and compressibility.

- Possible to enlarge the zone of contamination by enhancing the mobilization of NAPLs.

- Uncertain ecological risk due to remaining surfactants.

Land Farming

When do we need bioremediation?Role of Bio-remediation in GW Clean-up

River

Bioremediation

Bioremedation is useful when a plume (dissolved pollution at low concentration) is widely spread

Evaluating Bioremediation

Difficulties in evaluation

• Definition of success varies among the several parties involved.

• No one measure is universally applicable (site specific issues, limitation in standardization of methods, etc.)

• Complexity and heterogeneity in contamination as well as biogeohydrological conditions.

NRC’s recommonded evaluation strategy (also see Table 15.11)

1. Documented loss of contaminants from the site

2. Lab assays showing the presence of microorganisms potential for in situ biodegradation

3. One or more pieces of evidence showing that the biodegradation potential is actually realized in the field (p.724-725)

Bioremedation is not everything!

Treatment TrainsLife Cycle Assessment

(cost, CO2, benefits, impact etc.)