Soil contam. and remediationMethods of decontamination II.

Monitored Natural Attenuation, Fracturing, Lasagnaprocess, Electrokinesis, Phytoextraction

MNA - Monitored Natural Attenuation• attenuation = to diminsh, to decrease• as fire eats the candle, subsurface consumes the contamination• definition by EPA: relying on natural processes in reaching goals

of remediation for the given site• it does not mean – to do nothing, leaving alone• MNA is not basic obvious primary method of decontamination• As standalone method must be used with the highest caution• must be evaluated together with other alternatives and chosen

only if set goals (limits) can be reached in reasonable time (up to 30 years)

• might be physical, chemical or biological• processes of attenuation for oil products: biodegradation,

dispersion, dilution, chemical reactions, volatilization, sorption, destruction

components of MNA• required components of MNA:

– control – removal of contamination source– monitoring of contamination spreading

• required conditions of MNA:– data characteristics for the site– risk assesment

demonstration of MNA efficiencyhistorical chemical data show clear decreasing trend of the

compound volume or concentrationhydrogeological or geochemical data demonstrate indirectly

processes of MNAfield study of microcosmos, demonstration MNA processes

natural processes in oil product decay

aerobic biodegradationoxygen is electron acceptor2C6H6 + 15O2 → 12CO2 + 6H2Oindicators of aerobic biodegradation

decrease of dissolved oxygen(3 mg of dissolved oxygen are necessary to metabolize 1 mg of benzene)

decrease of hydrocarbons concentration

order of BTEX aerobic biodegradationethylbenzene, toluene, benzene, xylene

denitrificationnitrate is electron acceptor6NO3

– + 6H+ + C6H6 → 6CO2↑ + 6H2O + 3N2 ↑in reality this process is split into several steps, influenced by various bacteria NO3

– → NO2– → NO → N2O → NH4

+ → N2

indicators of biodegradation by denitrificationdecrease of nitrate contentdecrease of hydrocarbon contentpresence of denitrification bacteriareduction conditions (dissolved oxygen < 1 mg/L)

iron reduction

insoluble trivalent iron is electron acceptoris reduced onto divalent60H+ + 30Fe(OH)3 + C6H6 → 6CO2 + 30Fe2+ + 78H2O

indicators of biodegradation by iron reductionincrease of dissolved irondecrease of hydrocarbon concentrationnone or very low concentrations of dissolved oxygen

reduction of sulphatessulphate is electron acceptor30H+ + 15SO4

2- + 4C6H6 → 24CO2 + 15H2S + 12H2O

methanogenesis(methane fermentation)

is not redox but fermentation reactiontakes place in highly anaerobic conditions4C6H6 + 18H2O → 9CO2 + 15CH4

indicatiors of methanogenesisincrease of methane and carbon dioxide concentrationdecrease of hydrocarbon concentrationnone to very little of dissolved oxygenpresence of methanogenetic bacteria

neutralization of carbon dioxideall degradation processes produce CO2CO2 + H2O → H2CO3H2CO3 + CaCO3 → Ca2+ + 2HCO3-

neutralization of CO2 increases alcalinity of the environment

order of MNA processes

analytical protocol of MNAgroundwater

total amount of hydrocarbons – confirm decreasearomatic hydrocarbons – confirm BTEX decreaseoxygen – confirm consumption, redox environmentnitrates – confirm consumptiondivalent iron – confirm productionsulphates – confirm consumptionmethane – confirm productionalkality – confirm production of CO2 and its neutralizationredox environment – prove geochemical conditions – pH, temperature, electrical conductivityprove one layer system of groundwater

biological conditionsprove presence of aerobic bacteriavolatile fatty acids – semiproduct of biodegradation of complex organic compoundsstudy of microcosmos – prove functioning of biodegradation

relative fraction of processes on BTEX biodegradation

source: http://www.afcee.brooks.af.mil/er/ert/download/natattenfuels.pptaverage of 42 sites, MNA practical time limits: 9 days – 9 years, 1 year in average

H2 concentration impact (ng/L) on various processes

denitrification < 0.1, iron reduction 0.2 - 0.8,

sulphate reduction 1 – 4, dechlorination (chlorinated hydrocarbons) > 1, methanogenesis 5 - 20

sulphate reduction

74%

aerobic oxidation3%

nitrate reduction3%trivalent iron

reduction4%

methanogenesis16%

BioscreenModels of MNA processes estimation

Bioscreen - application

time

dist

ance

Anaerobic PCE and TCE degradation

CCl2=CCl2 → CHCl=CCl2 → CHCl=CHCl →CH2=CHCl → CH2CH2 → CH3CH3PCE → TCE → cis-1,2-DCE →vinylchloride → ethene → ethane

redox conditions:reduction of sulphates PCE → DCE, TCE → DCEmethanogenesis PCE → eten, TCE → eten

byproducts of degradation: CO2, ethane, ethene,chloride

Transformation of chlorinated ethenes

TCE

DCE

VC

eten

“Dechlorination” takes please when atoms of chlorine are substituted by atoms of hydrogen. In such case harmless ethene is the final product.

Cl

H

C

Case study– Plattsburgh Air Force Base, New York

Wiedermeier et al, 1999 & MIT Opencourseware

Wiedermeier et al, 1999 & MIT Opencourseware

Case study– Plattsburgh Air Force Base, New York

Wiedermeier et al, 1999 & MIT Opencourseware

Case study– Plattsburgh Air Force Base, New York

MNA – advantages

• wastes are not produces in clean-up process• human contamination risk is lowered• almost noninvasive to the environment

(monitoring boreholes only)• effective for organic compound destruction• might be applied to part of the site only• might be applied along or as a complement to

other remediation technique• is cheaper than other methods

MNA - disadvantages

• requires longer time for reaching limits• site survey might be more expensive and more

complex (finding microbial activities, sources of nutrients)

• during degradation, semiproducts might be more toxic than original compound

• longer period of monitoring• proofs of long term productivity for the authorities• threat of contaminant migration• hydrogeological and geochemical conditions originally

suitable for MNA might change with time –mobilization of the contaminant

• difficult to explain to public that “doing-nothing” is the best solution

Fracturing

• technology known from the oil industry

• supporting technology to increase efficiency of other in-situtechnologies in difficult soil and rock conditions – clays, silts.

• extends existing fissures and fractures in width and length

• creates new fractures, predominantly in horizontal direction

Processes of fracturing

• pneumatic• hydraulic• explosive• LasagnaTM process

Proceses of fracturingpneumatic and hydraulic

fracturing• wells are in contaminated

unsaturated environment left uncased (uninstrumented)

• air or water (or solution with polymers) is repeatedly pressed into the environment in short intervals (>10 bar)

• method helps air to escape and enlarges pathways for water

Proceses of fracturingexplosive• penetration of explosive and its ignition in the well• enlarges well yield and extent by increase of

environment productivity

Fracturing - advantages

• increases efficiency of other traditional methods in the environment with low hydraulic conductivity of soils and rocks

• shortens time of remediation• overall costs of remediation are decreased• means of fracturing might be part of the

remediation process (heated zones in vitrification, nutrients in bioremediation or electrodes in electrokinesis)

Fracturing - disadvantages

• enlarges fractures contain more of the liquid, needed to be treated – extra costs

• poor control of the process may contribute to spreading of contamination

• fracturing may cause land subsidence and threaten stability of nearby constructions

Fracturing process

LasagnaTM process

LasagnaTM is integrated remediation methodcombines hydraulic fracturing, electroosmosis andclean-up zones installed into the soil environmenthydraulic fracturing is used for creation of sorption/degradation zones in the soil environment

although...

LasagnaTM process

vertical or horizontal setupelectrical field is created by two

electrodes (metal rods x graphite grains)

degradation zones contains grained iron, activated carbon

three ways of cleanup:extent of degradation zonestransport by electrokinesis into

deg.z.altering the direction of flow by

switching the electodes

vertical

horizontal

horizontal setup allows to clean very deep contamination

Electrokinesis - coloids

Core – negative charge

Difuse layer

solution

Stern layer

Coloids (acc to charge) Acidoids (adsob cations)

Bazoids (adsorb anions)

Amfolytoids (charge acc. to pH)

pH ... bazoids pH ...acidoids

Acidoid coloid

Electrokinesis - electric double layer

• surface of coloids with negative charge attracts cations – repels anions

• cations form spherical envelope around the coloid

• positive cations charge neutralizes negative charge of the coloid surface

• layers of anions and cations – electricdouble layer

Electrokinesiselectric field is applied in contaminated environment aiming the motion of:

• ions (electrolysis)• water (electroosmosis)• coloids (electrophoresis)

• high efficiency for metals, but more than 25x of pore volumes must be exhanged

• cca 1 MWh/kg soil – expensive• change of pH and movement of all

ions may not be desired

schéma pórézní kapiláry

soil

Electrokinesis - advantages

• applicable in heterogeneous soils with low hydraulic conductivity

• applicable for wide spectrum of contaminants metals – thanks to charge, no charge particles – motion caused by flow

• flexible in use in-situ + ex-situ• cheaper than other remediation technologies• tailor-made acc. to site conditions

Electrokinesis - disadvantages

• electrolytical reaction near electrodes may change soil pH anode / catode specific and may thus create complicated geochemical environment

• old buried metal object may shortcut electrical currents and lower the efficiency of the method

• acidic condition and electrolyte decay may corrode anode

• stagnation zones may appear • volatiles are released into the soil air

PhytoremediationPlant enhanced soil cleanup• phytotransformation –

contaminant uptake from soil and groundwater by plants and transformation in plant body

• bioremediation of rhizospheremultiplication of the bacterial processes

• phytostabilization – hydrauliccontrol of water uptake by trees, physical stabilization of soil by plants

• phytoextraction – use of plants capable to bind and concentrate metals in roots, stems or leaves

• rhizofiltration – plant roots help to sorb, concentrate or precipitate metals

Phytoremediationquickly grown wood or water plants are used for

sewage water treatmentadvantageslow costesthetic outlooksoil stabilization, safety, low energy consumptiondecrease of pollutant outwashlimitsonly shallow root zone (rhizosphere) is cleanedhigh concentrations might be toxic to plantsslow rate of remediationpilot studies necessary for the efficiency evaluation

Phytoremediationmechanisms:direct plant uptakesuitable for organic medium hydrophobic

compounds onlycapillary forces evacuate the contaminationcontaminant is accumulated in the plant,

metabolized (respired) or evaporated by leaves

special enzymes necessary for metabolizationof some compounds (this property is utilized in herbicide research)

Phytoremediation

degradation in root zonerhizosphere has microbial content, with addition

of “sweated out” enzymes from plants and microbes

plants also release sugar, hydrocarbons, aminoacids, supporting good microbial and fungi life

by the enzymatic way, the BTEX, hydrocarbons, PAU and chlorinated carbons is supported

Phytoremediation

Phytoextraction of heavy metalssome plants may accumulate metals in high

concentrations relative to their biomass (2-5%)some plants with hyperaccumulative ability may

transport metals into leaves and stems (100x more than other species)

mustard – nickel and lead hyperaccumulation,– 2tons/ha x 3 crops per year)

plants may be harvested and deposited in landfill

Phytoremediationplants v. treesplants may influence the contamination down to 60

cm depth onlytrees, mostly poplar may decontaminate down to 3

meters (direct uptake of TCE, enzymes for TNT-also fig trees)

poplars are popular for their quick growth, high transpiration and deep roots

uptake from soil preventing volatilization may run for several months

transport of the falling leaves has to be eliminatedtrees – decrease of wind – transportation of

contaminated dust

Phytoremediationaqueous systemswater plants may accumulate metals and other toxins

directly from wateradditional algae in the system have the ability to uptake

Cd, Zn, Ni and Cusome studies prove uptake of radionuclides, or nitrate

compounds in high concentrationartificial wetlands for

explosive cleanup (TNT)

Phytoremediationconditions / limits

planted regions must be approx 17x larger than contamination source

soil and rock conditions, groundwater table has to considered

in order to increase water uptake, surface must be covered by membrane and divert direct surface runoff

some plantation have to be irrigated for approx. 3 years to reach the high rate of growth

alternative to phytoremediation is soil incineration approx 100 euro/ton

Phytoremediationuse

municipal sewage, water from parks, rain sewagedefrost fluids (glycol – airplanes)landfill leachateagriculture sewage waterswastes from metallurgymine and industrial waters – paper productionindustrial and municipal sludgecontaminated soil and groundwater

Phytoremediationexample – Chernobyl, phytoextraction of radionuclides and

heavy metalsApril 1986 – spreading 137Cs, breaktrough through

sandy soils in the vicinity of the power plantsurfactants application– chelates for desorption of Pb –

secondary plantation of maize and peaconcentration 0.5-10g/kg per dry matterphytoextraction of radioactive Cs efficient for first 3

weeks after start of accumulation, decrease ofradioactivity by 21%

- hyperaccumulation in sunflower and artichoke

• MIT Open courseware Civil and Environmental Engineering » WasteContainment and Remediation Technology, Spring 2004 http://ocw.mit.edu/OcwWeb/Civil-and-Environmental-Engineering/1-34Spring2004/LectureNotes/index.htm

• Nyer, E.K. et al: 2001 In Situ Treatment Technology. 2nd edition. Lewispublishers.

• Keller, A.A. ESM 223 Soil and Groundwater Quality Management http://www2.bren.ucsb.edu/~keller/esm223_syllabus.htm

• Wiedermeier T., Rifal, H.S., Newell, C.J. and Wilson, J.T. Natural Attenuation of Fuels and Chlorinated Solvents in the Subsurface, Jon Wiley & Sons, Inc. 1999

web sites of• Schlumberger• US Oil & Gas• C.S. Garber & Sons

References