Soil contam. and remediationOverview of technologies, Multiphase flow

Remediation - Methods of decontamination I.

Pump-and-treat, Air Sparging, Solvent VaporExtraction, Soil Flushing

Technologies according to capability to decrease the risk

• Degradationdecay of toxical compound – spontaneous, enhanced (UV light)

• Chemical transformationoxidation, reduction, synthesis

• Sterilizationimpact on organisms

• Dilutionmost common simple technology (mixing with sand, peat, soil)

• Fixationdecreasing migration ability

• Izolationpreventing migration

Technologies according to the processes involved

• Physicaldilution, homogenization, destilation, gravity separation,flotation, solidification, stabilization, sedimentation, filtration, magneticseparation, extraction (by water, steam, air, plants, microbes), microfiltration, termic processes (heat agglomeration, vitrification), venting, stripping

• Physical-chemicaladsorption, dialysis (sorption), chem-sorption, ion exchange, reverse osmosis, solidification, electrochemical processes, termic processesdesorption

• Chemicalneutralization, dissolution, precipitation, oxidation (drying, ozonization, burning, aeration, UV light), reduction, coagulation, photosynthesis, dehalogenization

• Biologicalaerobic + anaerobic processes, degradation in flow, phytoextraction, bioreactors

Technologies according to the mechamism of toxins elimination

• Mechanicalexcavation, granulation

• Degradationdecay stimulation, burning

• Extractionrelease, pumping, extraction by mining

• Fixationpreventing dissolution, difussion or filtration

• Izolationpassive vertical – sealing trenches, injection screenspassive horizontal – foils, concrete panels, asphalt clay,..active – hydraulic barriers

Technologies according to site• Methods "ex situ“

extraction of primary (e.g. subsurface fuel tank) and secondary (contaminated soil) sources to eliminate the origin of contamination of the areaElimination is selective – extraction by excavation of soil and its decontamination in on site or transporting of the material into certifice decontaminating site - off site

• Methods "in situ"technological process is applied by non-destructive means into soil or rock environment incl. ground and soil water and air

Technologies In Situ• Air Sparging• Bioremediation• Bioslurping• Circulation wells• Solvents/surfactants• Dual phase extraction• Dynamical subsurface

stripping• In situ oxidation (Fenton

reagent, KMnO4-Potassiumpermanganate )

• Natural attenuation of non-chlorinated compounds

• Reactive barriers• Pump and Treat• Phytoremediation• Steam flushing • Vertical barriers

•NAPL (Non Aqueous Phase Liquids) – different physical and chemical propertion on the phase interface preventing mixing

•simultaneous movement of woaterand NALPs

Multiphase flow

D-N

APL

L

-NA

PL

•L-NAPL (Light Non Aqueous Phase Liquid) – easier extraction from the water table

•D-NAPL (DenseAqueous Phase Liquid) – difficult extraction from the bedrock/or low permeable material (e.g. clay lens)

Multiphase flow

USGS

Metyl-T-Butyl-Eter (MTBE)Benzene, Toluene, Ethylbenzene a Xylene (BTEX)Perchloroethylene (PCE), Trichloroethylene (TCE),

Dichloroethylene (DCE), Vinylchloride (VC), ethene

Volatile Organic Compounds (VOCs)

NAPLs examples

Sites with NAPL presence• Chlorinated solvents and degreasers

TCE : most common DNAPL – wood, metal industry

• Industrial production of gas - tars• Oil refineries LNAPL (MTBE)• Military areas LNAPL/DNAPL

Criteria of difficulty to remediate site with NAPL contamination

443333fractured bedrock

433322multiple heterogeneous layers

433322one heterogeneous layer

32-32-321-21multiple homogeneous layers

32-32-321-21one homogeneous layer

DNAPL phase

LNAPL phase

Stronglysorbed or dissolved

Stronglysorbed or dissolved(decay / volatile)

Mobile dissolved

Mobile and dissolved(decay / volatile)

Hydrogeological conditions

easy = 1 / difficult = 4

Remediation methods I.Pump-and-treat

• Basic active method in-situ for clean-up of soil and rock environment

• Retention of contaminatedgroundwater

• Prevention of contamination propagation of contaminant into clean areas

• Extraction of contamination from the subsurface envrinment and consecutive clean-up of water

• Decrease of contaminant concentration in the groundwater

Principles of groundwater flow• Groundwater hydraulics - Darcy’s law

Q= K i A K = hydraulic conductivityi = hydraulic gradientA = area perpendicular to flow

Principles of pumping

(capture zone)shape and extent of the area influenced by pumping in the general groundwater flow relates to:- aquifer transmisivity T (m2/s)- hydraulic gradient i (-)- pumping intensity Q (m3/s)

xy

⎟⎟⎠

⎞⎜⎜⎝

⎛±=

QTiy

xy π2tan

shape and extent of the influence

stagnation pointwith of the zone

TiQxπ2

=TiQw =

well

Principles of pumpingcouples of infiltration and extraction wells

set of infiltration and extraction wells, or their combination can createdynamic protection of thegroundwater and direct flow ofcontamination (e.g. invert the flow)

R - exctraction wellP – infiltration well

flow inducedby wells

Optimalization of pumping to reach goals

mathematical models – can help increase effectivity of pumping, evaluation of scenarios of i/e wells combination and rate of decontamination respecting properties of the environment

effectivity of the borehole depends on well designet and situated screen and proper sand/gravel filter (appropriate grain sizes), hydraulic “complete” well at the bedrock, pumping test

disadvantage is in relatively low effectivity, i.e. long time to remediation is accomplished – economical and practical aspects discrepancy

Clean-up of pumped watercommon contamination – oil productsand other volatile hydrocarbons, mineral oils and dissolved metals

• Air stripping - column withgravitational flow of water - air watercontact

• Chemical oxidation• Thermal oxidation• granular active carbon

(GAC) – sorption on the filter grains• Gravitational oil separation• Metal precipitation

Air stripping –intensive vertical aeration

Fetter, C. W. Contaminant Hydrogeology, Second Edition. Upper Saddle River, NJ:Prentice Hall, 1999.

• Cleanup of volatiles in water(VOC), BTEX- light parts of oil product (MTBE)- aromatic and chlorinatedhydrocarbons (PCE, TCE, DCE, VC)- radon, dissolved gases

• nearly 100% efficient

• most frequent method for elimination of chlorinated hydrocarbons

“blowing” through the column of gravity falling water by upward induced air flow

Air stripping - intensive aeration (horizontal)• Horizontal aerator in block shaped container, water is “bubbled”

through• Lower height than column, easy maintenance / clean-up• Higher energy consumptions, higher noise

Gravitational oil separation• employs different specific density of fluids• Separtion of oil contaminant o the surface (L-

NAPL) or bottom (D-NAPL) - (separated from water)

• Sepatated contaminant is pumped out and given over to environmental destruction

• Soption secondary clean-up unit is often placed after the separation unit – fillings: fabrics - cloth, hydrophobic materials,

Contaminant transferred into the gas phase is often being trapped on the activated carbon or biofilter

Activated carbon is universalin secondary air and watercleanup

AC is prepared from peat/wooddehydrating in mixture withP2O5 and heating to500-800°C

In remediation technologies usedfor sorption of oil productsaromatic, chlorinated,polycyclic aromatic hydrocarbons

Activated carbon can be regenerated and used multiple times

Wet sorption on activated carbon

Lage and small molecules

Organic carbon matrix

Pores for small moleculesadsorption only

Pores available for bothsmall and largemoleculesadsorption

Chemical oxidation• strong oxidation reagents

used as catalysts ofcompound decay in gasand water phase

• ozone, hydrogenperoxide or UV

• Destruction ofcompounds (on-site)

• Reaching levels underdetection

• Secondary wastes andgases are not produced

• Quiet and compact, subtile devices, lowoperational costs

Chemical oxidation is used to intensify in situ methods -pump-and-treat/soil flushing. As catalyst KMnO4, H2O2 orFenton reagent (H2O2+Fe2+)

Thermal oxidation - destruction• volatiles may be incinerate or pyrolyzed• suitable PAH a chlorinated hydrocarbons, if complete

decomposition is reached• Oxidation of chlorinated compound may produce highly

toxic daughter products temporarily • is effective for highly concentrated vapors• in low concentration,

operation (fuel) is dominating cost - expensive

• Complex flow control –expensive electronics

• may reach (>99.9%)destruction

Steam stripping• Suitable for volatile compounds with low Henry constant, due

to their solubility (MTBE and alcohols)• Works as distillation, separation in the process of

condensation• Source of energy – heat is fundamental

Hollow fiber membranes• transfers oganics via hydrophobic membrane onto gas phase

without presence of water• requires very small amounts

of air to reach efficiency of air stripping

• less of contaminated air• lower operational costs

Air spargingin-situ air stripping, in-situ volatilisation, (bioventing)

• air (often oxygen) is blowed under pressure directly intosaturated aquifer in soil or rock environment

• Aeration cause transfer of volatile compounds in water and on soil particles into the gas

• Contaminants easily desorb in gas phase than in liquid phase

Air sparging• volatiles move upwards and are trapped in transition into

the vadose zone, commonly extracted by vapour in soil vapor extraction – sve

• gas phase is evacuated by teh system of combined andventing borehole under sealed + under suction

decontamination LNAPL : air sparging/sve

Air sparging

Decontamination of dissolvedvolatile compounds

Prevention of contaminant spreading

• Air sparging ismore efficient thanpump-and-treatbut...

• Saturated aquifermust be relativelythick to make themethod efficient

• Available fordecontaminationboth in saturatedand vadose zonesin contrary to SVE (soil vapor extraction - vadose zone only)

Air sparging – air flow scenarios

method is not effective in the environment with preferential pathways

Air sparging – well network design

basic setup

liquid phase has to be extracted prior to installation typical clean-up lasts ½ - 4 years

optimization

Air sparging – effectivity• Method si most suitable for volatile

organic contaminants in homogeneous environment with medium to high permeability

• Enhances biodegradation by additional oxygen – biosparging: degradation under injection of oxigen is main decontamination process rather than volatilization

suitable environment

horizontal air sparging/sve

Remediation efficiency

0

10

20

30

40

50

60

70

80

90

100

oil products mineral oil diesel mazut tar

fluid density

% o

f ext

ract

ed c

ompo

und

bioremediation

sparginga volatilization

Stripping in recirculation wellsIn-Well Air stripping/Groundwater Circulating Wells

• based on injection of pressurized air at the well bottom• well behaves as small stripping column/tower, where

contaminants are volatilized• well as whole is kept under negative pressure, vapours are

evacuated• In-well air stripping is combined with circulation to enlarge

the area of influence:– air causes the clean-up - volatilization– suction causes the groundwater swell and thus

circulation around the well

• recirculation well has two screens: at the bottom and at the watertable to cause hydraulic gradient

• causes 3D flow: pumping and infiltration of water• shapes of flow are highly dependent on the well desigh in the

environment of installation

Stripping in recirculation wellsIn-Well Air stripping/Groundwater Circulating Wells

Advantages/limitations relative to air sparging• extraction of volatiles without pumping of the

groundwater and its clean up at the surface• permission for pumping is not necessary, saves energy

esp. in deep aquifers• applicable in “sensitive geological conditions”, effective

on fraction of sites due to improper ratio of horizontal and vertical hydraulic conductivity (good in Kh/Kv~ 3-10)– low permeable soils – resistance to circulation– very permeable – shortcuts– layering – prevents recirculation in general

Stripping in recirculation wellsIn-Well Air stripping/Groundwater Circulating Wells

Soil vapor extraction (SVE)vacuum extraction, soil venting

• complementary to air sparging• caused by vacuum – in the vicinity of the contamination source,

volatilization occurs with consequent evacuation and cleanup• suitable for volatile products prone to evaporation• evacuation is functional above the groundwater table only• method is not efficient in elevated water table near the surface• sometimes groundwater pumping

is necessary• is suitable for urban areas,

with penetration of toxic fumes into buildings proudění vzduchu podporuje biodegradaci,

• ventilation promotes biodegradation, mostly for heavier andless volatile compounds

Soil vapor extraction (SVE)

• Soil structure and stratification are important for efficiency, impact on flow of vapors,layering may cause preferential flow and lowered efficiency – longer time of remediation

• High soil moisture and fine grain size (strong capillary forces) also decrease the air flow

• Area of influence is basic parameter for the system design, radius is defined as the farthest point to the well to promote ventilation and evacuation,

• Perimeters should overlap to cover the whole area

Soil vapor extraction (SVE)• Soil permeability influences air and

vapor rate of movement, soils with higher permeability are more suitable for SVE

• Design must take daily or seasonalfluctuation of the groundwater, urgent for horizontally installed systems

• Soil surface might be covered with insulating foils to prevent infiltration or additional air inflow from the atmosphere (shortcut)

• Pilot projects, are necessary for the final design, after assessing the site and contaminant remediation efficiency

• Installation involves drilling of suction wells in the system with air pump

Soil vapor extraction (SVE)

• Number of wells is dependent on the area of contamination, soil density and time required for decontamination

• Passive system option –enhanced soil air exchange

• Low operation costs, basic cleanup of filters, pumps and wells

• Evacuated products are sorbed, incinerated or catalytically oxidized, condensed, biodegraded

• Clean air might be pumped back into the subsurface

Steam flushingsteam stripping, hydrous pyrolysis/oxidation

• Hot air is injected into soil to enhance volatility of compounds• Very expensive, cost effection only for several weeks or months,

similar to air sparging and sve

zone of influenceextraction by well

contaminatedgroundwater

zone of thermaldegradation

extraction wellsteam+O2

Multiple phase extractiondual phase extraction / slurping

air filterwater filter

vacuum pump oil product

airair

evacuationairseal water

oil productwaterfilter

• Stripping of drops of oil phase from the groundwater table under very high suction

• Negative depression is caused in the aquifer, elevated water table, thicker layer of LNAPL

• method is technically simple and is much more efficient than pump-and-treat

• Enhances compound mobility by their dissolution an consequetextraction

• Method is based on the injection, spraying, ponding or infiltration of solution into the contaminated soil (both under and above the groundwater)

• Consequently water is pumped down the gradient, cleaned and reused

• Applied solution mai contain surfactants (decrease surface tension), solvents-alcohols, acids or bases

Soil flushingin-situ flushing, soil washing, injection/recirculation

• Technical point: infiltration wells or galleries, drainages ditches, pumping wells• Good knowledge of local hydrogeology is essential• Suitable for soils with medium to high permeability• Applicable for NAPLs as well as inorganic compounds – metals.

Limitations• Flushing may leave the site with traces of solvent-surfactant• Flushing may appear out of the bounds of planned treatment• Solvents must be pumped and recycled• Wastes must be properly destroyed or deposited• Surfactants may decrease porosity

Soil flushingin-situ flushing, soil washing, injection/recirculation

Applicability• Radioactive compounds, metals,

volatiles, fuels, pesticides can be extracted by this method

• Too expensive for organic compounds

Uranium ore chemical mining by sulfuric acid leachingand consecutive remediation (next 30 years)

Stráž p. Ralskem, CR, state enterprise Diamo

• MIT Open courseware Civil and Environmental Engineering »Waste Containment 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. Lewis publishers.

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

• http://www.hgcinc.com/watersupp.htm• http://www.srs.gov/general/enviro/erd/technology/Pages/g05p.html• www.g-servis.cz• www.diamo.cz• http://www.fliteway.com/pages/pumpandtreat.html• http://www.gwrtac.org/html/tech_topic.htm

References