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Soil contam. and remediationOverview of technologies, Multiphase flow
Remediation - Methods of decontamination I.
Pump-and-treat, Air Sparging, Solvent VaporExtraction, Soil Flushing
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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
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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
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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
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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
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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
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•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
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•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
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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
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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
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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
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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
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Principles of groundwater flow• Groundwater hydraulics - Darcy’s law
Q= K i A K = hydraulic conductivityi = hydraulic gradientA = area perpendicular to flow
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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
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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
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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
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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
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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
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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,
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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
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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+)
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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
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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
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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
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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
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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)
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Air sparging – air flow scenarios
method is not effective in the environment with preferential pathways
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Air sparging – well network design
basic setup
liquid phase has to be extracted prior to installation typical clean-up lasts ½ - 4 years
optimization
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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
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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
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• 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
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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
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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
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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
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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
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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
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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
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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
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• 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
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• 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
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• 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