Soil contam. and remediation

Transcription

1 Soil contam. and remediation Overview of technologies, Multiphase flow Remediation - Methods of decontamination I. Pump-and-treat, Air Sparging, Solvent Vapor Extraction, Soil Flushing

2 Technologies according to capability to decrease the risk Degradation decay of toxical compound spontaneous, enhanced (UV light) Chemical transformation oxidation, reduction, synthesis Sterilization impact on organisms Dilution most common simple technology (mixing with sand, peat, soil) Fixation decreasing migration ability Izolation preventing migration

3 Technologies according to the processes involved Physical dilution, homogenization, destilation, gravity separation,flotation, solidification, stabilization, sedimentation, filtration, magnetic separation, extraction (by water, steam, air, plants, microbes), microfiltration, termic processes (heat agglomeration, vitrification), venting, stripping Physical-chemical adsorption, dialysis (sorption), chem-sorption, ion exchange, reverse osmosis, solidification, electrochemical processes, termic processes desorption Chemical neutralization, dissolution, precipitation, oxidation (drying, ozonization, burning, aeration, UV light), reduction, coagulation, photosynthesis, dehalogenization Biological aerobic + anaerobic processes, degradation in flow, phytoextraction, bioreactors

4 Technologies according to the mechamism of toxins elimination Mechanical excavation, granulation Degradation decay stimulation, burning Extraction release, pumping, extraction by mining Fixation preventing dissolution, difussion or filtration Izolation passive vertical sealing trenches, injection screens passive horizontal foils, concrete panels, asphalt clay,.. active hydraulic barriers

5 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 area Elimination 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

6 Technologies In Situ Air Sparging Bioremediation Bioslurping Circulation wells Solvents/surfactants Dual phase extraction Dynamical subsurface stripping In situ oxidation (Fenton reagent, KMnO 4 -Potassium permanganate ) Natural attenuation of nonchlorinated compounds Reactive barriers Pump and Treat Phytoremediation Steam flushing Vertical barriers

7 Multiphase flow NAPL (Non Aqueous Phase Liquids) different physical and chemical propertion on the phase interface preventing mixing simultaneous movement of woater and NALPs D-NAPL L-NAPL

8 Multiphase flow L-NAPL (Light Non Aqueous Phase Liquid) easier extraction from the water table D-NAPL (Dense Aqueous Phase Liquid) difficult extraction from the bedrock/or low permeable material (e.g. clay lens) USGS

9 NAPLs examples Metyl-T-Butyl-Eter (MTBE) Benzene, Toluene, Ethylbenzene a Xylene (BTEX) Perchloroethylene (PCE), Trichloroethylene (TCE), Dichloroethylene (DCE), Vinylchloride (VC), ethene Volatile Organic Compounds (VOCs)

10 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

11 Criteria of difficulty to remediate site with NAPL contamination Hydrogeological conditions Mobile and dissolved (decay / volatile) Mobile dissolved Strongly sorbed or dissolved (decay / volatile) Strongly sorbed or dissolved LNAPL phase DNAPL phase one homogeneous layer multiple homogeneous layers one heterogeneous layer multiple heterogeneous layers fractured bedrock easy = 1 / difficult = 4

12 Remediation methods I. Pump-and-treat Basic active method in-situ for clean-up of soil and rock environment Retention of contaminated groundwater 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

13 Principles of groundwater flow Groundwater hydraulics - Darcy s law Q= K i A K = hydraulic conductivity i = hydraulic gradient A = area perpendicular to flow

14 Principles of pumping (capture zone) shape and extent of the influence y x = ± tan 2πTiy Q shape and extent of the area influenced by pumping in the general groundwater flow relates to: - aquifer transmisivity T (m 2 /s) - hydraulic gradient i (-) - pumping intensity Q (m 3 /s) with of the zone w = Q Ti y x stagnation point x = Q 2πTi well

15 Principles of pumping couples of infiltration and extraction wells R - exctraction well P infiltration well set of infiltration and extraction wells, or their combination can create dynamic protection of the groundwater and direct flow of contamination (e.g. invert the flow) flow induced by wells

16 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

17 Clean-up of pumped water common contamination oil products and other volatile hydrocarbons, mineral oils and dissolved metals Air stripping - column with gravitational flow of water - air water contact Chemical oxidation Thermal oxidation granular active carbon (GAC) sorption on the filter grains Gravitational oil separation Metal precipitation

18 Air stripping intensive vertical aeration blowing through the column of gravity falling water by upward induced air flow Cleanup of volatiles in water (VOC), BTEX - light parts of oil product (MTBE) - aromatic and chlorinated hydrocarbons (PCE, TCE, DCE, VC) - radon, dissolved gases nearly 100% efficient most frequent method for elimination of chlorinated hydrocarbons Fetter, C. W. Contaminant Hydrogeology, Second Edition. Upper Saddle River, NJ:Prentice Hall, 1999.

19 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,

20 Wet sorption on activated carbon Contaminant transferred into the gas phase is often being trapped on the activated carbon or biofilter Activated carbon is universal in secondary air and water cleanup AC is prepared from peat/wood dehydrating in mixture with P 2 O 5 and heating to C Pores available for both small and large molecules adsorption Lage and small molecules Organic carbon matrix Pores for small molecules adsorption only In remediation technologies used for sorption of oil products aromatic, chlorinated, polycyclic aromatic hydrocarbons Activated carbon can be regenerated and used multiple times

21 Chemical oxidation strong oxidation reagents used as catalysts of compound decay in gas and water phase ozone, hydrogen peroxide or UV Destruction of compounds (on-site) Reaching levels under detection Secondary wastes and gases are not produced Quiet and compact, subtile devices, low operational costs Chemical oxidation is used to intensify in situ methods - pump-and-treat/soil flushing. As catalyst KMnO 4, H 2 O 2 or Fenton reagent (H 2 O 2 +Fe 2+ )

22 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

23 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

24 Air sparging in-situ air stripping, in-situ volatilisation, (bioventing) air (often oxygen) is blowed under pressure directly into saturated 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

25 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 and venting borehole under sealed + under suction decontamination LNAPL : air sparging/sve

26 Air sparging Prevention of contaminant spreading Air sparging is more efficient than pump-and-treat but... Saturated aquifer must be relatively thick to make the method efficient Available for decontamination both in saturated and vadose zones in contrary to SVE (soil vapor extraction - vadose zone only) Decontamination of dissolved volatile compounds

27 Air sparging air flow scenarios method is not effective in the environment with preferential pathways

28 Air sparging well network design liquid phase has to be extracted prior to installation typical clean-up lasts ½ - 4 years basic setup optimization

29 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 horizontal air sparging/sve Remediation efficiency suitable environment % of extracted compound sparging a volatilization bioremediation 0 oil products mineral oil diesel mazut tar fluid density

30 Stripping in recirculation wells In-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

31 Stripping in recirculation wells In-Well Air stripping/groundwater Circulating Wells recirculation well has two screens: at the bottom and at the water table 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

32 Stripping in recirculation wells In-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

33 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 and less volatile compounds

34 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

35 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 seasonal fluctuation 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

36 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

37 Steam flushing steam 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 extraction well steam+o2 zone of influence extraction by well contaminated groundwater zone of thermal degradation

38 Multiple phase extraction dual phase extraction / slurping 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 air filter vacuum pump water filter oil product evacuation air seal air air water filter water oil product

39 Soil flushing in-situ flushing, soil washing, injection/recirculation Enhances compound mobility by their dissolution an consequet extraction 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

40 Soil flushing in-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 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 leaching and consecutive remediation (next 30 years) Stráž p. Ralskem, CR, state enterprise Diamo

41 References MIT Open courseware Civil and Environmental Engineering» Waste Containment and Remediation Technology, Spring Nyer, E.K. et al: 2001 In Situ Treatment Technology. 2nd edition. Lewis publishers. Keller, A.A. ESM 223 Soil and Groundwater Quality Management