Transcript No Slide Title

Contaminated Land
Full-Scale Remediation Technologies
•
Physical
•
Chemical
•
Thermal
Physical Remediation Technologies
• Overview and Principles
• Physical Technologies
Ex Situ
– Soil Washing
In Situ
– Soil Vapour Extraction
– Electro-Remediation
• Examples
Physical Remediation Technologies
Overview and Principles
Soil Washing (Bergmann, Lurgi, BioTrol)
– intensive, water-based removal of non- and semi-volatile
contaminants from soil
– washed fractions replaced
– contaminated fractions to disposal or further treatment
Soil Vapour Extraction (SVE) or Venting
– extensive, vacuum extraction of vapour phase from between soil
particles; advection for sorbed organics
– extracted vapours further treated
Electrokinetic Remediation (Geokinetics BV)
– electrical current (DC) transports charged (ionic) contaminants
towards electrodes
– contaminants accumulate at electrode
Physical Remediation Technologies
Ex Situ Soil Washing
Pretreatment
– screening, crushing
Washing and Rinsing
– Slurrying, attrition scrubbing, ultrasonic treatment
– reduced to individual particle size
Particle Sizing and Classification (Fractionation)
– sedimentation, hydrocyclones, sieving and screening
(cf.sand and gravel operations)
– flotation
– flocculants, dewatering
– Clean Coarse Fractions
– Contaminated Fines - clays, humics
Wastewater Treatment
– wash water recycle
Process works better with coarser soils
Soil structure impaired
Physical Remediation Technologies
Ex Situ Soil Washing
Time
– Intensive process (days - weeks)
Costs
– £20 - 160 per m3
– silt and clay content significant determinant
(economic upper limit of 30 - 40%)
Resources
– plant and power
Application Range
– most volatile and non-volatile organics
– inorganics, heavy metals
– Not Asbestos
Example
Ex Situ Soil Washing
• Site
– Canal Sediment, Birmingham
• Contamination
– Zinc, copper, nickel, chromium
– mineral oils
• Remediation Method
– soil washing
– landfill of contaminated fines
• Performance
– 90 % contaminants concentrated into reduced volume
(30% of original sediment)
• Time
– months due to low capacity of system (10m3 /day)
• Cost
– £ 30 per m3 including disposal off-site
Soil washing
Physical Remediation Technologies
In Situ Soil Vapour Extraction
• Established Process (Terra Vac )
– also known as Soil Venting
• Extraction Wells
– slotted PVC pipe, grouted upper section
– depth 1.5m to 90m (Vadose only)
– numbers depend on soil permeability
– placement critical - short circuiting
– Soil surface preparation - compaction, membranes
• Infiltration Wells
– optional
– passive or forced flow
– Induced air flow aids bioremediation
• Groundwater Abstraction
– depression of groundwater table (greater exposure)
Physical Remediation Technologies
In Situ Soil Vapour Extraction
• Critical Factors
– Boiling point / vapour pressure
– volatility VOC only (KH > 10-2 atm.l/mole )
– Subsurface temperature
– soil permeability
– soil organic matter content
• System Monitoring
– vapour concentration (pulsed extraction)
– mass balance
– Oxygen and Carbon dioxide (biodegradation)
• Treatment of Extracted Vapours
– to atmosphere
– Combustion engine
– thermal oxidation
– GAC adsorption
Physical Remediation Technologies
In Situ Soil Vapour Extraction
Supplementary Methods
• Thermally Enhanced SVE (Steam Stripping)
– extends application to less volatile SVOC’s
– Steam or hot air injected
• Air Sparging
– Air bubbled through contaminated groundwater
– strips VOC from water
• Directional Drilling
– contaminated zone geometry
– specific positioning of well around
existing structures and obstructions
• Pneumatic or Hydraulic Fracturing
– new channels created
SVE
Physical Remediation Technologies
In Situ Soil Vapour Extraction
Time
– extensive (1 - 2 years)
Costs
– £ 5 - £ 40 per m3
– £ 15 – 70 per m3 (with thermal enhancement)
Resources
– Power
– Emission control equipment
Application Range
– VOC (some SVOC)
– only certain soil types
In Situ Soil Vapour Extraction
Example
• Site
– Service Station
• Contamination
– 5000 litres fuel beneath road and forecourt
– max depth 3m
• Remediation Method
– Soil Vapour Extraction (Venting), then bioventing
– extraction at 25 - 60 m3/h
• Performance
– TPH from 10,000 mg/kg to 260 mg/kg
– half removal by biodegradation (bioventing)
• Time
– 2 years
• Cost
– estimated £60 per m3 (includes the bioventing time)
Physical Remediation Technologies
In Situ Electrokinetic Remediation
• New Full-Scale Process
– Patent licence Geokinetics International Inc.
• Electrodes
– spacing 1 - 2m
– graphite with membrane sheath
– electrolyte recirculation and regeneration
• Principle
– electrokinetic and electro-osmotic movement
– Electrode design (recirculated electrolye)
– Anions move to anode (+ve electrode)
– Cations, metals move to Cathode
– Electrolysis of water produces H+ at anode
– Acid front sweeps through soil, extracts metals
– extensive process (in situ)
– intensive (ex situ)
Physical Remediation Technologies
In Situ Electrokinetic Remediation
• Power Requirement
• Low voltage DC 20 - 40 V/m
• current at a few Amps/m2
• 500 kWh/m3 at 1.5m electrode spacing
• Applicability
– Performs well in fine grained, saturated, low-permeability
soils ( e.g. clays)
– vertical and horizontal process
– metal removal
– enhanced degradation of organics (Lasagne process)
• Considerations
– buried metal objects, power cables
– soil CEC and alkalinity
– safety - hydrogen and chlorine gas generation
• Soil Condition
– structure and fertility retained
electrokinetics
Chemical Remediation Technologies
• Overview and Principles
• Chemical Technologies
• Examples
Ex Situ
Soil Washing (with chemicals)
Chemical Reactors
In Situ
Soil Flushing
Funnel and Gate
Chemical Remediation Technologies
Overview and Principles
• Extractive
– dissolve contaminant into extractant phase
– does not destroy contaminants
– Extractants require regeneration
– residual extractant left in soil
• Destructive
– most contaminants are unsuitable (unreactive)
– reactivity of soil interferes
– reagents may be environmentally unacceptable
• Detrimental to Soil Structure and Fertility
• Application
– few operational commercial processes in use
– numerous novel pilot demonstrations
Chemical Remediation Technologies
Ex Situ Soil Washing
• A Development of the Physical “Soil Washing” process
– acids
– Alkalis
extractant class
– chelating agents (EDTA)
– surfactants
• Benefits
– All solid fractions treated
– contaminant moved into wash-waters
– water treatment possible
• Drawbacks
– soil structure
– residual extractant in soil
Chemical Remediation Technologies
Ex Situ Chemical Reactors
Ex Situ Solvent Extraction
– batch or continuous , single stage or counter-current reactors
– extraction into liquid solvent - water/triethylamine
– SCF super-critical fluid extractants - CO2 , propane
– vegetable oil regeneration of extractant
• Drawbacks
– residual solvent contamination
– Soil structure
• Applications
– PCB’s
– Viscous, non-VOC
– Metals
Chemical Remediation Technologies
Ex Situ Chemical Reactors
Chemical Dehalogenation (Destructive)
• Soil Pretreated
• Soil Mixed with reagents
– APEG, alkaline polyethylene glycol, (KPEG)
• Heated
– 100 -180 C for 1 - 5 hours
– chlorine removed, glycol ether derivative is formed
• Neutralization
Time
– intensive but limited plant capacity - (months per site)
Application
– chlorinated contaminants, PCB, solvents, Dioxins
Cost
– High £300 - 500 per m3
Chemical Remediation Technologies
Ex Situ Chemical Reactors
Other Potential Destructive Methods
• Oxidation
– O3, H2O2 and Ferrous ion, ClO2, Wet Air Oxidation
– for PAH, TCE, PCP, phenols , Cyanide
• Hydrolysis
– reaction with water, better at high pH
– enzymes
– for Cyanide, organophosphorus pesticides,
• Reduction
– Sodium borohydride for many organics
– Iron (zero valent) powder for halogenated organics
• Polymerization
– pre-polymer contaminants (styrene, vinyl chloride)
Chemical Remediation Technologies
In Situ Soil Flushing
• In Situ version of Soil Washing
– no physical mixing
• Infiltration and recycle of extractant
– shallow soil (galleries, collection channels)
– deep soil (extraction well, Pump and Treat)
• Mild Extractants
– dilute acids, alkalis
– chelating agents
– surfactants
• External Treatment
– adsorption, flocculation, biological degradation
• Soil Neutralization
– must attenuate residual reagents
Soil flushing
Chemical Remediation Technologies
Example Soil Flushing
• Site
– Photographic Paper Factory, Holland
• Contamination
– 30,000 m3 soil with Cadmium (20 mg/kg)
– Complex site, buried structures (tanks)
• Remediation Method
– In Situ Soil Flushing (0.001M HCl)
– Ion exchange
• Performance
– Cd reduced to < 1 mg/kg
• Time
– 1 year
• Cost
– experience limited, this case £ 90 per m3
Chemical Remediation Technologies
Funnel and Gate
(Permeable Reacive Barrier, PRB )
• Barriers (Funnel)
– divert groundwater flow
– focus contaminants
• Reactive Cell (Gate)
– Chemical dehalogenation (zero valent Iron filings)
– Oxidation
• chemical (oxygen precipitation of metal oxides)
• biological (bacterial oxidation of BTEX)
– Other types of reactive cell
• Adsorption (activated carbon)
• Biofilter media (biodegradation)
Thermal Remediation Technologies
• Overview and Principles
• Thermal Technologies
• Examples
Ex Situ
Thermal Desorption
Incineration
(Vitrification)
Thermal Remediation Technologies
Overview and Principles
• Ex-situ Method
• Fixed Centralized Plant or On-site Plant
• Standard Industrial Thermal Processors
– cement kiln, asphalt dryer
• Soil Destroyed
– inert ash
Thermal Desorption
• organic contaminant moved from solid-phase to gas-phase
• relatively low temperatures 400 - 600 C
Incineration
• organic contaminant degraded (oxidised or Pyrolysed)
• very high temperatures 800 - 1200 C
Vitrification
• extremely high temperatures 1200 - 1600 C
Thermal Remediation Technologies
Thermal Desorption
• Treatment Train Process
– soil pretreatment
– desorption with Gas Emission Control
– cooling
• Kiln
– rotary, conveyor, screw
– direct or indirect heating
• Energy required 2500MJ per tonne (400 C, 20% moisture)
• 300m3 gas per tonne
• Gas Treatment
– Thermal oxidation
– Cooling
– Scrubbers (acids)
– carbon adsorption
• Cost
– scale dependent £50 - £300 per m3
– water content (75% of costs for wet soil > 20% moisture)
Thermal desorption
Thermal Remediation Technologies
Incineration
• Treatment train process but the main destruction occurs in the
kiln
• Kiln
– Direct Fired Rotary Kiln
– Fluidised Bed
– infra-red incinerator
• Flue Gas
– PIC (products of incomplete combustion)
– dust
– water
– acid
– metals
• Costs
– Off-site plant £200 - £1000 per m3 (petroleum contaminant)
– £1000 - £5000 per m3 (for PCB contaminants)
Thermal Remediation Technologies
Example Incineration
• Site
– Oil Refinery, USA
• Contamination
– 7,000 tonnes sediment
– PCB at 5 mg/kg
• Remediation Method
– Incineration
• Performance
– PCB < 0.9 mg/kg
• Time
– 2 months
• Cost
– £500 per m3