contaminated land full-scale remediation technologies physical chemical thermal

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 TechnologiesOverview 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 TechnologiesEx 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 TechnologiesEx 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 TechnologiesIn 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)


• 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


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


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 TechnologiesIn 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 TechnologiesIn 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 SituSoil Washing (with chemicals)

Chemical ReactorsIn Situ

Soil FlushingFunnel and Gate


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


Ex Situ Soil Washing

• A Development of the Physical “Soil Washing” process– acids– Alkalis– chelating agents (EDTA)– surfactants

• Benefits– All solid fractions treated– contaminant moved into wash-waters– water treatment possible

• Drawbacks– soil structure– residual extractant in soil

extractant class


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 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



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)


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


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

• 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)


Funnel and Gate(Permeable Reacive Barrier, PRB )

Thermal Remediation Technologies

• Overview and Principles

• Thermal Technologies• Examples

Ex SituThermal Desorption

Incineration(Vitrification)


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 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


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)


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

contaminated land full-scale remediation technologies physical chemical thermal

Documents

principles soil

example ex situ soil

soil particles advection

asbestos slide

electrode slide

disposal offsite slide

contaminated fractions

ultrasonic treatment