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Bioremediation (Biological Remediation Technologies)
• Overview and Principles
• Bioremediation Technologies
Ex Situ
Biopiles
Landfarming
Bioslurry Reactors
In Situ
Pump and Treat
Bioventing
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BIOREMEDIATION - Overview and Principles
• Aim of Bioremediation?– use biological systems to destroy / modify the chemical components of
contaminated soil
• Destructive process– organics– inorganics
• Contaminants as substrates for microorganisms– Complexity and recalcitrance– concentration and toxicity– Accessibility– natural or anthropogenic
• Microbes – Indigenous (habituated, acclimated)– Specific Inocula
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Overview and Principles
• Metabolism– Aerobic
• supply of oxygen– Anaerobic
• absence of oxygen• alternative electron acceptors
– Cometabolism• analogue• non-analogue
• Enzymes– specificity– degradative pathways (Tol plasmid)
• Biosurfactants
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Overview and Principles
Operational Requirements• Competent Biomass
– Pilot Study
• Suitable contaminant– petroleum hydrocarbons, solvents, aromatics
• Ideal physiological conditions– Temperature– pH, buffering– Nutrients– Oxygen (electron acceptor), H2 (electron donor)
• Engineering considerations– complexity of site– in situ, ex situ
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Overview and Principles
• Advantages of Bioremediation– permanent solution– soil structure retained– biomass is self-generating (cheap)– low energy– low-tech (adaptation of agricultural implements)– Cost (relatively cheap)
• Limitations– limited range of applications– ground conditions, hydrology– presence of inhibitors, mixed contaminants– Rate of biodegradation– Extent of Biodegradation
• simple substrates 98%• complex substrates 50% - 85% (e.g. PAH)• dead-end metabolites
– Cost (In-vessel)
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Ex Situ Bioremediation
Biopiles (Engineered Soil Banks, Static Piles)
• Pretreatment – oversize removal– homogenisation– amendments
• Bed Construction– aeration - pressure or vacuum pipes – drainage channels, porous base– heating– Surface covers and insulation
• Control and Monitor• oxygen, water, contaminant, etc.
• Dispose of Treated Soil– landfill, site backfill
• Costs– £70 - £140 per m3
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biopiles
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Ex Situ Bioremediation
Landfarming, Windrows (Composting)• Large Areas• Mechanically mixed by Agricultural equipment• Prepared base
– drainage galleries– membrane
• Bed Construction– 400mm lifts– 2m high windrow
• Irrigation– leachate recycle
• Covers (sheeting)– Rain protection, heat retention
• Costs– Landfarming £60 per m3
– Windrows £110 per m3
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Landfarming, windrow
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Case Study 1 (ex situ)
• Site– Wood Treatment Facility, USA
• Contamination– 15,000 tonnes soil – PAH up to 63,000 mg/kg
• Remediation Method– Landfarming
• Performance– Total PAH from 700 mg/kg to 155 mg/kg – Benzo(a)pyrene 23mg/kg to 10 mg/kg
• Time– 3 to 6 months
• Cost– £60 per m3
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Case Study 2 (ex situ)
• Site– old coking plant site – Grassmoor Lagoons, Derbyshire
• Contamination– 65,000 m3 sediment / sludge– PAH 10,000 mg/kg
• Remediation Method– Biopile– mix with ameliorants
(wood chip, mine spoil, peat, fertilizer)• Performance
– 80% degradation ( poor for 4 and 5-ring PAH)• Time
– 240 days• Cost
– not published
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Ex Situ Bioremediation
Bioslurry Reactors• High Solids Biological Stirred Tank Reactors
– controlled conditions• Pretreatment
– Screening, Soil Washing– biomass development
• Biodegradation– few hours aeration
• Dewatering– settlement, centrifuges, presses
• Time – Hours to days in tank, site time months
• Cost– Not well established (medium to high)
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In Situ Bioremediation
Pump and Treat (Biorestoration, Bioslurping)• Nutrients and oxygen added into soil through water
abstraction and reinjection– Pure Oxygen , H2O2
– biodegradation in situ • External Treatment
– Phase separation– Biofilter (SAF)– degradation ex situ
• Requirements– favourable soil and geological conditions
• Time– 3 to 48 months
• Costs– wide range £5 - £170 per tonne
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Pump & treat
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Case Study (in situ)
• Site– Petrol Station, Holland
• Contamination– Petrol at 1% in soil, 90 mg/l in groundwater– 15,000 m3 soil to a depth 4m
• Remediation Method– Pump and Treat
• Performance– Acceptable but variable (uneven re-circulation)
• Time– 12 months
• Cost– 15 - 40% less than landfill
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In Situ Bioremediation
Natural Attenuation• Spontaneous process
– mostly biological– BTEX half life (chemical =108 yr , biological = <1 yr)
• Long Term
• Risk Based Corrective Action (RBCA)– Environmental benefit v. Cost– may be better to address consequences than to treat the source
(e.g. borehole contaminants)
• Lines of Evidence– Primary
(concentration v. time, concentration v. distance)– Secondary (supportive)
(DO level, pH, electron acceptors, active microbes)
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In Situ Bioremediation
Monitored Natural Attenuation• Not a Do-Nothing Option
– quantify the natural breakdown process • Monitor Plume
– position of the 10 ppm threshold
Receptor
Monitoring wells
Sentinelwell
flow
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In Situ Bioremediation
Monitored Natural AttenuationExamples• Perchloroethylene (PCE) , Trichloroethylene (TCE)
– anaerobic dead-end product Vinyl Chloride (VC)– VC degraded aerobically to CO2
– restricted redox range (FeIII will oxidise VC)– sequential reducing / oxidising is best
• Addition of reducing agent– molasses (generates reducing conditions)– Chromium (VI) converted to Chromium (III)
(Cr(III)hydroxide insoluble)– SO4
2- reduced to S2- (metal sulphides precipitate)
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In Situ Bioremediation
Bioventing• Enhanced natural biodegradation through air and nutrient
supply– vacuum extraction of air– air injection well (with or without vacuum extraction)– air sparging with vacuum extraction
• Nutrients– infiltration wells
• Vadose zone– extended by lowering water table
• Treatment of extracted air– e.g. VOC removal
• Time– months to years
• Costs – Low £6 - £50 per m3
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bioventing
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Others
• Phytoremediation
– Uptake of metals by plant roots
– Individual species of hyperaccumulators for example cadmium and zinc
– Mycorrhizal fungi• mobilise contaminants
• extracellular enzymes (degrade aromatics)
• White rot Fungi
– Phanaerochaete sordida
– aromatics e.g. PCP, PAH