Bioremediation
(Biological Remediation Technologies)
• Overview and Principles
• Bioremediation Technologies
Ex Situ
Biopiles
Landfarming
Bioslurry Reactors
In Situ
Pump and Treat
Bioventing
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
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
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
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)
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
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
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
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
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)
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
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
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)
In Situ Bioremediation
Monitored Natural Attenuation
• Not a Do-Nothing Option
– quantify the natural breakdown process
• Monitor Plume
– position of the 10 ppm threshold
In Situ Bioremediation
Monitored Natural Attenuation
Examples
• 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)
– SO42- reduced to S2- (metal sulphides precipitate)
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
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