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

biopiles

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

Landfarming, windrow

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

Pump & treat

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

Receptor

Monitoring wells

Sentinelwell

flow

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)

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

bioventing

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