In-Situ Bioremediation for Contaminated Soil

Presented by : A.R.M Sharif NawyazMonisha Alam

Sharmeen Moushumi

Outline• Definition• Methods• Process Descriptions• Advantages & Disadvantages• Applicability• Limitation• Cost & Performance• Case Study• Conclusion & Recommendations

What is In-Situ Bioremediation?

In place, on site

Remediation by Microorganisms

In-situ

Bioremediation

Process of In-Situ Bioremediation

Contaminant intake

Digestion & Metabolism

Non-toxic end products released

Non Toxic End Products- CO2 & H2O (Aerobic) CH4 , SO4

2- etc. (Anaerobic)

In-SituBioremediati

on

Intrinsic/Natural Attenuation

(no site manipulation)

Enhanced/Engineered

Bioremediation(site & microbial manipulation)

Biostimulation Bioaugmentation

Bioventing Air Sparging

Phyto-remediatio

nLand

Farming

Methods of In-Situ Bioremediation

Alteration or manipulation of environmental conditions to enhance microbial growth & activity

Lack of proper condition to survive & growth

Bio-stimulation

Addition of adequate nutrients (N, P, S, Ca, Mg etc)

Biostimulation

Soil unsaturated zone mostly aerobic O2 required

•Modification of Soil Vapor Extraction (SVE)

•Low air flow rate

• O2 in soil air above 2%

Bioventing process

Bioventing

Landfarming

• Tilling soil, adding fertilizer, surfactants etc.

Bioaugmentation

Advantages

Disadvantages

•Easy & Low cost

•Combines with other technologies

•Less Fugitive emission

•Public acceptance

•Requires long time

•Contaminant mobility increases, leaching ground water

•Less certainty of uniform treatment

•Complete destruction, no residuals

Advantages & Disadvantages

Site ConditionsFactors

affecting Contaminant properties

Required Data: Soil properties and contaminants’ physical & chemical properties

Applicability

• Microorganisms present in soil able to degrade

the contaminants• Adequacy of Nutrients – sufficient N, P, S, Ca, Mg etc.• pH- 6 to 8• Temperature – optimum 20° C to 30°C• Moisture Content – 40-60% of the field capacity • Bioavailability of contaminants to microorganism• Oxygen availability – for aerobic microorganisms• Soil Permeability & Homogenity• Organic fraction of soil

Favourable Site Conditions

Following properties of contaminants affect applicability:

• Biodegradability• Source • Distribution in soil

• Solubility & sorption coefficient

• Chemical reactivity• Volatility

Contaminant Properties

• Polyaromatic Hydrocarbons (PAH)• Semi Volatile Organic Compounds (SVOCs, TCE &

PCE)• BTEX (Benzene, Toluene, Ethylene, Xylenes)• Petroleum Hydrocarbons (PHC) (Gasoline, diesel,

fuel)• Pesticides• Organic Solvents• Wood Preservatives

Treated Contaminants

PAH Biodegradation

Limited to following site conditions:

• Low temperature – slows down biodegradation• Clay, highly layered, or heterogeneous soil-

limiting transfer of oxygen or other electron acceptor

Limited for contaminants:• Highly chlorinated organics like PCB • heavy metals• inorganic salt

Biodegradation resistant, because-• Toxic for microorganism• Microbes prefer feeding on other substrate• Lack of microbes’ genetic capability to use them

as source of Carbon & energy

Limitations

Operational Limitations:• Capacity of bioventing wells decreases with

time• Profuse microbial growth-clog the injection

wells• Circulation of water-based solutions through

soil increases contaminant mobility and necessitate treatment of underlying ground water

Limitations (cont’d..)

• Effective if cleanup achieved in a compatible time frame

• Simultaneous treatment of soil & ground water

• High efficiency of bioventing combined with SVE.

• Remediation time: 1 to several years

• Higher MW compounds take longer to degrade

Performance

• Less expensive over ex-situ methodsCost depends on: Site condition & Contaminants• Larger site: lower unit costIn-situ bioremediation cost/m3

Enhanced bioremediation: $30 to $100 Bioventing: $ 79 to $928 Phyto-remediation: $147 to $2322

Other process cost/m3

In-Situ - SVE: $405-$1275, Solidification/Stabilization: $150-$250

Ex-Situ - Biopiles: $130-$260Composting: $370-$442

Cost

Site name & Location

Contaminants Cost DurationReduction in Contaminant

Concentration

Toronto, Canada

BTEX, TPHApprox. $42/m3

Approx. 4 months (1995)

7,000 ppm to <100 ppm

Longwood TS, ON, Canada

BTEX, TPHApprox. Total

$65,000Approx. 30 days (1995)

14,000 ppm to <100 ppm

Ontario, Canada

PAH, PCPApprox. Total

$741,0001993-1994

439 mg/Kg to 10-50 mg/kg

Cost & Performance - Overview

CCME report 2001 estimated that 60% of Canada’s contaminated sites involve PHC contamination

Challenges faced

• Low temperature• Characterization of contaminants • Inappropriate analytical methods• Complexity of site conditions

Application in Alberta

Site Strachan Gas plant – Near Rocky mountain House

Period Late summer to mid winter, 1994

Technology Bioventing preceded by SVE.

Contaminants

NG gas condensate, BTEX, PAH, amine, BTEX Conc. 10-20 mg/L in HC plume. Contaminant area- 1 hectre

Waste source

LPG recovery area of the plant

Result Total removal 17,000 kg, 3,500 kg degraded through Bioventing

Cost Capital cost: $150,000, Semiannual operating cost: $ 15,000 , unit cost about $10/kg

Details From Dec 1994 to march 1995 biodegradation rate: 200 kg/day, Air flow rate: 50 L/s

Case Study

Present condition of the site

Source : http://sulvaris.com/company/projects/

Conclusion & Recommendation

• Effective application in Canada & Alberta

• Bioventing preceded by SVE - better performance

• Inadequate site characterization-leads to under design or overdesign; influence time!

• Low cost, lower risk to site workers & public

• Complete contaminant destruction

• Ecologically acceptable