in-situ bioremediation for contaminated soil
TRANSCRIPT
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