Soil contamination and remediation
Bioremediation
Biodegradation technologies in-situ / ex-situ
Bioremediation
Utilization of microorganisms to destroy or
immobilize the contamination
Dominantly these organisms are used:
• Bacteria (aerobic and anaerobic)
• Fungi
History of bioremediation
1972
First commercial project: oil pipeline leak Sun Oil, Ambler, Pennsylvania, USA
80.
focus on the bacterial research
(bioengineering), expected goals were not reached
....... until today
return to natural microorganisms,
research focuses in their best utilization
Mechanisms of bioremediation
Microorganisms destroy organic contaminants in
process of metabolism or cometabolism
Organic compounds supply:
carbon – construction of live cells
electrons – source of energy
Cells catalyze oxidation of organic compounds (of
electron donors). Extra electrons from organic
matter must be used by electron acceptors.
Electron acceptors
Aerobic conditions:
oxygen
Anaerobic conditions (see natural attenuation):
nitrates
manganese
iron
sulphates
Microorganisms need basic nutrients such as
nitrogen or phosphorus as well
Oxygen is elec. acceptor
Decrease of the energy gain during electron transfer
Redox potential (V) (at pH=7)
Anaerobic (alternative elec. acceptors)
Area of electron acceptors efficiency
Aerobic
Population of bacteria
Growth is very steep where “food” is present –
source of carbon. Population doubles each 45
minutes.
Clean soils contain 100 to 1000 aerobic bacteria per
gram of soil.
Population grows to 105 where source of carbon is
not depleted.
Suitable conditions for
bioremediation
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Sufficiently large bacteria population
Presence of electron acceptors
Presence of nutrients (nitrogen and phosphorus)
Chemicals not toxic for bacteria (NAPL free phase
is often toxic)
• Sufficient source of carbon for bacterial growth
(contradicting remediation limits for toxicants)
degradability
Relative capability of
biodegradation
Simple hydrocarbons
degradability decreases with growth of molar weight
Aromatic hydrocarbons
Alcohols, esters
Nitrobenzenes and ether
Chlorinated hydrocarbons
degradability falls with increasing chlorine
substitutions – highly chlorinated compounds (e.g.
PCB) and chlorinated solvents can not be degraded
easily
Pesticides
Bioremediation technologies
EX-SITU
Composting
suitable for oil hydrocarbons
Slurry phase bioremediation
aqueous slurry combines soil, sediment, or sludge with
water and other additives - mixed with microorganisms,
later dewatered and disposed
Biopiling ex-situ – managed biodegradation in heaps
(industrial composting)
suitable for oil hydrocarbons up to 50000 ppm
Landfarming
application of the organic matter and consequent irrigation
and tillage
Managed slurry phase bioremediation
soil is decontaminated in the form of slurry within
bioreactors or lagoons
Zdroj: US ARMY ENVIRONMENTAL CENTER, http://aec.army.mil/usaec/technology/
Composting
composting – degradation by microorganisms at raised
temperature
• Typically 55 – 65°C
• Heat is produced by microorganisms
• Decrease of bulk density and supply of organic carbon –
straw, alfa-alfa, manure, wood chips
• Spreading into long rows
• Rows are regularly turned over and mixed
• Monitoring of pH, temperature and contaminant
concentration
Composting in rows
http://www.rrskw.com/compost_turners.htm
Ex-situ managed bioremediation
– Biopiling
• Soil is mixed with additives and placed onto suitable site
• Ventilation device is installed during piling
• Pile is 6 m high (max), covered with PE foil
Monitoring device
air pump
pipe
perforated pipe
Ex-situ managed bioremediation
– Biopiling
Biopiling – optimal conditions
Factor
Soil moisture
Optimal value
25-85% of saturated
Oxygen content
>0.2 mg/L dissolved O2
>10% air filled pores
REDOX potential
Eh > 50 mV
Nutrients
Temperature
C:N:P = 120:10:1 (ratio of molar
amounts)
15-45°C
pH
5.5 – 8.5
Bioremediation technologies
IN-SITU
Enriching in situ vadose zone
Biostimulation – addition of nutrients into soil environment
Bioventing
Addition of oxygen to ventilate soil
Biosparging
Aeration of saturated zone
Enriching saturated zone
support of bacterial growth and cometabolic processes,
addition of alternative electron acceptors
Bioremediation IN-SITU
Steps of project preparation
1) Field survey
• Is contamination under control, does it grow?
2) Laboratory tests
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•
•
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•
•
Amount of bacteria
Speed of bacterial activity
Bacterial adaptation
Concentration of inorganic carbon
Concentration of electron acceptors
Side products of anaerobic activity
Creation of semiproducts of metabolic processes
Ration of non-degradable and degradable compounds
Bioremediation IN-SITU
Steps of project preparation (cont.)
3) Semiroutine experiment in-situ
• Stimulation of bacterial growth in the frame of the part of
contaminated area
• Measurement of consumption of electron acceptor
• Monitoring of non-biodegradable tracer compound
4) Modeling
• Modeling of abiotic weight loss of contaminant (dissolution,
transport, volatilization)
5) Performing the remediation?
Bioventing
Adding of oxygen (electron acceptor) in unsaturated zone
by pressing in or vacuum extracting out of air.
Applicable mostly for oil product degradation (also used
for PAH).
Compared with air sparging – venting uses by far smaller
amounts of air.
Compressor
Air injection
Monitoring
Contaminant
Bioventing
Area of bioventing
efficiency for
chosen
hydrocarbons
Approximate time for
biodegradation
Time of
landfarming
(days)
Time of
composting
(days)
Time of
compost.+
vacuum
aeration
(days)
Benzene
80-105
60-70
50-58
Toluene
55-79
30-40
20-28
Ethyl-benzene
20-29
22-28
20-26
Xylene
180-206
70-78
60-68
-
184-230
130-184
Total oil
hydrocarbons
VIRARAGHAVAN, T.; MIHIAL, D.; THOMSON, R.B. A MORTIN M.D.: Bioremediation of a petroleum contaminated site - a feasibility analysis. <http://ce.ecn.purdue.edu/~alleman/w3-piwc/papers/virara.html>
Saturated zone enrichment
Applicable for oil products (and chlorinated
hydrocarbons in limited cases)
Saturated zone enrichment
Technology of enrichment
infiltration by boreholes
infiltration by ditches
infiltration by irrigation
Chemical compouds (carbon source) suitable for
enrichment
acetate, ethanol, lactate, vegetable oil
Enrichment of the groundwater by electron acceptors
oxygen, hydrogen peroxide, methane, nitrate
Bioremediation – case studies
Brown Wood Preserving Superfund Site (Live Oak,
Florida (USA)
contaminants: PAH (benzo(a)pyrene, benzo(a)anthracene,
chrysene, benzo(b)fluorantene)
concentration prior to remediation: 100-208 mg/kg
soil amount: 6200 m3
technology: land farming
concentration after remediation: 23 – 92 mg/kg
time of remediation: 18 months (1989-1990)
costs: $ 565 400, approx $90 / m3
More at: http://www.clu-in.org/products/costperf/LNDTREAT/Brown.htm
Bioremediation – case studies
French Limited Superfund Site (Crosby, Texas, USA)
contaminants: benzo(a)pyrene, VC, benzene
concentration prior to remediation: 400-5000 mg/kg
soil amount: 300 000 tons
technology: managed slurry phase bioremediation
concentration after remediation : 7 – 43 mg/kg
costs: $ 49 000 000
More at: http://www.clu-in.org/products/costperf/BIOREM/French.htm
References
M. Kubal, J. Burkhard, M. Březina, VŠCHT, Praha 2002,
http://www.vscht.cz/uchop/CDmartin/8-nejcasteji/3-2.html
VIRARAGHAVAN, T.; MIHIAL, D.; THOMSON, R.B. A MORTIN M.D.: Bioremediation of
a petroleum - contaminated site - a feasibility analysis.
<http://ce.ecn.purdue.edu/~alleman/w3-piwc/papers/virara.html>
Norris et al. Handbook of Bioremediation, Lewis publishers, 1994
MIT Open courseware Civil and Environmental Engineering » Waste Containment and
Remediation Technology, Spring 2004 http://ocw.mit.edu/OcwWeb/Civil-andEnvironmental-Engineering/1-34Spring2004/LectureNotes/index.htm