1.Microbial Approaches In Remediation Of Metal Contaminated Soils & Sediments 2.Microbial Approaches In Remediation Of Metal Contaminated Aquatic systems

1. 1
Microbial Approaches In
The Remediation Of
Metal-Contaminated
Soils & Sediments &
Metal-Contaminated
Aquatic Systems
by Shams-ud-Duha Syed

2. 2
Microbial
Approaches In
The
Remediation Of
Metal-
Contaminated
Soils &
Sediments

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Goals Of Microbial
Remediation Of Metal-
Contaminated Soils &
Sediments
1.Immobilize the metal to reduce metal
bioavailability & mobility
2.Remove the metal from the soil

4. 4
Methods For Microbial Remediation
Of Metal-Contaminated Soils &
Sediments
They include:
1.Microbial leaching
2.Microbial surfactants
3.Microbially induced metal volatilization
4.Microbial immobilization & complexation

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1.Microbial Leaching (Bioleaching,
Biomining)
The process by which metals are dissolved
from ore bearing rocks using microorganisms.
 Bioleaching is cheaper than chemical
extraction, safer for the environment, and
more efficient in extracting metals with low
concentration in ores.
 It is performed by iron and sulfide oxidizing
bacteria or acid producing fungus.

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Miroorganisms used for Leaching
 Most commonly used microorganisms are:
1. Thiobacillus thiooxidans
2. Thiobacillus ferrooxidans
 Others microorganisms which can be used are:
1. Bacillus licheniformis 2. B. luteus
3. B. megaterium 4. B. polymyxa
5. Leptospirillum ferrooxidans
6. Pseudomonas fluorescens
7. Sulfolobus acidocaldarius
8. Thermothrix thioparus
9. Thiobacillus thermophica

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Leaching Process
 There are three commercial methods used in
leaching:
1. Slope Leaching
2.Heap Leaching
3.In-situ
Leaching

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1.Slope Leaching
 About 10,000 tonnes of ores are ground first to
get fine pieces
 Then dumped in large piles down a mountain
side leaching dump.
 Water containing inoculum of Thiobacillus is
continuously sprinkled over the pile.
 Water is collected at bottom. It is used to
extract metals and generate bacteria in an
oxidation pond.

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(ii) Heap Leaching.
 The ore is dumped in large heaps called leach
dump. Further steps of treatment are same to
slope leaching.

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3.In-situ Leaching
 In this process ores remain in its original
position in earth. Surface blasting of rock is
done just to increase permeability of water.
 Thereafter, water containing Thiobacillus is
pumped through drilled passage to the ores.
Acidic water seeps through the rock and
collects at bottom.
 Again from bottom water is pumped, mineral is
extracted and water is reused after generation
of bacteria.

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Examples Of Bioleaching
 Copper Leaching
 Uranium Leaching
 Gold and Silver Leaching
 Silica Leaching

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2.Microbial surfactants
 Biosurfactants (BS) are amphiphilic
compounds produced on living surfaces,
mostly microbial cell surfaces, or
excreted extracellularly and contain
hydrophobic and hydrophilic moieties
that reduce surface tension (ST) and
interfacial tensions between individual
molecules at the surface and interface,
respectively.

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General Characteristics
 Biosurfactants are lipid-containing molecules,
which are normally produced under aerobic
conditions
 Biosurfactants can be of high or low molecular
weight, and based on their composition,can be
glycolipids, phospholipids, lipopeptides, or a
mixture of amphipathic polysaccharides,
proteins, lipoproteins, or lipopolysaccharides.
 Biosurfactants with low molecular mass are
efficient in lowering surface and interfacial
tensions, whereas biosurfactants with high
molecular mass are more effective at stabilizing
oil-in-water emulsion

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Biosurfactant-producing Bacteia
Microorganism Biosurfactant
1.Pseudomonas aeruginosa Rhamnolipids
2.Pseudomonas fluorescens
3.Pseudomonas stutzeri
4.Pseudomonas cepacia
Ornithine lipids
5.Acinetobacter calcoaceticus Lipopolysaccharides (biodispersant)
6.Acinetobacter radioresistens Heteropolysaccharide protein
(alasan)
7.Bacillus subtilis Lipopeptides and lipoproteins
(surfactin)
8.Bacillus licheniformis Lipopeptides (lichenysin)
9.Rhodococcus erythropolis
10.Mycobacterium sp. Nocardia sp.
Trehalolipids
11.Tsukamurella sp. Di- and oligosaccharide lipids

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Biosurfactant-producing yeast
Microorganism Biosurfactant
1.Candida bombicola
2.Candida apicola
3.Candida rugosa
4.Candida mucilaginosa
5.Rhodotorula bogoriensis
Sophorolipid
6.Candida lipolytica Carbohydrate–protein (Liposan)
7.Yarrowia lipolytica Carbohydrate protein lipid
complex (Yansan)
8.Saccharomyces
cerevisiae 2031
Mannoprotein
9.Schizonella malanogramma
10.Ustilago maydis
Erythritol and mannose lipid

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Mode Of Action Of Biosurfactants:
 The ability of biosurfactants to form complexes
with metals is the main reason for their utility in
remediation of heavy metal-contaminated soil.
Specifcally, anionic biosurfactants form ionic
bonds with metals, generating nonionic
complexes with stronger stabilizing forces than
those between the metals bonds and soil. Once
formed, metal–biosurfactant complexes desorb
from the soil matrix and move into the soil
solution due to the neutral charge of the
complex with a sub-sequent incorporation of the
metal into micelle

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3.Microbially induced metal volatilization
 Microorganisms can transform metal and
metalloid species by oxidation,reduction,
methylation and dealkylation
.Biomethylatedmetal derivatives are often
volatile and may be eliminated from the system
by evaporation.
 Volatilization mechanisms involve turning metal
ions into a volatile state. This is only possible
with Se and Hg, which have volatile states.

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MICROBIAL
APPROACHES IN THE
REMEDIATION OF
METAL-
CONTAMINATED
AQUATIC SYSTEMS

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Specific interactions for metal
removal include:
 Metal binding to microbial cell surfaces &
exopolymer layers
 Intracellular uptake
 Metal volatilization
 Metal precipitation via microbially facilitated
metal redox reactions

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Methods/Treatments Of Removal Of
Metals From Contaminated Water
1.Wetland Treatment
2.Microbial Biofilms

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1.Wetland Treatment
 Wetland remediation is based on
1.Microbial adsorption of metals
2.Metal bioaccumulation
3.Bacterial metal oxidation
4.Sulphate reduction
Although these various processes
contribute to the removal of toxic metals from
the water column, the metals are not destroyed.

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Bioaccumulation
Uptake of heavy metals actively is
called bioaccumulation.
Adsorption
Microorganisms uptake heavy metals
passively i.e.Heavy metals can be
biosorbed by microbes at binding sites
present in cellular structure without the
involvement of energy.

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 Wetlands are constantly monitored
for any environmental change that may
adversely affect metal removal.
E.g. a decrease in pH may solubilize
precipitated metals
A disturbance of the wetland
sediment may change the redox conditions
& oxidize reduce metals.

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Advantages:
 The high organic matter content of
wetlands provided by high plant & algal
growth encourages both the growth of
sulphate-reducing microorganisms and
metal sorption.
 Wetlands are resilient systems,& as long
as new vegetative growth and organic
inputs occur,can effectively remove
metals for an indefinite petiod of time.

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2.Microbial Biofilms:
 The most common treatment for metal-
contaminated waters is with microbial
biofilms.
 Many microorganisms produce
exopolymers as part of their growth
regime.Metals have high affinities for
these anionic exopolymers, due to which
metals adsorb with these exopolymersm.
 Microbial biofilms may be viable or non-
viable when used in remediation

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Exopolymer Producing
Microorganisms:
 Pseudomonas
 Arthrobacter
 Bacillus
 Citrobacter
 Streptomyces
 Yeasts(Sacharomyces)
 Candida

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The biofilm is immobilized on a support as contaminated
water is passed through the support toxic metals get
attached to the anionic exopolymer produced by biofilm
forming MOs.Often,a mixture of biofilm producing MOs on
these supports,providing a constant supply of fresh biofilm.

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Examples:
Live Citrobacter spp. biofilms are
used to remove uranium from contaminated
water.
Both Arthrobacter spp. biofilms &
biomass (non-living) are used in recovery of
cadmium, chromium, copper, lead & zinc
from wastewaters.
Non-living Bacillus spp. biomass
preparations effectively bind cadmium,
chromium, copper, mercury & nickel.

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Commercially Available
Immobilized, Non- living
Preparations:
 AMT-BIOCLAIM(Bacillus biomass)
 AlgaSORB(Chlorella vulgaris)

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Treatment Of Metal-
Contaminated Marine Waters:
 Mcrobial biofilms are also used in
treatment of metal-contaminated marine
waters.However,marine bacteria such as
Deleya venustus & Moraxella sp. Are
used.

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Treatment Of Metal-Contaminated
Domestic Waste Waters:
 Microbial biofilms are used in the
removal of metals from domestic
wastewater.In domestic waste treatment,
the important biofilm producing
organisms include:
1. Zoogloea
2. Klebsiella
3. Pseudomonas spp.