This presentation discusses bioremediation of heavy metals like mercury. It explains how certain microorganisms can immobilize or mobilize metals through various mechanisms. A case study on bioremediation of mercury using Pseudomonas putida bacteria is described. The bacteria enzymatically reduces Hg2+ to volatile Hg0, removing mercury from wastewater. Within 10 hours, a 97% mercury retention efficiency was achieved, meeting discharge limits. Bioremediation is an effective natural and economical approach for cleaning heavy metal pollution.

1. Presentation date: 18th January, 2018
BIOREMEDIATION OF HEAVY
METALS
Presentation by
Kumuda J.

2. CONTENTS
 Introduction
 Mobility of metal contaminants
 Mechanisms for metal remediation
Immobilization
Mobilization
 Bioremediation of Mercury-Case study
 Advantages and Disadvantages
 Conclusion

3. 1. Introduction

4. 2. Mobility of metal contaminants
Chemical and physical
properties affect the mobility
of metals in soils and
groundwater
Under acidic conditions metal-
cations are mobile while anions
tend to transform to oxide
minerals.
When a microorganism oxidizes
or reduces species, this reaction
causes metals to precipitate.
Mercury is an example of a
metal that can be precipitated.

5. 3. Mechanisms for Metal
Remediation
Isolation Immobilization
Mobilization
Physical
separation
Extraction

6. 3.1.Immobilization
Reduce the mobility of contaminants by
altering the physical or chemical
characteristics of the contaminant.
In situ treatment is below the ground
Ex-situ waste is excavated or pumped
above the ground for treatment

7. 3.1.1. Solidification and Stabilization
Achieved by mixing the contaminated material with appropriate amounts of stabilizer
material and water
Ex situ requires excavation, transport, and disposal of
hazardous
material.
Deep stabilization/solidification up to 50 ft can be
achieved by using gauged augers (up to 3 ft in diameter
each) that can treat 150-400 cubic yards per day
Cement-based binders
and stabilizers are used
when implementing the
solidification &
stabilization technique.

8. 3.2. Mobilization
Autotrophic leaching
Heterotrophic leaching
Methylation
Redox transformations.

9. 3.2.1.Mechanisms of Mobilization
Autotrophic
leaching-
Acidophilic bacteria
obtain energy from
the oxidation of the
ferrous iron or
reduced sulfate
compounds, causes
solubilization of
metals.
Heterotrophic
Leaching-
Microorganisms
acidify their
environment by
proton efflux
leading to the
acidification
resulting in the
release of free metal
cations.
Methylation-
methyl groups that
are enzymatically
transferred to a
metal, forming a
number of different
metalloids.
Redox
transformation
-allow
microorganisms to
mobilize metals and
organometallic
compounds by
reduction and
oxidation processes.

10. 4.1. Characteristics of Mercury metal
State:
metallic
Color:
Silver-
white
Form:
Cationic
Dissolves
metals such as
gold and silver
to
form amalgams
4.Bioremediation of Mercury

11. 4.2. HEALTH &
TOXICOLOGY
Memory
Loss
Severe
salivation
Gingivitis
Abdominal
cramps &
Bloody
Diarrhea

12. 4.3. Bioremediation Process
Methyl mercury and Mercuric Chloride
Toxic forms of mercury
Pseudomonas putida
It involves the reduction of Hg2+ to volatile Hg0 by the inducible
enzyme mercuric ion reductase coded by the merA gene..

13. 4.4.Removal of Mercury from chemical
wastewater by Microorganism(Wagner-
Dobler, Von Canstein, Li, Timmis, and Deckwer, 2000)
• Pseudomonas putida
• Inoculated48hrs at 300 C in Liq Medium
• Transferred 150liter fermentation vessel 3L of Liq
media.
• Fermentation Fed-batch 4 days at 350 C.
Bacteria
• Analyzed using Automated instruments from Mercury
Instruments(Karlsfeld,Germany).
• Reduction of Hg(II) to Hg(0) was seen.
Mercury
concentrations
• Mercury-resistant bacteria and wastewater was added to
the bioreactor.
• Initial Hg outflow concn = 900μg/L, After 3 hrs = 306
μg/L.
• Full mercury Removal achieved after inoculation.
Bioreactor

14. 4.5. Conclusion
Mercury Resistant Bacteria enzymatically
reduced Hg(II) to Hg(0).
7 Strains of pseudomonas were used
Chloralkali electrolysis water having 3-10
mg/L Hg conc.was fed.
Within 10hrs Hg retention efficiency of
97% was obtained
Bioreactor outflow concn.was 50μg of
Hg/L, which fulfills the discharge limit for
industrial wastes.
3)
2)
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15. 7. Advantages
 Bioremediation a natural process
 Residues for the treatment are usually harmless products
 Bioremediation is useful for the complete destruction of a wide variety of
contaminants
 Carried out on site, often without causing a major disruption of normal
activities
 Less expensive than other technologies that are used for clean-up of
hazardous waste.

16. 8. Disadvantages
 Bioremediation is limited to those compounds that are biodegradable
 Highly specific
 Difficult to extrapolate from bench and pilot-scale studies to full-scale field
operations
 Takes longer than other treatment options
 Regulatory uncertainty remains regarding acceptable performance criteria
for bioremediation.

17. 9. Conclusion
 Bioremediation, a process whereby natural degradation rates are
accelerated through simulation of indigenous microorganisms is an
effective ecological and economical reclamation alternative.
 A beneficial addition to chemical and physical methods of managing
wastes and environmental pollutants – offers a saving of 60 to 90% over
landfills disposal costs.