Soil,Soil Pollution, Sources of Soil Pollution, Effects Of Soil Pollution, Control Of Soil Pollution, Physically Control of Soil Pollution, Chemically Control of Soil Pollution, Thermally Control of Soil Pollution , Biologically Control of Soil Pollution

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7 Important Sources of Soil Pollution and its Effects
Some of the sources of soil pollutions are discussed below:
1. Industrial wastes:
There are two kinds of wastes that are generated from industrial activities:
unused chemicals and unwanted industrial garbage.
Unused chemicals like fly ash, sludge, plastics and sawdust are some of the chemicals that are discharged
from industries.
Unwanted garbage from industrial activities like glass, metals and wood are the other kinds of wastes
which industries generate. When these wastes are left on the soil’s surface, they change the chemical
composition of the soil. The physical qualities of soil are also altered. Such sources of soil pollution make
the soil harmful as well as barren.
Effects:
i. They spoil the fertility of the soil.
ii. The chemicals released are harmful to living organisms dependent on the soil.
iii. Contamination of the soil is a direct cause of contamination of the crops. As a result harmful
chemicals enter the food chain.
2. Agricultural practices:
Sometimes, excessive chemical fertilizers are applied to the crops. Plants absorb what they need and the
excess goes into the soil. Animal excreta, debris and crop residues are some other contaminants that result
from agricultural practices. These contaminate the soil by changing its physical and chemical properties.
Effects:
i. Soils that have been spoiled due to excessive use of chemicals and pesticides become barren.
ii. When plant macronutrients like potassium, phosphorus and nitrogen are used excessively, the soil
becomes deficient in micronutrients like boron and zinc.
iii. Excess chemicals from agricultural practices harm the survival of a number of friendly microginism.
iv. Pesticides that contaminate the soil seep lower down the soil layer and contaminate groundwater that
is used for domestic purposes.

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3. Biological agents:
Biological agents like bacteria, fungi, virus and protozoan’s are a major cause of soil pollution. Human
and animal excreta, poor sanitary conditions, wastes from hospitals and food joints cause soil pollution
because they perpetrate growth of biological agents in the soil.
Effects:
i. They cause diseases in human beings.
ii. They harm the development and existence of flora and fauna.
iii. They spoil qualities of fruits and vegetables grown in the polluted soil.
4. Mining and smelting:
Mining and smelting activities are lethal causes of soil pollution. Extraction and processing of mineral
ores causes harm to the top soil layer. Mining fires destroy lands around the area and mining wastes cause
heaps of wastes to be produced if the activity is not checked. Similarly, on one hand, installation of
cement factories in the mountainous region weakens the soil strata leading to landslides, and on the other
hand, the cement dust that falls on natural vegetation and crops blocks their stomata to cause their
eventual death.
Effects:
i. Mining wastes often cover the top soil, thus spoiling a precious natural resource.
ii. It makes the soil infertile.
iii. It harms the existence of microorganisms thriving on the soil.
iv. Heavy metals that enter the soil enter the food cycle. These metals are particularly absorbed by infants
and children.
5. Radioactive pollutants:
Radioactive pollutants arise from nuclear activities like explosion devices, nuclear tests and laboratories,
as well as nuclear power plants. Refining of plutonium and thorium as well as fuels for industrial and
domestic uses are some other causes of radioactive pollution. Radioactive elements that are released into
the air also enter the soil as radionuclide’s with rainwater.
Effects:

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i. The rainwater that passes through the polluted soil picks up radioactive elements. This harms the flora
and fauna that thrive on rainwater.
ii. Radioactive elements are absorbed by soil particles, causing harm to soil qualities.
iii. They can cause health problems for human beings.
6. Dispersion of acids and acid rain:
Acids that enter the soil along with heavy metals or acid rain harm soil properties. This polluted soil
becomes acidic in nature and becomes unproductive for crops, which require alkaline or neutral soils.
Acidic gases like SO2 and NOx when combine with atmospheric moisture form acids and fall on the earth.
They cause soil pollution by changing the pH of the soil.
Effects:
i. Acids harm growth of plants that are sown in these soils.
ii. When acids are present in the soil, they are carried away with flowing water, causing harm to water
bodies.
iii. Acid deposition changes the chemical qualities of soil.
7. Urban wastes:
Urban wastes that result in residential areas cause contamination of the soil at places where the wastes are
not properly disposed. Wastes like glass, plastic, human excreta, fuel residues, metals and vehicular
products are common urban wastes.
Not only does accumulation of these wastes result in poor human health, they also cause pollution of the
soil. Urban wastes do not dispose easily, and therefore cause a lot of harm to the soil and its properties.
Nonbiodegradable wastes like plastic, metal cans and glass cause great harm to the soil.
Effects:
i. Urban wastes dirty residential areas, resulting in the growth of insects and pathogens.
ii. They are harmful to human health.

16. Effect of soil pollution on human health
10
Generally, people can be exposed to contaminants in soil through
ingestion (eating or drinking), dermal exposure (skin contact) or
inhalation (breathing).

17. Heavy metals
Environmental pollution by heavy metals is of major health
concerns all over the world even if it is at low
concentrations due to their long-term cumulative health
effects.
Intake of heavy metal through food materials:
• Impairs the function of other metal ions
• Decreases the immunology of body
• Retardation of growth
• Poor mental development
11

18. Pesticides
Major categories of pesticides and their persistence in the soil:
• Chlorinated hydrocarbons - DDT, heptachlor, etc—2-15 years
• Organophosphates - Malathion, methyl parathion—1-2 weeks
• Carbamates - Carbaryl, maneb, aldicarb—days to weeks
• Pyrethroids - Pemethrin, decamethrin—days to weeks
12
Some of the chronic and acute toxicological effects of
pesticides are:
• Chronic liver damage
• Endocrine disorders
• Reproductive disorders
• Immune-suppression
• Various cancer
• Parkinson’s and Alzheimer’s diseases

19. PAHs
• Human exposure to PAHs has been associated with an
increased risk of developing cancer in the variety of
organs (such as lung, bladder, stomach, skin, larynx,
scrotum, breast, oesophageal, prostate, kidney and
pancreas).
• Furthermore, they are known to suppress the immune
system and are suspected of being endocrine disrupters.
13

20. Effect on soil fertility
• Soil fertility refers to the ability of the soil to supply essential plant
nutrients and water in adequate amounts and proportions required
for plant growth and reproduction in the absence of toxic substances
which may inhibit plant growth.
• A fertile soil has good physical and chemical environment for
growth of plant roots as well as for beneficial soil microflora and
fauna responsible for carrying out nutrient transformation leading
to optimum supply of plant nutrients.
• Entry of pollutants in agroecosystem affects different soil properties
(such as pH, available nutrients, soil enzyme activity, available and
total heavy metal concentration, etc.) resulting in loss of soil fertility
and hence crop productivity.
14

21. Phytotoxicity of Heavy Metals
• Significant part of the metal loaded effluents, generated particularly
from small scale industries in developing and under-developed
countries are released untreated into land and water bodies.
• Also, some of the metals are impurities/constituents of extensively
used agrochemicals like fertilizers (e.g. Cd in phosphatic fertilizer),
pesticides (e.g., Zn, Cu, Sn, Hg, organic pollutants) etc. and
contaminate the rhizosphere when these are used in intensive
agriculture.
• Some impacts of heavy metals toxicity in plants include:
 Growth reduction (As, Cd, Cr, Pb, Ni, Hg, Cu)
 Chlorosis (Cd, Ni, Hg, Cu)
 Necrosis (As, Cd, Ni)
15

22. Socio-economic effects of soil
pollution
• It can worsens the effects of poverty and dependence.
• It weakens populations and institutions.
• It reduces food security.
• Socio-economic development is disequilibrium.
16

23. Nitrogen cycle
17

24. Eutrophication
• We humans may not be able to fix
nitrogen biologically, but we
certainly do industrially!
(Fertilizers)
• Increase in nutrient levels
1. Algal blooms: block sunlight from
photosynthetic marine plants
under the water surface.
2. Decay of algae by MOs: use up all
the oxygen in the water, leaving
none for other marine life, and
producing free toxic compounds ,
such as ammonia and hydrogen
sulphide (H2S).
18

25. NO toxicity
19
Formation of N‐nitroso compounds from NO3
−, NO2
−, NO, and their effects on human health.
• NO3
− is applied in increasing
amounts in the fertilizers for
agricultural production.
• They accumulate in the soil.
• They can reach groundwater.

26. Methemoglobinemia
• The ferrous iron of hemoglobin is
exposed continuously to high
concentrations of oxygen and, thereby,
is oxidized slowly to methemoglobin, a
protein unable to carry oxygen.
20

27. Impacts of radioactive pollution on soil
Effects of radioactive pollutants:
• Radiation affects the soil and soil
fertility.
• The radioactive leaching or dumped
into the soil is more complicated,
because they remain in soil for
thousands of years.
• Radioactive pollution in soil can
lead to mutations, malformations,
carcinogenicity, and abortion for
animals as well as humans.
21

28. 22

29. Remediation technologies
• According to the scale of pollution, the risk level and the
financial and time constraints on the remediation project,
treatment of the soil may take place immediately in place (in
situ) or the soil may be transported to special facilities where
remediation may be carried out in special reactors or vessels,
that are specially designed for this purpose (in tank method).
• An example of this process is the washing of heavily polluted
soils in special tanks.
• The polluted soil may also be transported and spread on a
surface prepared to prevent the spread of contamination in
lateral and vertical directions.
• Beds prepared in this way form the so-called prepared beds
upon which the remediation process will take place. This
method is especially suitable for soils contaminated by oil
products.
23

30. Remediation
technology
Chemical and
physical treatment
Oxidation
Photolysis
AOPs
Ion exchange
Adsorption
Pump-and-treat
Chemical
dehalogination
Soil vapour
extraction
Soil washing
Soil flushing
Solidification/
stabilization methods
Thermal treatment
Incineration
Thermal desorption
Vitrification
Biological treatment
In situ
Ex situ
24

31. Chemical and physical remedial
techniques
• The aim of all chemical and physical methods of
remediation is to change the chemical
environment in a way that the transport of toxic
substances to other elements of the soil system is
prevented.
• Examples here can be given by transport to
plants; to ground water; or to soil organisms.
• Such preventive measures may include
decreasing mobility or change of chemical
constitution.
25

32. 1. Oxidation
• Oxidation is a common highly effective remediation
technology for soils contaminated by toxic organic chemicals
and cyanides.
• Oxidising agents used in this technology include a wide range
of substances among which the most common are hydrogen
peroxide, ozone and potassium permanganate.
• All three methods are according to EPA of high treatment
efficiency, reaching over 90% at short times in many cases.
• For example efficiency reaches >90% for unsaturated
aliphatic compounds such as trichlorethylene (TCE) as well as
for aromatic compounds such as Benzene.
• Oxidation technology has been successfully used for in situ
remedy at source areas as well as for flume treatment. It is
mostly used for benzene, ethylbenzene, toluene and xylene
(BTEX) as well as for PAH's, phenols and alkenes.
26

33. • Oxidation of trichlorethylene if potassium permanganate (KMnO4)
was used, takes the following path:
2KMnO4 + C2HCl3  2CO2 + 2MnO2 + 2KCl + HCl
Permanganate in Situ Oxidation Application
27

34. Ozone destruction of toxic contaminants takes place in the following
manner:
O3 + H2O + C2HCl3  2CO2 + 3HCl
General conceptual model of in-situ ozonation in the saturated zone with
soil vacuum extraction to capture volatile emissions and O3(g)
28

35. 2. Photolysis
• Photolytic degradation technology depends upon
degrading the organic contaminants with Ultraviolet
radiation.
• This may be carried out using artificial UV light or
just by exposing the soil to sunlight, which may be
sufficient for degrading shallow soil contaminants.
• This process can be carried out in situ or in prepared
bed. However, deeply contaminated soils must be
excavated and transported to special facilities,
where the process would be carried out in special
tanks.
29

36. 3. Advanced Oxidation Processes
(AOPs)
• AOPs are based on the generation of in situ
hydroxyl radicals (O˙H) in very mild, near
ambient pressure and temperature experimental
conditions(by irradiation). These radicals are
strong enough oxidants that are able to degrade a
great variety of bio-recalcitrant organic
compounds.
• Peroxide based/ ozone
• Fenton (Fe2+ & peroxide)
• Metal based nanoparticles (ZnO or/and TiO2)
(MO/doped N) + EM radiations (UV, Laser,
Ultrasound, and sunlight)
30

37. Mechanism of action in AOPs remediation
technology
The organic
pollutant
(Hydrocarbons)
31

38. 4. Ion exchange
• Soil components with high CEC values are capable of
binding positively charged organic chemicals and metals
in a way that makes them chemically immobile and thus
reduce the risk imposed by them on the soil environment.
• Addition of soil conditioners such as synthetic resins
zeolites or clays may help increasing the CEC
characteristics of the soil and thus enhance the binding of
positively charged contaminants on the negative
functional groups of the soil matter.
32

39. 5. Adsorption
• Adsorption is the most widely used, fastest,
inexpensive technology for the treatment of
groundwater, chemical spills, and for removing a
series of toxic chemicals such as BTEX,
ethylbenzene, xylene, trichloroethene,
tetrachloroethene, dichloroethane, PCBs,
pesticides, herbicides, explosives, and anions
like perchlorate and heavy metals.
33

40. Adsorption on granulated active carbon (GAC)
• Activated carbon is the most common adsorbent.
• The technology depends upon the tendency of most organic compounds to
adsorb on the surface of activated carbon.
• Remediation through adsorption on activated carbon is a method that can
be carried out in the liquid phase as in treatment of ground water or in the
gas phase as in treating off-gases from soil vapour extraction remediation
methods.
• One of the earliest applications of this method was the use of (GAC) in
adsorbing military gases by gas masks in the first world war.
• Adsorption on activated carbon is a process carried out ex-situ in special
tanks or in prepared beds.
34

41. 6. Pump-and-Treat
• In pump-and-treat, the
groundwater is pumped and
then treated using granular
activated charcoal.
• Generally, the pump-and-treat
approach requires 50–100 years
to reach remedial goals, and in
most cases the goals are never
achieved.
• Moreover, disposal of
contaminants that become
bound to activated carbon after
treatment becomes a problem.
• Because of these drawbacks, surfactant-enhanced remediation,
metallic iron technology, permeable reactive barriers, etc., have
emerged as alternatives to traditional pump-and treat-systems.
35

42. 7. Chemical dehalogenation
• This treatment technology is used to dehalogenate (remove halogens)
halogenated compounds.
• During chemical dehalogenation, contaminated soils and reagents are
mixed, and heated in a treatment vessel.
• Reagents could be either sodium bicarbonate (base-catalyzed
decomposition process—BCD) or polyethylene glycol (alkaline polyethylene
glycol or glycolate technology—APEG).
• Dehalogenation was successful in removing PCBs, PCDD/Fs and pesticides
from soil.
• An example of this may be given by the change of trichlorethylene into
ethene.
36

43. 8. Soil vapour extraction (SVE)
• Soil vapour extraction is a popular technology for remediation of soils.
• It is a relatively simple process to remove volatile and easily evaporated
organic contaminants within the vadose zone.
• Technical processes of these technology comprise injecting clean air into the
unsaturated zone to effect a separation of organic vapours from the soil
solution by partitioning between the soil solution and the soil air.
• The vapours joining the soil air are then removed via vacuum extraction
wells.
37

44. 9. Soil washing
• Soil washing is also known as mechanical scrubbing, soil scrubbing,
physical separation or attrition scrubbing.
• This approach can be either ex-situ or in-situ .
• It is a water-based approach for treating excavated soils.
• It makes use of the selective binding of contaminants to fine material ( silt
and clay) rather than to coarse soil material such as sand and gravel.
• Adding chemical additives or surfactants to the water may enhance this
process.
• After separating the two soil fractions, fine material carrying the major part
of contaminants is further treated by other methods of remediation to get
rid of the separated contaminants, while the coarse material if cleaned up
may be returned to the plot.
39

45. 10. Soil flushing
• Soil flushing is a remediation method used for in situ treatment of inorganic
and organic contaminants.
• Known sometimes as the cosolvent flushing method, this technique
depends upon injecting a solvent mixture such as water and alcohol or
surfactants into the vadose or saturated zone.
• The leachate i.e. the solvent with leached contaminants is drawn from
recovery wells to be treated above ground or be disposed of.
Diagrammatic illustration of soil flushing techniques
41

46. 11. Solidification / stabilisation methods
• This is a group of technologies aiming at immobilising or stabilising
contaminants in the soil and preventing them from entering the
environment either by enclosing them into a solid mass or
converting them to the least soluble , mobile or toxic form.
• Used for soils contaminated with heavy metals, radionuclides,
organic compounds.
43

47. a. Bitumen- based solidification
• In this technology, the
contaminated material is
embedded in molten bitumen
and left to cool and solidify.
• The contaminants thus
encapsulated in the molten
bituminous mass are changed to
an immobile form that cannot
enter the environment.
Refined asphalt
44

48. b. Encapsulation in thermoplastic
materials
• Thermoplastic materials (e.g. Modified sulphur cement)
are molten and mixed with the contaminated material in
special tanks and vigorously mixed to form a
homogenous slurry fluid.
• After cooling the resulting solid may safely be disposed
of.
45

49. c. Polyethylene extrusion
• The contaminated soil is mixed with
polyethylene binders, heated and then left to
cool.
• The resulting solid may be disposed of or used in
other ways.
46

50. d. Pozzolan / Portland cement
• Pozzolanic-based materials ( e.g. fly ash, kiln
dust, pumice) are mixed with the contaminated
matter in presence of water and alkali additives.
• At this environment, heavy metals may
precipitate out of the slurry.
• The rest mass solidifies enclosing the remaining
organic contaminants.
47

51. Remediation
technology
Chemical and
physical treatment
Oxidation
Photolysis
AOPs
Ion exchange
Adsorption
Pump-and-treat
Chemical
dehalogination
Soil vapour
extraction
Soil washing
Soil flushing
Solidification/
stabilization methods
Thermal treatment
Incineration
Thermal desorption
Vitrification
Biological treatment
In situ
Ex situ
48

52. Thermal treatment
49

53. Thermal treatment
• Volatilisation and destruction of contaminants
by thermal treatment is a very effective
technique .
• It is achieved by heating the contaminated soil in
kilns to temperatures between 400 and 700°C,
followed by further treatment of the kiln off gas
at higher temperatures( 800- 1200°C) to secure
total oxidation of the organic volatile matter.
50

54. 1. Incineration
• In this technology, contaminants are combusted at high temperatures
(970°C - 1200°C) .
• It is particularly effective for halogenated and other refractory organic
pollutants.
• Properly operated incinerators may be of very high destruction and removal
efficiency (DRE) reaching to as much as 99.9 %, which is normally required
for PCB' s and dioxins.
Ex situ incineration includes the excavation of contaminated soils, which are
incinerated under oxygen-rich conditions. Off-gases are collected for reuse or disposal.
51

55. 2. Thermal desorption
• Other than incineration, Thermal desorption (TD) technology aims to
physically separate the contaminants from the soil.
• TD involves the application of heat to contaminated soils with the intention
of volatilizing/desorbing hydrocarbons, which are then carried away by a
sweep gas or vacuum and eventually destroyed via incineration or carbon
adsorption.
• TD can be divided into low-temperature thermal desorption (LTTD, 100–
300 °C) and high-temperature thermal desorption (HTTD, 300–550 °C).
Schematic diagram of a Thermal desorption system
52

56. 3. Vitrification
• In this process the contaminated soil is encapsulated into a monolithic mass
of glass.
• Vitrification may be carried out in situ or ex situ.
• Introducing graphite electrodes into the soil and heating it electrically by
powerful generators to temperatures between 1600-1800 °c perform in situ
Vitrification.
• At these temperatures the soil melts and forms a glass block on cooling.
• Organic contaminants are pyrolysed and reduced to gases during the
melting process, while heavy metals remain enclosed in the stabilised glass
mass.
• This method has also been successfully used in treating soils contaminated
by radioactive materials.
• Vitrification may also be done in special appliances where contaminated
soil would be molten in presence of borosilicate and soda lime to form a
solid glass block.
53

57. In situ vitrification
54

58. Remediation
technology
Chemical and
physical treatment
Oxidation
Photolysis
AOPs
Ion exchange
Adsorption
Pump-and-treat
Chemical
dehalogination
Soil vapour
extraction
Soil washing
Soil flushing
Solidification/
stabilization methods
Thermal treatment
Incineration
Thermal desorption
Vitrification
Biological treatment
In situ
Ex situ
55

59. III Biological remediation
56

60. Biological remediation
57
• Vegetation (Phytoremediation)
• Several plant species have the
ability to bioaccumulate heavy
metals found in the soil.
• Some tree species can sequester,
destroy, and/or evapotranspire
various organic compounds.
• Naturally occurring micro-
organisms in the soil
• Many microorganisms can
transform hazardous
chemicals to substances that
may be less hazardous.
Capable of degrading toxic materials, while carrying out
their daily biological activities.

61. Bioremediation
In situ
Phyto-
remediation
Microbial
bioremediation
Ex situ
Slurry phase
treatment
Solid phase
treatment
58

62. In situ bioremediation
Microbial
bioremediation
Bioventing
Bioaugmentation
Nano-bioremediation
Phytoremediation
Phytoextraction
Rhizofiltration
Phytodegradation
Enhanced
rhizosphere
biodegradation
Phtovolatilization
59

63. Phytoremediation
60

64. 1. Phytoextraction
62

65. Threshold for different metals
• A metal hyperaccumulator is a plant which, when grown
in metal-enriched habitats, can accumulate 100–1,000-
fold the level of metals than normal plants can.
• This corresponds to concentrations in aboveground
tissues of:
• >10 mg g−1 (1 %) for Mn or Zn;
• >1 mg g−1 (0.1 %) for As, Co, Cr, Cu, Ni, Pb, Sb, or Se
• >0.1 mg g−1 (0.01 %) for Cd
63

66. Use of hyperaccumulators
64
Thlaspi caerulescens Brassica juncea
For example, B. juncea, although with only one-third the
concentration of Zn in its tissues compared with T. caerulescens (a
known hyperaccumulator of Zn), is considered to be more effective
at removing Zn from soils.
This advantage is primarily due to the fact that B. juncea produces
ten times more biomass than T. caerulescens .

67. Mechanism of phytoextration
• Generally, only a small fraction of the total content is readily
available (bioavailable), as most of the metals are commonly found
as insoluble compounds or are strongly bound to the soil matrix.
65
Bioavailability
of metals
Secretion of
phytosiderophores
to chelate and
solubilize metals
Acidification of the
rhizosphere due to
proton pumps and
exudation of
organic acids

68. 2. Rhizofilteration
• Rhizofilteration is a process through which a well developed root system
is used as a filter for metals.
• This process takes place more readily in water than in soil and that is
why it is mainly used to extract metals or radioactive matter from water.
• Other than in the phytoextraction process, here only the roots, where
the metal accumulation has taken place, are harvested and disposed of.
66
• In rhizofiltration, the
contaminants are adsorbed or
absorbed, i.e., plant roots
precipitate and concentrate toxic
metals from polluted effluents.

69. • Terrestrial rather than aquatic plants may also be used
because the former have extensive fibrous root systems
covered with root hairs with extremely large surface
areas.
• Roots of many hydroponically grown terrestrial plants
such as Helianthus annuus, Phragmites australis, and
various grasses have been used to remove toxic metals
such as Hg, Cu, Cd, Cr, Ni, Pb, Zn, and uranium from
aqueous solutions
67
Phragmites australis
Common reed
Typha domingensis
Bardi
Helianthus annus
The common sunflower

70. 3. Phytodegradation
• Phytodegradation utilises plants to
uptake / degrade organic
contaminants in soils.
• Internal process: through
metabolic processes.
• External process: enzymes break
down contaminants.
• Examples: chlorinated solvents
and herbicides.
68

71. 4. Enhanced rhizosphere biodegradation
• Rhizodegradation refers to the
breakdown of contaminants within the
plant root zone, or rhizosphere.
• Rhizodegradation is believed to be
carried out by bacteria or other
microorganisms whose numbers
typically flourish in the rhizosphere.
• Microorganisms (yeast, fungi or
bacteria) consume and digest organic
substances for nutrition and energy.
69

72. 5. Phytovolatilization
Phytovolatilisation refers to plants being capable of absorbing organic
contaminants from the soil, biologically converting them to gaseous
species.
70
Phytovolatilization is often considered
beneficial, as phytovolatilization of the
contaminant generally results in substantial
dilution and photochemical decay in the
atmosphere.
However, phytovolatilization may be viewed
as a risk in urban areas, where exposure
potential exists and air quality is degraded.

73. Phytovolatilization of heavy metals
• This technique can also be used for some heavy metals like Hg and
Se because these metals can form volatile chemical species through
reduction and methylation reactions.
• Biological volatilization has the advantage of removing Se from a
contaminated site in relatively nontoxic forms, such as
dimethylselenide (DMSe).
• Nevertheless, phytovolatilization of Hg may cause secondary
contamination of the environment with Hg0.
• For this reason, another alternative to promote a higher efficiency of
phytoextraction could be the use of genetic engineering to integrate
genes from other organisms in plants so that they could accumulate
Hg without releasing Hg0 into the atmosphere.
71

74. Plant mechanisms work together
72

75. Advantages of phytoremediation
• It can be applied to more multiple and mixed
contaminants and media.
• It is less costly and if properly managed is both
environmentally friendly and aesthetically
pleasing to the public.
73

76. Limitations of phytoremediation
• A longer time period is likely to be required for
phytoremediation, as this technology is dependent on
plant growth rates for establishment of an extensive root
system or significant aboveground biomass.
• Phytoremediation is most effective only at sites with
shallow contamination in the soils and/or sites with
shallow water table.
74

77. Bioremediation
In situ
Phyto-
remediation
Microbial
bioremediation
Ex situ
Slurry phase
treatment
Solid phase
treatment
75

78. Microbial bioremediation
76

79. Microorganisms
77
Microorganisms can be
isolated from almost
any environmental
conditions.
They can adapt and grow at varied temperature and
pH values.
They can live with an excess
of oxygen and in anaerobic
conditions

80. Microbial bioremediation
78
• Microbes can adapt and grow with the
presence of hazardous compounds or on
any waste stream.
• Thus, they can be used to degrade or
remediate environmental hazards.
• Natural organisms, either indigenous or
extraneous (introduced), are the prime
agents used for bioremediation.
• The organisms that are utilized vary, depending on the chemical
nature of the polluting agents, and are to be selected carefully as they
only survive within a limited range of chemical contaminants.

81. Microorganisms Having Biodegradation Potential for Xenobiotics
79

82. Microbes utilizing Heavy Metals
80

83. Mycoremediation
81
White rot fungus accounts for at least 30% of the total research on fungi used in
bioremediation. White rot fungi have been used for bioremediation of
pesticides, degradation of petroleum hydrocarbons.
Pleurotus ostreatus
Degrade PAHs
Trametes versicolor
Degrade PAHs, PCBs
Lentinus edodes
Degrade
pentachlorophenol
(PCP)

84. In situ bioremediation
Microbial
bioremediation
Bioventing
Bioaugmentation
Nano-bioremediation
Phytoremediation
Phytoextraction
Rhizofiltration
Phytodegradation
Enhanced
rhizosphere
biodegradation
Phtovolatilization
82

85. 1. Bioventing
• In situ treatment and involves supplying a gas and nutrients through wells into the
subsurface to stimulate the indigenous bacteria.
• The gas can be used to keep the subsurface aerobic or anaerobic to enable
degradation to occur.
• It works for simple hydrocarbons and can be used where the contamination is deep
under the surface.
83
Schematic diagram of a typical bioventing
system

86. Aerobic bioventing
• Treating aerobically degradable contaminants, such as fuels.
• Using the supplied oxygen, the microbes oxidize the contaminants
to gain energy and carbon for growth.
• Oxygen is typically introduced by air injection wells that push air
into the subsurface.
84

87. Aerobic bioventing (cont.)
Aerobic bioventing has treated a variety of
contaminants such as:
• Fuels
• Nonhalogenated solvents, such as benzene, acetone,
toluene, and phenol
• Lightly halogenated solvents, such as 1,2-dichloroethane,
dichloromethane, and chlorobenzene
• SVOCs, such as some PAHs
85

88. Anaerobic Bioventing
• While aerobic bioventing is useful for degrading many
hydrocarbons, some chlorinated compounds such as PCE, TCE,
some PCBs and some pesticides, such as lindane and DDT are not
effectively treated aerobically.
• Anaerobic bioventing uses the same type of gas delivery system as
aerobic bioventing, but instead of injecting air, nitrogen is used to
displace the soil oxygen.
• The reductive dehalogenation is done by anaerobic bacteria such as
Dehalococcoides and Dehalobacter.
86
Reductive dechlorination of PCE

89. • Since aerobic and anaerobic bioventing share similar gas
delivery systems, the switch can be made by simply
changing the injected gas.
87
Aerobic bioventing
Volatile and semivolatile organic compounds
(not anaerobically degradable)
Anaerobic bioventing

90. 2. Bioaugmentation
• Bioaugmentation is the way to enhance biodegradative capacity of
the contaminated sites by inoculation of bacteria with desired
catalytic capabilities.
• The basic principle of this intervention is to enhance genetic
diversity leading to a wider repertoire of biodegradative reactions.
• Bioaugmentation is the remediation process involving wild-type or
genetically modified microorganisms for treatment of sites
contaminated with hazardous organic chemicals.
88

91. Construction of GMMs
• Genetic engineering is a modern technology, which allows to design
microorganisms capable of degrading specific contaminants.
• It offers opportunity to create artificial combination of genes that do not
exist together in nature.
• The most often techniques used include engineering with single genes or
operons, pathway construction and alternations of the sequences of existing
genes.
89

92. • Bacteria, especially from genus Pseudomonas are the major
object of genetic manipulations.
• There are ubiquitous inhabitants of many environment and
are known as efficient degraders of many toxic substances.
• Both their chromosome and plasmids may carry genes for
metabolism of these compounds.
• Therefore, such microorganisms are the main source of
catabolic genes for genetic engineering.
90

93. GMMs degrading organic compounds
91

94. 3. Nanobioremediation
• The possibility of using physicochemical technology (fast, but expensive) to
treat the high concentrations initially followed by biological technology
(cheap, but relatively slow), is presented as a viable practical and
sustainable alternative to in-situ application.
• This remediation method is known as Nanobioremediation, and the
scientists are currently evaluating the potential of this technology for its
effectiveness and sustainability for residual clays contaminated with
chlorinated organic contaminants.
92
Concept of nanobioremediation: Initial injection of nZVI to reduce the source zone concentrations and then
initiate biormediation of residual source contamination (if any) and any produced byproducts.

95. Bioremediation
In situ
Phyto-
remediation
Microbial
bioremediation
Ex situ
Slurry phase
treatment
Solid phase
treatment
94

96. b) Ex situ biological remediation
• Ex situ bio remedial methods involve excavation
of soil and treat it at a different site.
• These methods are normally faster than the in
situ methods.
• They are applicable for a wider range of
contaminants, yet they are more expensive.
95

97. 1) Slurry phase treatment
• In this technology the polluted soil is excavated and transported to special facilities,
where, it is mixed with water in special tanks (bio reactors).
• Oxygen and nutrients are later added, and the so formed mixture is thoroughly mixed
to form a thin slur.
• Temperature, nutrients and oxygen concentrations are controlled so that the
organisms may have the best conditions to sustain their bioactivities leading to the
degradation of the pollutants.
96

98. 2) Solid phase treatment
• Here the polluted soil is treated above the
ground in prepared beds.
• Despite the benefit of being less expensive than
the slurry bed treatment, it is not so effective
and needs more time and space to prepare the
beds.
• Three main techniques are commonly used to
carry out this remediation method - land
farming, soil biopiles and composting.
97

99. a) Land farming
• The soil is excavated and spread on a pad with a built in system for
collecting any possible leachates seepage.
• The so-formed bed is regularly mixed and turned over in order to
facilitate aeration and enhance biological activity in the bed.
• Nutrients are added if required, since lack of nutrients and oxygen
may lead to retardation of the bio degradation processes.
98

100. b. Composting
• Composting is the technique that involves combining contaminated
soil with nonhazardous organic amendments such as manure or
agricultural waste.
• This supports the development of rich microbial population
characterized at higher temperature for growth.
• Composting takes place between 40 and 50 °C and the thermophilic
microorganisms are active at this temperature.
• Proper conditions of oxygen, moisture, and temperature are
maintained.
• Frequent mixing is carried out for aeration and surface irrigation is
done for maintaining moisture level.
99

101. • Microorganisms degrade organic matter to CO2, water, and humic acid as
end products.
• Degradation is brought about by a consortium of aerobic organisms,
predominantly bacteria, fungi, and actinomycetes.
• They break down complex organics to smaller molecules which are used
as carbon and energy sources.
• Compost is either dark brown or black and is not soluble in water.
• Composting has been successfully applied to soils and bio-solids
contaminated with petroleum hydrocarbons, e.g., fuels, oils, grease,
solvents, chlorophenols, pesticides, herbicides, and nitro-aromatic
explosives.
100

102. c) Soil biopiles
• The excavated soil is heaped in piles of several meters height.
• To enhance degradation activities by the microorganisms, air is blown
through the pile.
• If required, nutrients are also added.
• Due to emissions from the piles, the whole process is sometimes carried
out in inclusions that control any volatile contaminants.
101

103. Comparison of different methods of bioremediation
LimitationsBenefitsType of
bioremediation
Long durationNatural atenuationIn situ
bioremediation:
Bioventing
Bioaugmentation
Mass transfer problem
Long duration
Low costLand farming
Composting
Biopiles
Require soil
excavation
High operatoional cost
Rapid degradation
Optimized parameters
Ex situ
bioremediation:
Slurry reactors
102