Transcript Slide 2

SAB 4973:
HAZARDOUS WASTE
TREATMENT TECHNOLOGIES
Technologies
• Chemical methods
Coagulation, flocculation, combined with flotation
and filtration, precipitation, ion exchange,
electroflotation, electrokinetic coagulation.
• Physical methods
Membrane-filtration processes (nanofiltration,
reverse osmosis, electrodialysis, . . .) and adsorption
techniques.
• Biological treatments
Biodegradation methods such as fungal
decolorization, microbial degradation, adsorption
by (living or dead) microbial biomass and
bioremediation systems
Adsorbents
• Adsorption techniques employing solid sorbents are
widely used to remove certain classes of chemical
pollutants from waters, especially those that are
practically unaffected by conventional biological
wastewater treatments. However, amongst all the sorbent
materials proposed, activated carbon is the most popular
for the removal of pollutants from wastewater
• They must have high abrasion resistance, high thermal
stability and small pore diameters, which results in higher
exposed surface area and hence high surface capacity for
adsorption.
• The adsorbents must also have a distinct pore structure
which enables fast transport of the gaseous vapors.
Most industrial adsorbents fall into one of
three classes:
• Oxygen-containing compounds – Are
typically hydrophilic and polar, including
materials such as Silica gel and Zeolites.
• Carbon-based compounds – Are typically
hydrophobic and non-polar, including
materials such as activated carbon and
graphite.
• Polymer-based compounds - Are polar or
non-polar functional groups in a porous
polymer matrix.
Concept of hydrophilic and hydrophobic
Concept of polar and non-polar
Silica gel
• prepared by the coagulation of colloidal
silicic acid results in the formation of porous
and noncrystalline granules of different sizes.
It shows a higher surface area as compared to
alumina, which ranges from 250 to 900 m2/g.
• silica is expensive adsorbent
• prepared by the reaction between from
sodium silicate and acetic acid
Silica gel
Zeolites
• natural or synthetic crystalline
aluminosilicates which have a repeating pore
network and release water at high
temperature. Zeolites are polar in nature.
• Zeolites have a porous structure that can
accommodate a wide variety of cations, such
as Na+, K+, Ca2+, Mg2+ and others.
Zeolites
Alumina
• Aluminium oxide (Al2O3), a synthetic porous
crystalline gel, which is available in the form
of granules of different sizes having surface
area ranging from 200 to 300 m2 /g
• The most common form of crystalline
alumina is known as corundum, a octahedral
crystalline.
Alumina
Activated carbon
• is the oldest adsorbent known and is usually
prepared from coal, coconut shells, lignite, wood etc.,
using one of the two basic activation methods:
physical and chemical
• is a highly porous, amorphous solid consisting of
micro crystallites with a graphite lattice, usually
prepared in small pellets or a powder. It is non-polar
and cheap. One of its main drawbacks is that it is
reacts with oxygen at moderate temperatures (over
300 °C).
Activated carbon
Structure of activated carbon
Process of producing
activated carbon
Environmental applications
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Spill cleanup
Groundwater remediation
Drinking water filtration
Air purification
Volatile organic compounds capture from
painting, dry cleaning, gasoline dispensing
operations, and other processes.
Activated carbon is
usually used in water
filtration systems.
Low cost activated carbon
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Chitosan
Banana peel
Orange peel
Bagasse pith
Saw dust
Coconut shell
Bark
Bamboo dust
Biodegradation/bioremediation
• The chemical breakdown of materials by
living organisms in environment.
• Organic material can be degraded aerobically
with oxygen, or anaerobically, without
oxygen.
• The process depends on certain
microorganisms, such as bacteria, yeast, and
fungi.
Biodegradation factors of
polymer
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Polymer structure
Polymer morphology
Effects of radiation
Molecular weight
Polymer structure
Natural macromolecules, e.g. protein, cellulose,
and starch are generally degraded in biological
systems by hydrolysis followed by oxidation.
Linear structure
Branched structure
Amylopectin
Network structure
Biodegradability
Since most enzyme-catalyzed reactions occur in
aqueous media, the hydrophilic–hydrophobic
character of synthetic polymers greatly affects their
biodegradabilities. A polymer containing both
hydrophobic and hydrophilic segments seems to have a
higher biodegradability than those polymers containing
either hydrophobic or hydrophilic structures only.
the flexible aliphatic polyesters are readily degraded
by biological systems, the more rigid aromatic polymer
compound is generally considered to be bioinert.
Polymer morphology
One of the principal differences between biopolymer
and synthetic polymers is that biopolymer do not have
equivalent repeating units along the chains.
This regularity enhances crystallization, making the
hydrolyzable groups inaccessible to enzymes. It was
reasoned that synthetic polymers with long repeating
units would be less likely to crystallize and thus might
be biodegradable.
Effects of radiation
Photolysis with UV light and the γ-ray
irradiation of polymers generate radicals and/or
ions that often lead to cleavage and
crosslinking. Oxidation also occurs,
complicating the situation, since exposure to
light is seldom in the absence of oxygen.
Molecular weight
• Low molecular weight
hydrocarbons, however,
can be degraded by
microbes.
• Plastics remain relatively
immune to microbial
attack as long as their
molecular weight
remains high.
Aerobic biodegradation pathways of
aromatic compounds in bacteria and fungi
Anaerobic biodegradation of benzoate
Methods of biodegradation
Under appropriate conditions of moisture,
temperature, and oxygen availability,
biodegradation is a relatively rapid process
Two types of microorganisms are of particular
interest in the biodegradation of natural and
synthetic polymers: bacteria and fungi.
Bacteria
Shape of bacteria
Mushroom
Type of fungi for biodegradation
• White rot mushroom
• Brown rot mushroom
• Soft rot mushroom
White rot mushroom
White rot fungi can degrade all cell wall
components, including lignin. They often cause
a bleaching of normal wood coloration. Their
ability to metabolize large amounts of lignin in
wood is unique among microorganisms.
Brown rot mushroom
Brown-rot mushroom depolymerase cellulose
rapidly during incipient stages of wood
colonization. Considerable losses in wood
strength occur very early in the decay process,
often before decay characteristics are visually
evident.
Brown-rot mushroom commonly cause decay in living trees,
downed timber and wood used in buildings.
Cell wall carbohydrates are degraded extensively during
decay leaving a modified, lignin-rich substrate .
Scanning electron micrograph of brown-rotted wood. Only
slight pressure causes the wood cell walls to crumble into
minute fragments.
Soft rot fungi
• Fungi that cause soft-rot are taxonomically
classified in the subdivisions, Ascomycota
and Deuteromycota.
• However, soft rots can occur in dry
environments and may be macroscopically
similar to brown rot.
Soft rot in wood often appears brown and can be confused
with decay caused by brown rot fungi.
Soft rot is different from other types of wood decay.
Chains of cavities are produced inside the cell wall. This
micrograph taken of a section from soft-rotted wood and
viewed with a light microscope shows cavities within the
cell walls.
Two distinct types of soft rot are currently
recognized.
•Type 1 is characterized by longitudinal
cavities formed within the secondary wall of
wood cells and
•Type 2 used to describe an erosion of the
entire secondary wall. The middle lamella is
not degraded (in contrast to cell wall erosion
by white-rot fungi), but may be modified in
advanced stages of decay.
Different of white and brown rot
White rot fungi, found in the wood of deciduous trees,
first attack the lignin of wood. Once the lignin is
digested, the fungi destroy cellulose and other major
parts of cells. The partially decayed wood with residual
cellulose is off-white in color, hence the name "white rot
fungi." Brown rot fungi, found in conifers, damage the
cellulose first but do very little, if any, damage to the
lignin. The name "brown rot fungi" came about because
infected wood becomes dark reddish-brown to golden
in color.
White Rot mushroom Degradation System:
Three types of extracellular enzymes are
produced by white rot fungi that are nonselective yet effective in attacking lignin. These
are often referred to as Lignin Modifying
Enzymes (LMEs)/ligninolytic enzymes, and
they are Lignin Peroxidase (LiP), ManganeseDependent Peroxidase (MnP) and Laccase
(Lac).
Lignin peroxidase
• LiP: Not all white rot fungi produce LiP, but it
is a key component for the fungi that are being
investigated for use.
• LiP oxidises methoxyl groups on aromatic rings
(R-O-CH3), and can work on substrates with
quite high redox potentials.
Manganese peroxidase
• MnP is another enzymes containing
peroxidase, and uses H2O2 to catalyse
oxidation of Mn²+ to Mn³+, this in turn
oxidises phenolic substrates.
• Although similar in action to LiP, it does not
have the same ability to oxidize substances
with higher redox potentials.
Laccase
• Laccase is a multi copper oxidase which has
the ability to oxidise phenolic
compounds. In the presence of oxygen, it
converts phenolic compounds into quinone
radicals and then further converts them to
quinones. It also produces some cosubstrates which can be useful for
degradation.