Copper Adsorption through Chitosan Immobilized on Sand to Demonstrate the Feasibility for InSitu Soi

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Copper Adsorption through Chitosan Immobilized on
Sand to Demonstrate the Feasibility for In-Situ
Soil Decontamination

• Meng-Wei Wan, Ph.D.

Department of Environmental Engineering and
Science
College of Environment
Chia Nan University of Pharmacy and Science
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Outline

• Introduction
• Methodology
• Chitosan immobilized on sand
• Copper adsorption isotherm
• Desorption study
• Conclusion

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Problem

• Ubiquitous contamination by toxic metals raises
  serious environmental and health issues
• Industrial and mining wastes are the most
  significant sources of environmental pollution by
  heavy metals

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Current Technologies

• Physical-Chemical processes for water treatment
• Filtration
• Chemical precipitation
• Ion exchange
• Adsorption
• Electro-deposition
• Membrane systems
• Excavation followed by burial at a hazardous
  waste site for soil treatment

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Drawback

• Expensive High capital cost or high maintenance
• Disruptive nature
• Inadequacy at removing trace levels of metals
• Only efficient for certain concentrations

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Biological Technologies

• Bioremediation
• Phytoremediation
• Advantage
• Cost-efficient
• Non-disruptive
• Easy to maintain

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Challenge

• Microorganisms do not have the ability to degrade
  metals but rather to transform them
• Phytoremediation is only effective for low to
  moderate contamination and may take long periods
  of time

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Bioremediation Technology
(A) Bioventing
(B) air sparging
(C) on-site bioreactors
(D) in situ simulation
(E) zonal bioremediation
(Yen, Environmental Chemistry. VOL. 4B)
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In-situ Bioremediation

• Microbially derived polymers can be efficiently
  used as binding agents to help the soil matrix
  become stronger and less permeable - stop the
  migration of hazardous leachates
• Biopolymers can prevent fluid migration by
  promoting the generation of biopolymer-filled
  soil layers to generate a capsule around the
  spill - similar to slurry wall
• Pollutant plume will be sealed off so that
  naturally-occurring bioremediation can take place
  preferentially in the remaining less-contaminated
  regions

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Methodology

• A feasibility study indicates that biopolymer
  coated sand can remove metals in ground water
  efficiently
• A permeable reactive barrier

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Supporting Facts

• The use of chelating materials can hold great
  potential for metal adsorption and removal from
  both water and soils.
• Biopolymers are high molecular weight compounds
  and also can be produced by different living
  organisms
• Biopolymers have many repeating units and can
  survive in diverse geological conditions

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Three Types of Biopolymers

• Chelating polymers (polycationic)
• Chitin/ Chitosan
• Fungal Mycelia
• Stabilization or crosslinking polymers
  (polyanionic)
• Xanthan
• Bacteria Xanthomonas campestris
• Binding polymer (semi-penetrating network former)
  
• PHB (poly 3-hydroxbutyrate)
• Bacteria Alcaligenes eutrophus

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Chitin and Chitosan

• One of the most abundant biopolymers in the
  biosphere is chitin - linear structure composed
  of N-acetyl-glucosamine residues, and its
  de-acetylated derivatives are called chitosan
• Main sources are from the animal and plant
  kingdoms
• The shells of crustaceans and mollusks
• The algae commonly known as marine diatoms
• The cell walls of fungal species

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Structure of Chitin and Chitosan
Chitin
Chitosan
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Chitosan

• Is an abundant and inexpensive natural source
• Contains many reactive sites including the
  repetitive amino groups.
• Is an excellent chelating material for metals.
• Can be used alone, as cross-linked chitosan, or
  in the form of several derivatives.

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Chitosan Immobilized on Sand
5 g Chitosan 100 g Sand
Stirred for 5 hours
Neutralized with NaOH
dissolved in 5 HCl
Particles' size greater then 0.5 mm were
collected as adsorbent
Drop by drop
Filtered from solution, washed and dried in oven
Chitosan bind with sand formed by precipitation
Grinded and sieved
Chitosan-Coated Sand
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Copper Adsorption Isotherm

• Cu (II) solutions of different concentrations
  were prepared in deionized water using CuSO4
• An adsorbent was mixed with metal solution at
  different concentrations
• A shake machine, reaching a static speed of 50
  rpm, provided continuous mixing
• The contact times were 2 hr, 4 hr and 6 hr
• Cu concentrations were analyzed by AA Spectrometer

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Adsorption Capacity

• Equation

Where
C0 Initial Cu2 conc. (mg/L)
C Final Cu2 conc. (mg/L)
V Volume (L) of Cu2 solution
W Weight (g) of the adsorbent

• Adsorbents can be chitosan-coated sand, pure
  chitosan and sand used alone

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Cu2 adsorption capacity mg Cu2/g chitosan
In this case mg Cu2/g sand only
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Explanation

• Its three dimensional structure, which is
  different for each of the adsorbents used, and
  thus may fit differently with Cus ionic size
• The chelating groups of chitosan (amino groups
  especially) allow for different chelating
  combinations, making the interaction with metal
  complex
• Combining chitosan with sand, chitosan may have
  changed its three dimensional structure to one
  that fits better for the interaction with Cu

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Adsorption Model

• Langmuir equation is valid for monolayer
  adsorption
• The model contains a limited number of sites and
  predicts a homogeneous distribution of adsorption
  energies

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• Langmuir Equation

Where
KL Langmuir equilibrium constant (L/g)
Cads amount of Cu2 adsorbed (mg/g),
Ceq equilibrium conc. of Cu2 in solution
(mg/L) ,
b Langmuir constant (L/mg)
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• The chitosan used in our study has a high degree
  of purity (high nitrogen content of 7.57), which
  is very closed to the calculated value (7.91)
• The ratio of N/Cu from different adsorption
  studies are listed

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Desorption Study

• Deionized water, dilute acetic acid solutions and
  5 HCl acid solutions were used
• Certain quantity of solutions were added to each
  adsorbent with different concentrations of Cu2
  adsorbed (from the adsorption studies)
• The solutions were shaken for two hours
• Cu concentration in each supernatant was
  determined by the AA Spectrometer

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Most naturally occurring acid streams are above
pH3
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Conclusion

• The feasibility of meal uptake from ground water
  has been demonstrated.
• The metal adsorption follows the Langmuir
  isotherm.
• It is possible to regenerate the metals recovered
  from waste ground water.

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Conclusion

• Permeable reactive barrier is a suitable example
  of this work.

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Thank You
Questions?