Cadmium Adsorption by Mixedculture Biofilms under Metabolizing and Nonmetabolizing Conditions

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Cadmium Adsorption by Mixed-culture Biofilms
under Metabolizing and Non-metabolizing Conditions

• Jose Roberto Diaz
• University of Puerto Rico at Mayaguez
• August 3, 2006
• Advisors Dr. Robert Nerenberg
• Dr. Jeremy Fein
• Mentors Leon Downing
• Brian Ginn

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Introduction

• Heavy metals are common cause of pollution
• Conventional treatment methods increasingly
  expensive
• Microorganisms treat heavy metal-polluted wastes

heavy metals polluted waters
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Introduction

• Immobilized systems
• Biofilms in wastewater treatment
• Immobilized-cell bioreactor technology
• Microbial treatment may be more cost effective

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Introduction

• Prior adsorption work
• Why biofilms?
• Why live vs. dead?

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Introduction
Metabolizing vs. Non-metabolizing
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Objectives

• Determine extent of Cd adsorption onto
  mixed-culture bacterial system under two
  conditions
• biofilm growth, metabolically active
• biofilm growth, metabolically inactive

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Experimental method
Biofilm Growth
Air is humidified to provide O2 as the electron
acceptor
Acetate Feed 16mM Phosphate buffer with
16.6356g CH3COOK (1 g/L acetate) to provide
acetate as the electron donor
Air
N2
Q 1mL/min Retention time of 60 min
Continuous flow packed bed reactor
To waste
reactor is inoculated with Mishawaka activated
sludge
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Experimental method

• Cd Adsorption

Bulk solution

• no ammonium
• 2 ppm Cd
• 70 ppm Acet (dead)
• 150 ppm Acet (live)

Cs-irradiation 35,000 rads/hr
divide to test tubes (5 mL each)
add one-tenth of a gram of biofilm to each test
tube
mix for approximately 2 hours centrifuge and
filter
analyze samples
Cd in bulk liquid by ICP-OES
Acetate by Ion Chromatography
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Results and discussion

• Live or Dead?
• Acetate consumption
• Cd Adsorbed

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Live or Dead?
Live-Dead staining

• metabolically inactive

• metabolically active

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Acetate Consumption (live)
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Acetate Consumption (dead)
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Discussion

• bacteria are surviving the radiation treatment
• Non-metabolizing bacteria are still consuming
  acetate in some samples more than others
• Metabolizing bacteria seem to be adsorbing less
  Cd (27) than samples that have non-metabolizing
  bacteria (49)

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Conclusions

• Radiation treatment is not effective in killing
  bacteria and must be modified
• Non-metabolizing bacteria certainly showed an
  effect on how much Cd was adsorbed
• Samples with varying amounts of acetate
  consumption adsorbed around the same percent of
  Cd for metabolizing and non-metabolizing bacteria

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Future work

• Different method of killing bacteria
• Non-metabolizing vs. metabolizing in suspended
  growth system
• Different electron acceptors and donors for
  growing biofilm

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Acknowledgements

• EMSI
• CEST
• Dr. Valli Sarveswaran
• Leon Downing
• Brian Ginn
• Dr. Jeremy Fein
• Dr. Robert Nerenberg