Colonization, biofilm formation and biodegradation of polyethylene by soil bacteria

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Colonization, biofilm formation and
biodegradation of polyethylene by soil bacteria
Alex Sivan
The Institute for Applied Biosciences and The
Department of Biotechnology Engineering, Ben
Gurion University, Beer Sheva, Israel
Environmental Engineering, 17.12.02
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Polyethylene for soil mulching
In the U.S. ca. 1,000,000 Ton/year in
agriculture
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Polyethylene waste

• 25,000,000 Ton/year
• Makes up to 40 of the plastic waste
• Highly flammable burning releases toxic gases
• Pollutes marine and fresh water habitats
• Highly recalcitrant gt 400 years for
  degradation

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Control
Bacteria
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Effect of pH
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Biofilm on polyethylene
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Biofilm Mineral oil (16hr)
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Biofilm Mineral oil (7 days)
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Mix C30
Effect of an anionic surfactant and mineral oil
on biofilm formation on polyethylene
Biofilm density index 0 No biofilm 4
Dense biofim
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Improved biodegradation of polyethylene by
mineral oil
Increased weight loss ()
Mineral oil concentration ()
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Combined photolysis and biodegradation

• Polyethylene Linear LDPE MW 100,000
• contains UV sensitizer
• UV pretreatment Accelerated Weathering
  Tester (Q.U.V)
• 60 Hr of UV 312nm

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Degradation of CH2 groups
2.5
60 Hr U.V.
2920
2
1.5
Absorbance
1
1463
0.5
0
0
1000
2000
3000
4000
2.5
2920
U.V. 30 days incubation
2
1.5
Absorbance
1
1463
0.5
0
0
1000
2000
3000
4000
Wavenumber (cm-1)
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Degradation of CH2 groups
U.V. 60 Hr
2.5
1.5
Absorbance
0.5
U.V. 30 days incubation
2.5
2
1.5
Absorbance
1
0.5
0
2500
2700
2900
3100
Wavenumber (cm-1)
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Summary

• Enrichment cultures gave rise to bacterial
  strains that could utilize PE as a sole carbon
  and energy source
• Maximal biodegradation (up to 30) was obtained
  after two-steps incubation with combined cultures
• PE degrading bacteria are hydrophobic and form a
  biofilm on the PE surface
• Mineral oil enhances biofilm formation and PE
  biodegradation
• The degrading bacteria utilize carbonyl residues
  in the PE which are formed during UV irradiation
• Combination of UV photolysis and biodegradation
  showed a synergistic effect

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Collaborators
Irit Gilan Deborah Bitty Dr. Valentina Pavlov Dr.
Mark Karpassas Prof. Shimona Geresh