Colonization, biofilm formation and biodegradation of polyethylene by soil bacteria

Colonization, biofilm formation and biodegradation of polyethylene by soil bacteria Alex Sivan The Institute for Applied Biosciences and The Department of Biotechnology Engineering, Ben

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

Polyethylene for soil mulching

In the U.S ~ ca 1,000,000 Ton/year in agriculture

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; > 400 years for degradation

Polyethylene recycling

• Applications: fences, side-walks, acoustic walls.

• Cost of recycled products.

• Currently, only ca 15% of the waste is recycled.

Alternative polyethylenes

–Contains toxic metals Contains toxic metals.

–Requires long exposure to sunlight Requires long exposure to sunlight.

PE degradation in soil

0 10 20 30

40

Loess A Ein Tamar Loess B

Peat

Temperature (C°)

Weight loss (%)

Soil

Control Bacteria

• Polyethylene: Linear LDPE; M.W 100,000

U.V photosensitizer - iron chelate (5%)

• ca 100 mg polyethylene in carbon free

20

15 10

5 0

Effect of pH

0 2 4 6 8 10 12

Biofilm on polyethylene

0.20 0.16

0.12 0.08

0.04 0.00

70 80 90

100

Log hexadecane Stat hexadecane Log octane

Hydrophobicity of PE - degrading bacteria

measured by contact angle

Medium pH

Bacillus 707 36.7±1.5 60.6±4.0 62.0 ± 3.4

Bacillus 712 51.6±2.8 58.3±2.8 69.6

±0.5

Rhodococcus rhodochrous 49.2 ± 2.9 67.5 ±

40 35

30 25

20 15

10 5

0 0 1 2 3 4

Effect of mineral oil on biofilm formation

Biofilm + Mineral oil (16hr)

Biofilm + Mineral oil (7 days)

Incubation time (days)

(%;v/ v)

0.01 2* 3 3 3 Mineral oil 0.05 3 4 4 4

0.1 3 4 4 4

0.1 0 0 0 0 Tween 60 0.5 0 0 0 0

1.0 0 0 0 1 Control 0 0 1 1

Effect of an anionic surfactant and mineral oil on biofilm formation on polyethylene

* Biofilm density index: 0 = No biofilm; 4 = Dense biofim Mix C30

0 0 2 0.05 0.1 0

10 20 30 40 50

Mineral oil concentration (%)

300 200

100 0

0.0 0.1 0.2

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

90 75

60 45

30 15

0 0 5 10 15 20

Low density PE

0 0.5 1 1.5 2 2.5

500 1000

1500 2000

2500 3000

3500 4000

Effect of U.V on polyethylene

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

1300 1400

1500 1600

1700 1800

120 Hr U.V.

60 Hr U.V.

100 Hr U.V.

PE degradation with strain 707

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1300 1400

1500 1600

1700 1800

1718

1463

Carbonyl index of U.V irradiated PE

incubated with strain 707

Degradation of CH 2 groups

U.V + 30 days incubation

0 0.5 1 1.5 2 2.5

0 1000

2000 3000

0 1000

2000 3000

U.V 60 Hr

0.5 1.5 2.5

0 1 2

2500

2700 2900

2500

2700 2900

1 2 3 4

0 20000 40000 60000 80000 100000

Mineral oil degrading bacteria

st.208 st.489 st.490 st.547 st.555

I -707 II-707

I -707 II-490+555

I -490+555 II-490+555

I -707+490+555 II-707+490+555

Effect of combinations of bacteria on PE degradation.

Reduction of gravimetric weight

1st incubation 2nd incubation 1st+2nd

Effect of combinations of bacteria on PE degradation

Reduction in molecular weight

35

1st incubation 2nd incubation 1st+2nd incubation

• 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

Irit Gilan Deborah Bitty

Dr Valentina Pavlov

Dr Mark Karpassas Prof Shimona Geresh

Collaborators