Mass Transfer and
Bioremediation of PAHs in a
Bead Mill Bioreactor
Ryan Riess
PINTER and Associates
October 13, 2006
Outline
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Background
Experimental Procedures
Mass Transfer experiments
Biodegradation experiments
Scale up experiments
Summary/Conclusions
Questions
Background
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Polycyclic aromatic hydrocarbons (PAH’s)
are very stable, toxic compounds
Most are very hydrophobic, requiring
enclosed reactors to ensure minimal stripping
losses
Associated with oil and gas processing
Background
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PAH contamination in soil is usually free
solid particles or as large particles sorbed
directly to the organic portion of the soil.
PAHs generally have extremely low rates of
biodegradation because of low water
solubility, high hydrophobicity and low
bioavailability
Dissolution limited biodegradation
Background
Background
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Naphthalene, a simple PAH can be
biodegraded in a roller bioreactor using
Pseudomonas putida
Rate limiting step mass transfer rate
This project - economically increase the mass
transfer, biodegradation rates in a rotating
bioreactor
Concentration (mg/L)
Typical Biodegradation curve (Black, 1996)
250
Substrate
200
Biomass
150
100
50
0
0
2
4
Time(hours)
6
8
Concentration (mg/L)
Mass Transfer Controlled
600
Naphthalene
500
Biomass
400
300
200
100
0
0
20
40
Time (hours)
60
Approach
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Needed to increase mass transfer rates within
bioreactor
Explored some different options including
faster rotation, different reactor types and
baffles within reactor
Settled upon addition of inert particles to
roller bioreactor
Experimental Procedures
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Experiments were carried out in 1L working volume
Temperature: 22-23 °C
Pseudomonas putida was used as the candidate
bacterium
Bioreactor rotated at 50 rpms
Analysis carried out on HPLC
Mass Transfer Variations
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Used 3 mm glass beads for loading
experiments
Did experiments varying initial naphthalene
concentrations from 500 mg/L to 10,000 mg/L
Used some 1 mm beads, 5 mm beads, and 3
mm Raschig rings for comparison
NAPHTHALENE MASS TRANSFER: BEAD
LOADING
D isso lved N ap h tah len e (m g /L )
40
Loading 50%
30
25%
20
10%
10
Control
0
0
2
4
6
Time (h)
8
10
Increasing naphthalene concentration
2.5
k L a (1/h)
2
50% Loading
1.5
25%
1
10%
0.5
Control
0
0
2000
4000
6000
8000
10000
Particulate concentration (mg/L)
12000
Naphthalene Concentration in the
liquid phase (mg/L)
Inert particle size and type
40
C o nt ro l
R a s c hig rings
1 m m G la s s be a ds
30
3 m m G la s s be a ds
5 m m G la s s be a ds
20
10
0
0
1
2
3
Time (h)
4
5
Mass Transfer Quantification
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Ln((CL*-CL)/CL*)=-Klat
Where:
CL*=saturation concentration of naphthalene
(mg/L)
CL= concentration of naphthalene (mg/L)
Kla= volumetric mass transfer coefficient(1/h)
t = time (h)
Mass Transfer Quantification
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Volumetric Mass Transfer coefficients (1/h)
Control:
0.06
10% beads: 0.17
25% beads: 0.34
50% beads: 0.52
Mass Transfer Summary
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Optimum: 5 mm beads, 50% loading
Naphthalene
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Methylnaphthalene
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70 hours, 8 hours
212 hours, 28 hours
Dimethylnaphthalene
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148 hours, 12 hours
Biodegradation Procedure
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Followed literature procedures as closely as
possible
Increased mass transfer rates demanded more
oxygen
Total naphthalene concentration
Naphthalene Concentration in the
liquid phase (m g/L)
Biodegradation results naphthalene
600
Control (no beads)
500
25% Loading
50% Loading
400
300
200
100
0
0
10
20
30
Time (h)
40
50
Biodegradation methylnaphthalene
M eth yl Nap h th alen e (m g /L )
600
500
400
300
Control
200
100
Optimum BMB
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0
50
100
Time (h)
150
200
Scale up biodegradation
Naphthalene Concentration(mg/L)
Scale up biodegradation
600
400
200
0
0
10
20
30
Time(h)
40
50
Toxicity?
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Experiments performed with brine shrimp
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96% alive after two hours – control
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89% alive in bioreactor effluent
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0% alive in saturated naphthalene solution
Biodegradation Summary
PAH compound
Roller Bioreactor
Bead Mill Bioreactor
Naphthalene
10.5
118.8
2-Methyl Naphthalene
2.7
22.8
Naphthalene
(in mixture)
9.9
98.8
2-Methyl Naphthalene
(in mixture)
3.4
31.4
Scale up naphthalene
10.9
148
Literature comparison (Naphthalene)
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Freely suspended cells, partitioning reactor:
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Large scale partitioning reactor
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85 mg/L-h (Janikowski et. al, 2002)
119 mg/L-h (Daugulis et. al, 2001)
Present work (Free cells)
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148 mg/L-h
Conclusions
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Bead Mill Bioreactor Increases Mass Transfer
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Bioremediation of PAHs Increased Up to
Fourteen Fold
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Product of reactor exhibits greatly improved
toxicity
Applications/Recommendations
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Treating PAH contaminated water
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Work with Naphthenic acids
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Work with PAH contaminated soil
Acknowledgements
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John Headley-Environment Canada
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Gordon Hill, Mehdi Nemati
Questions?