Transcript MICROBES INVOLVED IN CONCRETE SEWER PIPE CORROSION

MICROBES INVOLVED IN CONCRETE
SEWER PIPE CORROSION (title)
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INTRODUCTION
Eulyn Pagaling1, Kun Yang1, and Tao Yan1 (Authors)
of Civil and Environmental Engineering, University of Hawai’i at Mānoa (Institution)
*Corresponding Author: Tao Yan
Email： taoyan@****.edu
Cell：180********
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• Concrete corrosion weakens the structure of the sewer pipe
• Leads to pipe failure and release of raw sewage into the environment posing a public health risk
• Costs the US millions of dollars for remediation
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MECHANISM:
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Surface of severely corroded
concrete sewer pipe
Concrete corrosion has
led to complete failure of
this concrete pipe
When sediment builds up, SulfurReducing Bacteria (SRB) break down
organic matter to produce H2S.
H2S volatizes into the sewer atmosphere.
Sulfur-Oxidizing Bacteria (SOB) consume
the H2S to produce sulfuric acid (H2S04).
H2S04 corrodes the concrete to produce
gypsum and ettringite, which weakens
the structure of the pipe.
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Mechanism of concrete corrosion
Taken from Roberts et al (2002). Int Biodet Biodeg 49: 227-234
AIMS: Discover the SOB involved in the final stages of concrete corrosion
Correlate bacterial community composition with environmental factors
Moana Park sampling area
METHODS
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Corroded sewer pipe
at Moana Park
Sample sewer pipe crowns from 6 sites in situ at Moana Park, Honolulu, HI
Collect environmental data using a gas probe: [H2S], [02], [volatile gas]
X-ray Diffraction (XDR) on the samples to determine the extent of corrosion products
Total genomic DNA extraction followed by:
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Quantitative PCR (qPCR) to measure cell density
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Pyrosequencing of the 16S rRNA genes to determine the bacterial species present
RESULTS
Sample
1A
1B
1C
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3
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5
6
[H2S]
(ppm)
102.8
95.5
222
76.7
29.5
9.2
11.3
5.5
LEL (%)
[O2] (%)
pH of corrosion
products
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8
8
19
0
2
0
2
18.5
18.2
19.0
19.1
19.2
19.4
20.0
19.3
0.80
0.28
0.58
0.28
0.24
1.45
1.18
1.47
Table 1. Environmental Data Collected On-site
• The environmental data showed that the sewer atmospheres contained high [H2S], were
depleted in 02 and some contained volatile gases.
• The corrosion products were also shown to be highly acidic.
Log (cell density) (CCE/ml)
• All samples were compared
to the standard peaks for
elemental sulfur and gypsum
(bottom two panels).
• All samples consisted mainly
of either elemental sulfur or
gypsum, but not both.
• No ettringite was detected in
the samples.
• The samples that contained
gypsum also contained other
unidentified compounds not
related to concrete corrosion.
Diversity/Richness
Fig. 1 X-Ray Diffraction Peaks
for Corrosion Products
Fig.2 Bacterial Diversity, Richness
and Density varied with pH
• The qPCR results showed that
bacterial cell density was low in the
sewer crown.
• However, the density was even
lower as the pH dropped further.
• Bacterial diversity and richness
was also low in the sewer crown,
but dropped further as the pH
dropped.
Fig 3. Heat Map of the Pyrosequencing Results
• The pyrosequencing results showed that Mycobacterium and Acidithiobacillus were the main
SOB corroding concrete in our sewer system.
• Acidithiobacillus is a well-known SOB, but mycobacteria are only just becoming known as
SOB. Therefore this study confirms observations by others.
• When correlated with the environmental data, Acidithiobacillus only appeared to proliferate
in less acidic pHs, while Mycobacterium was dominant in all samples, but was more prolific in
the highly acidic samples.
• Bacteria that use methane as an energy source i.e. Methylacidiphilum infernorum also
proliferated, but were not involved in concrete corrosion
CONCLUSIONS
ACKNOWLEDGEMENTS
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The authors would like to thank Prof Henglin Cui for his assistance with sampling and Mrs
Bunnie Yoneyama for her assistance in the lab. They also acknowledge the Characterization
Facility at the University of Minnesota for the x-ray diffraction analysis of the corrosion
products.
This work was funded by the EPA.
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Species diversity and richness and bacterial cell density is low in the sewer crown. They are
directly influenced by pH (lower pHs gives lower diversity, richness and density).
Mycobacterium and Acidithiobacillus are important SOB involved in concrete corrosion.
Acidithiobacillus proliferates in less acidic pH, while Mycobacterium proliferates in highly
acidic pH.