reduction of pathogenic bacteria in organic waste through
TRANSCRIPT
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Reduction of pathogenic bacteria in organic waste
through production of biogas
Lauren Harroffa, Vianney Tumwesigeb, Andrew Apsleyb, Lisa Averyc, Norval Strachanb, Jo Smithb
a Makerere University; b University of Aberdeen;
cJames Hutton Institute
a b c
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Lauren Haroff,
Makerere University
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Reduction of pathogenic bacteria in organic waste
through production of biogas
Lauren Harroffa, Vianney Tumwesigeb, Andrew Apsleyb, Lisa Averyc, Jo Smithb
a Makerere University; b University of Aberdeen;
cJames Hutton Institute
a b c
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As few as 15% of household in SSA
have access to improved water
supply (WHO, UNIEF,
2009)
In 2004, only 37% of the population of SSA had access to sanitation (WHO,
UNIEF, 2006)
~5M people die from water related disease each year Momba et
al., 2008)
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Widely accepted that small sale
biogas digesters can reduce pathogen
burden (eg. Clarsen et al., 2007)
Is this true in Sub-Saharan
Africa?
9 biogas digesters installed in Tiribogo, Uganda
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Approach
Measure faecal coliforms and indicator organisms (Escherichia coli, total aerobic coliforms, Clostridium perfringens and Enterococcus faecalis)
• Samples refrigerated overnight
• Serial dilutions with buffered peptone water
• Plated on Chromocult and Chromoselect agar
• Incubated ~24 hours at 37° C and 44° C
• Colonies counted
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Approach
Measure pathogens in feed and digestate
Feed
Digestate
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Around animals
Inside home
Approach Sample in local environment
before and after installation
On hands
Around home
Door handles
Dishes
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Pathogens in Digester
0
2
4
6
8
10
12
E. coli Total coliforms C. perfringens E. faecalis
Log
CFU/
g sa
mple
Feed mean
Digestate Mean
Significant reduction in
aerobic bateria
Significant increase in anaerobic bacteria
Change not significant
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Environmental Results: In home
Small significant increase in E.coli with digesters
No significant change in E.coli without digesters
No significant change in C.perfringens
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Environmental Results: Outside home
Significant increase with digesters in both E. coli and
C. perfringens
No significant change without digesters
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Environmental Results: Animals
Significant increase with digesters in both E. coli and C. perfringens
Significant reduction in C. perfringens without digesters
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Environmental Results: Dishes
No significance due to high variability
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Environmental Results: Hands
Results below detection limits
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Cumulative environmental results in and around the home
0
1
2
3
4
5
6
Total Coliforms E. coli C. perfringens
Mean
Log
CFU/
sample
BeforeDuringAfter
Significant increase in
aerobic bateria
Change not significant
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Increase in aerobic bacteria in the local
environment following
installation of the digester
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Contamination during handling
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Importance of design of layout
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Limitations • Need better replication to make robust comparisons
between paired households with and without digesters
• Need longer sampling period to allow users to adapt to the digester before sampling
• Need to consider the impact of retention time
• Not a strictly controlled experiment
Strengths • Not a strictly controlled experiment so more
representative of what actually happens in the field
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Conclusions • Aerobic pathogens in bioslurry are
significantly reduced by anaerobic digestion
• Anaerobic pathogens in bioslurry are not significantly reduced during anaerobic digestion
• Aerobic pathogens are increased in the local environment
• Spillage and excessive handling of manures should be avoided when feeding the digester
• Users are washing hands sufficiently
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Acknowledgements
Thanks to the Department for International Development (DfID) for supporting this work