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

Lauren Haroff,

Makerere University

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

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)

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

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

Approach

Measure pathogens in feed and digestate

Feed

Digestate

Around animals

Inside home

Approach Sample in local environment

before and after installation

On hands

Around home

Door handles

Dishes

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

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

Environmental Results: Outside home

Significant increase with digesters in both E. coli and

C. perfringens

No significant change without digesters

Environmental Results: Animals

Significant increase with digesters in both E. coli and C. perfringens

Significant reduction in C. perfringens without digesters

Environmental Results: Dishes

No significance due to high variability

Environmental Results: Hands

Results below detection limits

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

Increase in aerobic bacteria in the local

environment following

installation of the digester

Contamination during handling

Importance of design of layout

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

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

Acknowledgements

Thanks to the Department for International Development (DfID) for supporting this work