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Research article - Peer-reviewed, 2021

Assessing the microbial risk of faecal sludge use in Ugandan agriculture by comparing field and theoretical model output

Butte, G.; Niwagaba, C.; Nordin, A.


Reuse of faecal sludge in agriculture has many potential benefits, but also poses risks to human health. To better understand the potential risks, Quantitative Microbial Risk Assessment (QMRA) was performed for three population groups in Kampala, Uganda: wastewater and faecal sludge treatment plant workers; farmers using faecal sludge; and consumers of faecal sludge-fertilised vegetables. Two models were applied for farmers and consumers, one based on pathogen concentrations from field sampling of sludge, soils and vegetables, and one based on theoretical pathogen contribution from the last sludge application, including decay and soil to crop transfer of pathogens. The risk was evaluated for two pathogens (enterohaemorrhagic E. coli (EHEC) and Ascaris lumbricoides ). The field data on sludge, soil and vegetables indicated that the last application of faecal sludge was not the sole pathogen source . Correspondingly, the model using field data resulted in higher risks for farmers and consumers than the theoretical model assuming risk from sludge only, except when negligible for both. For farmers, the yearly risk of illness, based on measured concentrations, was 26% from EHEC and 70% from Ascaris, compared with 1.2% and 1.4%, respectively, considering the theoretically assumed contribution from the sludge. For consumers, the risk of illness based on field samples was higher from consumption of leafy vegetables (100% from EHEC, 99% from Ascaris) than from consumption of cabbages (negligible for EHEC, 26% from Ascaris). With the theoretical model, the risk of illness from EHEC was negligible for both crops, whereas the risk of illness from Ascaris was 64% and 16% for leafy vegetables and cabbage, respectively. For treatment plant workers, yearly risk of illness was 100% from EHEC and 99.4% from Ascaris . Mitigation practices evaluated could reduce the relative risk by 30-70%. These results can help guide treatment and use of faecal sludge in Kampala, to protect plant workers, farmers and consumers.(c)& nbsp;2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license ( )


Faecal sludge; Fertiliser; Health burden; Reuse; Wastewater sludge; QMRA

Published in

Water Research
2021, volume: 197, article number: 117068

Authors' information

Butte, G.
Newcastle University - UK
Niwagaba, C.
Makerere University
Swedish University of Agricultural Sciences, Department of Energy and Technology

Sustainable Development Goals

SDG3 Good health and wellbeing
SDG12 Ensure sustainable consumption and production patterns

UKÄ Subject classification

Environmental Sciences related to Agriculture and Land-use

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