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Predicting the transport of Escherichia coli to groundwater
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering. (Environmental Management and Assessment)ORCID iD: 0000-0002-5290-5704
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Groundwater contamination with pathogens poses a health risk worldwide. Predictive modeling could provide decision support for risk analysis in this context. This study therefore aimed to improve predictive modeling of the transport of Escherichia coli (E. coli) to groundwater. Primarily, it included a review of the state-of-the-art of the underlying process, influencing factors and modeling approaches that relate to E. coli transport in the unsaturated zone. Subsequently, two recently developed models were innovatively applied to the context of microbial contamination. The Active Region Model was evaluated as an alternative to the traditional, uniform flow model (Richard’s equation) to describe bacterial transport in a wastewater treatment facility. It resulted in removal rates that were two orders of magnitude smaller than the traditional approach, more consistently with observations. The study moreover assessed the relevance of a spatial probit model to estimate the probability of groundwater source contamination with thermotolerant coliforms in a case study in Juba, South Sudan. A conventional probit regression model resulted in spatially auto-correlated residuals, pointing to that the spatial model was more accurate. The results of this approach indicated that the local topography and the near presence of areas with informal settlements (Tukul zones) were associated with contamination. Statistical analyses moreover suggested that the depth of cumulative, long-term antecedent rainfall and on-site hygiene were significant risk factors. The findings indicated that the contributing groundwater was contaminated in Juba, and that contamination could be both local and regional in extent. They are relevant for environments with similar climatic, hydrogeological and socioeconomic characteristics, which are common in Sub-Saharan Africa. The results indicated that it is important to consider spatial interactions in this subject area. There is a need for studies that assess the distance within which such interactions can occur, using both mechanistic and statistical methods. Lastly, the results in this study consistently emphasized the importance of flow patterns for E. coli transport. It is thus recommended that future studies evaluate how models of preferential flow and transport can incorporate microbial fate. The multidisciplinary nature of the subject calls for a systems approach and collaboration between disciplines.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , x, 34 p.
Series
TRITA-LWR. PHD, ISSN 1650-8602 ; 2015:04
National Category
Environmental Engineering
Identifiers
URN: urn:nbn:se:kth:diva-168242ISBN: 978-91-7595-618-3 (print)OAI: oai:DiVA.org:kth-168242DiVA: diva2:815125
Public defence
2015-06-15, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20150529

Available from: 2015-05-29 Created: 2015-05-29 Last updated: 2015-05-29Bibliographically approved
List of papers
1. Water Transport, Retention, and Survival of Escherichia coli in Unsaturated Porous Media: A Comprehensive Review of Processes, Models, and Factors
Open this publication in new window or tab >>Water Transport, Retention, and Survival of Escherichia coli in Unsaturated Porous Media: A Comprehensive Review of Processes, Models, and Factors
2015 (English)In: Critical reviews in environmental science and technology, ISSN 1064-3389, E-ISSN 1547-6537, Vol. 45, no 1Article, review/survey (Refereed) Published
Abstract [en]

The vadose zone can function as both a filter and a passage for bacteria. This review evaluates when and why either effect will apply based on available literature. It summarizes theories and experimental research that address the related, underlying bacterial attenuation processes, the applied macro-scale modeling approaches, and the influencing factors - including the cell, soil, solution and system characteristics. Results point to that the relative importance of each removal mechanism depends on the moisture content and the solution ionic strength. The limitations of available modeling approaches are discussed. It remains unclear in which contexts these are reliable for predictions. The temporal first-order kinetic Escherichia coli (E. coli) removal coefficient ranges three orders of magnitude, from 10(-4) to 10(-1)/min. Results suggest that this rate depends on the pore-water velocity. Spatial filtration of E. coli increases with slower flow and higher collector surface heterogeneity. It could be insignificant in the case of heavy and sudden infiltration and subsequent transport in preferential flow paths, induced, for example, by plant roots or cracks in clayey soils. Future research thus needs to address transport as an effect of extreme weather events such as droughts and subsequent floods.

Keyword
Unsaturated Attachment, Straining, Survival, Preferential transport, Escherichia coli, Subsurface modeling
National Category
Environmental Sciences
Identifiers
urn:nbn:se:kth:diva-138609 (URN)10.1080/10643389.2013.828363 (DOI)000343312400001 ()2-s2.0-84923350845 (Scopus ID)
Funder
StandUp
Note

QC 20141114

Available from: 2013-12-20 Created: 2013-12-20 Last updated: 2017-12-06Bibliographically approved
2. Modeling bacterial attenuation in on-site wastewater treatment systems using the active region model and column-scale data
Open this publication in new window or tab >>Modeling bacterial attenuation in on-site wastewater treatment systems using the active region model and column-scale data
2015 (English)In: Environmental Earth Sciences, ISSN 1866-6280, E-ISSN 1866-6299, Vol. 74, no 6, 4827-4837 p.Article in journal (Refereed) Published
Abstract [en]

Bacterial attenuation in porous media is often higher in columns than in the field. This study investigates whether this inconsistency could be attributed to finger flow, as assessed by the active region model (ARM). It develops a numerical model of flow and transport of the fecal indicator Escherichia coli  in a wastewater infiltration basin from the literature. Modeling was based on the traditional, uniform flow approach (Richard’s equation) as well as the ARM, representing finger flow. The uniform flow model resulted in flow rates that decreased rapidly with filter depth and an underestimation of the observed average relative effluent concentration by three orders of magnitude. With the ARM, the flow rates remained high throughout the filter, more consistently with observations, and the relative effluent concentration (0.018) was relatively accurate in reproducing the field result (0.025). Considering a range of removal rates derived from laboratory studies, the ARM consistently enabled more accurate and conservative assessments of the filter efficiency; thus, results indicated that the ARM provides a more relevant approach to bacterial transport in wastewater infiltration basins with sandy, unstructured soils.

Keyword
Unsaturated zone, Bacterial transport, Preferential flow, Soil aquifer treatment, Active region model
National Category
Environmental Engineering
Identifiers
urn:nbn:se:kth:diva-168239 (URN)10.1007/s12665-015-4483-7 (DOI)000360537700018 ()2-s2.0-84940726136 (Scopus ID)
Note

QC 20150929. Updated from e-pub ahead of print to published.

Available from: 2015-05-29 Created: 2015-05-29 Last updated: 2017-12-04Bibliographically approved
3. Prevalence of microbiological contaminants in groundwater sources and risk factor assessment in Juba, South Sudan
Open this publication in new window or tab >>Prevalence of microbiological contaminants in groundwater sources and risk factor assessment in Juba, South Sudan
Show others...
2015 (English)In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 515-516, 181-187 p.Article in journal (Refereed) Published
Abstract [en]

In low-income regions, drinking water is often derived from groundwater sources, which might spread diarrheal disease if they are microbiologically polluted. This study aimed to investigate the occurrence of fecal contamination in 147 improved groundwater sources in Juba, South Sudan and to assess potential contributing risk factors, based on bivariate statistical analysis. Thermotolerant coliforms (TTCs) were detected in 66% of the investigated sources, including 95 boreholes, breaching the health-based recommendations for drinking water. A significant association (p<. 0.05) was determined between the presence of TTCs and the depth of cumulative, long-term prior precipitation (both within the previous five days and within the past month). No such link was found to short-term rainfall, the presence of latrines or damages in the borehole apron. However, the risk factor analysis further suggested, to a lesser degree, that the local topography and on-site hygiene were additionally significant. In summary, the analysis indicated that an important contamination mechanism was fecal pollution of the contributing groundwater, which was unlikely due to the presence of latrines; instead, infiltration from contaminated surface water was more probable. The reduction in fecal sources in the environment in Juba is thus recommended, for example, through constructing latrines or designating protection areas near water sources. The study results contribute to the understanding of microbiological contamination of groundwater sources in areas with low incomes and high population densities, tropical climates and weathered basement complex environments, which are common in urban sub-Saharan Africa.

National Category
Environmental Sciences
Research subject
Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-159751 (URN)10.1016/j.scitotenv.2015.02.023 (DOI)000352040700018 ()2-s2.0-84923383854 (Scopus ID)
Note

QC 20150519

Available from: 2015-02-09 Created: 2015-02-09 Last updated: 2017-12-04Bibliographically approved
4. Applying spatial regression to evaluate risk factors for microbiological contamination of urban groundwater sources in Juba, South Sudan
Open this publication in new window or tab >>Applying spatial regression to evaluate risk factors for microbiological contamination of urban groundwater sources in Juba, South Sudan
2017 (English)In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 25, 1077-1091 p.Article in journal (Refereed) Published
Abstract [en]

This study developed methodology for statistically assessing groundwater contamination mechanisms. It focused on microbial water pollution in low-income regions. Risk factors for faecal contamination of groundwater-fed drinking-water sources were evaluated in a case study in Juba, South Sudan. The study was based on counts of thermotolerant coliforms in water samples from 129 sources, collected by the humanitarian aid organisation M,decins Sans FrontiSres in 2010. The factors included hydrogeological settings, land use and socio-economic characteristics. The results showed that the residuals of a conventional probit regression model had a significant positive spatial autocorrelation (Moran's I = 3.05, I-stat = 9.28); therefore, a spatial model was developed that had better goodness-of-fit to the observations. The most significant factor in this model (p-value 0.005) was the distance from a water source to the nearest Tukul area, an area with informal settlements that lack sanitation services. It is thus recommended that future remediation and monitoring efforts in the city be concentrated in such low-income regions. The spatial model differed from the conventional approach: in contrast with the latter case, lowland topography was not significant at the 5% level, as the p-value was 0.074 in the spatial model and 0.040 in the traditional model. This study showed that statistical risk-factor assessments of groundwater contamination need to consider spatial interactions when the water sources are located close to each other. Future studies might further investigate the cut-off distance that reflects spatial autocorrelation. Particularly, these results advise research on urban groundwater quality.

Place, publisher, year, edition, pages
Springer, 2017
National Category
Environmental Engineering
Research subject
Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-168241 (URN)10.1007/s10040-016-1504-x (DOI)000401787800015 ()
Note

QC 20170614

Available from: 2015-05-29 Created: 2015-05-29 Last updated: 2017-06-14Bibliographically approved

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