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Modeling bacterial attenuation in on-site wastewater treatment systems using the active region model and column-scale data
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering. Lawrence Berkeley National Laboratory, Department of Hydrogeology, University of California, Irvine, CA, United States .ORCID iD: 0000-0002-5290-5704
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.

Place, publisher, year, edition, pages
2015. Vol. 74, no 6, 4827-4837 p.
Keyword [en]
Unsaturated zone, Bacterial transport, Preferential flow, Soil aquifer treatment, Active region model
National Category
Environmental Engineering
Identifiers
URN: urn:nbn:se:kth:diva-168239DOI: 10.1007/s12665-015-4483-7ISI: 000360537700018Scopus ID: 2-s2.0-84940726136OAI: oai:DiVA.org:kth-168239DiVA: diva2:815107
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
In thesis
1. Predicting the transport of Escherichia coli to groundwater
Open this publication in new window or tab >>Predicting the transport of Escherichia coli to groundwater
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:nbn:se:kth:diva-168242 (URN)978-91-7595-618-3 (ISBN)
Public defence
2015-06-15, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 14:00 (English)
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Supervisors
Note

QC 20150529

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

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Engström, Emma

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