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Modelling biofilm-induced formation damage and biocide treatment in subsurface geosystems.

Ezeuko CC, Sen A, Gates ID - Microb Biotechnol (2012)

Bottom Line: Persisters describe small subpopulation of cells which are tolerant to biocide treatment.Biofilm tolerance to biocide treatment is regulated by persister cells and includes 'innate' and 'biocide-induced' factors.Also, a successful application of biological permeability conformance treatment involving geologic layers with flow communication is more complicated than simply engineering the attachment of biofilm-forming cells at desired sites.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Petroleum Engineering, Schulich School of Engineering, University of Calgary, Calgary, Alberta, Canada. cezeuko@ucalgary.ca

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Related in: MedlinePlus

Schematic showing definitions relevant to our pore network model including flow through pore spaces and biofilm adsorption on pore walls. An enlarged picture of a Pseudomonas fluorescens biofilm is presented and highlights key components of biofilm in our model, which are cells and EPS matrix. White arrow indicates bacterial cell and black arrow indicates EPS produced by bacteria.
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fig01: Schematic showing definitions relevant to our pore network model including flow through pore spaces and biofilm adsorption on pore walls. An enlarged picture of a Pseudomonas fluorescens biofilm is presented and highlights key components of biofilm in our model, which are cells and EPS matrix. White arrow indicates bacterial cell and black arrow indicates EPS produced by bacteria.

Mentions: We recognize that various other factors (e.g. predation, etc.) can contribute to biomass removal, depending on the system under consideration. Endogenous decay as implemented in our model serves to capture cell death not related to biocide. For modelling purposes, we can either retain these dead cells in the biofilm or consider them now in the bulk phase and eventually removed from the system. This way, biomass can slightly decline over a significantly long period. However, even for laboratory scale bioclogging, it is expected that a bioclogged system remains clogged over fairly long timescales (e.g. Kim and Fogler, 2000) without recourse to different forms of external forces (e.g. shear forces, mechanical forces) or use of a highly reactive biocide. Therefore, retaining cells which died in a biofilm via an endogenous decay mechanism should be well within the limit of reasonable assumptions. Key design limitations of presented model are associated with the assumption of mono-species/mono-nutrient conditions and the assumption of zero-dimensional spatial resolution within a biofilm. In reality, biofilms are usually multispecies colonies and the resultant competition for nutrients can alter bacterial rate of growth. Assumptions of zero-dimensionality within a biofilm implies that the presented model needs further improvement to capture complex spatial distribution of components (e.g. cells, nutrients) within a biofilm and overcome the limitation of planar biofilm and substratum geometry. Figure 1 shows a schematic that describes interactions between flow through interconnected pores and biofilm growth as implemented in our model. The porous medium is treated as a two-dimensional (2D) network of interconnected pore elements (bonds). Each intersection of pore elements is referred to as a node. A constant pressure gradient is applied across the model domain. A summary of pore-level phases and species accounted for in our model is depicted in Fig. 2. Multiple flowing liquid phases can be modelled by adopting the capillary pressure concept (Ezeuko et al., 2010). We track temporal evolution of nutrient within each pore element by coupling flow, mass transport (advective and diffusive), and reaction processes.


Modelling biofilm-induced formation damage and biocide treatment in subsurface geosystems.

Ezeuko CC, Sen A, Gates ID - Microb Biotechnol (2012)

Schematic showing definitions relevant to our pore network model including flow through pore spaces and biofilm adsorption on pore walls. An enlarged picture of a Pseudomonas fluorescens biofilm is presented and highlights key components of biofilm in our model, which are cells and EPS matrix. White arrow indicates bacterial cell and black arrow indicates EPS produced by bacteria.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3815385&req=5

fig01: Schematic showing definitions relevant to our pore network model including flow through pore spaces and biofilm adsorption on pore walls. An enlarged picture of a Pseudomonas fluorescens biofilm is presented and highlights key components of biofilm in our model, which are cells and EPS matrix. White arrow indicates bacterial cell and black arrow indicates EPS produced by bacteria.
Mentions: We recognize that various other factors (e.g. predation, etc.) can contribute to biomass removal, depending on the system under consideration. Endogenous decay as implemented in our model serves to capture cell death not related to biocide. For modelling purposes, we can either retain these dead cells in the biofilm or consider them now in the bulk phase and eventually removed from the system. This way, biomass can slightly decline over a significantly long period. However, even for laboratory scale bioclogging, it is expected that a bioclogged system remains clogged over fairly long timescales (e.g. Kim and Fogler, 2000) without recourse to different forms of external forces (e.g. shear forces, mechanical forces) or use of a highly reactive biocide. Therefore, retaining cells which died in a biofilm via an endogenous decay mechanism should be well within the limit of reasonable assumptions. Key design limitations of presented model are associated with the assumption of mono-species/mono-nutrient conditions and the assumption of zero-dimensional spatial resolution within a biofilm. In reality, biofilms are usually multispecies colonies and the resultant competition for nutrients can alter bacterial rate of growth. Assumptions of zero-dimensionality within a biofilm implies that the presented model needs further improvement to capture complex spatial distribution of components (e.g. cells, nutrients) within a biofilm and overcome the limitation of planar biofilm and substratum geometry. Figure 1 shows a schematic that describes interactions between flow through interconnected pores and biofilm growth as implemented in our model. The porous medium is treated as a two-dimensional (2D) network of interconnected pore elements (bonds). Each intersection of pore elements is referred to as a node. A constant pressure gradient is applied across the model domain. A summary of pore-level phases and species accounted for in our model is depicted in Fig. 2. Multiple flowing liquid phases can be modelled by adopting the capillary pressure concept (Ezeuko et al., 2010). We track temporal evolution of nutrient within each pore element by coupling flow, mass transport (advective and diffusive), and reaction processes.

Bottom Line: Persisters describe small subpopulation of cells which are tolerant to biocide treatment.Biofilm tolerance to biocide treatment is regulated by persister cells and includes 'innate' and 'biocide-induced' factors.Also, a successful application of biological permeability conformance treatment involving geologic layers with flow communication is more complicated than simply engineering the attachment of biofilm-forming cells at desired sites.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Petroleum Engineering, Schulich School of Engineering, University of Calgary, Calgary, Alberta, Canada. cezeuko@ucalgary.ca

Show MeSH
Related in: MedlinePlus