Disclaimer

The following review is my own interpretation of the linked-to article. Please do not use my review as a complete reference for the article as I will most likely skip important information that you feel is relevant. If I do miss something, please feel free to comment about it in the comments section below. Please read the article before reading my review and remember, this is my notebook, which means these are my notes on the article and they will more-than-likely hold no relevance to you or your research.

Paper

van Loosdrecht MCM, Heijnen JJ, Eberl H, Kreft J, Picioreanu C (2002) Mathematical modelling of biofilm structures. Antonie van Leeuwenhoek 81: 245-256. doi:10.1023/A:1020527020464.

Review

In this paper, the authors did both experiments and calculations on biofilms. They used an interesting device called a Biofilm Airlift Suspension device which, is used to study wastewater treatment.

 

  • The authors confirmed my suspicion that the structures of biofilms are highly dependent on the flow of the medium that they are in. This paper does not go into that analysis rather they reference a paper that did.
    • Gjaltema A, Tijhuis L, van Loosdrecht MCM & Heijnen JJ (1995) Detachment of biomass from suspended nongrowing spherical biofilms in airlift reactors. Biotechnol. Bioeng. 46: 258–269.
  • The authors stipulate that the dominant factor governing biofilm morphology is a ratio of the detachment rate to the the biofilm surface loading rate.
    • While I agree with this statement, I do not believe it is the root reason why biofilms obtain a certain morphology. I still think is is dependent on flow rates of the environment the biofilm is in. So, I think Navier-Stokes has to come into play at some point.
  • They reference an article that states that shear rates govern the thickness of biofilms as do lower surface loading rates.
    • Kwok WK, Picioreanu C, Ong SL, van Loosdrecht MCM, Ng WJ & Heijnen JJ (1998) Influence of biomass production and detach- ment forces on biofilm structures in a biofilm airlift suspension reactor. Biotechnol. Bioeng. 58: 400–407.
  • They define the biofilm density as the amount of biomass per volume excluding the pores in the biofilm. They state that this is a measure for the number of cells in the biofilm.
  • They reference another paper that investigated biofilm density. This paper showed that biofilm density increased when the substrate used selected for slower growing bacteria. This paper also showed that fast growing bacteria in a low shear rate and a high loading rate led to more porous biofilms.
    • Villaseñor JC, van Loosdrecht MCM, Picioreanu C & Heijnen JJ (2000) Influence of different substrates on the formation of biofilms in a biofilm airlift suspension reactor. Water Sci. Techn. 41(4–5): 323–330.
  • They reference another attempt at mathematically modeling biofilms in one dimension.
    • Wanner O & Gujer W (1986) A multispecies biofilm model. Biotechnol. Bioeng. 28: 314–328.
  • They also discuss other references where more advanced studies were done modeling biofilms.
  • They are apparently using the model defined by Picioreanu. This model incorporates several parameters:
    • Convection
    • Diffusion
    • Reaction
    • Biofilm growth
    • Detachment
  • The authors note that at the time of the writing, proper measurements of the gel properties of biofilms still have not been accomplished. This is interesting and now gives me a better search term “biofilm properties”. They do give several references.
  • The author’s final thought is to obtain experimental data in the following areas in order to improve computational reliability.
    • EPS formation kinetics and stoichiometry.
    • Biofilm mechanical strength.
    • Kinetics of production and decay of quorum sensing signals.
    • Biomass spreading in the biofilm.
    • Movement of biofilm filaments.
    • Movement of the biofilm itself.

 

I think the take-home from this paper is that they were able to model biofilms. This was definitely a review paper even though it didn’t state that it was. The important things I learned were:

  • Fast flow rates give a denser less porous biofilm.
  • Low flow rates give a more porous biofilm.

Also, I completely agree with the author’s desire to get more experimental data in their closing remarks. Actually, everything they suggested are questions that I have about biofilms and I need to search for every term above.

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