Fouling biofilm formation

McCoy, W. F., Bryers, J. D., Robbins, J. and Costerton, J. W., 1981. Observation in fouling biofilm formation. Canadian Journal of Microbiology 27, 910-917. 

McCoy WF> Bryers JD, Robbins J, Costerton JW (1981) Observations of fouling biofilm formation. Can J Microbiol 27 910-917 McCoy WF (1987) Effects of fouling biofilms on systems performance. In Mittelman MW, Geesey GG (eds) Biological foufing of industrial water systems a problem solving approach. Water Micro Associates, San Diego, pp 234-246... 

In an effort to gain a better understanding of the initial fouling step leading to bacterial attachment and biofilm formation, we have investigated the adsorption of protein and polysaccharides onto thin metallic films and uncoated internal reflection elements from flowing solutions using attenuated total reflectance spectroscopy. The preliminary results will be described in this paper. 

Schafer et al. [35] studied the role of concentration polarization and solution chemistry on the morphology of the humic acid fouling layer. Irreversible fouling occurred with all membranes at high calcium concentrations. Interestingly, it was found that the hydrophobic fraction of the humic acids was deposited preferentially on the membrane surface. This result is similar to the work of Ridgway et al. [31], who showed that the hydrophobic interaction between a bacterial cell surface and a membrane surface plays a key role in biofilm formation. The formation of two layers, one on top of the other, was also observed by Khatib et al. [36]. The formation of a Fe-Si gel layer directly on the membrane surface was mainly responsible for the fouhng. 

Studies are required on effective removal of biofilms without damaging the membrane. Additional work needs to be done to find out what happens to the fouling resistance of chemically modihed membranes over the long term (i.e., after initial biofilm formation). Membrane resistance to humic acids is another area for further study. Furthemore, the molecular tools needed for exploring the biochemical details of the microbial adhesion process to membranes are now available. 

The importance of biopolymer deposition on the membrane has been highlighted by Chu and Li [34] who noted that such material may accelerate bacterial attachment to the membrane in addition to its contribution to fouling resistance. The formation of a slime layer on the membrane, comprising an EPS matrix with embedded bacteria, may be analogous to a biofilm, the significance of which is the difficulty of its removal by nonchemical methods. The question of whether biofilm formation plays a significant role in MBRs is yet to be addressed. Indeed, a comprehensive model of fouling in MBRs is not yet available. 

Bryers, J.D., and Characklis, W.G., 1981, Kinetics of initial biofilm formation within a turbulent flow stream, in Somerscales, E.F.C. and Knudsen, J.G. eds. Fouling of Heat Transfer Equipment. Hemisphere Pub. Corp. 313 -333. 

It is important to note that antimicrobial and biofilm resistance are two different characteristics though some materials show both properties at the same time. Antimicrobial materials do not automatically prevent biofilm formation and vice versa. Antimicrobial surfaces could kill bacteria on contact but if dead bacteria cell debris blocks the active biocidal surface, biofilm formation could eventually occur. For example, quaternary anunonium polymers can effectively kill bacteria but when the surface is fouled with dead bacteria debris, biofilm formation is inevitable [188]. Materials with antibiofilm properties will repel the bacterial adhesion very effectively but may not kill the bacteria when they do colonize the surface. PEG surfaces are well known to repel bacteria adhesion. However, PEG surfaces show little antimicrobial activity. Quantitative antibiofilm efficacy tests can be divided into two categories static (minimum biofilm eradication concentration assay, MBEC) and dynamic (flow cell assay). In addition, SEM is a semiquantitative assay, which is discussed in Section 2.5. 

In parallel to lab experiences, optical fouling monitors and coupons (removed at 14 days intervals and analysed for colony forming units of aerobic bacteria and sulphate-reducing anaerobic bacteria) have been used to monitor and measure biofilm formation on machines. 

No commercial substrate is completely resistant to surface bacterial growth and biofilm formation. In a study at the University of Minnesota, PFA with a smooth surface was found to be least hospitable to bacterial growth. Biofilm removal was easily and completely accomplished from PFA (Table 13.49). PFA was cleaned more completely than glass, stainless steel, and PVDF. Figure 13.112 shows the results of bacterial count in a dynamic ultrapure water system in which fouling of the surfaces of stainless steel, PVDF, and ECTFE were studied. ECTFE and PVDF were orders of magnitude less susceptible to biofouling than stainless steel. 

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