Biofilm biofouling

Despite these well-known aspects, reliable data and studies concerning solvent-resistant microorganisms in biofilm, biofouling, or biocorrossion processes are not shown. Nevertheless similar mechanisms in biofilms must be assumed as described above (see Section 14.4.2.3) because similar conditions occur (organic-aqueous systems). 

Pereira, M. O. and Vieira, M. J., 2001. Effects of the interactions between glutaraldehyde and the polymeric matrix on the efficacy of the biocide against Pseudomonas fluorescens biofilms. Biofouling, 17, 93-101. 

Dwyer D, Tiedje JM (1983) Degradation of ethylene glycol and polyethylene glycols by methanogenic consortia. Appl Environ Microbiol 46 185-190 Eashwar M, Martrhamuthu S, Palanichamy S, Balakrishnan K (1995) Sunlight irradiation of seawater eliminates ennoblement-causation by biofilms. Biofouling 8 215-221... 

Lee W, de BeerD (1995) Oxygen and pH microprofiles above corroding mild steel covered with a biofilm. Biofouling 8 273-280 Lens PN, De Poorter M-P, Cronenberg CC, Verstraete WH (1995) Sulfiite reducing and methane producing bacteria in aerobic wastewater treatment systems. Wat Res 29(3) 871-880... 

The non-random distribution of bacteria in biofilms has important applications for industry (biofouling, corrosion) and in medical practice (use of apphances within the human body). 

Fig. 5.1.10 (a) MR measured propagators and (b) corresponding calculated RTDs for flow in a model packed bed reactor composed of 241 -pm monodisperse beads in a 5-mm id circular column for a fixed observation time of 300 ms and as a function of biofilm fouling. As the porous media becomes biofouled, a high veloc-... 

Wieczorek SK, Todd CD (1998) Inhibition and facilitation of settlement of epifaunal marine invertebrate larvae by microbial biofilm cues. Biofouling 12 81-118... 

Biofouling involves the formation of biofilm, whereby hydrated algal- or bacterial-based slimes adhere to water-wetted cooling system surfaces and often contain scales, corrosion products, or other debris embedded within a polysaccharide matrix. The role of biofilms in reducing cooling system efficiency and life span is still imperfectly understood. 

Stoodley, P., J. D. Boyle, D. deBeer, H. M. Lappin-Scott. 1999a. Evolving perspectives of biofilm structure. Biofouling 14 75-90. 

Huckins et al.29 reported a 20-70% impedance in the uptake of PAHs in cases of severe biofouling on the surface of SPMDs. Their model describing the mass transfer in a biofilm indicated that it behaved like an immobilized water layer with a resistance that is independent of the biofilm/water partition coefficient. This would result in a similar mobility of compounds in the biofilm since this is independent of their hydrophobicity.19 Similarly, Richardson et al.47 observed that biofouling caused a reduction of up to 50% in the uptake of PAHs and organochlorine pesticides by SPMDs. It has been suggested by several authors that PRCs can be used to correct biofouling during deployment,42,47 but more experimental evidence is needed. 

The buildup of biofilm on the membrane surface means an additional resistance to solvent flow as well as the possibility of enhancement of CP level by the biofilm, which is similar to the case of colloidal fouling [32,36], In general, the diffusivity is linked to the tortuosity factor of the biofilm [37]. Hence, it is likely that the backdiffusion of solutes in the biofilm on RO is hindered. The enhanced CP is important for two reasons. Firstly, the elevated concentration of solutes at the membrane wall means an increase in the osmotic pressure (CEOP) and hence a loss in the effective TMP. Secondly, the nutrient level is also enhanced and this will further accelerate the growth of the biofilm [32,36]. So, biofouling in RO becomes an interplay between C P and biofilm development. 

The relative contribution to performance loss (TMP rise at constant flux) of resistance PF or CEOP depends on the particle size. For particles >0.5 pm the resistance is relatively small (see effect of particle size in Equation 6.4) and CEOP due to cake height, 8C, is the major effect [48], It is also observed that biofilms can contribute substantial CEOP effects as well as resistance, and in a recent biofouling study more than 50% of the required TMP rise was due to CEOP effects [32]. 

Fig. 1 Examples of biofilms. Left typical mold in households. Center typical biofouling on a ship hull, including algaes and barnacles. Right microbial Pseudomonas aeruginosa biofilm on a catheter...

Leroy C, Delbarre-Ladrat C, GhUlebaert F et al. (2008) Effects of commercial enzymes on the adhesion of a marine biofilm-forming bacterium. Biofouling 24 11-22... 

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