Biofilms microbial activity

Chemical weathering of minerals during pedogenesis can be enhanced by microbial activity by a factor as high as 106 (Kurek 2002). Microorganisms can dissolve minerals by direct and indirect actions under aerobic and anaerobic conditions (Robert and Berthelin 1986 Ehrlich 2002 Kurek 2002). In some cases of attack, the microorganisms may be dispersed in the soil solution in others, they may grow in biofilms on the surface of susceptible minerals. 

Fermentation may take place in the three major microbial subsystems of a sewer, i.e., the wastewater, the biofilm and the sediments (Figure 3.2). Sulfate-reducing bacteria are slow growing and are therefore primarily present in the biofilm and in the sediments, where sulfate from the wastewater may penetrate (Nielsen and Hvitved-Jacobsen, 1988 Hvitved-Jacobsen et al., 1998 Bjerre et al., 1998). However, as a result of biofilm detachment, sulfate reduction may, to some minor extent, take place in the wastewater. Methanogenic microbial activity normally requires absence of sulfate — or at least a low... 

Basically, a concept for microbial transformations in sewer networks should cover soluble and particulate components and relevant processes in the water phase, in the biofilm and in the sewer sediments. In addition, mass transfer between these phases and an air-water transfer of oxygen should be taken into account (Figures 1.3 and 5.2). Although only the aerobic microbial activity will be focused on in the concept presented in this chapter, anoxic and anaerobic processes should be considered possible extensions (cf. Chapter 6). 

Monochloramine, used as a residual disinfectant for distribution, is usually formed from the reaction of chlorine with ammonia. Careful control of monochloramine formation in water treatment is important to avoid the formation of di- and trichloramines, because these can cause unacceptable tastes and odours. The formation of nitrite as a consequence of microbial activity in biofilms in the distribution system is a possibility when monochloramine is used as a residual disinfectant, particularly if ammonia levels are not sufficiently controlled. 

Microbial activity is a major concern in systems in which water-based fluids are used. Particularly, glycol fluids provide a good source of nutrition to some types of biological species. In salt-based brines, however, microbes do not survive because of high osmotic pressure. When microbes start to grow inside a system, they create a layer known as biofilm on the walls of the pipes and heat exchangers. This reduces the heat transfer rate. Some microbes are capable of creating acids and hence cause a substantial amount of corrosion in the system. 

Hamilton, W.A., 1987, Biofilms microbial interactions and metabolic activities. Symp. Soc. Gen. Microbiol. 41, 361 - 385. 

Mozes, N. and Rouxhet, P.G., 1992, Influences of surfaces on microbial activity, in Melo, L.F., Bott, T.R., Fletcher, M. and Capdeville, B. eds. Biofilms -Science and Technology, 126 - 136, Kluwer Academic Publishers, Dordrecht. 

The increasing occurrence of microbial and nosocomial infection has stimulated research activities into antimicrobial polymers and textiles [19, 25, 34]. Most medical textiles and polymeric materials used in hospitals are conductive to crosstransmission of diseases, as most microorganisms can survive on these materials for hours to several months [17, 26]. Thus, it would be advantageous for polymeric surfaces and textile materials to exhibit antibacterial properties so as to reduce and prevent disease transmission and cross-contamination within and from hospitals. N-halamines exhibit a similar antimicrobial potency to chlorine bleach, one of the most widely used disinfectants, but they are much more stable, less corrosive and have a considerably reduced tendency to generate halogenated hydrocarbons, making them attractive candidates for the production of antimicrobial polymeric materials. N-halamine compounds are currently used as antimicrobial additives to produce polymers with antimicrobial and biofilm-limiting activities. 

Biofilm formation at the air-water interface. The bathtub ring often formed at the air-water interface around the sides of the basin is likely to be a biofilm due to microbial activity. This film acts like a trap and is known to concentrate caesium and other radioactive isotopes contained in the basin water. This biofilm should be removed mechanically by wet brushing, using water to hold down any airborne activity. A 35% solution of hydrogen peroxide has proven effective in suppressing microbial activity and could be used to assist in biofilm removal without corrosive attack on aluminium alloys. 

The oil-water interfacial tension of oil treated by the artificial brine reduced slightly, while the oil-water interfacial tension of oil treated by the bacterial suspension decreased continuously (Fig. 4). There are several possible explanations for the reduced activity, metabolites of microbial activity such as biosurfactant gathered at the oil-water interface making the decrease of oil-water interfacial tension. A more likely explanation is that the microbes attach in the oil-water interface forming biofilms with a different wettability than the porous rock interact with the residual oil, then a spontaneous redistribution will occur in response to the local disturbance of the curvature, which may result in the residual oil being mobilized. 

Various microelectrode techniques can be powerful tools for evaluating effects of microbial activities on corrosion behavior at metal surfaces. Membrane tyjje microelectrodes have been developed for measuring microprofiles of dissolved O2, N2O, H2S, and pH across the thickness of microbial mats and biofilms [101-106], These have been used successfully to determine oxygen diffusion fluxes [101,102], microbial photosynthetic and respiration rates [103], nitrogen cycling [104], and to locate the oxic/anoxic boundary [105,106]. 

We asked this question to determine whether a biofilm with higher activity can produce higher current and whether nonuniform activity is connected with the EET mechanism. We expected that somehow microbial activity and EET mechanism should be optimized to maximize electron transfer rates. 

H. von Rege and W. Sand, Evaluation of biocide efficacy by microalorimetric determination of microbial activity in biofilms. J. Microbiol. Methods 33 221-235 (1998). 

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