Microbial films

Microbial cells transported with the stream of fluid above the surface interact with conditioning films. Immediately after attachment, microorganisms initiate production of slimy adhesive substances, predominantly exopolysaccharides (EPS) that assist the formation of microcolonies and microbial films. EPS create bridges for microbial cells to the substratum and permit negatively charged bacteria to adhere to both negatively and positively charged surfaces. EPS may also control interfacial chemistry at the mineral/biofilm interface. 

There are a few other kinds of industrial plants. An air-lift tower fermenter was developed by ICI for the production of single-cell protein from methanol which employs an external loop for heat removal. Trickle beds for the treatment of waste waters employ packing structures or packing elements of 4-6 cm dia and porosities above 50%. Microbial films are formed on the packing that react with the organic substrate and the air as the liquid flows down and the air up. 

If the activity of the immobilised catalyst is sufficiently high, the reaction which it mediates occurs essentially at the interface between the catalyst and the substrate solution. In the case of the surface immobilised enzyme or a thin microbial film this will, of course, occur irrespective of the level of activity. Under these conditions the limiting process for transporting substrate from the bulk of the solution to the immobilised enzyme is molecular or convective diffusion through the layer of solution immediate to the carrier. Under steady-state conditions, the rate of reaction at the active sites is equal to the rate at which substrate arrives at the site. This... 

In the case of gel entrapped biocatalysts, or where the biocatalyst has been immobilised in the pores of the carrier, then the reaction is unlikely to occur solely at the surface. Similarly, the consumption of substrate by a microbial film or floe would be expected to occur at some depth into the microbial mass. The situation is more complex than in the case of surface immobilisation since, in this case, transport and reaction occur in parallel. By analogy with the case of heterogeneous catalysis, which is discussed in Chapter 3, the flux of substrate is related to the rate of reaction by the use of an effectiveness factor rj. The rate of reaction is itself expressed in terms of the surface substrate concentration which in many instances will be very close to the bulk substrate concentration. In general, the flux of substrate will be given by ... 

The simplest case to consider is that of an uniform microbial film or of an enzyme which is immobilised uniformly through a slab of supporting material which has infinite area but finite depth. As in the previous discussion the local rate of reaction is assumed to be described by Michaelis-Menten or Monod kinetics, so that at... 

Wieczorek, S.K., Clare, A.S., and Todd, C.D., Inhibitory and facilitatory effects of microbial films on settlement of Balanus amphitrite amphitrite larvae, Mar. Ecol. Prog. Ser., 119, 221, 1995. 

Another source of cues for larval settlement are the films of microorganisms (biofilms) found on most underwater surfaces. Microbial films have long been recognized as necessary for the settlement of some invertebrate larvae,23 and the settlement of many, but not all, groups of invertebrate larvae are facilitated by the presence of microbial films.3,24 In some cases, specific types of bacteria present in biofilms may be responsible for facilitating settlement,24-26 and chemicals bound to or released from bacteria may function as settlement inducers. 

The importance of marine biofilms for settlement of polychaete larvae has long been recognized. The spirorbid Janua brasiliensis releases larvae that show strong preferences for settlement on the green alga Ulva lobata. However, experimental evidence demonstrated that microbial films growing specifically on the surfaces of U. lobata contain the inductive cue for larval settlement of... 

Brancato, M. S. and Woollacott, R. M., Effect of microbial films on settlement of bryozoan larvae Bugula simplex, B. stolonifera, and B. turrita, Mar. Biol., 71, 51, 1982. 

Baier, R.E., Initial events in microbial film formation, in Marine Biodeterioration an Interdisciplinary Study, Costlow, J.D. and Tipper, R.C., Eds., Naval Institute Press, Annapolis, MD, 1984, 52. 

Ghommidh et al. [45] investigated the performance of Acetobacter ctWs immobilized in a monolith reactor operated with a pulse flow. A very high productivity up to 2.9 X 10" kg m see" of acetic acid was achieved due to the very intensive transfer of oxygen from the gas to the solid. Oxygen transfer in the microbial film was evaluated as controlling the reactor productivity. 

Tubular fluidized and fixed bed fermenters are deviations from the simple bubble column fermenter. Often utilized in producing beer and ciders, these fermenters contain immobilized microorganisms or microbial films on support surfaces. Microbes lost with the product are continuously replenished by adding fresh microorganisms into the packed bed fermenters. In the fixed bed case, slow downward flow of the medium significantly reduces the shear removal (mobilization) of the microbes from the support materials and increases the residence time in the packed column. This is a typical characteristic of the trickle bed fermenter for continuous operation. Readers are referred to the packed bed reactor entry in this volume for a more... 

It seems that water absorption serves as one of the key parameters in microbial growth in WPC materials. When a whole cross section of a composite deck board is tested by immersion in water, water absorption after 24 hr is typically between 1 and 3% by weight, after 7 days between 3 and 10%, after 20 days about 8 to 15% (see Chapter 12). These values depend on temperature, and the lower the the temperature, the lower the water absorption [1]. However, water absorption by the top layer of a composite board (1 mm in depth, 50 50 mix of woodiplastic) was in excess of 15% after 24 hr [2]. On other data, water absorption by the 5-mm top layer of Trex deck board in the temperature range from 5 to 25°C was 45 and 60%, respectively. This level of moisture content is well in excess of that necessary to support fungal decay. In fact, authors [1] noticed that when the 25°C trial was run for 30 days using Trex samples, a thick microbial film was developed on the surface of the material. This is a rather common observation in the course of long-term water absorption studies. 

Cook, P.E. and Gaylarde, C.C., 1993, Microbial films in the light engineering industry, in Denyer, S.P. and Sussman, M. eds. Microbial Biofilms Formation and Control. Blackwell Scientific Publications, London. 

Mack et al (57) studied the development and ecological succession of microbial films in a newly commissioned trickling filter system. A biofilm formed over the rock surfaces and consisted of a micro-jungle of bacterial colonies, fungi, algae and protozoa. 

The overall description (model) of a reactor is obtained through process synthesis by combining models of reactor hydrodynamics, mass transfer and heat exchange with an appropriate cell (subcellular) or population model ( 1).Description of a population should take into consideration possible dispersed or aggregated (the distinct morphological appearances of a culture pellets, mycelium, flocks, growth on reactor wall in the form of microbial film) forms of population. Biomass support particles are gaining appreciable importance in aerobic (40) as well as in anaerobic processes. 

Microbial films will affect the general corrosion only when the film is continuous. This is not the case in general and microorganisms form in discrete deposits or colonies and the resulting corrosion is localized. 

The BRE shows that only one kinetic equation can exist for various geometries of the biological mass. In the past, attempts were often made to formally utilize zero-order equations with microbial particles (floes) and to formally use first-order equations with microbial films, and this discrepancy was the starting point of Atkinson s work. 

Due to the adhesion capacity of microbes, biofilm formation must be taken into account in river analysis as well as in the chemostat or fixed beds (percolating or trickling filter). The significance of microbial films in fermenters has been extensively studied and reviewed (Atkinson, 1973, 1974 Atkinson and Fowler, 1974 Atkinson and Knights, 1975 Charaklis, 1981 Harremoes, 1978). 

CMMFF completely mixed microbial film fermenter... 

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