*3.2.4 Adhesion of microorganisms*

*Inverse Heat Conduction and Heat Exchangers*

common to numerous bacteria.

*3.2.2 Conditioning of the surface*

*3.2.3 Adsorption of molecules*

faces to colonize.

(**Figure 8**).

encode its motor functions and environmental sensitivity, and those that generate adhesins and other proteins [30–33]. The factors that directly affect its development depend mainly on the microbial species, although a part of these characteristics is

Once initial biofouling adhesion is produced, cell growth and expansion begin on the surface, forming monolayer microcolonies. At the same time, the cells modify their activity and begin the complex process of structure formation of the biofilm. The most obvious of these changes is the production of the exopolymer matrix (EPS), which will unite the whole [34]. If the conditions of the medium allow it, the biofilm will grow and spread to non-colonized areas releasing cells that will be distributed through the water in search of new sur-

The formation of the biofilm is a systematic process of predictable evolution, in which five phases are differentiated [35]: (1) the reversible adsorption of the bacterium to the surface, (2) the irreversible union, (3) the first maturation phase with growth and division, (4) the growth phase with production of the exopolymer, and (5) the final development of the colony with dispersion of colonizing cells

The ability to bind to different materials depends on the specific proteins of its coat and the bacterial motor appendages. According to Pedersen [36], stainless steel can be as susceptible to the formation of biofilms as plastic. This is because the organic matter present in the water previously comes in contact with the surface, depositing an organic layer in the water/surface interface that changes the chemical and physical

The adsorption of ions and other dissolved substances (sugars, amino acids, proteins, fatty acids, etc.) begins when the material submerges under seawater

properties of the surface, improving the possibilities of fixing the bacteria.

*Phases of biofilm formation (Source: By courtesy of Center Biofouling Engineering).*

**70**

**Figure 8.**

The adhesion of microorganisms to a substrate can be active (by flagella, fimbrias, adhesins, capsules, and surface charges) or passive (by gravity, diffusion, and fluid dynamics). In the absence of these mechanisms, the bacterial cells would be repelled by the surface when presenting electric charges of the same sign [38].

In a few minutes, the free bacteria form a reversible EPS matrix with the "conditioned" surface (**Figure 9**) [39], whose characteristics depend on the electrical charges of the bacteria. These attractive forces have their origin in hydrogen bonds, cation bonds, and van der Waals forces that compete with the forces of repulsion. If this union is maintained long enough, new chemical and physical structures appear that make it permanent and irreversible [40].

In cases of high microbial population density or lack of nutrients in the water, some microorganisms are able to individually alter their cell wall to make it more hydrophobic and increase its greater affinity of adhesion toward the surfaces. When the microorganisms approach the surface, with almost no water flow, they are attracted, proving their affinity for union and fixation (**Figure 10**) [41].

During the reversible adsorption stage, the bacterial cells still show Brownian motion and are easily removed with a nonaggressive cleaning method. The irreversible union implies the anchoring of bacterial appendages and the production of exopolymers, which determines that the mechanical action necessary to detach them will be greater depending on the time that the biofilm is active.

Bacteria undergo important transformations in their structure to adapt to the environment. These transformations activate different genes that encode new structural proteins and enzymes, which explains the adhesion and resistance of biofilm bacteria to antibiotics and disinfectants. In recent years, the advances made in the field of proteomics and genomics have allowed the identification of 800 proteins that modify their concentration throughout the five phases of the biofilm development and clarify the complex process of biofilm formation [42, 43].

#### **Figure 9.**

*Binding forces in an EPS matrix: (i) hydrogen bonds, (ii) cation bonds, (iii) van der Waals forces and (iv) repulsion force [38].*

#### **Figure 10.**

*Water flow transport of a bacterial cell to the conditioned surface: (i) adsorption, (ii) reversible adsorption, (iii) detachment and (iv) irreversible adsorption [40].*

#### *3.2.5 Maturation*

Environmental stability favors biofouling growth and multiplication of cells which allows to generate a polyanionic polymer mixture of silty and sticky consistency whose are excreted to the outside to facilitate union cells onto surface.

Although its composition is not completely known, the mixture of exopolymers is formed by polysaccharides or glycoproteins of various sugars (glucose, fructose, mannose, N-acetylglucosamine, and others) [44] and, additionally, may contain free proteins, phospholipids, and nucleic or teichoic acids [45]. These free proteins are useful for retaining nutrients and protecting bacteria from various biocides.

Extracellular exopolymeric material or glycocalyx is expelled from the bacterial cell wall and adopts a reticular structure reminiscent of a spider. This structure is formed from groups of polysaccharides both neutral and carriers of electric charges, which act as ion exchange systems, capable of capturing and concentrating the nutrients present in the medium.

The structure of the biofilm interacts in a complex way, showing a behavior similar to that of multicellular organisms. If a microorganism generates toxic waste, another will use it as food and, in this way, coordinate the biochemical resources of all the beings that inhabit the matrix of the biofilm. In addition, some bacteria clump together within the matrix with a series of enzymes that allow them to digest nutrients that no isolated species could digest. Also, these enzymes will be used to respond to the attack of various biocides.

Anaerobic biofilms can be developed under the aerobic layer whose structure is permeabilized with a mesh of furrows crossed by water, bacterial debris, enzymes, nutrients, metabolites and oxygen. The gradients of ions and molecules that are established between the different zones generate the necessary impulse to take the substances to the periphery of the biofilm where most of the cells are located. The number of these cells is reduced with the age of the biofilm, being 80% in a young matrix and 50% in an aged shade [42].

#### *3.2.6 Growth and dispersion*

Biofilm formation has continuous divisions of the cellular matrix colony, which means a periodic detachment of groups of cells that deposit downstream.

**73**

**Figure 11.**

*Engineering).*

*Fouling in Heat Exchangers*

of bacteria [30].

speed of 1.2 ms<sup>−</sup><sup>1</sup>

*DOI: http://dx.doi.org/10.5772/intechopen.88079*

releasing whole areas of the biofilm colony.

*3.2.7 Contribution of nutrients to the biofilm*

These new colonies take advantage of the release of residues and nutrients from the original colonies to prepare the new surface and to feed other cells, and, as a consequence, the new colonies will grow and spread much more rapidly than in the original biofilm. This colonization is related to the long-term evolution and survival

If the conditions of the fluid allow it, the equilibrium that is established between the growth of the colony and the movement of the water releases few cells (**Figure 11**). With an intense or turbulent flow, many more can be released, even

for an increase in the nutrient level of 4 mg L<sup>−</sup><sup>1</sup>

*Microbial cell transport during the growth phases of the biofilm (Source: By courtesy of Center Biofouling* 

The chemical composition of the waters determines the number, diversity, metabolic state of the bacteria, and their tendency to adhere to surfaces [51]. So far there has been no study that directly relates nutrients, biofilms, and colonization. Huang et al. [52] demonstrated in the laboratory that the availability of nutrients and the synthesis of new proteins for the formation of biofilms of *Pseudoalteromonas spongiae* under static conditions and without added nutrients affected the induction and adhesion of the biofilm to the surface. The effects of organic substances in the form of amino acids on the bioactivity of the biofilm were studied by Jin and Qian [53, 54]. The results of this study showed that the incorporation of aspartic acid and glutamic acid causes a significant increase in the bacterial mass, modifies its structure, and increases the inducing effect of biofilm formation. In addition, Huang et al. [55] found that the characteristics of biofilms generated in habitats with different environmental conditions show remarkable differences in the bioactivity of the larval settlements of the barnacle, which

The main factor controlling the growth of the biofilm is the availability of dissolved nutrients and their conversion into accumulated biomass. In cooling water circulation systems, the transfer of nutrients to the biofilm tends to increase with flow velocity [41]. Also, the rough surfaces of biofilms increase the transfer of nutrients about three times in relation to smooth surfaces [30, 46]. The control of nutrients is a way to control the development of the biofilm [47–49]. Melo and Bott [50] observed, in an industrial refrigeration system, an increase of 400% in the thickness of the biofilm at a

at 10 mg L<sup>−</sup><sup>1</sup>

.

#### *Fouling in Heat Exchangers DOI: http://dx.doi.org/10.5772/intechopen.88079*

*Inverse Heat Conduction and Heat Exchangers*

*(iii) detachment and (iv) irreversible adsorption [40].*

*3.2.5 Maturation*

**Figure 10.**

biocides.

the nutrients present in the medium.

respond to the attack of various biocides.

matrix and 50% in an aged shade [42].

*3.2.6 Growth and dispersion*

Environmental stability favors biofouling growth and multiplication of cells which allows to generate a polyanionic polymer mixture of silty and sticky consistency whose are excreted to the outside to facilitate union cells onto surface.

*Water flow transport of a bacterial cell to the conditioned surface: (i) adsorption, (ii) reversible adsorption,* 

Although its composition is not completely known, the mixture of exopolymers is formed by polysaccharides or glycoproteins of various sugars (glucose, fructose, mannose, N-acetylglucosamine, and others) [44] and, additionally, may contain free proteins, phospholipids, and nucleic or teichoic acids [45]. These free proteins are useful for retaining nutrients and protecting bacteria from various

Extracellular exopolymeric material or glycocalyx is expelled from the bacterial cell wall and adopts a reticular structure reminiscent of a spider. This structure is formed from groups of polysaccharides both neutral and carriers of electric charges, which act as ion exchange systems, capable of capturing and concentrating

The structure of the biofilm interacts in a complex way, showing a behavior similar to that of multicellular organisms. If a microorganism generates toxic waste, another will use it as food and, in this way, coordinate the biochemical resources of all the beings that inhabit the matrix of the biofilm. In addition, some bacteria clump together within the matrix with a series of enzymes that allow them to digest nutrients that no isolated species could digest. Also, these enzymes will be used to

Anaerobic biofilms can be developed under the aerobic layer whose structure is permeabilized with a mesh of furrows crossed by water, bacterial debris, enzymes, nutrients, metabolites and oxygen. The gradients of ions and molecules that are established between the different zones generate the necessary impulse to take the substances to the periphery of the biofilm where most of the cells are located. The number of these cells is reduced with the age of the biofilm, being 80% in a young

Biofilm formation has continuous divisions of the cellular matrix colony, which means a periodic detachment of groups of cells that deposit downstream.

**72**

These new colonies take advantage of the release of residues and nutrients from the original colonies to prepare the new surface and to feed other cells, and, as a consequence, the new colonies will grow and spread much more rapidly than in the original biofilm. This colonization is related to the long-term evolution and survival of bacteria [30].

If the conditions of the fluid allow it, the equilibrium that is established between the growth of the colony and the movement of the water releases few cells (**Figure 11**). With an intense or turbulent flow, many more can be released, even releasing whole areas of the biofilm colony.
