*3.2.3 Adsorption of molecules*

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

**71**

**Figure 9.**

*(iv) repulsion force [38].*

*Fouling in Heat Exchangers*

sign [38].

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

that make it permanent and irreversible [40].

on the surface in a few minutes [37].

*3.2.4 Adhesion of microorganisms*

and accelerates when the fluid begins to circulate through the heat exchanger. This adsorption occurs rapidly on the surface, saturating the concentration of substances

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

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

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

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 develop-

them will be greater depending on the time that the biofilm is active.

ment and clarify the complex process of biofilm formation [42, 43].

*Binding forces in an EPS matrix: (i) hydrogen bonds, (ii) cation bonds, (iii) van der Waals forces and* 

**Figure 8.** *Phases of biofilm formation (Source: By courtesy of Center Biofouling Engineering).*

and accelerates when the fluid begins to circulate through the heat exchanger. This adsorption occurs rapidly on the surface, saturating the concentration of substances on the surface in a few minutes [37].
