*3.2.7 Contribution of nutrients to the biofilm*

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 speed of 1.2 ms<sup>−</sup><sup>1</sup> for an increase in the nutrient level of 4 mg L<sup>−</sup><sup>1</sup> at 10 mg L<sup>−</sup><sup>1</sup> .

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

#### **Figure 11.**

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

suggests that the nature of the nutrients is a determining factor of the biological activity in the biofilm.

The nutrients required by microorganisms for feeding are divided into two broad categories [56]:


In nature, these elements are combined as part of organic and inorganic substances. Some of the nutrients will be incorporated to build macromolecules and cellular structures; others only serve for energy production not directly incorporated as cellular material, and others can perform both functions [56].

The bacterial colony exhibits a great metabolic versatility in the use of nutrients. Autotroph bacterials obtain their carbon by reducing CO2 and other elements from inorganic sources. On the other hand, heterotroph bacterials use to wide ranges of organic carbon sources. In turn, within the heterotrophs, you can find many and varied types of nutrition, from methylotrophic bacteria that only use methane or methanol as carbon and energy sources to the very versatile *Pseudomonas*, which can resort to degrade more than 100 types of carbon sources (including aliphatic and cyclic hydrocarbons). In any case, among the heterotrophs, the most widespread source of carbon is glucose [56].

#### *3.2.8 Abiotic and biotic factors that influence the development of the biofilm*

Alterations in the structure of biofilms can be caused by abiotic factors such as [30]:


**75**

*Fouling in Heat Exchangers*

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

become unfavorable [63].

ers are the following [5]:

clean them

the installation

isms, and biological disturbances [58–60]

**3.3 Effects produced by biofouling in heat exchangers**

unscheduled shutdowns of the installation

counteract the effects of biological fouling

the environment to counteract biological fouling

exchangers of a refrigeration installation

chemical and/or mechanical devices

logical corrosion (MIC) [66]

The biotic factors that can alter the structure of the biofilm are [40]:

• Availability and physiological state of organisms, interaction between organ-

• Properties of adhesion of microorganisms under conditions of turbulence.

• Physiological state of the organisms that have a selective advantage for the formation and development of the biofilm [61]. This capacity is reinforced by the secretion of EPS that are more resistant to high flow rates and chemical agents [62]. Microorganisms in the biofilm are released when conditions

Biofouling has a great influence on the thermal performance of heat exchangers, due to the accumulation of biotic deposits with insulating characteristics in heat exchange surfaces. This accumulation adds not only an additional thermal resistance to the flow of heat but a greater frictional resistance to the passage of the fluid. The formation of these biofilms produces important modifications, since they alter the physical–chemical conditions at the metal-solution interface and form barriers for the exchange of elements between the metallic surface and the surrounding liquid medium [64]. Among the negative consequences, the decrease of the heat output of the heat exchangers and the lower durability of the construction materials of the equipment can be mentioned [65].

The main consequences produced by microfouling (biofouling) in heat exchang-

• Production losses due to the decrease in efficiency and the scheduled and

• Maintenance costs, resulting from the elimination of biofouling deposits with

• Increased corrosion processes in metallic components, induced by microbio-

• Increased consumption of water, electricity, fossil fuels, and other sources to

• Increase in manufacturing costs of heat exchangers to consider an acceptable biological fouling without losing design power and to be able to mechanically

• Increase in environmental risks due to the use of biocides and CO2 emissions to

• High costs caused by the complexity of the cleaning of the macroorganisms of

• Losses of power produced by the loss of flow and thermal efficiency in the heat

The main consequences of macrofouling in a heat exchanger are [40]:

*Inverse Heat Conduction and Heat Exchangers*

• Macronutrients (C, H, O, N, P, S, K, Mg)

• Micronutrients or trace elements (Co, Cu, Zn, Mo, etc.)

rated as cellular material, and others can perform both functions [56].

*3.2.8 Abiotic and biotic factors that influence the development of the biofilm*

activity in the biofilm.

broad categories [56]:

source of carbon is glucose [56].

• Depth.

• Illumination.

• Exhibition time.

• Height of the tides.

• Physical alteration.

• Water chemistry.

• Supply of nutrients.

development [57].

• Latitude.

• Season.

• Water circulation regime.

suggests that the nature of the nutrients is a determining factor of the biological

The nutrients required by microorganisms for feeding are divided into two

In nature, these elements are combined as part of organic and inorganic substances. Some of the nutrients will be incorporated to build macromolecules and cellular structures; others only serve for energy production not directly incorpo-

The bacterial colony exhibits a great metabolic versatility in the use of nutrients. Autotroph bacterials obtain their carbon by reducing CO2 and other elements from inorganic sources. On the other hand, heterotroph bacterials use to wide ranges of organic carbon sources. In turn, within the heterotrophs, you can find many and varied types of nutrition, from methylotrophic bacteria that only use methane or methanol as carbon and energy sources to the very versatile *Pseudomonas*, which can resort to degrade more than 100 types of carbon sources (including aliphatic and cyclic hydrocarbons). In any case, among the heterotrophs, the most widespread

Alterations in the structure of biofilms can be caused by abiotic factors such as [30]:

• Physical and chemical (abiotic) conditions at the seawater/biofilm interface are an important factor for the development of the biofilm. As the thickness of the biofilm increases, variations in pH, dissolved oxygen, and metabolic by-products are more important and generally directly influence its

**74**

The biotic factors that can alter the structure of the biofilm are [40]:

