**2.1 Biological fouling**

The biological fouling or biofouling in the Anglo-Saxon literature depends on the material on which the accumulation of macrofouling or macrobial biofouling occurs, which originates from microfouling or microbial biofouling.

### **2.2 Fouling by chemical reaction**

Deposits caused by chemical reaction can be initiated by the contact of two chemicals in a heat transfer process. In some cases, the metal surface favors precipitation by acting as a catalyst.

This type of fouling is frequently observed in the petroleum industry, in which the refining processes induce the polymerization of unsaturated hydrocarbons (**Figure 3**).
