*2.1.4 Oxidation*

Oxidation is based on electrochemical reactions between the oxidizing agent and the pollutant by changing the electrons. This technique aims to modify the characterization of refractory pollutants by making them insoluble to facilitate their elimination, or soluble but non-toxic. The most commonly used chemical oxidants are oxygen, hydrogen peroxide, chlorine, ozone, potassium permanganate, and ferric chloride. This system is known for its strong elimination of bad odors, either natural or produced during anaerobic conditions. In addition, the combination of ozone with ultraviolet rays (UV) or hydrogen peroxide produces free radicals that are powerful oxidants and can eliminate a large part of the COD [24]. The advantages and disadvantages of this process are depending on the oxidant agent and the type of pollutant (**Table 1**).

According to the literature, several types of research have shown the efficiency of this process for the elimination of sulfides, of which hydrogen peroxide is the most used. This oxidant can eliminate 85–100% of sulfides by using 1.3 to 4.0 mg/L of H2O2 for 1 mg/L of sulfides [26].

In recent decades, this process has been developed using the combination of two powerful chemical oxidants (H2O2/Fe2+ and H2O2/O3), photo-catalysis (UV),


### **Table 1.**

*Advantages and disadvantages of oxidation agents [25].*

### *Biological versus Physicochemical Technologies for Industrial Sewage Treatment… DOI: http://dx.doi.org/10.5772/intechopen.100325*

sonochemical oxidation, or electrochemical oxidation. As a result, this oxidation is called advanced oxidation (POA), which is considered an innovative process and an emerging technology for the treatment of industrial sewage. The principle of advanced oxidation is based on the production of hydroxyl radicals, which are very active and react rapidly on organic and inorganic compounds [9]. This advanced process has several qualities like high removal rates in a short time and minimal sludge production. However, it also has some disadvantages namely the high operating and investment costs, as well as the treatment efficiency depends on nature and pollutant concentration.
