Activated carbons are efficient adsorbent materials for removing pollutants from water. The physical-chemical nature of the activated carbons surface plays an important role in the process of adsorption and should be considered when selecting or preparing activated carbon for application purposes in adsorption and/or oxidation. Based on the obtained results regarding the characterization of carbonaceous adsorbents surface chemistry as well as the nitrite adsorption capacity as function of pH value, mechanisms of pollutants adsorption were proposed [1]. For the initial activated carbons, which are poor in functional groups on the surface, in the adsorption process Cπ sites participate. These sites or adsorption centers (Cπ) are strongly influenced by the solution pH value, in the acidic domain, protons (H+) are concentrated on Cπ sites and the positively charged graphitic structure of activated carbon attracts the nitrite ions (Figure 1). For the modified activated carbons (modified with chlorine ions), adsorption proceeds via the mechanism of protonation of hydroxyl groups (-OH) on the activated carbon surface. On the surface of initial activated carbons, with a weak basic surface, there are few hydroxyl groups from alcohols and phenols, while on the surface of oxidized activated carbons there are more hydroxyl groups from alcohols, phenols and carboxylic acidic. In the basic domain, OH- ions are competitive with the nitrite ions, the graphitic surface of activated carbon becomes negatively charged and, consequently, rejects the nitrite ions [2]. + nH+ → +nNO2 - ↔ Fig. 1. Schematic presentation of the nitrite ions adsorption on the surface of the modified activated carbon. (1) - protonation of functional groups on the surface of activated carbon; (2) - adsorption of nitrite ions by electrostatic interaction [1].