Adsorption is the process of the accumulation of particles from the liquid or gas phase to the surface of the solid phase. As a separation process, it is of great importance in industry and is being studied on a daily basis. It is used for gas purification (removal of SO2, CO2, NOx, etc.), and its most important application in the purification of liquids is the removal of organic compounds from water and the purification of drinking water and wastewater. In this work, the adsorption of formic acid, acetic acid, and 1,4-dioxane on granular activated carbon (commercial) and on carbon prepared from hazelnut shells by Method 1 (activation with sulfuric acid) and Method 2 (activation with hydrochloric acid) was compared. The specific active surface area of the activated carbons was determined by recording the adsorption-desorption isotherms of nitrogen. The study was carried out by batch adsorption. By comparing the obtained Freundlich isotherms, the adsorption affinity of individual organic pollutants on different types of activated carbon was estimated. From the analysis of the results, it can be concluded that granular activated carbon has a larger specific surface area and pore volume than the activated carbon prepared from hazelnut shells by Method 1, while the average pore diameter is the same for both types of activated carbon. The largest amount of carboxylic acids can be adsorbed by granular activated carbon, then by carbon prepared from hazelnut shells by Method 1, and the smallest amount can be adsorbed by carbon prepared from hazelnut shells by Method 2. Granular activated carbon can adsorb a greater amount of 1,4-dioxane than the carbon prepared from hazelnut shells by Method 2.