Comparing the efficiency of unmodified dried sludge adsorbents and those modified via chemical and microwave methods in removing 2,4-dinitrophenol from aqueous solutions.

2,4-dinitrophenol (DNP) is found in small amounts in the effluent of many wastewater treatment plants. The contamination of drinking water with this pollutant, even in trace amounts, causes toxicity, health problems, and unfavorable taste and odor. This study aims to compare the efficiency of non-modified and modified dried sludge adsorbents in removing 2,4 DNP from aqueous solutions. The results of 2,4DNP removal by high-performance liquid chromatography method at the wavelength of 360 nm in a batch mode were obtained by changing the influential factors including contact time, pH, initial concentration of the contaminant, and adsorbent dosage. Eventually, the results were analyzed by kinetic and isotherm models. In this research, the optimal time was obtained as 60 min and pH as seven for all three adsorbents. The results showed that the removal percentage increases by rising adsorbent dosage and reducing contaminant concentration. The correlation coefficient value of linear and non-linear led that in kinetic studies, it follows the pseudo-second order model. In contrast, in isotherm studies, examining linear and non-linear models of isotherms showed that the data for every three types of adsorbents follow the Freundlich model well. The adsorption process is highly dependent on pH and affects the adsorbent surface properties, ionization degree, and removal percentage. At high pH, hydroxide ions (OH) compete with 2,4 DNP molecules for the adsorption sites. The adsorption occurs quickly and gradually reaches a constant value because, over time, the adsorption sites are occupied until reaching a saturated limit. By increasing the adsorbent dosage, the adsorption percentage increased significantly, which is due to the fact that higher amounts of adsorbent cause more adsorption sites.