Removal of nonylphenol ethoxylate from laundry wastewater using modified and functionalized activated carbon

Abstract

Nonylphenol ethoxylate surfactants find wide applications in various industries. These surfactants could be used mainly as washing agents, pesticides, and in textile and leather manufacturing. However, their presence in aquatic environments has raised significant global health concerns. To address this issue, we conducted a study to investigate the impact of surface chemical groups on the removal of nonylphenol ethoxylate (NPEO) from synthetic laundry wastewater using different samples of coal-based activated carbon. The following treatments were carried out to prepare a series of samples: acid treatment with 10% HCl at 75 °C, heat treatment at 900 °C under N₂ flow, and oxidation in 10% HNO₃ at 75 °C. The impact of carbon treatments on the NPEO_3–17 and COD adsorption were examined by conducting batch adsorption using the modified carbons and synthetic laundry wastewater (SLWW) containing NPEO with the ethoxylate chain in the range of 3 to 17. Unmodified and modified activated carbon samples were characterized in terms of structural, morphological and chemical properties. The samples obtained by thermal treatment under N₂ flow at 900 °C achieved the highest removal efficiency (of up to 99%) for the adsorption of NPEO_3–17. Our results have proven that the highly improved removal efficiency of NPEO_3–17 is due to the increase of surface hydrophobicity of the heat-treated activated carbon. When the concentrations were below the critical micelle concentration, the ethoxylated surfactants are adsorbed as monomers by their hydrophobic moiety on a hydrophobic surface of activated carbon. Additional experiments were carried out to describe the sorption phenomenon, followed by the determination of the kinetic of NPEO_3–17 and COD removal using modified activated carbon. The application of Langmuir isotherm provided the best fit for NPEO_3–17 removal and allowed the determination of the adsorption rate constant (K_a = 0.0506 L μg⁻¹) and the maximum adsorption capacity (Q_m = 2168.3 μg g⁻¹). The initial adsorption rate for COD removal was 420 mg g⁻¹ min⁻¹. After ten cycles, the COD removal efficiency reduced from 80% to 50%, indicating the presence of unoccupied active sites in the activated carbon.