Enhanced efficiency of a chemically modified hyperbranched Kraft lignin in the removal of pharmaceuticals from water at low microgram per liter levels

This study describes a way to increase the efficiency of Kraft lignin to remove emerging contaminants such as pharmaceutically active compounds (PhACs) at the level of µg L⁻¹. A hyperbranched polymer was prepared by chemically modifying Kraft lignin introducing nitrogen atoms in its structure using urea-formaldehyde as precursors and thus increasing the amount of active sites of lignin. The so-obtained biosorbent was characterized by infrared spectroscopy, SEM-EDS microscopy, elemental analysis, helium pycnometry and N₂ physisorption. The bioadsorbent obtained showed an increase in density of 8.5% and 1.4 times in the content of N compared to lignin. While a decrease in solubility of 56% in water at pH 7. The adsorption of PhACs were carried out using different types of compounds such as antibiotics, anti-inflammatory, psychiatric and stimulant, lipid regulators, and diuretics at initial concentrations ranging from 5 to 150 µg L⁻¹, as found in wastewater. The modification process promoted the formation of functional groups onto the surface which favor the sorption of contaminants. This bioadsorbent showed a higher adsorption coefficient especially for those PhACs that do not have chlorine and fluorine atoms in their structure since they reduce the π electron charge of the aromatic ring. By a thermodynamic analysis, it was found that the PhACs sorption on the used biosorbent is endothermic and spontaneous.