Simultaneous removal of non-steroidal anti-inflammatory drugs and cadmium in aqueous phase by activated carbon: Behaviors, mechanisms and application potentials

Abstract

The combined pollution of pharmaceuticals and heavy metals has received increasing attention in recent years. Adsorptive strategy is a promising application in the simultaneous removal of pharmaceutical-metal complexes. In this study, the non-steroidal anti-inflammatory drugs (NSAIDs consisting of ibuprofen (IBP) and naproxen (NAP)) and cadmium (Cd) were selected as representative pharmaceuticals and heavy metals, respectively, and their removal behaviors on a typical adsorbent of powdered activated carbon (PAC) were investigated. The influencing factors (i.e., contact time, concentration, pH, temperature, addition sequence, background substances) and related mechanisms during the adsorption processes were explored with experimental and theoretical methods. Additionally, the reusability and performance of PAC in actual wastewater were evaluated. The results showed that Cd promoted IBP and NAP adsorption through bridging and electrostatic interactions. Lower concentrations (<20 mg/L) of NSAIDs moderately enhanced adsorption capacity of Cd, while higher concentrations inhibited the Cd adsorption due to potential blockage and competitive effects. In the presence of Cd, the adsorption capacity of NSAIDs increased with pH, with the adsorption capacity of IBP and NAP increased by 2.58 and 1.49 times at pH= 7, respectively. In contrast, the effect of NSAIDs on Cd adsorption remained relatively consistent over the pH range of 2–7. Hydrochloric acid had a good recovery ability for the reuse of saturated PAC (regeneration efficiency >80%). Adsorption of NSIADs in actual wastewater decreased by 37.5% to 75.0% because of competition with high organic matter, while the removal of Cd was relatively stable. These results provide new insights into the control of combined pharmaceutical-heavy metal contamination from wastewater.