Adsorption of selected micropollutants on powdered activated carbon and biochar in the presence of kaolinite

Commercially available powdered activated carbon (PAC) and activated biochar (produced in the laboratory), combined with kaolinite, were used to determine the adsorption of a beta-blocker (atenolol, ATN) and sunscreen compounds (benzophenone, BZP; and benzotriazole, BZT); a hypothesis was made that the presence of kaolinite would increase the adsorption of those target compounds. Various synthetic solutions were prepared by altering the pH, background ions, ionic strength, and glucose/humic acid content to mimic various natural water conditions. The removal efficiency of biochar–kaolinite was higher than that of PAC–kaolinite, presumably because the relatively high surface area and pore volume of biochar resulted in a higher adsorption capacity for the target compounds. Removal of the compounds in the absence of kaolinite followed the order BZP > ATN > BZT (a (mg/g); Langmuir maximum adsorption capacities were as follows: 85.0, 20.6, and 15.6 for PAC, and 125, 37.5, and 25.9 for biochar, respectively). An increase in the pH from 3.5 to 10.5 decreased the adsorption of ATN, BZP, and BZT by 14.5, 2.1, and 14.4%, respectively, by biochar–kaolinite. Additionally, an increase in background ions and their ionic strength, using NaCl, Na₂SO₄, and CaCl₂, increased the adsorption of the target compounds slightly, by 2.0–6.6%, depending on the target compound. Overall, biochar had a higher adsorption capacity for all chemicals tested compared with PAC, suggesting that biochar derived from loblolly pine chip may be a promising sorbent for water/wastewater treatment and environmental applications.