Magnetic activated carbon was prepared by adding a magnetic material to activated carbon that had been prepared from waste citrus peel in Jeju. The adsorption characteristics of an aqueous solution of the antibiotic trimethoprim (TMP) were investigated using the magnetic activated carbon, as an adsorbent, and response surface methodology (RSM). Batch experiments were carried out according to a four-factor Box-Behnken experimental design affecting TMP adsorption with their input parameters (TMP concentration: 50～150 mg/L; pH: 4～10; temperature: 293～323 K; adsorbent dose: 0.05～0.15 g). The significance of the independent variables and their interaction was assessed by ANOVA and t-test statistical techniques. Statistical results showed that TMP concentration was the most effective parameter, compared with others. The adsorption process can be well described by the pseudo-second-order kinetic model. The experimental isotherm data followed the Langmuir isotherm model. The maximum adsorption capacities of TMP, estimated with the Langmuir isotherm model were 115.9-130.5 mg/g at 293-323 K. Also, both the thermodynamic parameters, △H and △G, have both positive values, indicating that the adsorption of TMP by the magnetic activated carbon is an endothermic reaction and proceeds via an involuntary process.

The adsorption characteristics of bisphenol A (BPA) were investigated using activated carbon based on waste citrus peel (which is abandoned in large quantities in Jeju Island), denoted as WCP-AC, and surface-modified with various P2O5 concentrations (WCP-SM-AC). Moreover, coconut-based activated carbon (which is marketed in large amounts) was surface-modified in an identical manner for comparison. The adsorption equilibrium of BPA using the activated carbons before and after surface modification was obtained at nearly 48 h. The adsorption process of BPA by activated carbons and surface-modified activated carbons was well-described by the pseudo second-order kinetic model. The experimental data in the adsorption isotherm followed the Langmuir isotherm model. With increasing P2O5 concentration (250-2,000 mg/L), the amounts of BPA adsorbed by WCP-SM-AC increased till 1,000 mg/L of P2O5; however, above 1,000 mg/L of P2O5, the same amounts adsorbed at 1,000 mg/L of P2O5 were obtained. With increasing reaction temperature, the reaction rate increased, but the adsorbed amounts decreased, especially for the activated carbon before surface modification. The amounts of BPA adsorbed by WCP-AC and WCP-SM-AC were similar in the pH range of 5-9, but significantly decreased at pH 11, and increased with increasing ionic strength due to screening and salting-out effects.

Waste citrus peel-based activated carbon (WCAC) was prepared from waste citrus peels by activation with KOH. The removal of Cu and Pb ions from aqueous solution by the prepared WCAC was investigated in batch experiments. The solution pH significantly influenced Cu and Pb adsorption capacity and the optimum pH was 4 to 6. The adsorption of Cu and Pb ions by WCAC followed pseudo-second-order kinetics and the Langmuir isotherm model. The maximum adsorption capacity calculated by Langmuir isotherm model was 31.91 mg/g for Cu and 92.22 mg/g for Pb. As the temperature was increased from 303 K to 323 K, the ΔG˚ value decreased from –7.01 to –8.57 kJ/mol for Cu ions and from –0.87 to –2.06 kJ/mol for Pb ions. These results indicated that the adsorption of Cu and Pb by WCAC is a spontaneous process.