THERMODYNAMIC AND KINETICS STUDIES OF THE ADSORPTION OF PHOSPHORUS BY BIORETENTION MEDIA

The objective of this study is to explore the mechanism of phosphorus adsorption in the bioretention media. The phosphorus adsorption characteristics of four media of bioretention are studied by four isothermal adsorption experiments. The result indicate that the maximal adsorption capacity (q(m)) of phosphorus of the four bioretention media are found to be media I (0.3365 mg/g), media II (0.3302 mg/g), media III (0.2751 mg/g) and media IV 0.8435 mg/g), respectively. The negative values of Gibbs free energy of phosphorus indicate that each of the phosphorus adsorption process by the four bioretention media is a spontaneous process. The mean sorption energies obtained from DR isotherm were 0.0758, 0.0772, 0.0803 and 0.0632 kJ/mol respectively, which indicate the physical nature of the adsorbate/adsorbent interactions. Two kinetic models including pseudo first-order and pseudo second-order equation were selected to follow the adsorption process. The results showed that the adsorption of phosphorus with the four types of bioretention media could be described by the pseudo second-order equation. The media IV was the better media of bioretention with high phosphorus removal capacity.