Impacts of soil humic acids on the presence of PPCPs in reclaimed water

Abstract

A multidisciplinary approach investigates the interaction between selected PPCPs with diversified physicochemical propertiesand humic acids (HAs) extracted from Elliot and volcanic soils in reclaimed water (RW). Principal component analysis (PCA) reveals significant differences between the two HAs and how these differences affect PPCP-HA interaction which are characterized by UV spectroscopy. The sorption of PPCPs on either IHSS HA or CAN HA fit a pseudo-second-order kinetic reaction in RW, indicating that the adsorption rate was controlled by the diffusion of the PPCP, followed by adsorption on the HA surface. The sorption of each individual PPCP on both HAs was characterized by applying sorption isotherm models, showing that chemisorption is involved. Moreover, the simultaneous PPCP-HA interactions between the selected PPCPs and both HAs in RW (at different pHs) fitted Freundlich's model (R² > 0.9890), where, K_F values are 0.0003 and 0.085 for simultaneous adsorption on IHSS HA and CAN HA, respectively. The greater K_F value obtained for CAN HA suggests that the simultaneous PPCP adsorption is more favourable in this HA than in IHSS HA. Meanwhile, coexisting Ca²⁺ (>50 mM) in RW could inhibit the PPCP-HA interaction due to the aggregation of HAs. This study highlights the importance of the HA origin in the interaction with PPCPs in RW, which can affect the fate and transport of these pollutants and the associated environmental risk.

Keywords: Adsorption isotherms; PPCP-HA interaction; PPCPs; Reclaimed water; Soil humic acids; Volcanic ash soil.