Co-contaminant effects on ofloxacin adsorption onto activated carbon, graphite, and humic acid

Given their voluminous application, significant amounts of fluoroquinolones are discharged into the environment through wastewater effluent. Adsorption has been shown to be a critical process controlling the environmental behaviors of fluoroquinolones. Competition between ofloxacin (OFL) and naphthalene (NAP)/bisphenol A (BPA) and their adsorption on activated carbon (AC), graphite (GP), and humic acid (HA) were investigated. The suppressed adsorption of OFL was observed on AC and GP, but not on HA, by NAP or BPA. Moreover, for AC, the competition by NAP was slightly stronger than that by BPA. However, for GP, the competition with BPA was higher than that with NAP. These observations indicate that competitive adsorption of OFL with respect to NAP/BPA depends on the degree of overlap of adsorption sites, as interpreted by the following: (i) AC can provide overlapping adsorption sites for OFL, BPA, and NAP, which include non-specific adsorption sites, such as hydrophobic sites, π-π interactions, and micropore filling; (ii) π-π interactions and hydrogen bonding might be responsible for the strong competitive adsorption between BPA and OFL on GP; and (iii) OFL adsorbs on HA through specific adsorption force-electrostatic attraction, with which NAP and BPA cannot compete.