Competitive sorption and desorption behavior for three fluoroquinolone antibiotics in a wastewater treatment wetland soil

Significant amounts of pharmaceuticals are discharged into the environment through wastewater effluent. Sorption has been shown to be a significant aqueous removal pathway for many of these compounds. Competition between ciprofloxacin (CIP), ofloxacin (OFL) and norfloxacin (NOR) and their sorption to, and desorption from, a surrogate Louisiana wastewater treatment wetland soil were investigated to gain insight into the fate and transport of the pollutants within wastewater treatment wetlands. This study was undertaken in the context of a treatment wetland that continuously receives pharmaceuticals. Therefore it is important to understand the total capacity of this soil to sorb these compounds. Sorption to this treatment wetland soil was found to provide a major and potentially long-term removal pathway for these antibiotics from wastewater. LogKF values for all three compounds were between 4.09 and 3.90 for sorption and 4.24 and 4.05μg1-1/n(cm3)1/ng-1 for desorption. The compounds were sorbed in amounts ranging from 60% to 90% for high and low loading, respectively. The majority of the compounds were sorbed to the soil within the first 20h, indicating that treatment wetland may not need long retention times (weeks to months) in order to remove these compounds. Sorption KD values for competition (20ppm of each compound for 60ppm of total fluoroquinolones) ranged from 2300 to 3800cm3g-1 which is between both the 20 (4300-5800cm3g-1) and 60 (1300-3000cm3g-1) ppm single compound KD values, indicating that there is competition between these three compound for sorption sites. Sorption and desorption data (single component and mixture) collectively provide the following evidence: (1) NOR and, to a lesser extent, CIP outcompete OFL for sorption sites, (2) OFL sorbes to its share of quality sorption sites, and (3) competition only occurs for lesser quality binding sites. © 2010 Elsevier Ltd