Removal of aqueous phenanthrene by brown seaweed Sargassum hemiphyllum: Sorption-kinetic and equilibrium studies

Abstract

The batch sorption-kinetics and equilibrium uptake of phenanthrene (PHE), a hydrophobic organic compound (HOC), in aqueous compartment were investigated using dead tissue of brown seaweed Sargassum hemiphyllum under various conditions for 24 h. It was found that the higher the shaking rates (50–250 rpm) and temperatures (15–35 °C), the higher the sorption rates of PHE, but no significant changes were observed for the maximum sorption capacities. Study with different initial PHE concentrations (50–1000 μg L −1) showed that a higher ambient level of PHE resulted in a faster initial uptake rate and greater sorption capacity. The presence of ionic species (0.01–1 M NaCl) changed the sorption-kinetics of PHE markedly by altering the maximum removal of PHE, but not the initial sorption rates. No significant removal variations were noted under various initial pH (pH 2–11), while constant alkalinity resulted in an alleviated PHE sorption by Sargassum. The sorption-kinetics of PHE typically followed more closely to the pseudo-second-order model ( r 2 > 0.85) than pseudo-first-order equation ( r 2 > 0.72). Removal capacities were in the range of 430–460 μg g −1 for tests spiked with 1000 μg L −1 PHE. Typical percentage removals of aqueous PHE by Sargassum for all the investigated factors (e.g. initial pH and ionic strength) were in the range of 91.7–98.4%. Log Sargassum-water and the organic carbon normalized partition coefficient were calculated as 3.83 and 3.96 mL g −1, respectively. The present study provided valuable information for achieving optimal sorption of aqueous PHE using Sargassum as an effective sorbent for removing HOCs in wastewaters and urban runoffs.