Sorption of benzothiazoles onto sandy aquifer material under equilibrium and nonequlibrium conditions

Abstract

In this study, the sorption behaviour of 1,3-benzothiazole (BT) and 2-(methylthio)benzothiazole (MTBT) was investigated on Danube geosorbent under equilibrium and nonequilibrium conditions. All sorption isotherms fitted well with the Freundlich model (R2=0.932-0.993). The results showed that organic matter of the Danube geosorbent has a higher sorption affinity for the more hydrophobic MTBT compared to BT. However, sorption-desorption experiments showed that MTBT was more easily desorbed than BT molecules, which indicates the importance of absorption relative to adsorption in the overall sorption mechanism of MTBT. In general, molecules of BT and MTBT were more easily desorbed in the lower concentration range, which resulted in an increase in the hysteresis indices with increasing concentrations. Column experiments revealed that retention of the investigated compounds on the aquifer material followed the compound?s hydrophobicity. BT showed a lower retention, in accordance with its lower sorption affinity obtained in the static experiments, while MTBT showed a greater sorption affinity, and thus had a longer retention time on the column. Thus during transport BT represent greater risk for groundwaters than MTBT. These results have increased our understanding of benzothiazoles sorption and desorption process which represent one of the most important factors which influence the behaviour of organic compounds in the environment.