Sorption/desorption behavior of triclosan in sediment-water-rhamnolipid systems: Effects of pH, ionic strength, and DOM.

Effects of pH, ionic strength and DOM on the sorption and desorption of triclosan (TCS) in sediment-water-rhamnolipid systems were systematically investigated through controlled batch experiments. Results showed that solubilization enhancement of TCS by rhamnolipid was higher in acid pH range than in alkaline pH range and was the highest at the ionic strength of 5×10(-2) M. Sorption of rhamnolipid onto sediment decreased with the increase of pH while the result was contrary to ionic strength. Moreover, the apparent distribution coefficients of TCS (Kd()) decreased from 73.35 to 32.30 L/kg with an increase of solution pH, as varying pH had significant influence on sorption of RL onto sediment and degree of ionization of TCS. Rhamnolipid presented the largest distribution capacity of TCS into the aqueous phase at moderate ionic strength (5×10(-2) M) with the Kd() of 17.26 L/kg. Further results also indicated that the presence of humic acid in aqueous phase could increase the desorption of TCS from contaminated sediment. The desorption enhancement was much higher in the system containing both rhamnolipid and DOM than in the single system. These findings provide meaningful information for enhanced migration of TCS from sediment to water by rhamnolipid.