The Study Of Major Influencing Factors On Distribution Of Triclosan In Sediment-water-rhamnolipid Systems

As a broad spectrum antibacterial agent, triclosan(TCS) is one of emerging environmental pollutants which belong to PPCPs(Phamaceuticals and personal care products). Owing to its high octanol/water partition coefficient(log Kow = 4.76), TCS is easy to adsorb onto soil, sediment,suspended solids and other solid medium.TCS is difficult be degraded by microorganisms under anaerobic conditions in sediment.Surfactant can make organic pollutants transfer from soil/sediment to water by desorption and therfore enhance their biological effectiveness.Due to its good surfaceperformance, low toxicity, and easy biodegradability, the biosurfactan t of rhamnolipid has received wide attention.In this study by investigating the solubilizing abilities of rhamnolipid for TCS, adsorption of rhamnolipid and TCS onto sediment,sorption of TCS in the presence of rhamnolipid and desorption of TCS from contamninated sediment under different p H values, ionic strength, concentration of HA and emperature, the distribution of TCS in sedimen-water-rhamnolipd system affected by these four environmental factors was studied in-depth.Then the sorting of influencing factors, the optimum desorption conditions and control strategy of desorption were determined by the Box- Behnken response surface method(RSM).The objective was to provide theory basis for application of rhamnolipid biosurfactant in strengthening the ecological restoration in situ for water polluted by TCS.Results of sorption/desoptionequilibrium experiments showed that when solution p H is weak alkaline, the efficiency of TCS desorption by rhamnolipid was higher than acidic condition.Considering the fact that the suitable p H value formost microorganisms for biodegradation of contaminants is nearly neutral, the optimum p Hvalues of 7~8 was chosen to obtain the relatively high desorption efficiency.When solutionwas at the middle ionic strength of 5 x10-2 M, the solubilization capacity of rhamnolipid for TCS and the desorption rate of TCS from contaminated sediment were all maximum. The desorption ability of rhamnolipid for TCS was stonger than HA and the desorption was more obvious when these two agents was mixed. With the temperature increasing, TCS was more easily migrated into aqueous phase.Results of desorption experiment affected by single factor indicated that the higher the rhamnolipid concentration,the lower the ratio of sediment to water, the greater the time,the lower the iitial TCS concentration, the more TCS molecules desorbed. RSM results showed that it was accurate and reliable for the method of response surface to optimization fordesorption process of TCS from contaminated sediment by rhamnolipid.The influence factors was ordered as follows: the ratio of sediment to water> rhamnolipid concentration > p H > time. The optimum desorption conditions for rhamnolipid concentration, theratio of sediment to water, time, and p H were found to be 2996.96mg/L, 10g/L, 30 h and 7.95, respectively and an optimum value of TCS desorption percent from sediment of about 90.6967% was obtained under this condition.