| Poyang Lake is the largest freshwater lake in my country.Due to the need for schistosomiasis control,more than 170 tons of niclosamide(NCL)are used to kill snails in its shallow lakes every year.With the repeated use of NCL in the Poyang Lake basin,it has an impact on the water environment.As a kind of hydrophobic organic compounds(HOCs),NCL is easily adsorbed in solid-phase media such as soil and sediment,and is difficult to be degraded by microorganisms in a solid-phase anaerobic environment,posing a threat to the stability of the surrounding ecosystem.Rhamnolipid,as the most widely used biosurfactant at present,can transfer HOCs in the solid phase medium to the water phase,so that it can be better taken up and utilized by microorganisms in the water body,and the biodegradability of HOCs is enhanced.It has low toxicity and can be biodegraded by itself,and has good application prospects in environmental remediation.This study takes NCL as the target pollutant,and explores the influence of different environmental factors(p H,DOM,ionic strength)on the distribution behavior and mechanism of NCL in the rhamnolipid-bottom mud-water mixed system,mainly for the water phase The characteristics of solubilization and adsorption/desorption of the sediment phase are studied.The simulated NCL contaminated sediment was selected as the experimental object to study the kinetic characteristics of NCL desorption on the sediment under the action of rhamnolipid,and to investigate the influence of various factors on the desorption capacity of NCL,and use the Box-Behnken response surface method(RSM)carried out experimental optimization,determined the main influencing factors of the experiment and the best conditions for desorption,and provided a theoretical basis for exploring the directional control of the migration of rhamnolipids in the sediment-water system and realizing the in-situ remediation of NCL contaminated sediments.Experimental investigations on environmental factors have shown that p H has a significant effect on the distribution of NCL in the rhamnolipid-bottom mud-water environment.The role of rhamnolipid in an alkaline environment promotes the migration of NCL in the bottom mud to the water phase;HA has a significant effect on NCL.The mechanism of desorption in the bottom mud is similar to that of rhamnolipid,but its strength is slightly weaker than that of rhamnolipid.When the two coexist in the system,it shows a synergistic effect,and the desorption effect is more significant;in the ion of rhamnolipid solution Under moderate strength(10-2 M)conditions,the solubilization effect of rhamnolipids on NCL and the desorption of NCL in contaminated sediments are the strongest.The results of desorption experiments show that the desorption capacity of NCL in the rhamnolipid solution from the bottom sludge is related to the concentration of rhamnolipid in the system,the ratio of mud to water and the aging time of the NCL contaminated bottom sludge.The results of response surface methodology show that three factors,p H,rhamnolipid concentration,and mud-water ratio can significantly affect the desorption effect of NCL,and the order of the strength of each factor is:p H> mud-water ratio> rhamnolipid concentration;according to the model Analysis shows that the most suitable conditions for the experiment are p H=9.5,mud-water ratio 10 g/L,and rhamnolipid concentration 2700 mg/L.At this time,the desorption rate of NCL is 73.85%;response surface method is used to optimize rhamnolipids The experimental conditions for the desorption of NCL in the contaminated bottom sludge under the action have strong reliability. |
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