| With the rapid progress of industria lization and urbanization, and the rapideconomic and socia l developme nt in China, the explo itation of water resourcescontinued to increase. At the same time, the water po llution was getting more andmore serio us. The declining resource water qua lity, especia lly organic pollutionhad become a potentia l danger for drinking water security. Activated carbonadsorption techno logy had ma ny advantages, such as high effic iency, inexpens ive,flexib le operation, easy recycling and easy to be used in practice. Theseadvantages enabled the activated carbon being widely used in hand ling organicpollution. However, the activated carbon retention time was much longer than thehydraulic retention time, whic h easily led to the desorption of conta minantsadsorbed in the activated carbon in the water treatme nt process, thus had a risk ofsecondary pollution on water quality.In this paper, in order to solve the proble m that contaminants adsorbed inthe activated carbon would be desorbed in water treatment process and had a riskof secondary pollution, some experiments was conducted to figure out theinfluenc ing factors of the desorption o f contaminants and identify the desorptionlaw. The influenc ing factors of conta minant desorption, suc h as the dir ectcompetitive adsorptio n, pore clogging, the concentration gradient andtemperature was investigated. This study was to lay a theoretica l foundation forthe developme nt of related techno logies in order to avoid or reduce the risk ofsecondary pollution whic h would caused by conta mina nts desorption.Ethylbenzene and chlorobenzene could form a strong competitiveadsorption. Under this effect, chlorobenzene showed a significant desorption ratein the s urface of PAC, and the desorption speed was fast, desorption equilibriumwas achie ved after20-40min. In this research, the desorption rate ofchlorobenzene ranges from3.3%to61.73%. A positive correlation was foundbetween the desorption rate of c hlorobenze ne and the concentratio n ofethylbenzene. The desorption rate of chlorobenzene decreased with theincreasing chlorobenzene concentration in the surface of PAC, and the rate increased with the increasing ethylbenze ne concentratio n in the surface of PAC.Sodium po lystyrene sulfonate, which is a larger mo lecule, had relative ly littleinfluence on the adsorption and desorption capacity of chlorobenzene in thesurface of PAC.Macromolecular organic matters twith a mo lecular weight greater than3600Da have a pore b lockage effect, this fact reduce d the desorption speed ofchlorobenzene in the activated carbon, but had little influe nce on the desorptionrate. For organic matters which had a mo lecular weight less than1000Da, besidesthe pore blockage effect, they also had a strong competitive adsorption effectsimilar to ethylbenzene, this fact served not only slow down the desorption speedof chlirobenzene from activated carbon, but also increased chlorobenze nedesorption capacity by more than15percent.Concentration grad ient caused a significant desorption of chlorobenzenefrom PAC, the desorptio n rate increased with the increasing o f concentrationgradient. When the dilutio n rate reaches1:5, the desorption rate ofchlorobenzeneachieved34.8%, when the dilution rate was1:20, the desorptionrate was about40%and the desorption speedwas sma ller.The desorptio n of chlorobenze ne was affected by the change of temperature,and the desorption rate increased with the decreasing of te mperature anddecreased with the increasing of te mperature. Temperature ha d a significanteffect on the concentration-driven desorption of chlorobenze ne, when theconcentration was different, the desorption rate of chlorobenzene increase d withthe decreasing of temperature. Concentration-driven desorption rate ofchlorobenzene was found to achieve38.8%at room temperature, whe n thetemperature was below15C, the desorption rate was higher than50%. However,temperature had little influence on the non-concentration-drive n desorption ofchlorobenzene. |
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