Study On Degradation Of Triclosan In Aqueous Solution With Advanced Oxidation Technology Based On Persulfate

PPCPS?pharmaceuticals and personal care products?is a new type of orga nic micro-pollutants which has drawn a great degree of attention from environ mental workers in recent years.Triclosan?TCS,2,4,4'-trichloro-2'-hydroxy diph enyl ether?as a broad-spectrum antimicrobial agent has been incorporated into a variety of typical PPCPs,including soaps,mouth rinses,shampoos and so on.Studies have shown that it possesses lipophilicity,bioaccumulation,genetic tox icity and may generate methyl-triclosan,chloroform,dioxins and other more to xic intermediates in the degradation process,there are many potential and large hazards of ecological environment and human health.Strong oxidizing SO₄^-·an d·HO which produced by persulfate activated with transition metals,ultraviolet have shown great degradation effects on such pollutants.Triclosan?TCS?remo val in aqueous solution by sodium persulfate activated with transition metal(Fe²⁺)and short wavelength ultraviolet?UV254?were studied in this paper.?1?Fe???/SPS was employed to remove triclosan?TCS?in aqueous solution.The degradation products were identified by GCMS and the effects of several factors such as Fe²⁺and sodium persulfate dosages,TCS initial concentration,pH,HA and HCO₃^-on TCS degradation were studied.The dominant free radical was also identified by methanol?MA?and tert-butanol?TBA?.Finally,TCS degradation efficiency in different types of water was compared in consciously.The results indicated that sodium persulfate activated with Fe²⁺ process can remove TCS effectively and 2,4-dichlorophenol?2,4-DCP?is the main degradation product of TCS during the process.The removal rate of initial TCS concentration of 460?g·L-1could reach 93.87% within 2 min under the conditions of concentration of sodium persulfate is 1 mmol·L-1 and dosages of Fe²⁺ is 0.4 mmol·L-1.TCS degradation fitted with the pseudo-first-order kinetic model in slow reaction period and the apparent pseudo-first-order rate constant being 0.140min-1.TCS degradation efficiency increase firstly and then decrease with the increase of Fe²⁺ concentration,High concentration of Fe²⁺was detrimental to the degradation of 2,4-DCP.Appropriately increase the concentration of sodium persulfate enhanced TCS removal rate and2,4-DCP degradation rate.TCS degradation efficiency decreased with the raise of initial concentration of TCS.Acidity condition was conducive to the TCS removal.The removal of TCS was inhibited in the presence of HA and HCO₃^-.HCO₃^-and low concentration of HA was detrimental to the removal of 2,4-DCP.SO₄^-· was thedominant free radical under acidity condition and ·HO was the dominant free radical under alkaline condition in the experiment.The removal efficiency of TCS in tap water was relatively close to that of in Milli-Q water,and TCS removal efficiency was slightly worse in natural water.?2?UV/SPS was employed to remove TCS in aqueous solution.The effects of several factors such as UV wavelength,UV254 intensity,sodium persulfate dosage,pH value,HA and inorganic anions(HCO₃^-?CO₃^2-?Cl^-)on TCS degradation were investigated.Changes of SO42-release concentration and pH valves of TCS degradation were monitored.The second-order rate constants of free radicals?·OH?SO₄^-·?reacting with TCS and their contributions to TCS removal were determined,respectively.The dominant free radical was also identified.Furthermore,TCS degradation efficiency in natural water by UV254/SPS and UV254/H₂O₂ was compared in consciously.Finally,the possible pathway and intermideate products of TCS degradation were analyzed with GCMS.The results indicated that UV254 activated sodium persulfate can remove TCS effectively.The removal rate of TCS can reach98.15% within 100 s under the conditions of UV wavelength of 254 nm,UV intensity is 11.5?W·cm-2,sodium persulfate dosage of 1mmol·L-1,and TCS initial concentration of 275?g·L-1.TCS degradation followed the pseudo-first-order kinetic model and the pseudo-first-order rate constant was determined to be 0.0392s-1.Pseudo-first-order rate constant for TCS degradation increased with the increase of UV254 intensity?I?and sodium persulfate dosage within experiment ranges.The effect of UV wavelength on TCS removal was not notable.Neutral condition was detrimental to TCS degradation.TCS removal was inhibited in the presence of HA,inorganic anions also inhibite TCS removal and the order of the inhibitive action was CO₃^2->HCO₃^->Cl^-.pH value decreased gradually in TCS degradation process.Meanwhile,the SO42-concentration was increased.The reaction rate constants for ·OH and SO₄^-· reacting with TCS were 7.62×109L·mol-1·s-1 and9.86×109L·mol-1·s-1,respectively.SO₄^-· was the dominant free radical and its contribution rate to TCS removal was 97.63% in UV254/SPS system.The K?s-1?value of UV254/SPS was 4.13 times higher than that of UV254/H₂O₂ process,which demonstrated that UV254/SPS process could remove TCS more effectively than UV254/H₂O₂.The main intermediate products found were 2,4-DCP,phenol in the degradation process of TCS in Milli-Q water by UV254/SPS.The TOC value of the solution decreased gradually in TCS degradation process.