Alachlor acetanilide is among the most widely used pre emergence herbicides all over the world. Due to its extensive usage and moderate persistence, both alachlor and its metabolites could be accumulating in agricul turally related waters and the peak concentrations for alachlor of _1 reported. Concerns have been rising regarding the health risks associated with its occurrence in natural waters because alachlor is toxic and mutagenic. To avoid potential human exposure to alachlor via drinking water, US EPA has set a and European Union has even more strictly regulated an MCL for any particular pesticide at 0. 1 lg L 1 and the sum of all pesticides 25 lg L in Kansas River and 4. 8 lg L in US groundwater were maximum contaminant level of 2.
0 lg L, Once alachlor emerges in source water with a concentration above the regulated MCL, appropriate water treatment processes have to be applied to comply with the drinking water standards. However, conventional unit operations for drinking water treat ment such as pre oxidation by Apoptosis permanganate, coagulation, filtra tion and chlorination show low removal efficiency for alachlor. The appli cation of ozone for disinfection and oxidation of drinking water is widespread all over the world. However, conventional ozonation process at water plants could not provide a complete removal of alachlor, generally achieving a removal efficiency of about 63%. The complete degra dation of alachlor only occurred at higher O 3 dosages. The second order rate constant of alachlor with molecular ozone is relatively low, while that with OH is up to the diffusion controlled rate.
There fore, advanced oxidation process which generates abundant OH has a great efficacy for the elimination of alachlor. The combination of O 3 with H 2O 2 is the most Apoptosis com 2. 3. 1. Degradation of alachlor The oxidation of alachlor by O 3 and O 3/H 2O 2 was first carried out in a batch reactor to determine the degradation kinetics by varying initial alachlor concentration and temperature. Ozone stock solutions were prepared by sparging ozone containing oxy gen produced with an ozone generator into a receiving solution. The aqueous ozone concentration in the stock solution was moni tored with Hach DR5000 spectrophotometer at 258 nm. To determine the degradation kinetics of alachlor by molecular O3, the reaction was performed at pH 7. 0 and 10 26 C in Milli Q water.
tert Dasatinib Butyl alcohol was added to scavenge OH formed from O 3 decomposition. The reaction was initiated by injecting 5 10 mL of the fresh ala chlor solution into 100 mL of ozone stock solution. Samples were withdrawn at pre selected time intervals to deter mine the residual ozone and alachlor concentrations. For alachlor analysis, residual ozone was first quenched with sulfite. AOP O 3/H 2O 2 experiments were performed at pH 7. 0 and 10 C. The reaction was initiated by adding 4 mL of ozone solution with different initial concentrations to 4 mL of alachlor solution containing 0. 4 mM H 2O 2. After total ozone consumption, the samples were analyzed by HPLC. Due to the low reactivity of alachlor with molecular O 3, OH was probably the predominant oxidant for ala chlor degradation in O 3/H 2O 2.
2. 3. 2. Identification of HMW degradation byproducts Solid phase extraction was applied prior to the analysis and identification of HMW byproducts. Each reaction sample was c-Met Signaling Pathway ex tracted using a 500 mg Agilent SampliQ C18 extraction cartridge. The cartridge was conditioned with 5 mL of methanol and then 5 mL of distilled water. After passage of 100 mL of sample at a rate of approximately 60 drops min, the cartridge was vacuum dried and eluted with 4 mL of dichloromethane and 4 mL of methanol successively. The extracts were concentrated with a light stream of nitrogen gas to a final volume of 250 lL. GC/MS coupled with an HP 5 MS column was em ployed to analyze HMW byproducts with low polarity. Helium gas was used as carrier gas at a ow rate of 1 mL min.
The oven temperature started at 60 C and held for 1 min, ramped linearly to 260 C at 4 C min and held for 1 min, and further increased to 280 C at 10 C min. The MSD was operated in the electron ioni zation mode at 70 eV. Liquid chromatography/hybrid quadrupole time of right mass spectrometry was used for the identification of polar byproducts. The chromatographic conditions were as same HSP as those aforementioned for determina tion of alachlor with HPLC. The HPLC was connected to a TOF mass spectrometer with an electrospray interface operated under the following conditions: capillary voltage 3. 50 kV, cone voltage 20 V, source temperature 120 C, desolvation temperature 300 C, and collision energy 5 eV. Accurate mass measurements were carried out at a resolution higher than 5000 using an independent reference spray via the LockSpray interference to ensure accuracy. Propachlor was used as the internal lock mass with m/z 212. 0842.