Kinetic removal of acetaminophen and phenacetin during LED-UV365 photolysis of persulfate system: Reactive oxygen species generation.

Acetaminophen (ACT) and phenacetin (PNT) removal during light-emitting diode (LED)-UV photolysis of persulfate (PS) was evaluated with a typical wavelength of 365 nm. Decay of PNT and ACT in pH ranges of 5.5-8.5 followed pseudo-first order kinetics. Maximum pseudo-first order rate constants (kobs) of ACT and PNT decomposition of 1.8 × 10-1 and 1.2 × 10-1 min-1, respectively, were obtained at pH 8.5. Hydroxyl radicals (·OH), sulfate radicals (SO4·-), superoxide radicals (O2-·), and singlet oxygen (1O2) were determined in-situ electron paramagnetic resonance (EPR) and alcohol scavenging tests. The average contributions of ·OH and SO4·- were 23.5% and 53.0% for PNT removal, and 15.9% and 53.0% for ACT removal at pH ranges of 5.5-8.5. In samples subjected to chlorination after LED-UV365/PS pre-oxidation, a relatively small total concentration of five halogenated disinfection by-products (DBPs) was obtained of 90.9 µg L-1 (pH 5.5) and 126.7 µg L-1 (pH 7.0), which is 58.5% and 30.2% lower than that in system without LED-UV365/PS pre-oxidation. Meanwhile, a higher maximum value of total DBP concentration was obtained at pH 8.5 (445.6 µg L-1) following LED-UV365/PS pre-oxidation. The results of economy evaluation showed that UV365 was more cost-effective in application for organic contaminant removal compared with UV254.

Enhanced degradation of sulfadiazine by novel ß-alaninediacetic acid-modified Fe3O4 nanocomposite coupled with peroxymonosulfate.

Magnetic nanocomposite ß-alaninediacetic acid-modified Fe3O4 (ß-ADA@Fe3O4) was prepared, characterized and evaluated to activate peroxymonosulfate (PMS) for improved degradation of sulfadiazine (SD). The results reveal that ß-ADA@Fe3O4 express more efficient catalytic activity in PMS inducement compared with Fe3O4, and the observed pseudo first rate constant (kobs) of SD degradation is enhanced from 1.05 × 10-2 to 7.02 × 10-2 min-1 when Fe3O4 is replaced by ß-ADA@Fe3O4. The highest removal rate 54.0% occurs when [PMS]0 and m(ß-ADA@Fe3O4)0 was 0.3 mM and 0.8 g/L at neutral pH. High intensity of hydroxyl radicals (OH) and relatively low intensity of sulfate radicals (SO4-) are distinguished in system by scavenging experiments and electron paramagnetic resonance (EPR) tests. Results point that ß-ADA would significantly promote the circulation of Fe2+-Fe3+ on the surface of ß-ADA@Fe3O4, producing more radicals (OH, SO4-). The findings herein imply that ß-ADA@Fe3O4 is an efficient and green catalyst in activation of peroxymonosulfate under neutral environment.