Theoretical insights into the degradation of tyrosol stimulated by hydroxyl and sulfate radicals in wastewater and ecotoxicity evaluation

Abstract

The photochemical degradation of tyrosol (TY) in wastewater was investigated by theoretical method. The highly oxidative radicals (⋅OH and SO4•-) were employed to study the TY transformation behaviors and kinetic properties. The ⋅OH-addition and H-abstraction reaction mechanisms were predominant for ⋅OH and SO4•--initiated reactions, respectively. The rate constants of TY + ⋅OH and TY + SO4•- systems were determined as 9.15 × 109 M−1 s−1 and 3.14 × 1010 M−1 s−1 at 298 K. The generated SO4•- from advanced oxidation processes (AOPs) showed good performance for TY degradation in liquid phase. The direct photolysis was also considered in the excited state in order to reveal the photo-excited reaction mechanism. Due to high endothermicity and energy barrier, direct photolysis is difficult to proceed spontaneously compared to indirect photochemical processes initiated by strong oxidative radicals. Half-life values of TY with ⋅OH reactions demonstrated that the high concentration of free radicals would significantly shorten the exposure time of TY in water environment. The results of the ecotoxicity to aquatic organisms suggested TY degradation was a mainly less harmful process. However, hydroxylation product P7 (hydroquinone) was a potential developmental toxicant with greater aquatic toxicity than TY, which was an exception to deserve more concern in environment.