Effect of Fe(II/III) on tetracycline degradation under UV/VUV irradiation

Photodegradation of tetracycline (TTC) under VUV/UV (185/254 nm) or sole UV (254 nm) irradiation in the presence of Fe(II/III) species was investigated at near-neutral pH (6.0-7.5) in pure water matrix. The VUV/UV process was more efficient to degrade TTC than sole UV process and the photodegradation rate was an order of magnitude higher. A relatively higher pH favored TTC photodegradation under both UV and VUV/UV irradiations. The effects of Fe(II/III) on TTC degradation under VUV/UV or sole UV irradiation were controlled by different reaction mechanisms. Fe(III) could promote TTC degradation under sole UV irradiation by complexation and subsequent oxidation, where the TTC degradation rate reached the maximum value ((14.7 ± 0.4) × 10−3 min−1) at a Fe(III):TTC molar ratio of 1:1. The promotion of TTC degradation by Fe(III) under VUV/UV light can be negligible because of the dominated role of OH radicals produced by VUV/UV irradiation in TTC degradation. In contrast, Fe(II) facilitated TTC degradation under VUV/UV irradiation due to the additional OH radicals formed by the potential Fenton process. However, there was no obvious enhancement of TTC degradation with the addition of Fe(II) under sole UV irradiation. The total organic carbon (TOC) evaluation indicated Fe(II) and Fe(III) could enhance TTC mineralization under VUV/UV or sole UV irradiation. The electrical energy per order (EE/O) was also assessed and results suggested that VUV/UV (+Fe(II)) was a cost-effective way to degrade and mineralize TTC.