Enhanced removal of cytotoxicity from wastewater by silica gel-activated ferrate (VI).

Ferrate (Fe(VI)) is a highly efficient oxidant with great potential for advanced wastewater treatment. In this study, a Fe(VI)/silica gel (SiO2) process was developed to enhance the detoxification performance of Fe(VI). While SiO2 alone showed no cytotoxicity removal, the addition of 0.1 g/L SiO2 to Fe(VI) reduced the cytotoxicity of wastewater from 8.3 to 8.5 mg/L to 4.8-5.6 mg/L, corresponding to a 47.3 % removal efficiency for the secondary effluent. Compared to Fe(VI) alone, the activated process achieved improved reductions in UV254 absorbance and fluorescent components, including tryptophan-like, humic-like, and fulvic-like substances. High-resolution mass spectrometry (HRMS) revealed that the number of CHON-type dissolved organic matter (DOM) species removed increased from 709 (Fe(VI) alone) to 982, with the majority being highly toxic and aromatic compounds. Moreover, many micropollutants which exhibited poor reactivity and low degradation efficiency when treated with only Fe(VI), were effectively removed in the activated process. The Fe(VI)/SiO2 process achieved removal efficiencies over 30 % higher than the Fe(VI) process for 27 compounds, including highly toxic CHON-type micropollutants such as 1,2,3,4-tetrahydropyridin-4-one and 4-aminoantipyrine. The enhanced removal performance is because of the enhanced •OH formation, rather than Fe(IV)/Fe(V) formation or flocculation. Mechanistic analysis revealed that hydroxyl and silanol groups on the silica surface act as activation sites for Fe(VI), facilitating •OH generation and accelerating the degradation of toxic pollutants. These findings highlight the potential of the Fe(VI)/SiO2 process as an efficient solution for advanced detoxification in wastewater treatment.