Enhanced sulfamethoxazole removal in water and wastewater by ferrate(VI)/perborate system via borate buffering

Ferrate(VI) is prone to self-decomposition in water, leading to the loss of active substances Fe(V) and Fe(IV). Therefore, the use of Fe(VI) alone has limited practical applicability in municipal wastewater and industrial wastewater treatment scenarios due to its insufficient pollutant removal efficiency. This study discussed the removal efficiency of the Fe(VI)/perborate system for sulfamethoxazole and other 6 drugs in pure water within 5 minutes, and the removal efficiency of the Fe(VI)/perborate system for sulfamethoxazole in effluent and secondary effluent in a wastewater treatment plant (WWTP) within 5 minutes. Results show that the sulfamethoxazole removal efficiency reached 88.63 % in the influent of Lijiang B WWTP and 79 % in the secondary effluent of Wuhan WWTP. The removal efficiency of sulfamethoxazole in pure water reached 25.8 % in 5 minutes. This finding is explained by the buffering with the borate produced by the hydrolysis of Fe(VI)/perborate, which maintains the pH around 9 and, in turn, inhibits the reduction of active species. Moreover, H₂O₂, ¹O₂, and O₂^•- radicals generated by Fe(VI)/perborate accelerate the activation of Fe(VI), and the Fe²⁺ produced in the system participates in Fenton reactions with H₂O₂. This study offers a novel approach for using ferrate in practical water treatment.