Utilization of iron-based waste derived from the biogas desulfurization process as an economic catalyst for tetracycline oxidation in water

This study examined the degradation of tetracycline (TC) in a sulfate radical-based advanced oxidation process (SR-AOP) by using iron sulfide (FeS) derived from the biogas desulfurization process waste as a catalyst. The study focused on the degradation mechanism and operational variables, including FeS catalyst dosage, concentration of potassium persulfate (PS) as an oxidant, initial TC concentration, and solution pH. FeS was revealed to be mesoporous that mainly consists of pyrrhotite with low levels of crystalline impurities. The optimal condition for TC degradation was obtained at neutral pH, that is, more than 90% TC degradation at pH 6.5. Both sulfate radicals (SO₄^•− and hydroxyl radicals (•OH) were the primary oxidizing agents generated by the solution and surface phase reactions, and a plausible reaction mechanism was proposed. The TC degradation rate remained constant, even after several reusability tests, suggesting the stability of the FeS catalyst. A total of eight TC transformation products were identified after the FeS/PS process. FeS originating from waste material in the biogas desulfurization process is a practically economic and efficient catalyst in SR-AOP systems for the degradation of emerging pollutants including antibiotics. Thus, activating PS with FeS has great potential considering its high added economic value.