Ferrate(VI) ((FeO42-)-O-VI Fe-VI) is usually effective in oxidizing a wide range of antibiotics on a time scale of seconds, but some recalcitrant antibiotics such as trimethoprim (TMP) and flumequine (FLU) require a longer time and higher dose of Fe-VI for their removal from water. The current study presents the Fe-VI-sulfur(IV) (or Fe-VI-sulfite/bisulfite) system, which could give near-instantaneous oxidation of these two antibiotics (20.0 mu M) (i.e., in 15 s time scale) at a lower dose of Fe-VI (100.0 mu M) than is needed with Fe-VI oxidation alone. Experiments on the removal of TMP were performed as a function of the molar ratios of S(IV) to Fe-VI (0.2-15.0) and Fe-VI to TMP (2.0-30.0 mu M) at three different pH values (7.0, 9.0 and 11.0) under both oxic (air saturated) and anoxic (nitrogen saturated) conditions. In case of oxidation of FLU under the same conditions, the molar ratios were used at 1.0 ([S(IV)]:[Fen) and 5.0 ( [Fen: [FLU]) under the same solution pH. Removal of these two recalcitrant antibiotics depended on the pH and the amount of oxygen in the reaction solution. Significantly, TMP was removed by Fe-VI-S(IV) system under anoxic condition, whereas the removal percentage was lower than that under oxic condition. The relative amounts of the oxidized products of TMP were also different in the oxic and anoxic environments. A set of reactions that were involved in the oxidation of TMP by the Fe-VI-S(IV) system may demonstrate the participation of multi-oxidizing species (Fe-V/Fe-VI, SO3(center dot)(-), SO4 center dot- and center dot OH) in the removal of TMP from water. Representative anions and natural organic matters had little or no significant interference on the removal of TMP by the Fe-S(IV) technique in water.