Degradation of indigo carmine by coupling Fe(II)-activated sodium persulfate and ozone in a rotor-stator reactor

Rotor-stator reactor (RSR), a novel high-gravity device, was employed in the O 3 /persulfate (PS)/Fe 2+ process to enhance the degradation of indigo carmine (IC) in simulated wastewater. It was found that IC degradation efficiency increased with the increase of Fe 2+ concentration, RSR rotation speed, O 3 concentration and gas-liquid ratio, but decreased with the increase of IC concentration and temperature. When the rotation speed of RSR increased from zero to 1200 rpm, IC degradation efficiency increased from 25.6% to 64.2%. Because of the synergetic effects of the oxidative species (O 3 , OH, SO 4 − etc.), IC degradation efficiency in the O 3 /PS/Fe 2+ process was significantly higher than that in the O 3 or PS/Fe 2+ process. The high IC degradation efficiency can also be attributed to the good micromixing effect of the RSR. When the O 3 /PS/Fe 2+ process in the RSR was adopted before the sequencing batch reactor activated sludge process , both IC and COD degradation efficiencies increased significantly as a result of the improved biodegradability of the IC wastewater. Furthermore, a possible degradation mechanism of IC in the O 3 /PS/Fe 2+ process was proposed.