Combined oxidation and in situ coagulation in an iron-activated sulfite process for tribromophenol removal in an actual water matrix†

In this study, an Fe(III)/sulfite (S(IV)) system was used to treat two actual water samples including a lake water sample and a secondary sedimentation tank effluent sample containing tribromophenol (TBP) with the combined pre-oxidation and coagulation process. This process not only efficiently removed TBP but also facilitated the removal of background organic compounds. The treatment efficiency increased with increased S(IV) addition time. The results from scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) showed that the in situ generated flocs in the Fe(III)/S(IV) system exhibited enhanced specific surface area, adsorption capacity, and coagulation properties compared to those produced in single Fe(III) coagulation, with the generation of more Fe₃O₄ particles. The treatment efficiencies of TBP and background organic materials initially rose and then fell with an increase in the S(IV) dosage. A moderately increasing Fe(III) dosage also boosted the removal of TBP and background organic substances, whereas an excessive Fe(III) dosage provided limited additional benefits. In the selected pH range of 3–8, good removal of turbidity could be always achieved, and the best removal of TBP and background organic substances was found at pH 4. Overall, this study indicated that the Fe(III)/S(IV) system with the combined pre-oxidation and coagulation process would be an effective treatment strategy for aquatic organic micropollutants.