A novel and quick method to avoid H₂O₂ interference on COD measurement in Fenton system by Na₂SO₃ reduction and O₂ oxidation

Hydrogen peroxide interference on chemical oxygen demand (COD) measurement has been a big problem in the application of the Fenton process. However, there is no simple and effective method available to address this problem, although several methods have been reported in the literature. In this study, a new method has been developed based on Na₂SO₃ reduction and O₂ oxidation, which has easy operation and short time requirement. Na₂SO₃ reduction was used to remove H₂O₂ in water samples, which was independent of pH in the investigated range of 2.50–11.95. Residual Na₂SO₃ was removed by subsequent O₂ oxidation, and effects of initial solution pH, ferric ion dosage, and stirring speed were explored. Solution pH below 3.0 and stirring speed of 700 rev min⁻¹ could ensure a sufficiently high oxidation rate for Na₂SO₃ with ferric ion higher than 0.469 mM. This new method was proven to be effective in the matrix of Fenton treating real landfill leachate. Meanwhile, the procedure for this method in other applications was proposed in detail. To the best of our knowledge, this newly developed method is the most simple and effective way to avoid H₂O₂ interference on COD analysis.