A method for removing persulfate interference in the analysis of the chemical oxygen demand in wastewater

In recent years, sulfate radical-based advanced oxidation hasreceived increasing attention for the treatment of water and wastewater. However,the chemical oxygen demand (COD), a common measure of gross organic contamination,is subject to interference from residual persulfate in the treated water. In this study, a new method, based on addition of sodium sulfite (Na2SO3) and heating, has been developed to eliminate the interference of remaining potassium persulfate (PSk) on COD analysis. Results of batch experiments show that potassium persulfate can be efficiently removed with molar ratio of Na2SO3/potassium persulfate 2 and heating at 90 degrees C for 60min. This method (Na2SO3-heating treatment) was further tested in aphenol wastewater and a coal industry wastewater. The deviation of COD values of Na2SO3-heating treatment was lower than5%, which was much lower thanthe deviation of thecalibration curve method, ofmore than 14%. This new method could be applied to water samples containing persulfate and organic substances and help researchers to accurately evaluate performance of sulfate radical-based advanced oxidation processes.