Probable problems in the analysis of chemical oxygen demand of wastewaters treated by advanced oxidation process: residual H_2O_2and acidity of the treated waters

摘要

The remainder of H2O2, which is usually used in advanced oxidation processes (AOPs) treatment of wastewaters, reacts with the oxidant (e.g. KMnO4) utilized in chemical oxygen demand (COD) analysis, resulting in the overestimation in COD analysis. The residual H2O2 was decomposed successfully using Na2CO3 as catalyst under a heated condition (95 degrees C for 2h) and consequently the H2O2-derived COD, typically after the AOPs treatment of oxalic acid solution using peroxone (H2O2-O-3 mixture), could be brought to below the detection limit. However, the overdose of acid (H2SO4) added for neutralizing the Na2CO3-containing sample solution after the decomposition of residual H2O2 was found to cause new interference in COD analysis. It is considered that in strong acid solutions the decomposition of KMnO4 may be accelerated during COD analysis, leading to its overestimation. The results suggest that a suitable decomposition of residual H2O2 (e.g. after AOPs treatment) as well as a suitable control of acidity (to neutrality) of the sample solution subjected to COD analysis is essentially necessary for the correct COD estimation.