Rapid determination of chemical oxygen demand (COD) using focused microwave digestion followed by a titrimetric method.

Abstract

water-pollution control analysis. It is closely related to the organic contamination level of a water or wastewater sample. The Cr-COD method is used as the standard in USA and Taiwan. Compared to Japanese Mn-COD method, it has a higher detection limit and severe chloride ion interference because of the stronger oxidant and the longer digestion time. In order to reduce the chloride-ion interference, the mercury salt (e.g. HgSO4) is usually added to mask the chloride ion. On the other hand, the closed reflux-titrimetric method is recommended by the Standard Method to reduce the large amount of hazardous waste.1 However, it still requires a long time (2 h) for the digestion step to be completed in this COD analysis, and the tolerance of the chloride ion interference is only up to 2000 mg Cl–/L. The objective of this research was to investigate the availability of a rapid procedure to determine the COD in water and wastewater by digesting samples in open vessels located in a focused microwave system followed by ferrous ammonium sulfate titration. The results obtained using this microwave system were also compared with those obtained by a closed reflux method described in the Standard Method.