Application of PeCOD and dichromate methods for the analysis of chemical oxygen demand (COD) in the wastewater sample

Abstract

Chemical oxygen demand (COD) is one of the critical environmental parameters in determining the organic matter in water matrices. The conventional dichromate method employs hazardous reagents and heat reflux. In order to reduce hazardous waste, several alternative methods have been proposed to replace the dichromate. The photoelectrochemical COD (PeCOD) method has become a promising one for being less time-consuming, environmentally friendly, and more reliable. To ensure the result, a comparison between PeCOD and dichromate methods should be conducted. In this study, we analyzed the technical features of the PeCOD method, especially for the accuracy in measuring certified reference material (CRM), and identify the advantages and disadvantages of this method. Afterward, we applied both PeCOD and dichromate methods to analyze tofu processing wastewater as a representative of environmental samples. The result showed that PeCOD gave a recovery of 113.1±4.8% whereas the dichromate method gave a recovery of 98.4±1.7%, which indicates that the PeCOD method had lower accuracy than the dichromate method. Meanwhile, the COD concentration of tofu processing wastewater using PeCOD and dichromate methods was 11516±669 mg/L and 9109±680 mg/L, respectively. This difference might be due to overestimation by the PeCOD method, the complex matrix of the wastewater, and chloride interference.