The Dichromate Method versus the Photoelectrochemical Method: the Synergistic Influence of Turbidity and Chlorides on Chemical Oxygen Demand Analysis

Abstract

This paper compares the dichromate method with the photoelectrochemical method (PeCOD), with regards to the influence of chloride and turbidity with chemical oxygen demand (COD) determination. Whereas the upper limits of chloride concentration are well established for both techniques, the influence of turbidity and the combined interference of underdosing chlorides and turbidity together have never been reported. When only potassium hydrogen phthalate or sorbitol were analyzed, the results show no significant difference in either method when 607 mg Cl -L -1 or 230 NTU of turbidity were added to the samples within the range of 100-900 mg L -1 COD. However, a combined effect of these two interferents leads to significantly different results, mainly for low COD range, as evidenced by the Student's t-test for paired samples (p = 0.05).

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

“…Despite these drawbacks, PeCOD has the advantages of being less time-consuming and practical in application [9]. Further studies should be conducted on factors that interfere with COD measurement using this method.…”

“…The Standard Method [8] suggests using the closed reflux-titrimetric method to reduce the large amount of hazardous waste. Mercury salt (for example, HgSO4) is usually added to reduce chloride ion interference by complexing the halide to mask the chloride ion [9]. This method is widely used because it provides high accuracy (94-104 %) and therefore is the standard method for COD analysis.…”

“…Even though the PeCOD method has advantages for COD analysis compared to the dichromate method, the data of the application on wastewater samples is still limited [9]. It is necessary to evaluate PeCOD application on tofu processing wastewater samples.…”

Compact fluidic electrochemical sensor platform for on-line monitoring of chemical oxygen demand in urban wastewater

“…An important limitation of the standard analytical technique based on dichromate titration is that it does not allow on-site measurements. Indeed, since it makes use of hazardous chemicals that require careful handling and controlled disposal by trained personnel, water sampling and transportation to centralized laboratories are required, thus increasing the cost and turnaround time of the analysis [5,6,10].…”