Elimination of persulfate interference in determination of COD in organic wastewater
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Abstract:
As a new advanced oxidation technology, advanced oxidation process of persulfate has been widely used in wastewater treatment and chemical oxygen demand(COD)is usually taken as an important indicator to identify the characteristics of organic wastewater. When COD is determined by potassium dichromate method, the residual persulfate in organic wastewater has interference with the measurement results. Therefore, the interference mechanism is investigated and the elimination measures of the interference are proposed. The results reveal that CODCr testing values are higher than the actual values for the reducibility of residual sulfate (S2O82-). The interference degree varies with the concentrations of S2O82- in the wastewater. The relationship between concentration of S2O82-and CODCr is obviously linear in both high and low CODCr concentration measuring range. For CODCrranging from 0 to 150 mg/L and CODCrranging from 0 to 1 500 mg/L, the linear relationship and the contributions of CODCr concentration variation by 1g S2O82- are y=36.120 2x+0.571 1(R2=0.997 9), 36.120 2 mg and y=45.171 6x+38.031 6(R2=0.998 4), 45.171 6 mg respectively. In CODCr standard solution system and the actual wastewater system, the percentage of △CODCr1 (contribution value of CODCr by S2O82-) and △CODCr2 (the difference between CODCr measured value and raw wastewater actual value) is less than 10% of the actual CODCrin raw wastewater. The actual CODCr value of water sample could be accurately calculated by deducting △CODCr1 based on the linear equation which could effectively eliminate the interference caused by residual S2O82- in CODCr determination.
