过硫酸盐对有机废水COD_(Cr)测定的干扰及消除

Elimination of persulfate interference in determination of COD in organic wastewater

采用过硫酸盐高级氧化技术处理有机废水时通常用化学需氧量(COD)表征处理效果,使用重铬酸钾法测定COD时,残余的过硫酸盐对测定结果存在干扰。考察了过硫酸根(S_2O_8^(2-))对COD_(Cr)干扰情况,分析干扰机理并提出消除干扰的措施。结果表明,水样中残留的S_2O_8^(2-)作为还原剂使COD_(Cr)测定值高于实际值,S_2O_8^(2-)对不同水样COD_(Cr)测定干扰程度也不同,在低(0~150mg/L)、高(0~1 500mg/L)2种量程的COD_(Cr)测定组中,S_2O_8^(2-)与COD_(Cr)之间分别呈现显著的线性关系,线性关系分别为y=36.120 2x+0.571 1(R^2=0.997 9),y=45.171 6x+38.031 6(R^2=0.998 4),1g的S_2O_8^(2-)对COD_(Cr)变化值的贡献在低、高质量浓度水样体系中分别为36.120 2mg和45.171 6mg。在COD_(Cr)标准溶液体系以及实际废水体系中,线性方程计算的ΔCOD_(Cr1)(S_2O_8^(2-)引起的COD_(Cr)的变化值)与ΔCOD_2(COD_(Cr)测定值与原水COD_(Cr)的差值)占原水COD_(Cr)的百分比在10%以下。通过扣除过硫酸盐引起的COD_(Cr)变化后的数值能较准确的反映水体实际COD_(Cr),可用于消除过硫酸盐活化技术处理有机废水时S_2O_8^(2-)对COD_(Cr)测定的干扰。

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 （S2O8^2-）. The interference degree varies with the concentrations of S2O8^2- in the wastewater. The relationship between concentration of S2O8^2-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 S2O8^2- are y=36.120 2x＋0.571 1（R^2=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 S2O8^2-） 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 S2O8^2- in CODCr determination.