屏蔽氯离子干扰高盐榨菜废水中COD的测定方法

高盐废水中氯离子的存在会严重干扰COD的测定，因此，如何屏蔽氯离子干扰准确测定其COD的难点之一。为研究高盐榨菜废水中更为准确的COD测定方法，实验中采用了2种屏蔽氯离子的方法：硫酸汞屏蔽法和硝酸银屏蔽法，屏蔽后再通过传统回流冷凝法来测定实验模拟配水水样中的COD，并比较两种方法的屏蔽效果。结果表明：硫酸汞屏蔽法的最佳HgSO4/Cl -值为40，此时误差最小，为1.43%，硝酸银滴定法的误差为0.21%，得出硝酸银屏蔽法的屏蔽效果较好；再分别用这两种方法屏蔽榨菜废水中的氯离子后测定其COD值，结果显示两种方法测定的COD相差了20 mg/L，而硫酸汞屏蔽法更适合于榨菜废水中COD的测定。综合以上2种方法的屏蔽特点，采用先用硝酸银滴定氯离子浓度，再添加少量的硫酸汞的联合方法测定榨菜废水中的COD值，结果表明此方法更可靠。

The chloride mask in COD determination of pickled mustard wastewater with high salt

Chlorides in the wastewater with high salt seriously interrupts the determination of chemical oxygen demand(COD). Therefore, chloride mask in wastewater has been an important and difficult issue in recent years. In the present work, experiment design is used for more accurate and precise COD determination method of pickled mustard wastewater. Two methods for masking chloride are adopted: HgSO4 masking method and AgNO3 masking method. After masking chloride, use the traditional reflux digestion method to test COD in the experimental sample. The results show that when the ratio of HgSO4 to Cl - is 40, the chloride mask results in a minimum error of 1.43%, and the minimum error is 0.21% when AgNO3 is used. Obviously, AgNO3 masking method is superior to HgSO4 masking method. However, when these two methods are used in pickled mustard wastewater, there is a COD value difference of 20 mg/L and HgSO4 masking method is more accurate. By considering the characteristics of the two methods above, a combined method is proposed, which AgNO3 is added equivalently according to the concentration of Cl - first, and then a few amounts of HgSO4 are added to prevent the free Cl - in wastewater. The facts show that combined method is more reliable.