垃圾渗滤液COD检测方法中Cl^-干扰问题的讨论

Chloride Interference in the Determination of COD of Landfill Leachate

化学需氧量(COD)是垃圾渗滤液检测的一项重要指标,渗滤液中高浓度的氯离子(Cl-)对COD检测的干扰问题未引起足够的重视.通过实验对比了重铬酸钾回流法、快速消解分光光度法、碱性高锰酸钾法和紫外分光光度法检测渗滤液COD时的Cl-干扰程度.普遍采用的重铬酸钾回流法,由于Cl-存在干扰,掩蔽剂不能完全有效掩蔽,Cl-≤3550mg·L-1时测量结果并不准确;快速消解分光光度法并没有从根本上消除Cl-的干扰;碱性高锰酸钾法虽能消除Cl-干扰,但氧化效率只有重铬酸钾的60%左右;紫外分光光度法不仅时间短、效率高,还能有效避免Cl-带来的干扰.在COD值≤150mg·L-1的稳定水质中UV254与COD值有较高的显著相关性,相关系数为0.9985;UV365在COD值≤600mg·L-1都有很显著的相关性,相关系数为0.9996.UV365比UV254具有更广的检测范围和更高的COD相关性.

Chemical oxidation demand （COD） is one of the most important determination indicators of landfill leachate. However,the presence of high concentration chloride in leachate generates interference,which hasn＇t caused enough concern. The objective of this paper is to compare anti-interference ability of chloride among potassium dichromate reflux method,rapid digestion-spectrophotometric method,basic potassium permanganate method and UV spectrophotometry method. For the traditional potassium dichromate reflux method,masking agent can＇t prevent the chloride interference completely when the concentration of chloride is more than 3 550 mg·L^-1. The same thing happens with rapid digestion-spectrophotometric method. Though basic potassium permanganate method can successfully obviate the interference from chloride,low oxidizing ability results in more errors in COD measurement,and the efficiency of potassium permanganate is only 60% of potassium dichromate. UV spectrophotometry can not only shorten the measure time and improve the efficiency,but also avoid the interference from chloride. The result indicates that when COD values is less than 150 mg·L^-1 ,there is a prominent correlation between UV254 and COD,with a correlation coefficient of 0. 998 5. Furthermore,when COD values is less than 600 mg·L^-1 ,the correlation between UV365 and COD is more prominent than UV254 ,with a correlation coefficient of 0. 999 6.