[Chloride interference in the determination of COD of landfill leachate]

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 3550 mg x 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 x L(-1), there is a prominent correlation between UV254 and COD, with a correlation coefficient of 0.9985. Furthermore, when COD values is less than 600 mg x L(-1), the correlation between UV365 and COD is more prominent than UV254, with a correlation coefficient of 0.9996.