Effect of Chlorine Concentration on determining COD by acid and alkaline potassium permanganate

In water monitoring, effect of chloride ion in water body on determining COD can not be ignored. Potassium dichromate has a strong oxidizing, and it can oxidize most of the organic in matter. But it generally is used to determine the water body which COD is larger than 30mg/L, and easily influenced by Chloride ion. So we often use alkaline potassium permanganate method which has weak impact by Chloride ion in high chlorine concentration wastewater. For the tidal estuary, we often use acidic potassium permanganate method in upstream and alkaline potassium permanganate method in downstream. The different detection methods cause the disagreement of water quality evaluation. This paper describes the influence of chlorine level on the COD standard solution prepared by laboratory and river freshwater sample from Qiantang River upstream in detail, and analyses the difference between the acid potassium permanganate method and alkaline potassium permanganate by comparing the COD standard solution prepared by laboratory and the freshwater sample. Last, this paper discusses the variation of COD during a tidal period.