Research On Correlation Between COD And TOC Of Typical Rivers In Jilin Province

Chemical oxygen demand and total organic carbon are general indexes to scale organic pollutants in waters. COD is as a token of pollutants that can be oxidized by oxidant under given conditions and it is the summation of reductive substances that can be deoxidized easily in water. But COD can not reflect the total organic pollutantes truly. TOC shows the summation of organic carbon in water and it is not affacted by other inorganic reductive substances. So, TOC can reflect the total organic pollutantes truly. There are some abuses in conventional COD test,such as costing long time , causing secondary pollution and so on. On the contrary, TOC testing instrument has some advantages: simple flow, good repeatability, high sensitivity, no secondary pollution and so on.If there is a significant linearity correlation between COD and TOC, COD test can be replaced by TOC test. It will take shorter time and makes higher efficiency. At present, some scholars have studied the correlations between COD and TOC of kinds of waters and they have arrived at a conclusion that there is a nicer correlation between the two indicating indexes. But, the all-around research on correlation between COD and TOC of surface water is still a vacancy.Songhua River, Liao River, Yalu River and Tumen River are the main rivers in Jilin province, the valley area of which has covered 98.7% of the soil in Jilin province. The chief waste waters let into those rivers are living sewage and industry waste water. This paper selects the reaches of Songhua River, Liao River, Yalu River and Tumen River in Jilin province as study objects, in which 202 water samples are gathered at different periods of time in 2005 and 2006. The relation between COD and TOC has been discussed.The COD and TOC values were measured with Dichromate method and nondispersive infrared absorption method. To establish a quantitative relationship model between COD and TOC of typical rivers in Jinlin province, linear regression of COD and TOC was made with the least square method. At the same time, the correlation test was carried out. The differences of COD/TOC ratios at different sampling time and different sampling rivers were compared and the causes were analyzed.The experiment results indicate: In 2005 and 2006, the water quality of most of the water samples of typical rivers in Jilin province accord with the request of water area function; Exceptional sampling points fell short of the water quality control aim and overtook the standard gravely.The COD and TOC values of typical rivers in Jilin province have a significant correlation both at different sampling periods and at different sampling rivers. Most of the regression equations can be predigested by ignoring its intercept. The significant correlation between COD and TOC offers a gist that COD test can be replaced by TOC test, which fills the technique vacancy of research field in Jilin province. At practice work, relevant quantitative relationship model between COD and TOC can be selected to forecast the organic materials indicating index in water. There are marked differences of COD/TOC ratios between different waters and different periods. The marked differences of COD/TOC ratios show the complexity of environment variables. The change of factors, such as the flux of different waters at different time, the water temperature, the production status of industry and agriculture along rivers and so on, could affect the organic materials indicating index in water. So, it is still necessary to do further research on the token of organic pollutantes exactly and the COD/TOC ratios, internal differences of representative rivers in Jilin Province.