Study On Indicating Indexes Of Organic Pollutants In Typical Waters

Chemical oxygen demand (COD), permanganate value (PV) and total organic carbon (TOC) are indexes commonly used to measure the contents of organic pollutants in waters. COD and PV relate to 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. Many organic pollutants, especially aromatic compounds, are difficult to be oxidized or completely oxidized by oxidant, especially for permanganate. So COD & PV can not reflect the total organic pollutant contents truly. TOC relates to the total organic carbon content in water and it is not affacted by other inorganic reductive substances. So, TOC can reflect the contents of all organic pollutantes exactly. There are also some abuses in conventional COD test, such as the relatively long time needed, the large amount of reagents, causing secondary pollution and so on. On the contrary, TOC test has some advantages, such as the simple flow, the good repeatability and high sensitivity, the quickness and accuracy, and freedom from secondary pollutions. But as the experimental facilities for the determination of COD & PV are lower-cost, the COD was still used to evaluate the overall organic pollution of water in Environmental Quality Assessment and monitoring in our country at present.If there is linearity correlation between COD (or PV) and TOC values, COD (or PV) test can be replaced by TOC test. It will take shorter time and has higher efficiency. At present, some scholars have studied the correlations between COD and TOC of different kinds of waters and they have arrived the conclusion that there are significant correlations between the two indicating indexes. But, the systematic studies on correlation between COD and TOC of surface water and wastewater are still a vacancy.In this study, the COD (or PV) and TOC values were measured with dichromate method (or permanganate method) and non-dispersing infrared absorption method, respectively. To establish a quantitative relationship model between COD (or PV) and TOC of typical surface rivers, lakes and wastewaters in Jilin province, linear regression between COD (or PV) and TOC was made with the least square method. At the same time, the correlation tests and the significance tests of intercepts were carried out. The differences of models at different sampling time and different sampling valleys were compared and the causes were discussed. In addition, a kind of wastewater of a paper mill and the river water where the wastewater discharged to were selected as examples to analyze the types of organic compounds in the wastewater and river by GC-MS qualitatively. The results of the study revealed the intrinsic relationship between the indicating indexes of organic pollutants of representative water, and provide technical support for environmental management and pollution control.The rivers in Jilin province belong to Songhuajiang River system, Liaohe River system, Yalujiang River system, Tumenjiang River system and Suifenhe River system. The valley area of the front four river systems covered 98.7% total area of Jilin province. In this study, the reaches of Songhuajiang River system, Liaohe River system, Yalujiang River system, and Tumenjiang River system in Jilin province were selected as study objects, in which 266 water samples of 42 sections of 12 rivers are sampled at different periods of time in 2005 and 2006.The relation between COD and TOC has been discussed. The results indicate, in year 2005 and 2006, the PV and TOC values, COD and TOC values of typical surface waters in Jilin province have a nicer correlation both at different periods and at different sampling river systems. The quantitative relationship models between PV and TOC, COD and TOC of typical rivers in Jilin province at different periods were established via linear regression obtained with least square method and the significance test was carried out. Most of the regression equations can be simplified by ignoring their intercepts. The linear correlation between PV and TOC, COD and TOC offers a gist that PV & COD test can be replaced by TOC test, which fills the technique vacancy of research field in Jilin province. Besides, from the results it can be concluded that there are defects to evaluate the organic pollution of the water use PV or COD through that PV was not suitable for characterization of the serious pollution of surface water, and COD is not precise enough for the characterization of clean water, and they can not reflect truthfully the content of organic matter in water like TOC. According to China's current environmental protection standard analytical methods, because of the determination of the injection needle aperture restrictions, the TOC values determine only dissolved organic carbon (DOC), excluding particulate organic carbon in the suspended solids, while the determination of COD (or PV) values include their contribution. So the TOC values will be low if the contents of suspended solids in water were high, and then the ratio of COD / TOC (or PV / TOC) will be relatively high. The ratios of PV / TOC and COD / TOC are different of the main rivers in Jilin province because the flows of river are different with the season changing and the differences of types and amount of organic pollutants and inorganic reducible matters. There are remarkable differences between COD/TOC ratios of different waters, different periods and different months in a same period. The remarkable differences of COD/TOC ratios show the complexity of environment variables. The changes 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 value of organic pollutants indicating indexes of the waters. So, it is still necessary to do further research on the exact characterization of organic pollutants and the COD/TOC ratios, internal differences of representative surface waters in Jilin Province.Eight major lakes and reservoirs in Jilin province were also selected as study objects, in which 54 water samples of 20 sections are collected in 2005 and 2006. The relation between COD and TOC has been discussed. The results indicate that there are significant linear correlations between the COD and TOC value of the eight major lakes and reservoirs in Jilin province, and the TOC value can be used to replace COD value. It is necessary to deal with specific conditions with a specific manner because of the differences of the COD / TOC ratio of lakes and reservoirs, as the types of lakes and reservoirs are different (closed, open), and where regional climate are different, and the flows of lakes and reservoirs are different with the season changing, and the types and amount of organic pollutants and inorganic reducible matters are different.Nine typical kinds of industrial wastewater and municipal sewage in Jilin province were also selected as study objects, in which 57 water samples are gathered in 2005 and 2006. The relation between COD and TOC has been discussed. The results indicate that there are significant linear correlations between the COD and TOC value of the wastewater of paper mill, chemical products manufacturing industry, and chemical fiber manufacturing industry, as well as municipal wastewater treatment plant drainage in Jilin province. The ratio of COD / TOC would be higher where there is more suspended solids. As far as the indicating index of organic pollutants of one type of pollution sources concerned, there are significant linear correlations between the COD and TOC value, and the one index can be considered to replace another. However, there are differences among different types of wastewater due to their different compositions and characters. Therefore, when one index was replaced by another, it is recommended to establish their correlation equation for each type of wastewater. According to the qualitative analysis of the types of the organic compounds in water and the estimation of their amounts by their signal value, the relationships between the organic compounds in the wastewater of a paper mill and in the downstream river water where the effluent was discharged were qualitatively analyzed, which reveals the intrinsic relationship between indicating indexes of organic pollutants of typical water. The results indicate that most organic matters in wastewaters of paper mill after filtration could be oxidized by potassium dichromate, so the COD values can reflect the contents of organic matter fairly well. As far as the wastewater of the paper mill and the downstream river water are concerned, the theoretical ratios of COD / TOC of the water samples were similar to that measured actually, which indicated that the ratios of COD / TOC were determined mainly by the organic components in the water samples. In addition, the inorganic substances in the river water also have some impacts on the oxidation rate of potassium dichromate. From the comparison of the types and contents of organic pollutants in both the wastewater samples from the paper mill and the water samples in the downstream river, it could be concluded that the wastewater form the factory have direct and significant influence on the quality of water in downstream river. The difference of organic pollutants in the samples between wastewater and river water was reflected in the difference of ratios of COD / TOC.