Investigation Of The Mathematical Model Of The Measured Values Of COD In Rare-Earth Wastewater By Different Methods

COD（Chemical Oxygen Demand） is set as a comprehensive index reflecting water pollution by reducing agents, such as organic chemicals, nitrite, ferrous salt, sulphurous pollution, strict emission standards are formulated by countries for various industries, and the environmental monitoring department have to follow the relevant standard measurement method for experimental tracing determination, it is not only for the supervision the outlets of industries, but also a necessary measures taken for the environmental protection law enforcement investigation.Ganzhou is abundant in ion-adsorption type of rare earth in China, the rapid development of rare earth industry has fertile the city with substantial wealth at the same time, but also brought a certain degree of emissions of pollutants such as waste water, waste gas, waste residue, the emissions have led to serious environment pollution. However, organic waste water composition which results from the purification process of rare earth is complicated, which seriously interfere with the determination of chemical oxygen demand（cod）, besides, the value of COD varies with the complicated interfering factors, the limitation of experimental conditions and the methods adopted for the determination of COD.As a result, it’s necessary to explore the internal correlation between COD value and the determination method.This paper respectively describe the use of potassium dichromate, potassium iodide alkaline potassium permanganate, chlorine calibration method to parallelly study more than 150 portion of waste water samples from 22 rare earth companies of southern Ganzhou city. The test data are subjected to SPSS statistical analysis software for analysis, and then to Excel software to test model fitting and verification, the conclusion based on these data are finally made to explore the inherent law of COD value and the determination method described above, the results are listed as below:（1） By comparing the CODOH. KI and CODcr model summary b R square, F of sig. and standardization and regression residual standard P-P data observation accumulative total scatter diagram, which are acquired by alkaline potassium permanganate method and potassium iodide potassium dichromate method developed for the determination of chemical oxygen demand（COD）for rare earth waste water, with expected cumulative probability, we can know that the results of CODOH. KI and CODcr are in linear correlation; But constants value t corresponding to Sig arebigger than 0.05, so the constant was not significant. Through fitting of Excel software to model,the mathematical equation of CODOH. KI and CODcr could be established as CODcr = 4.8843 CODOH. KI.（2） By comparing the CODOH. KI and chlorine calibration method model summary b R square, F of sig. and standardization and regression residual standard P-P data observation accumulative total scatter diagram, which are acquired by alkaline potassium permanganate method and potassium iodide potassium dichromate method developed for the determination of chemical oxygen demand（cod） for rare earth waste water, with expected cumulative probability,we can know that the results of CODOH. KI and COD_Cl are in linear correlation; But constants value t corresponding to Sig are bigger than 0.05, so the constant was not significant. Through fitting of Excel software to model, the mathematical equation of CODOH. KI and COD_Cl could be established as COD_Cl = 4.6602 CODOH. KI.（2） The two sets of equations which are verified by model test and construction have very wide application in practice and guidance, and the detection range of CODOH. KI could reach as minimum as 0.2 5000 mg/L.