Theoretical And Experimental Studies On The Measurement Of COD In Water Using Ultraviolet Spectrum Method

Water resource is essential to the living of all biology. Recently, with the rapid explosion of population and developing of industrial economy, water environment pollution has become the most important problem for the water protection in the world. Chemical Oxygen Demand (COD), as a parameter of water organic content, is an important index to evaluate water pollution extent. At present, potassium dichromate method used to exactly measure the COD values, is the primary method. However, this method is time-consuming, tedious and prone to cause secondary pollution, so it can't meet the needs of on-line long term monitoring.At First, this paper discussed the current research statement and the progress of COD detection method in domestic and abroad, and presented a new idea to develop a novel instrument based on ultraviolet spectrum, which is based on the selective absorbance for ultraviolet light by organic content and the instrument is a drop into water one. By directly dropping the detector of the instrument into water, it could automatically accomplish the Ultraviolet-visible spectra scanning of the water sample, which achieved the COD detection with no sample pretreatment, no chemical reagents and quick real-time measurement. It is a brand new kind of measuring technology.Secondly, the key point whether the UV online COD detection instruments could accurately gain the COD values of water lies in how to establish mathematical model between ultraviolet absorbance and COD values. Because of the characteristic of complex diversity and vulnerable to environmental interference of real water components, a nonlinear relation existed between the ultraviolet absorbance data and COD values. In this paper, by using ultraviolet-visible band scanning, along with the inducement of principal component analysis, BP neural network and partial least-squares to establish a new prediction model between the characteristic values of light intensity and COD values of water sample. Based on which we developed the new prediction instrument and carried out some experimental tests with potassium hydrogen phthalate standard solutions and real water samples, from which we analyzed the interfaces of UV absorbance caused by turbidity, PH, temperature, and so on. And, we also discussed the method of eliminating the affects of turbidity. Experimental results show that both two kinds of mathematical model can be applied to predict and analyze the organic pollution in water sample. The results of this research will make an effective contribution to the technology development of the research of brand new on-line COD monitoring instruments.