Ultraviolet spectrophotometric determination of water quality COD is to use the characteristics of organic matter to absorb ultraviolet light to measure the concentration of organic matter in water. Using potassium hydrogen phthalate standard solution as the water sample, it was verified that there is a good linear relationship between the COD in water and the absorbance of 254nm ultraviolet light within a certain range. The linear regression equation is y=125.33x-2.360 5, and the correlation coefficient r=0.994 5. Because of the influence of suspended matter in general sewage, the UV spectrophotometric method is used to measure water turbidity.
Environmental pollution in modern society, especially water pollution, is one of the urgent problems to be solved. COD refers to the amount of oxidant consumed to oxidize reducing substances in 1L of water sample under certain conditions, expressed in mg/L of monooxygen. COD reflects the degree of pollution of water bodies by reducing substances. COD, as an important parameter for river and industrial wastewater research and sewage treatment plants, has been valued by various countries. The methods for measuring COD mainly include chemical methods and physical methods. Chemical methods are based on various chemical reactions, and physical laws are mainly spectrophotometry.
The UV method is a physical method that has been researched in recent years. The UV method uses ultraviolet spectrophotometry to indirectly determine the COD of sewage. Its theoretical basis is Lambert Beer's law. Lambert Beer's law means that when a beam of parallel monochromatic light passes through a uniform and non-scattering dilute solution, the degree of light absorption by the solution is proportional to the product of the concentration of the solution and the thickness of the liquid layer, namely:
A=KCL
In the formula: A is the absorbance; C is the solution concentration; L is the thickness of the liquid layer; K is the proportional constant.
The absorption law can be applied to those multi-component solutions that do not interact with each other. Their absorbance is linear, that is, the absorption of a certain wavelength of light by the solution is equal to the sum of the absorption of each component in the solution at that wavelength:
A total=A1+A2+A3+∧+An=K1C1L+K2C2L+K3C3L+∧+KnCnL
According to Lambert Beer’s law, in general, L is a constant value, and K is only related to the wavelength of the incident light, and is also a constant value. Therefore, in theory, A and C are proportional. By measuring A of a solution with known C, Then the proportional coefficient K can be obtained, and the linear straight line between A and C can be determined, so as long as the absorbance value of the unknown solution is known, the concentration value can be obtained.
Recommend a UV sensor that can be used in water turbidity detection by UV photometry. The UV sensor introduced from abroad-GUVC-T21GH, has high sensitivity and good light blindness, small size, chip size 0.4mm, TO 5 package, single power supply voltage operation. Can be widely used: UV intensity detection and control, UV index detection. Outdoor UV index equipment, etc., can also be used for UV disinfection and UV curing to monitor UV intensity. UV flame detector, etc.
