When evaluating water quality, Chemical Oxygen Demand (COD) is an extremely important indicator, which is mainly used to reflect the level of organic matter content in water bodies. Generally speaking, the higher the value of Chemical Oxygen Demand, the deeper the degree of organic pollution in the water body. Due to the different types and contents of reducing substances in water samples and the differences in measurement methods, the measurement results of Chemical Oxygen Demand also vary.
A high Chemical Oxygen Demand often means that there are a large number of reducing substances in the water, among which organic pollutants account for the largest proportion. The higher the value of Chemical Oxygen Demand, the more serious the organic pollution in the river water. The sources of these organic pollutants are very extensive. The irrational use of pesticides, the discharge of wastewater from chemical plants without strict treatment, and the inflow of organic fertilizers into rivers with rainwater may all lead to an increase in organic pollutants in water bodies.
If these organic pollutants are not treated, they will be adsorbed by the bottom mud at the bottom of the river and gradually deposited. In the next few years or even decades, these deposited pollutants will continuously poison aquatic organisms and disrupt the balance of the aquatic ecosystem.
As the top of the food chain, if humans consume organisms in polluted water bodies, they will ingest the toxins accumulated in these organisms. These toxins accumulate continuously in the human body and are highly likely to cause serious consequences such as carcinogenesis, teratogenesis, and mutagenesis, posing a great threat to human health. Therefore, controlling Chemical Oxygen Demand and treating water pollution are very important for protecting the ecological environment and human health.
The COD Analyzer adopts the UV254 absorption method. Many organic substances dissolved in water, especially those containing aromatic rings and unsaturated bonds, will absorb light energy when irradiated by ultraviolet light at a wavelength of 254nm. According to the Beer - Lambert law, under certain conditions, the absorbance of a substance in a solution is proportional to its concentration. Therefore, by measuring the absorbance of a water sample to ultraviolet light at a wavelength of 254nm, the concentration of organic substances in the water sample can be indirectly known.
In actual measurement, preparation work should be done first to ensure the normal operation of the UV254 detector. Representative water samples should be collected and then placed in a suitable quartz cuvette. When measuring, turn on the instrument to let the ultraviolet light at a wavelength of 254nm pass through the water sample. At the same time, in order to eliminate the interference of factors such as the turbidity and suspended solids of the water sample, the light at another wavelength (such as 590nm or 350nm) is usually measured as a reference. After that, the detector of the instrument will measure the light intensity after passing through the water sample, calculate the absorbance at a wavelength of 254nm, and then convert the absorbance into the corresponding organic matter concentration or relevant indicators such as Chemical Oxygen Demand according to the pre - established standard curve or empirical formula.
The UV254 absorption method has outstanding advantages. It is efficient and fast, does not require chemical reagents, can achieve real - time online monitoring, and has strong adaptability to various water qualities. Precisely because of this, it is widely used in water quality monitoring scenarios such as drinking water, surface water, industrial wastewater, and sewage treatment plants to help us evaluate the water pollution situation.
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