In the process of sewage treatment, in order to make the treated water meet the standard discharge, water quality monitoring equipment will be used to test the water quality in every link of sewage treatment. According to the data measured by the water quality monitoring equipment, corresponding treatment methods will be adopted to make this link The water quality index meets the requirements, and then enters the next treatment link. Among these water quality monitoring indicators, BOD
is one of the important detection indicators. So what are BODs? What are the methods for measuring BOD? What kinds of BOD detection equipment are there? What is BOD? BOD (biochemical oxygen demand): refers to the mass concentration of dissolved oxygen required for the biochemical process of microbial decomposition of organic matter in water under aerobic conditions. In order to make the BOD detection values comparable, a period of time is generally specified, and the consumption of dissolved oxygen in water is determined. Generally, five days are used, which is called five-day biochemical oxygen demand, recorded as BOD5, and five-day biochemical oxygen demand is often used. . The larger the BOD value, the more organic matter is contained in the water, so the pollution is more serious. BOD is an environmental monitoring index used to monitor the pollution of organic matter in water. Organic matter can be decomposed by microorganisms. Oxygen is consumed during this process. If the dissolved oxygen in water is not enough to supply the needs of microorganisms, the water body will be treated for pollution. What are the methods for measuring BOD? At present, there are usually the following methods for detecting BOD: 1.1 Standard dilution method After diluting the water sample to a certain concentration, culture it at a constant temperature of 20°C for 5 days, measure the amount of dissolved oxygen in the water before and after the culture, and then calculate the BOD value (that is, BOD5 ). This method was adopted by the Standard Methods Committee of the American Public Health Association in 1936, and became a common analytical method in the world. The water quality analysis method GB7488-87 promulgated by our country also adopts this method. Among all kinds of pollutants in the water environment, oxygen-consuming pollutants are still an important factor affecting the water quality of water bodies. The main harm is the consumption of dissolved oxygen in water, which leads to the deterioration of water quality. BOD can relatively represent the amount of organic matter that can be decomposed by microorganisms, that is, the dissolved oxygen consumed by the decomposition of organic matter in water, which is in line with the actual situation of water self-purification and most of the technical process routes of sewage treatment. Therefore, the determination of BOD has a more important role in controlling water pollution. significance. At present, there are usually the following methods for detecting BOD: 1.2 Microbial electrode method. The principle is to make the water sample and air enter the flow measurement cell at a certain flow rate to contact the microbial sensor. The role of microorganisms in the medium reduces the mass of oxygen diffused to the surface of the oxygen electrode. When the diffusion rate of biodegradable organic matter in the water sample to the bacterial film reaches a constant rate, the mass of oxygen diffused to the surface of the oxygen electrode also becomes constant and stable. A constant current is generated, and since the difference between the current and the biodegradable organic matter in the water sample has a quantitative relationship with the reduction of oxygen, the biochemical oxygen demand of the water sample can be converted accordingly. BOD5 standard samples are usually used for comparison to convert the BOD5 value of water samples. 1.3 The activated sludge aeration degradation method controls the temperature at 30°C to 35°C, uses the activated sludge to force aeration to degrade the sample for 2 hours, digests the samples before and after biodegradation with potassium dichromate, and measures the chemical oxygen demand before and after biodegradation. The difference is the BOD. According to the experimental results compared with the standard method, it can be converted into BOD5 value. 1.4 Manometry In a closed culture bottle, the dissolved oxygen in the water sample is consumed by microorganisms, and the microorganisms produce CO2 equivalent to the oxygen consumption due to respiration. When CO2 is absorbed by the absorbent, the pressure of the closed system is reduced. According to the manometer The measured pressure drop can be used to calculate the BOD value of the water sample. What kinds of BOD detection equipment are commonly used? 1. The five-day cultivation method BOD5 detector is based on the national standard 'HJ505-20095 daily cultivation method' bod detector. This equipment can simulate the biodegradation process of organic matter in nature in combination with a constant temperature incubator. It uses the principle of mercury-free differential pressure method to measure the water BOD value. 2. Microbial electrode method BOD tester LCD large-screen LCD displays the working status and measurement results, and the computer stores and automatically prints the data. The instrument is easy to operate, easy to use, large in measurement range, and high in detection accuracy. Microbial electrode method is used. The company has biofilm preparation technology. Conforms to the national BOD measurement method standard: HJ505-2009 has a fast detection speed, and the result can be obtained quickly in 8 minutes. It is driven by a peristaltic pump and operated by a constant-speed flow continuous sampling microcomputer, which can switch between manual measurement and automatic measurement modes.
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