Five Determination Methods of Direct-reading BOD Meter

BOD is the abbreviation of biochemical oxygen demand, which means biochemical oxygen demand, which refers to the amount of dissolved oxygen consumed in the biochemical reaction process of microorganisms decomposing biodegradable organic matter in water under certain conditions, expressed in mg/L Or expressed as a percentage or ppm. It is a comprehensive indicator reflecting the content of organic pollutants in water. Next, let's take a look at the five measurement methods of the direct-reading bod analyzer. 1. Dilution and inoculation method After diluting the water sample to a certain concentration, cultivate it at a constant temperature of 20°C for 5 days, and measure the dissolved oxygen in the water before and after cultivation. Amount, you can calculate the BOD value (ie BOD5). This method is a national standard method, and it is also a classic analysis method agreed by the world, and it is an arbitration method. 2. Mercury pressure difference method In a closed culture bottle, the dissolved oxygen in the water sample is consumed by microorganisms, and the microorganisms produce CO? equivalent to the oxygen consumption due to respiration. When CO? is absorbed by the absorbent, the pressure of the closed system is reduced. Decrease, so that the mercury column shows the pressure difference, and the BOD value of the water sample can be calculated according to the pressure drop measured by the pressure difference. 3. The mercury-free differential pressure method simulates the degradation process of organic matter in nature: the oxygen in the air above the test bottle continuously replenishes the dissolved oxygen consumed in the water, and the CO produced during the degradation of organic matter is absorbed by the sodium hydroxide in the sealed cover, and the pressure sensor Monitor the pressure change in the vial from time to time. A correlation is established between the biochemical oxygen demand BOD (corresponding to the amount of oxygen consumed in the test bottle) and the gas pressure, and this correlation is processed by the instrument, and then the biochemical oxygen demand BOD is directly displayed on the instrument screen. value. 4. The principle of the microbial electrode method is to make the water sample and air enter the flow measurement cell at a certain flow rate to contact the microbial sensor. The soluble and biodegradable organic matter in the water sample is affected by the microorganisms in the bacterial film, so that it can diffuse to the oxygen electrode. The mass of oxygen on the surface decreases. When the diffusion rate of the biodegradable organic matter in the water sample to the bacterial film is constant, the mass of oxygen diffused to the surface of the oxygen electrode is also constant and a constant current is generated, because the current and water There is a quantitative relationship between the difference of biodegradable organic matter in the sample and the reduction of oxygen, and 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. 5. 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 BOD. According to the experimental results compared with the standard method, it can be converted into BOD5 value. The activated sludge aeration degradation method is also a rapid method for the determination of BOD5. The biggest advantage of using the activated sludge aeration degradation method is that the activated sludge contains microorganisms suitable for specific components of wastewater, and the determination of a specific wastewater has high reliability. For unverified wastewater, BOD5 and BOD should be done on the same water sample, and then converted after statistical regression. The measurement range of BOD is wide, and it is generally not necessary to dilute the water sample. However, attention should be paid to whether the water samples contain high levels of toxic and harmful substances to microorganisms, such as fungicides and pesticides. In view of the influence of temperature on the determination of BOD, the temperature control accuracy in the process of aerated culture should be further improved (the temperature range required in the standard method is 30°C to 35°C). In addition, the entire measurement process is a little cumbersome. If the measurement time is appropriately shortened and the degree of automation of the measurement is improved, this method is more suitable for continuous on-line monitoring of a certain pollution source.
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