In general water quality monitoring, the more common detection items include chroma, turbidity, PH value, etc. COD
(chemical oxygen demand) and BOD
(biochemical oxygen demand) are also detected in sewage detection. For the detection of BOD, the conventional method is to measure the biochemical oxygen demand for 5 days to calculate the BOD value of the water sample to be tested. However, due to the complexity of this method, the requirements for operators are relatively high, and the detection time is five days. The main method now is to use the microbial electrode method to quickly measure BOD. The core of the microbial electrode method is the microbial electrode of the instrument. The normal operation of each part in the electrode can ensure the accuracy of the instrument detection data. Microbial electrodes are sensors that combine microbial technology with electrochemical detection technology. It mainly consists of a dissolved oxygen electrode and an immobilized microbial film attached to the surface of its gas-permeable membrane. The principle of the reaction to BOD substances is: when the bottom liquid without BOD substances is inserted at a constant temperature and a certain concentration of dissolved oxygen, the rate at which dissolved oxygen molecules in the bottom liquid enter the oxygen electrode through diffusion. The microbial film has a certain respiratory activity due to the microorganisms. Of course, the microbial electrode outputs a steady-state current; if a BOD substance is added to the bottom liquid, molecules of that substance will diffuse into the microbial film along with oxygen molecules, because the microorganisms in the film assimilate the BOD substance and consume oxygen to enter the microbial film . The reduction of the oxygen molecules in the oxygen electrode, that is, the reduction in the rate of diffusion into the oxygen electrode, causes the electrode output current to decrease and drop to a new steady-state value within a few minutes. In a suitable BOD substance concentration range, the reduction value of the electrode output current has a linear relationship with the BOD substance concentration, and the BOD substance concentration has a quantitative relationship with the BOD value. Therefore, the BOD of the water sample to be tested can be known according to the current drop value. The microbial film in the microbial electrode mainly performs assimilation during the detection process. Assimilation (also known as anabolism) is the process by which an organism converts nutrients obtained from the external environment into its own constituent substances and stores energy. That is, a series of metabolic pathways in which organisms use energy to synthesize small molecules into macromolecules. In the detection reaction, the liquid to be tested is equivalent to the external environment, and the dissolved oxygen in the liquid to be tested is the nutrient. When waiting for the liquid to be tested to flow through the microbial membrane, the organic matter in the liquid promotes the assimilation of microorganisms, consumes the dissolved oxygen in the liquid to be tested, and reduces the oxygen content, thereby affecting the potential change of the electrode, and then calculates according to the potential change. Obtain the BOD value of the liquid to be tested. Using the microbial electrode method can not only greatly shorten the detection time of samples (from the original 5 days to 8 minutes), but also greatly reduce the requirements for operators, and people who have never been exposed to chemical experiments can also receive simple training. Testing will be done independently soon. The microbial electrode method not only improves the detection speed, but also ensures the accuracy of the detection results. Compared with the measurement results of the five-day method, the error of our company's BOD220 rapid tester is kept below 5%, within a reasonable error range. The microbial electrode method BOD rapid analyzer provides a more complete solution for BOD determination in water quality monitoring.
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