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COD online analyzer principle and common problems

by:BOQU     2023-03-11
The COD on-line analyzer is a waste water on-line detection system, and it is the main project of the State Environmental Protection Administration to implement on-line automatic monitoring of pollution sources. COD is chemical oxygen demand, which reflects the degree of water pollution by reducing substances, including organic matter, nitrite, ferrous salt, sulfide, etc., but the amount of inorganic reducing substances in general water and wastewater is relatively small , and being polluted by organic substances is very common, therefore, COD can be used as a comprehensive indicator of the relative content of organic substances. So what is the principle of CDD online analyzer? The editor of BOQU Instruments will take you to understand. COD online analyzer principle: sample, potassium dichromate digestion solution, silver sulfate solution (silver sulfate is added as a catalyst to more effectively oxidize straight-chain fatty compounds), and the mixture of concentrated sulfuric acid is heated to 165 ° C, potassium dichromate It is reduced to trivalent chromium by organic matter in water, the content of trivalent chromium is measured at a specific wavelength, and then the mass concentration of oxygen consumption is converted according to the amount of trivalent chromium ions (the amount of dichromate ions consumed corresponds to the amount of oxidizable organic matter) Calculate the COD value. Reducing inorganic substances, such as nitrite, sulfide and ferrous ions, will enhance the measurement results, and their oxygen consumption will be added to the COD value. The interference of chloride ions can be eliminated by adding mercuric sulfate, because chloride ions can form stable mercuric chloride with mercury ions. Frequently asked questions about COD analyzers: Question 1: The location of the sewage outlet of the sampling pipeline is mostly in a relatively remote place. There is some distance between the instrument installation point and the outlet, and the sampling pipeline is correspondingly long; When the road is laid, the sampling pipeline is U-shaped, causing water accumulation in the pipeline; some enterprises use hard pipes for outdoor pipelines, with many right-angle elbows, and sometimes landfill protection is required. Since the working process of the COD online analyzer is discontinuous, over time, the above reasons cause serious pollution in the pipeline, especially some eutrophic water bodies, moss even cause pipeline blockage, and pipeline cleaning is very difficult. Problem 2: Sample collection During the quality control inspection, some abnormal data were tracked and checked, and it was found that a considerable part of the reason was due to insufficient sampling, no sampling or unrepresentative samples collected. Sampling problems not only cause abnormal monitoring data, but also adversely affect the performance of some instruments. For example, the flow injection COD online analyzer used by a certain company was always unstable for a period of time. After inspection, it was found that the lack of sampling caused air bubbles in the capillary of the instrument, resulting in unstable operation. Question 3: Instrument Operation In the specific work of instrument operation, some details, sometimes even key details, are often overlooked. For example, in the setting of working parameters, when inspecting a certain enterprise, the digestion time of the instrument was set to 20 minutes, and a satisfactory explanation was not obtained when asking about the setting basis, so a field test was carried out for this. After the instrument is debugged normally, use GB11914-1989 ((Water Chemical Oxygen Demand Determination of Potassium Dichromate Method) to test the potassium hydrogen phthalate solution and the outlet water samples respectively. The results show that the digestion time should be determined according to different situations. , The digestion time of water samples with complex components must be determined by comparison tests. Question 4: Waste liquid At present, the COD online analyzers in use basically adopt the national standard method, which will generate waste liquid and cause secondary pollution. On-line monitoring It is a part of environmental management, and enough attention should be paid to the problem of waste liquid. After a simple calculation, one instrument is monitored 8 times a day, plus calibration, cleaning pipelines, etc., and more than 1L of heavy metals and strong acids will be produced every day. High-concentration waste liquid, the amount of waste liquid produced in an area throughout the year is very considerable. If the waste liquid problem is not handled properly, it will not only be a potential source of pollution, but also have an incalculable negative impact on the social image of environmental protection work. Shanghai BOQU Instruments Co., Ltd. is a comprehensive enterprise focusing on the development, design, manufacture, sales and service of water analysis sensors and water analysis instruments. It was awarded the Shanghai High-tech Enterprise in 2015. BOQU Instruments has been engaged in the water quality monitoring instrument industry for many years 'Customer-centric', every BOQU person keeps in mind the corporate mission of 'being the bright eyes of the earth's water quality monitoring', constantly optimizes products and services, takes water quality monitoring as a lifelong career, and serves every customer with heart!
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