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What are the factors that affect the calibration of the bod meter

by:BOQU     2023-03-30
The bod meter is the biochemical oxygen demand meter. Biochemical oxygen demand is a comprehensive indicator reflecting the content of organic pollutants in water. It refers to the amount of dissolved oxygen consumed by microorganisms in the biochemical reaction process of decomposing biodegradable organic matter in water under certain conditions. Expressed in mg/L or percentage, ppm. Share the calibration method of the BOD detector: The performance and operation method of the device can be indirectly checked by using the glucose-glutamic acid standard solution assessment, but the operator of the BOD5 analyzer should be proficient in operating the device and the chemical dilution method , Accurately measure the glucose-glutamic acid standard BOD value, otherwise the influence of human error cannot be ruled out. The specific inspection steps are as follows: 1. Preparation of glucose-glutamic acid standard solution: place glucose and glutamic acid in a 103°C drying oven for 1 hour, weigh 150mg of solution dilution water each, transfer to a 1000mg volumetric flask and dilute to the marked line , shake well. 2. Inoculate the standard solution. The inoculum can generally be taken from domestic sewage, and the retrieved domestic sewage should be clarified at 20°C for 2-10 hours to obtain the supernatant. The amount of inoculum depends on the type of inoculum and the BOD value. If the BOD value of the inoculum is 30-40mg/l, 10-20% of the inoculum should be added to the standard solution (fresh inoculum is generally 10-15%). The standard solution after inoculation is called the standard sample. It should be fully stirred when inoculating. 3. Heat or cool the standard sample and inoculum solution to about 20°C, and inject the standard sample according to the water injection volume of 0-300mg/l; the inoculum solution is based on the estimated BOD value, and select a suitable file according to the water sample volume table Quantitative sampling. 4. The standard sample and the inoculum were measured in parallel at the same time. 5. After five days of cultivation, the theoretical BOD5 value of the standard solution should be 180-230mg/l, and the calculation formula is the same as the above formula. For example: select the standard sample with a range of 0-300mg/l and the reading of the mercury manometer is 62 bars, the domestic sewage inoculum is injected at the range of 0-50 mg/l and the reading of the mercury manometer is 100 bars, and the inoculation amount is 10%. (i.e. 9 parts of standard solution coupled with 1 part of inoculum solution). After all the pipelines of the BOD rapid detector are correctly placed, the buffer solution can be connected to the pipette and the power switch can be turned on to set the appropriate flow rate and temperature for the operation of the instrument to ensure the sampling and cleaning time of the BOD sample. . When the electrode potential is adjusted to a relatively stable standard parameter state, the measurement of BOD sample data will also be more stable. Factors affecting the calibration of the bod meter: 1. Visually inspect the bod meter cover for biological fouling or large scratches. Biological contamination can consume or produce oxygen, which can affect sample calibration. Large scratches on painted surfaces can also affect calibration. 2. Make sure there are no water droplets on the sensing element or thermistor, if any, clean them up. Also ensure a stable ambient temperature, preferably in a laboratory for testing operations. 3. Compensate for altitude or atmospheric pressure. Many water quality testing instruments now have atmospheric pressure sensors. They automatically take the barometric pressure value as part of the calibration procedure. 4. Compensation for salinity. When testing, the salinity of the sample should be tested in advance. In order to reduce the influence of salinity on the sample data.
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