Briefly describe the calibration and measurement items of BOD measuring instrument

Calibration and measurement items of bod analyzer 1. Preparation of standard solution Glucose-glutamic acid standard solution: after drying, dissolve 150mg of glucose (C6H12O6) and glutamic acid (HOOC-CH2-CH2-CHNH2-COOH) at 103°C for 1 hour. Dilute with water, add 5-10mL inoculum, then dilute to 1000mL with dilution water, and mix well. 2. Instrument calibration Take 167mL glucose-glutamic acid standard solution, select the range of 0~400mg/L, and follow the BOD5 detection procedure. The detected BOD concentration should be between 180mg/L and 230mg/L. Otherwise, it is necessary to check whether there is a problem with the inoculum or the experimental process, and whether there is a problem with the use of the instrument. The dilution water should be kept at a constant temperature of 20°C in advance, and aerated or stirred to saturate the dissolved oxygen. 3. Precautions 1. The temperature of the water sample should be around 20°C when bottling. Don't deviate too much. 2. In order to ensure the content of dissolved oxygen in the water, the water sample should be aerated by bubbling for 1 hour or placed in an open beaker and stirred with a magnetic stirrer for more than half an hour, so that the dissolved oxygen in the water sample can reach saturation. 4. Factors Affecting BOD Tester 1. Dissolved Oxygen Since the test temperature is set at 20°C in winter, the dissolved oxygen will be supersaturated, while the samples collected in summer may be undersaturated with dissolved oxygen at 20°C. Therefore, these samples should be stirred and aerated to adjust dissolved oxygen to a saturation point of approximately 20°C prior to BOD5 determination. 2. pH value test The pH value of the water sample should be adjusted to 6.7~7.5 (pH 7.2). A drop in BOD5 readings may be due to the pH of the sample being tested being outside this range. For samples containing large amounts of acid or base, the BOD5 reading may be lower than the actual content. Acidic or alkaline water samples should be neutralized with appropriate concentration of sodium hydroxide solution or dilute hydrochloric acid. The volume of conditioning solution used should not exceed 0.5% of the volume of the water sample. If it exceeds, you can increase the acid-base concentration of the conditioning solution and reduce the volume of the conditioning solution. 3. During the temperature experiment, place the host in an incubator at 20°C±1°C. The measurement of BOD can also exceed this temperature range. For example, it is proved by real experiments that the time required for BOD measurement at 35°C can be shortened to 2.5 days, and the measurement result is similar to that of 5 days at 20°C. The BOD value obtained at elevated temperature had a good correlation with the result measured at 20°C on the fifth day. If the sample temperature exceeds 20°C when sampling, or if the sample temperature is below 20°C, the sample can be placed in a constant temperature incubator. Samples need to be processed prior to sample measurement.

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