How to improve the accuracy of the determination of dissolved oxygen (iodine) in industrial wastewater Xu Yanhong (Biochemical Plant of Harbin Gasification Plant, Harbin 154854, China) Molecular oxygen dissolved in water is called dissolved. oxygen. When the dissolved oxygen in the water is too low, anaerobic bacteria multiply, and the water quality deteriorates. Therefore, prior to the discharge of industrial wastewater, dissolved oxygen is one of the most important test items, and the reliability of the measurement results, ie accuracy, is more important.
Potassium solution: 500:150); Sulfuric acid P = 1.84); Sodium thiosulfate standard solution 0.1 mol/l); 1% m/V) starch solution.
1.3 Determination of poly. Dissolved oxygen fixation; precipitation of iodine; titration; calculation of results.
2 Influencing factors and improvement measures 2.1 Selection of methods. Industrial wastewater often contains oxidizing and reducing substances, algae, suspended solids, etc., and is colored. In this case, the corresponding modified iodine method should be used. When the nitrite content in the water sample is higher than 0.05 mg/l and the divalent iron is lower than 1 mg/l, the sodium azide is used for correction; when the water sample is colored or there is suspended matter, the alum is used for flocculation correction; the water sample contains activity When the sludge was suspended, copper sulfate-sulfamate flocculation was used. Modified dissolved iodometric method is more accurate.
2.2 collection and preservation of water samples. The dissolved oxygen in the water is determined by the iodometric method. The water sample must be collected in a dissolved oxygen bottle, and care must be taken not to aerate the water sample or to retain bubbles. Immediately after the collection, fixatives were added to the samples and stored in cool dark places. At this point the measured dissolved oxygen will be closer to its true content, which is more instructive for wastewater treatment.
2.3 reagent preparation and preservation. The reagents used should be selected from analytical grade or pure grade preparations. The water used should be grade 3 water and be noted for storage. For example, the basic potassium iodide solution should be stored in the dark; the sodium thiosulfate standard solution should be stored in a brown bottle and calibrated before use; the starch solution should be added with appropriate amount of salicylic acid or zinc chloride for preservation. At this point, the error caused by the reagent can be ignored, which greatly improves the accuracy of the determination of dissolved oxygen.
2.4 operation process. In the process of fixing dissolved oxygen and iodine precipitation, the straw must be inserted under the liquid surface to avoid changing the dissolved oxygen in the sample; when titrating, the starch solution should be added dropwise at the end of the titration, and the titration should be continued until the end point. This can reduce the error caused by the operation process and effectively improve the accuracy of the measurement.
2.5 Other factors. If the water sample is strongly acidic or alkaline, use sodium hydroxide or sulfuric acid solution to adjust to neutrality; then if the water temperature and pressure are abnormal, record and record the water temperature and pressure.
The above method was used to analyze the dissolved oxygen content in industrial wastewater and the results were very accurate.
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