In the environment we live in, water quality safety is a vital link. However, the quality of water is not always obvious, and it hides many secrets that we cannot see directly with our naked eyes. Chemical oxygen demand (COD), as a key parameter in water quality analysis, is like an invisible ruler that can help us quantify and evaluate the content of organic pollutants in water, thereby revealing the true condition of water quality.
Imagine if the sewer in your kitchen is blocked, will there be an unpleasant smell? That smell is actually produced by the fermentation of organic matter in an oxygen-deficient environment. COD is used to measure how much oxygen is needed when these organic matter (and some other oxidizable substances, such as nitrite, ferrous salt, sulfide, etc.) are oxidized in water. Simply put, the higher the COD value, the more serious the water body is polluted by organic matter.
The detection of COD has very important practical significance. It is one of the important indicators for measuring the degree of water pollution. If the COD value is too high, it means that the dissolved oxygen in the water will be consumed in large quantities. In this way, aquatic organisms that need oxygen to survive (such as fish and shrimp) will face a survival crisis, and may even lead to the phenomenon of “dead water”, causing the entire ecosystem to collapse. Therefore, regular testing of COD is like doing a physical examination of water quality, discovering and solving problems in a timely manner.
How to detect the COD value of water samples? This requires the use of some professional “weapons”.
The most commonly used method is the potassium dichromate method. It sounds complicated, but the principle is actually very simple:
Preparation stage: First, we need to take a certain amount of water sample, then add potassium dichromate, a “super oxidant”, and add some silver sulfate as a catalyst to make the reaction more thorough. If there are chloride ions in the water, they have to be shielded with mercuric sulfate.
Heating reflux: Next, heat these mixtures together and let them react in boiling sulfuric acid. This process is like giving the water sample a “sauna”, revealing the pollutants.
Titration analysis: After the reaction is over, we will use ammonium ferrous sulfate, a “reducing agent”, to titrate the remaining potassium dichromate. By calculating how much reducing agent is consumed, we can know how much oxygen was used to oxidize the pollutants in the water.
In addition to the potassium dichromate method, there are other methods such as the potassium permanganate method. They have their own advantages, but the purpose is the same, which is to accurately measure the COD value.
At present, the rapid digestion spectrophotometry method is mainly used to detect COD in the domestic market. This is a rapid COD detection method based on the potassium dichromate method, and implements the policy standard “HJ/T 399-2007 Water Quality Determination of Chemical Oxygen Demand Rapid Digestion Spectrophotometry”. Since 1982, Mr. Ji Guoliang, the founder of Lianhua Technology, has developed the COD rapid digestion spectrophotometry and related instruments. After more than 20 years of promotion and popularization, it finally became a national environmental standard in 2007, bringing COD detection into the era of rapid detection.
The COD rapid digestion spectrophotometry developed by Lianhua Technology can obtain accurate COD results within 20 minutes.
1. Take 2.5 ml of sample, add reagent D and reagent E, and shake well.
2. Heat the COD digester to 165 degrees, then put the sample in and digest for 10 minutes.
3. After the time is up, take out the sample and cool it for 2 minutes.
4. Add 2.5 ml of distilled water, shake well and cool it in water for 2 minutes.
5. Put the sample into the COD photometer for colorimetry. No calculation is required. The results are automatically displayed and printed out. It is convenient and fast.
Post time: Jul-25-2024
