What is the significance of residual chlorine test in water

1. Sensory properties and general chemical indicators Chromaticity The chromaticity of water is an indicator for the quantitative determination of the color of natural water or various waters after treatment. Natural water often shows different colors. When the water body is polluted by industrial wastewater, it will also show different colors. Chromaticity is an important index to evaluate the sensory quality. The drinking water quality standard stipulates that the chromaticity should not be greater than 15 degrees. Turbidity Due to the suspended and colloidal particles in the water, the originally colorless, odorless and transparent water is turbid, and the degree of turbidity is called turbidity. Turbidity is an index that reflects the physical properties of natural water and drinking water. It is used to indicate the degree of clarity or turbidity of water, and is an important indicator to measure the goodness of water quality. Smell and Taste Polluted water often has an abnormal smell, which is called stink when smelled with the nose, and taste is what is tasted by the mouth. The sources of smell and taste in water may include: the reproduction and decline of aquatic plants or microorganisms; the decay and decomposition of organic matter, etc. Exceeding the standard of smell and taste will give people a feeling of disgust. According to the smell and taste of water, it can be inferred that there are impurities and harmful components in the water. The standard is that there is no peculiar smell or peculiar smell. PH value The closer the pH of the water is to the pH of the blood, that is, 7.35-7.45 is the best. But in human evolution, from drinking natural water, well water to tap water for nearly a hundred years, the pH is between 6.5-8.5. Therefore, as long as it is within this range, the human body has strong pH buffering and adjustment capabilities, and the standard pH is 6.5-8.5. Iron Iron is an essential element for the human body. When the iron content in water is less than 0.3 mg per liter, it is difficult to detect its taste. Iron can promote the growth of iron bacteria in the pipe network and form a viscous film on the inner wall of the pipe network. The standard limit is 0.3 mg per liter. Oxygen consumption Oxygen consumption refers to the total amount of oxidizable substances in the water sample under the specified oxidant and oxidation conditions, and it is expressed by the consumed oxygen. Oxygen consumption is an index reflecting the overall level of organic pollution in drinking water. The standard limit is 3 mg per liter. 2. Toxicological indicators Fluoride Fluoride exists widely in nature, and fluorine can enter the human body through water, food, air and other channels. An appropriate amount of fluorine is considered to be a beneficial element to the human body and is beneficial to the prevention of dental caries. Survey data show that excessive intake is harmful to the human body and can cause acute and chronic poisoning. The standard limit is 1 mg per liter. Cyanide Cyanide mainly comes from industrial wastewater and is highly toxic. Acts on certain respiratory enzymes, causing suffocation in tissues. Considering the strong toxicity of cyanide, a large safety factor is adopted, and the standard stipulates that the content of cyanide in drinking water shall not exceed 0.05 mg per liter. Mercury Mercury is mercury, a silvery-white luminous liquid. Inorganic mercury in surface water can be transformed into organic mercury under certain conditions, and can be enriched in aquatic organisms (such as fish, shellfish, etc.). After people eat these fish and shellfish, they will cause chronic poisoning. Based on the toxicity of mercury, the standard stipulates that the mercury content in drinking water shall not exceed 0.001 mg per liter. Nitrates Elevated levels of nitrite and ammonia in surface water indicate that sewage pollution has occurred. High concentrations of nitrates, especially nitrites in drinking water, can lead to methemoglobinemia. Infants, children, and pregnant women are susceptible to methemoglobinemia. The standard limit is 10 mg per liter. 3. Microbiological indicators Total number of bacterial colonies The total number of bacterial colonies refers to the total number of saprophytic bacterial colonies grown in 1 ml of water samples in nutrient agar medium after being incubated at 37°C for 48 hours. The total number of bacterial colonies in water can be used as an indicator for evaluating the cleanliness of water quality and evaluating the purification effect. Total coliforms Total coliforms mainly come from human and warm-blooded animal feces, and may also come from plants and soil. The total coliform group is one of the important microbial indicators for evaluating the sanitary quality of drinking water. 4. Indicators related to disinfection Free residual chlorine: refers to the free residual chlorine left in the drinking water after 30 minutes of contact time after chlorination disinfection. It has continuous sterilization ability, which can prevent pollution in pipelines and ensure the quality of water supply. Moreover, it also has a certain inactivation effect on enteroviruses such as infectious hepatitis and polio, and the water at the end of the pipe network should not be lower than 0.05 mg per liter. 5. Radiation indicators Radiation: Radiation rays can cause damage to human and biological tissues by ionization, causing radiation sickness. Radioactive pollution comes from waste water, waste gas, waste residue, fallout from nuclear weapons tests, and the production and application of radioactive isotopes in the nuclear industry and other industries.