The concept of residual chlorine
Residual chlorine is the amount of available chlorine remaining in the water after the water has been chlorinated and disinfected.
This part of chlorine is added during the water treatment process to kill bacteria, microorganisms, organic matter and inorganic matter in the water. Residual chlorine is an important indicator of the disinfection effect of water bodies. Residual chlorine can be divided into two categories, namely free residual chlorine and combined residual chlorine. Free residual chlorine mainly includes free chlorine in the form of Cl2, HOCl, OCl-, etc.; combined residual chlorine is chloramine substances generated after the reaction of free chlorine and ammonium substances, such as NH2Cl, NHCl2, NCl3, etc. Generally speaking, residual chlorine refers to free residual chlorine, while total residual chlorine is the sum of free residual chlorine and combined residual chlorine.
The amount of residual chlorine is usually measured in milligrams per liter. The amount of residual chlorine needs to be appropriate, neither too high nor too low. Too high a residual chlorine will cause the water to smell, while too low a residual chlorine may cause the water to lose its ability to maintain sterilization and reduce the hygienic safety of the water supply. Therefore, in tap water treatment, the level of residual chlorine is usually monitored and adjusted to ensure the safety and suitability of water quality.
The role of chlorine in urban sewage treatment disinfection
1. The role of chlorine disinfection
Chlorination is a commonly used disinfection method for urban sewage treatment. Its main functions are as follows:
1. Good disinfection effect
In sewage treatment, chlorine can kill most bacteria and viruses. Chlorine inactivates microorganisms by oxidizing their proteins and nucleic acids. In addition, chlorine can kill the eggs and cysts of some parasites.
2. Oxidizing effect on water quality
Adding chlorine can also oxidize organic matter in the water, causing the organic matter to be decomposed into inorganic acids, carbon dioxide and other substances. Chlorine reacts with organic matter in the water to produce oxidants such as hypochlorous acid and chlorine monoxide, which in turn decompose the organic matter.
3. Inhibit bacterial growth
Adding an appropriate amount of chlorine can inhibit the growth of some microorganisms, reduce the amount of sludge in the reaction tank, and reduce the difficulty and cost of subsequent treatment.
2. Advantages and Disadvantages of Chlorine Disinfection
1. Advantages
(1) Good disinfection effect: Appropriate dosage of chlorine can kill most bacteria and viruses.
(2) Simple dosing: The chlorine dosing equipment has a simple structure and is easy to maintain.
(3) Low cost: The cost of chlorine delivery equipment is low and easy to purchase.
2. Disadvantages
(1) Chlorine generates harmful substances such as hypochloronitrile: When chlorine reacts with nitrogen-containing organic matter, harmful substances such as hypochloronitrile are generated, which will cause environmental pollution.
(2) Chlorine residual problem: Some chlorine products are not volatile and will remain in water bodies, affecting subsequent water utilization or environmental problems.
3. Issues that need to be paid attention to when adding chlorine
1. Chlorine concentration
If the chlorine concentration is too low, the disinfection effect cannot be achieved and the sewage cannot be effectively disinfected; if the chlorine concentration is too high, the residual chlorine content in the water body will be high, causing harm to the human body.
2. Chlorine injection time
The chlorine injection time should be selected at the last process flow of the sewage treatment system to prevent the sewage from losing chlorine or producing other fermentation products in other processes, thereby affecting the disinfection effect.
3. Selection of chlorine products
Different chlorine products have different prices and performances on the market, and the selection of products should be based on specific circumstances.
In short, adding chlorine is one of the effective methods for urban sewage treatment and disinfection. In the sewage treatment process, rational use and injection of chlorine can effectively ensure water quality safety and improve sewage treatment efficiency. However, there are also some technical details and environmental protection issues that need to be paid attention to when adding chlorine.
Why chlorine is added in water treatment:
In the effluent stage of tap water and sewage treatment plants, the chlorine disinfection process is widely used to kill bacteria and viruses in the water. In the treatment of industrial circulating cooling water, the chlorine sterilization and algae removal process is also used, because during the cooling water circulation process, due to the evaporation of part of the water, the nutrients in the water are concentrated, bacteria and other microorganisms will multiply in large numbers, and it is easy to form slime Dirt, excess slime and dirt can cause pipe blockage and corrosion.
If the residual chlorine concentration in tap water is too high, the main hazards are:
1. It is highly irritating and harmful to the respiratory system.
2. It easily reacts with organic matter in water to produce carcinogens such as chloroform and chloroform.
3. As a production raw material, it may have adverse effects. For example, when it is used to produce rice wine products, it has a bactericidal effect on the yeast in the fermentation process and affects the quality of the wine. Because chlorine is generally used to purify tap water, and the residual chlorine will generate carcinogens such as chloroform during the heating process. Long-term drinking will cause great harm to the human body. Especially in recent years, water source pollution has become more and more serious, which directly leads to an increase in the residual chlorine content in tap water.
What are the measurement methods for residual chlorine?
1. DPD colorimetry
Principle: Under pH 6.2~6.5 conditions, ClO2 first reacts with DPD in step 1 to generate a red compound, but the amount appears only reaches one-fifth of its total available chlorine content (equivalent to reducing ClO2 to chlorite ions) one. If a water sample is acidified in the presence of iodide, chlorite and chlorate also react, and when neutralized by the addition of bicarbonate, the resulting color corresponds to the total available chlorine content of ClO2 . The interference of free chlorine can be controlled by adding glycine. The basis is that glycine can immediately convert free chlorine into chlorinated aminoacetic acid, but has no effect on ClO2.
2. Coated electrode method
Principle: The electrode is immersed in the electrolyte chamber, and the electrolyte chamber is in contact with water through a porous hydrophilic membrane. Hypochlorous acid diffuses into the electrolyte cavity through the porous hydrophilic membrane, forming a current on the electrode surface. The size of the current depends on the speed at which hypochlorous acid diffuses into the electrolyte cavity. The diffusion rate is proportional to the concentration of residual chlorine in the solution. Measure the current size. The concentration of residual chlorine in the solution can be determined.
3. Constant voltage electrode method (membraneless electrode method)
Principle: A stable potential is maintained between the measurement and reference electrodes, and different measured components will produce different current intensities at this potential. It consists of two platinum electrodes and a reference electrode to form a microcurrent measurement system. At the measuring electrode, chlorine molecules or hypochlorite are consumed, and the intensity of the current generated is related to the concentration of residual chlorine in the water.
Lianhua ‘s portable residual chlorine measuring instrument LH-P3CLO uses the DPD detection method, which is simple to operate and can produce results quickly. You only need to add 2 reagents and the sample to be tested, and you can get color comparison results. The measurement range is wide, the requirements are simple, and the results are accurate.
Post time: Apr-30-2024
