Why disinfect water?
1. The method of learning
1.1. Heat method
When boiling water at 1000C most microorganisms are destroyed. There are a few when high temperatures rise to spore form with a strong protective layer. They are not destroyed even if boiled continuously for 15 to 20 minutes. To destroy this group of spore bacteria, boil water to 1200C or heat it in the following order: boil at normal conditions for 15 to 20 minutes, let the water cool to less than 350C and keep for two hours Let the spores grow back, then boil the water again.
The thermal method is simple but energy-intensive, so it is usually applied on a small scale.
1.2. Disinfection by ultraviolet rays
Ultraviolet (UV) rays are electromagnetic radiation with a wavelength of about 4 - 400 nm (nanometer). The wavelength of ultraviolet rays is outside the detection and recognition areas of the naked eye. Using ultraviolet light to disinfect does not alter the chemical and physical properties of water.
Ultraviolet rays work to alter the DNA of bacterial cells, ultraviolet rays of 254nm wavelengths with the highest bactericidal ability.
1.3. Ultrasound method
Ultrasonic flow with an effect of not less than 2W / cm2 in a period of more than 5 minutes is capable of destroying all microorganisms in the water.
1.4.Filtration
The vast majority of microorganisms in water (except for viruses) are 1 - 2 µm in size. If water is filtered through a filter with a gap of less than 1 µm, most bacteria can be eliminated. The filter is commonly used in china, ceramic plates with extremely small hollows. With this method, the filtered water must have a residue content less than 2mg / l.
Disinfection by physical methods, has the basic advantage is not to change the physical and chemical properties of water, does not cause side effects. However, due to low efficiency, it is usually only applied in small scale with the permitted economic and technical conditions.
2. Chemical methods
The basis of the chemical method is to use strong oxidants to oxidize the enzymes of microbial cells and destroy them. Common chemicals are: chlorine, bromine, iodine, chlorine dioxide, hypochlorite acid and its salts, ozone, potassium permanganate, hydrogen peroxide. Due to high performance, chemical sterilization is now widely applied in all sizes today.
2.1. Disinfect water with chlorine and its compounds
Chlorine is a strong oxidizing agent, in any form, pure or compound when applied to water, creates HOCl acid hypochlorite molecule with a very strong antiseptic effect.
Microbial killing occurs through two stages. First, the disinfectant diffuses through the microbial cell shell, then reacts with the enzyme inside the cell and destroys metabolism which leads to the destruction of the cell.
The speed of the disinfection process is determined by the kinetics of the disinfectant diffusion process through the cell envelope and the kinetics of the cell enzyme decomposition process.
The speed of the disinfection process increases as the concentration of the disinfectant and the water temperature increases, and depends on the non-dissociated form of the disinfectant, because the diffusion process through the cell envelope occurs faster than the process. dissociation.
The sterilization rate is greatly reduced when there are organic substances, suspended sediments and other reducing agents in the water.
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