Ultraviolet disinfection principle
Ultraviolet sterilization is the use of appropriate wavelengths of ultraviolet light can destroy the molecular structure of DNA(deoxyribonucleic acid) or RNA(ribonucleic acid) in microbial body cells, resulting in growth cell death and/or regenerative cell death, to achieve the effect of sterilization. Ultraviolet disinfection technology is based on modern epidemiology, medicine and photodynamics, using specially designed high-efficiency, high-intensity and long-life UVC band ultraviolet light to irradiate water, and directly kill various bacteria, viruses, parasites, algae and other pathogens in the water.
High-quality UV lamps are the key to maximum disinfection
At present, only artificial mercury (alloy) light sources can output sufficient UVC strength for engineering disinfection. UV germicidal lamp tube is made of quartz glass, mercury lamp according to the difference of mercury vapor pressure in the lamp tube and the difference of ultraviolet output intensity is divided into three kinds: low pressure low intensity mercury lamp, medium pressure high intensity mercury lamp and low pressure high intensity mercury lamp.
The bactericidal effect of ultraviolet lamp
The bactericidal effect is determined by the radiation dose received by the microorganism, at the same time, it is also subject to the output energy of the ultraviolet light, related to the type of lamp, light intensity and use time, with the aging of the lamp, it will lose 30%-50% of the intensity. Uv exposure dose refers to the amount of UV of a specific wavelength required to achieve a certain bacterial inactivation rate: Irradiation dose (J/m2) = irradiation time (s) ×UVC intensity (W/m2) The higher the irradiation dose, the higher the disinfection efficiency, due to the size requirements of the equipment, the general irradiation time is only a few seconds, therefore, the UVC output intensity of the lamp becomes a measure of ultraviolet light "g(' disinfection equipment ');" > The most important parameters of disinfection equipment performance. In the disinfection of municipal sewage, the average radiation dose is generally above 300 J/m2. Below this value, there may be a phenomenon of photoreactivation, that is, the bacteria can not be completely killed, and when they flow out of the channel to receive visible light irradiation, they are revived, reducing the bactericidal effect. The higher the bactericidal efficiency, the larger the dose required. The main factor affecting the microbe to receive sufficient UV radiation dose is the transmittance (at 254 nm). When the UVC output intensity and irradiation time are fixed, the change of transmittance will cause the actual dose of microbe to change.
Advantages of ultraviolet water disinfection
Most UV devices use traditional low-voltage UV lamp technology, there are also some large water plants using low-voltage high-intensity UV lamp system and medium-pressure high-intensity UV lamp system, due to the production of high-intensity UV may reduce the number of lamps by more than 90%, thus reducing the footprint, saving installation and maintenance costs. And the ultraviolet disinfection method is also suitable for water with poor water quality.
It has a broad spectrum effect on pathogenic microorganisms and high disinfection efficiency;
It has a specific disinfection effect on cryptosporidium oocysts;
Does not produce toxic and harmful by-products;
Do not increase AOC, BDOC and other by-products that damage the biological stability of pipe network water quality;
Can reduce odor, taste and degrade trace organic pollutants;
Small footprint, disinfection effect is affected by water temperature, PH;
The insufficiency of ultraviolet water disinfection
01/No continuous disinfection effect, need to be used with chlorine;
02/Quartz tube wall is easy to scale, reduce the disinfection effect;
03/The disinfection effect is greatly affected by SS and turbidity in water;
04/The killed bacteria may be resurrected;
05/Less experience in domestic use.
Application of ultraviolet disinfection in drinking water
The application of ultraviolet disinfection technology in drinking water treatment has been favored since the outbreak of cryptosporidiosis in Milwaukee, USA in 1993, because chlorine disinfection can not effectively kill cryptosporidium oocysts, and studies have found that ultraviolet light has a good killing effect on cryptosporidium oocysts. Moreover, ultraviolet disinfection does not produce harmful by-products within the conventional disinfection dose range, so the application cases in Western developed countries have grown very rapidly in recent years, especially in small water plants. The International Ultraviolet Association was established in 1999.
The United States has historically been slow and conservative in the application of new technologies in the drinking water treatment process, but the application of ultraviolet technology has adopted unexpectedly fast action. The EPA approved the use of UV disinfection in drinking water just five years after it was laboratory proven effective in inactivating cryptosporidium. Large water plants such as Seattle Water plant will be built this year ultraviolet disinfection system, New York water Company 7.8 million m3/d of drinking water has decided to use ultraviolet disinfection, is currently preparing for construction
