What Is UV Disinfection?

Ultraviolet sterilization is to destroy the molecular structure of DNA (DNA) or RNA (ribonucleic acid) in the cells of microorganisms by using the appropriate wavelength of ultraviolet rays to achieve growth and / or regenerative cell death. effect. Ultraviolet disinfection technology is based on modern anti-epidemiology, medicine and photodynamics. It uses specially designed high-efficiency, high-intensity and long-life UVC band ultraviolet light to irradiate flowing water, and it will bring various bacteria, viruses, parasites, algae, and Other pathogens are killed directly. ^[1]

Studies have shown that ultraviolet rays mainly kill microorganisms through radiation damage to microorganisms (pathogens such as bacteria, viruses, spores, etc.) and damage to nucleic acids, thereby achieving the purpose of disinfection. The effect of ultraviolet light on nucleic acids can cause bond and chain breaks, interstrand cross-linking, and formation of photochemical products, etc., which changes the biological activity of DNA and prevents microorganisms from replicating themselves. This ultraviolet damage is also fatal. ^[2]

Ultraviolet disinfection is a physical method. It does not add any substance to the water and has no side effects. This is where it is superior to chlorinated disinfection. It is usually used in combination with other substances. Common joint processes include UV + H2O2 and UV + H2O2. + O3, UV + TiO2, so the disinfection effect will be better.

The economics of the UV system is determined by the following factors: equipment cost and life; electrical efficiency; reduction in sterilization effect during operation; electricity costs, etc. The economic analysis of the UV disinfection system has not yet been concluded. There are many analysis reports with different conclusions. Some people believe that the UV disinfection device has large power consumption, high equipment maintenance costs and high manufacturing costs. For large systems, the equipment investment is higher than that of ozone systems, and the operating costs are similar to ozone; but for small systems made of pure water, the investment is lower than that of ozone devices. There are also opinions that for treatment scales of thousands of tons per day or more, the investment and operating costs of UV disinfection systems are very advantageous, and are much lower than the cost of chlorine and ozone disinfection. For example, some analytical data report that when constructing a small drinking water treatment plant with a population of 10 to 25,000, the approximate ratio of ultraviolet, chlorine dioxide, and ozone disinfection costs is 1: 4: (8 to 9). For populations greater than For 50,000 social groups, the cost ratio is approximately 1: 2.5: 2.5.

These cost estimates do not include the cost of removing disinfection byproducts and cryptosporidium cysts that may be additional when using non-UV disinfection processes. In addition, analysis data show that the investment and operating cost of ultraviolet disinfection are lower than that of chlorine disinfection, and the cost of disinfection is about half that of chlorine, but the difference narrows with the expansion of water treatment scale.

In France and the former Soviet Union, ultraviolet disinfection was limited to small equipment. The large equipment established was to install ultraviolet lamps in series in the main pipe of filtered water. UV disinfection is also limited to small equipment and swimming pools in the United States, and is often combined with other disinfectants. However, in practice, it has been reported that the scale of drinking water plants using ultraviolet disinfection has exceeded 1.5 million tons per day.

At present, the ultraviolet disinfection in China is generally used for a small amount of water treatment, and it is widely used in pure water preparation systems. ^[4]

UV germicidal lamp

UV disinfection scope

For disinfection of indoor air, surface of objects and water and other liquids.

UV disinfection lamp

2.3.2.1 The ultraviolet rays used for disinfection are C-wave ultraviolet rays, whose wavelength range is 200-275nm, and the strongest sterilization band is 250-270nm. The ultraviolet light source used for disinfection must be able to produce sterilizing ultraviolet lamps with irradiation values that meet national standards.

2.3.2.2 For the preparation of ultraviolet disinfection lamps, graded quartz glass tubes shall be used in order to obtain a satisfactory intensity of ultraviolet radiation.

2.3.2.3 Ultraviolet disinfection lamps can be equipped with reflectors made of materials with a high reflectivity to ultraviolet rays (such as polished aluminum plates).

2.3.2.4 The UV intensity required for disinfection at a voltage of 220V, an ambient relative humidity of 60%, and a temperature of 20 ° C must not be less than 70uW / cm ^{2 at a} radiation intensity of 253.7nm. (Measured at 1 meter of the lamp tube, and measured by the special UV lamp at the use distance. The UV intensity meter used must be calibrated.)

2.3.2.5 During the use of the ultraviolet lamp, its irradiation intensity gradually decreases. Therefore, the intensity of the sterilizing ultraviolet rays should be measured frequently. Once it has fallen below the required intensity, it should be replaced in time.

2.3.2.6 The service life of the UV disinfection lamp, that is, the time when the intensity of the new lamp is reduced to 70 Uw / cm ² (power 30w), or the time when the intensity of the original new lamp is reduced to 70% (power <30w =, Should not be less than 1000h.

2.3.2.7 The ultraviolet disinfection lamps currently used in China are as follows

(1) Ordinary straight tube hot cathode low pressure mercury ultraviolet disinfection lamp: The lamp tube is made of quartz glass or other glass with high ultraviolet transmittance, and the power is 40W, 30W, 20W, 15w, etc. It is required that the new factory lamp emit 253.7nrn UV intensity (measured at a distance of 1 meter without a reflector): power> 30W lamp, 90Uw / cm; power> 20w lamp, 60Uw / cm2; power 150 lamp, 20Uw / cm2.

Because this lamp radiates 253.7nrn UV, it also radiates a part of 184.9nm UV. It can produce ozone.

(2) High-intensity ultraviolet disinfection lamp: The intensity required to radiate 253.7nm ultraviolet rays (measured at a distance of 1 meter) is:

Power 30w lamp,> 180uW / CM ² ; 11w lamp,> 30 uW / CM ² .

(3) Low ozone ultraviolet disinfection lamp: It is also a hot cathode low pressure mercury lamp, which can be a straight tube type or an H type. Due to the use of special processes and lamp tube materials, the ozone production is very low, and the ozone production is required to be <1mg / h.

(4) High ozone ultraviolet disinfection lamp: Due to the special technology adopted, this lamp produces a large proportion of ultraviolet rays with a wavelength of 184.9nrn, so the ozone production is large.

UV Sterilizer

(1) Ultraviolet air sterilizer: It is made of low ozone ultraviolet germicidal lamp, which can be used for indoor air disinfection under human condition.

(2) Ultraviolet surface sterilizer: It is manufactured with low ozone high intensity ultraviolet germicidal lamp, so that it can achieve satisfactory disinfection effect in an instant.

(3) Ultraviolet disinfection box: It is manufactured with high ozone and high intensity ultraviolet germicidal lamp. On the one hand, it uses the synergistic sterilization effect of ultraviolet and ozone, and on the other hand, it uses ozone to disinfect parts that are not exposed to ultraviolet rays.

UV disinfection range and conditions

2.3.4.1 Ultraviolet rays can kill a variety of microorganisms, including bacterial propagules, spores, mycobacteria, viruses, fungi, rickettsiae, and mycoplasma. All surfaces contaminated by the above-mentioned microorganisms can be disinfected with ultraviolet rays.

2.3.4.2 Ultraviolet radiation has low energy and weak penetrating power, and can only kill the directly exposed microorganisms. Therefore, the disinfection site must be fully exposed to ultraviolet rays during disinfection.

2.3.4.3 When disinfecting rough surfaces such as paper and fabric with ultraviolet rays, the irradiation time should be appropriately extended, and both sides should be exposed.

2.3.4.4 The most suitable temperature range for UV disinfection is 20-40 . Too high or too low temperature will affect the disinfection effect. The disinfection time can be appropriately extended. When used for air disinfection, the relative humidity of the disinfection environment is less than 80%. Otherwise, the irradiation time should be appropriately extended.

2.3.4.5 When using ultraviolet rays to kill microorganisms protected by organic matter, the irradiation dose should be increased. Suspended particles in air and water can also affect disinfection.

How to use UV disinfection

2.3.5.1 Disinfecting the surface of articles

(1) Irradiation method: It is best to use a portable ultraviolet sterilizer to move the radiation at a short distance, and it can also adopt an ultraviolet lamp pendant irradiation. Small items can be irradiated in a UV disinfection box.

(2) Irradiation dose and time: Different types of microorganisms have different sensitivities to ultraviolet rays. When sterilizing with ultraviolet rays, the irradiation dose must be used to achieve the irradiation dose required to kill the target microorganisms.

When killing general bacterial propagules, the irradiation dose should reach 10000 uW.s / CM ² ; when killing bacterial spores, it should reach 100,000 uW.s / CM ² ; the resistance of the virus to ultraviolet rays is between that of bacterial propagules and spores. The resistance of fungal brambles is stronger than that of bacterial spores, and sometimes it needs to be irradiated to 600,000 uW.s / CM ² ; when the target microorganism to be disinfected is unknown, the exposure dose should not be less than 100,000 uW.s / CM ² .

The irradiation dose is the product of the irradiation intensity and irradiation time of the ultraviolet lamp used at the surface of the irradiated article. Therefore, according to the irradiation intensity of the ultraviolet light source, the time required for irradiation can be calculated. For example, use an ultraviolet surface sterilizer with an irradiation intensity of 70 uW / CM ² to irradiate the surface of an object at a short distance; the selected irradiation dose is 100,000 uW.s / CM ² ; the time required for irradiation is:

100000 uW.s / CM ² ÷ 70 uW / CM ² = 24 minutes.

2.3.5.2 Disinfection of indoor air

(1) Indirect irradiation method: High-intensity ultraviolet air sterilizer is preferred, which not only has a reliable disinfection effect, but also can be used when there is activity in the room. Generally, disinfection can be achieved within 30 minutes after startup.

(2) Direct irradiation method: In the unmanned condition of the room, it can be directly irradiated by hanging or moving ultraviolet light.

When using indoor suspended UV disinfection, the number of indoor UV disinfection lamps (30W UV lamps, intensity> 70 uW / cm ² at 1.0 meters) is not less than 1.5W per cubic meter, and the irradiation time is not less than 30min. .

2.3.5.3 For disinfection of water and other liquids, internal or external irradiation can be used. When the internal irradiation method is used, the UV light source should be equipped with a quartz glass protective cover. No matter which method is adopted, the thickness of the water layer should be less than 2cm, determine the water flow speed according to the intensity of the ultraviolet light source. After disinfection, the water must meet national standards.

UV disinfection precautions

(1) During use, the surface of the ultraviolet lamp should be kept clean. Generally, it should be wiped with an alcohol cotton ball every two weeks. When dust and oil are found on the surface of the lamp, it should be wiped at any time.

(2) When sterilizing indoor air with an ultraviolet lamp. The room should be kept clean and dry to reduce dust and water mist. When the temperature is lower than 20 ° C or higher than 40 ° C and the relative humidity is greater than 60%, the irradiation time should be appropriately extended.

(3) When the surface of an article is disinfected with ultraviolet rays, the irradiation surface should be directly irradiated with ultraviolet rays, and a sufficient irradiation dose should be achieved.

(4) Don't expose the ultraviolet light source to people, so as not to cause damage.

(5) Calibrate the UV intensity meter at least once a year. ^[5]