Related Factors Affecting Ultraviolet Germicidal Effect

[Irradiation intensity and irradiation time] The lower the irradiation intensity of the ultraviolet lamp, the worse the bactericidal effect. When the intensity is lower than 70Lw.cm2, even if it is irradiated for 60 minutes, the killing rate of bacterial spores cannot meet the qualified requirements. The irradiation dose of ultraviolet light increases with the increase of irradiation intensity. When the irradiation dose is equal, the sterilizing effect of different irradiation intensities is similar 1-3. Therefore, the disinfection technical specification stipulates that the irradiation intensity of ultraviolet disinfection lamps should not be lower than 70Lw. cm2, when the disinfectant is unknown or to kill a variety of viruses and bacteria, the irradiation dose should not be lower than 100Lw.s.cm2. The irradiation intensity of the ultraviolet lamp is affected by voltage, temperature, irradiation distance, irradiation angle, etc. At the same time, attention should be paid to the cleanliness and service life of the lamp.

Experiments have shown that the intensity of the ultraviolet lamp decreases by 15-20Lw.cm2 when the voltage drops by 10V, and the ultraviolet lamp cannot work when the voltage is below 190V. Under the condition of a voltage of 220V and a room temperature of 0-40°C, the intensity of ultraviolet radiation increases with the increase of room temperature. For example, when the lamp temperature drops from 27°C to 4°C, the output will drop by 60%-80%. When the voltage is 190-240V and the room temperature is 16-35°C, the ultraviolet irradiation intensity has a linear relationship with the voltage and room temperature Y=-325.12+2.014X1+0.72X24,5.

The relationship between the intensity of ultraviolet radiation and distance is E=97.72, and the effective distance of ultraviolet radiation is 0.7-2.4m. Outside the vertical line at both ends of the ultraviolet lamp, the ultraviolet intensity attenuates significantly with the increase of the angle, and is 0 near the center line outside the ultraviolet. Therefore, during ultraviolet disinfection, multiple lamps are used at right angles to offset dark areas6,7.

[Types of microorganisms] Various microorganisms have different tolerances to ultraviolet rays. Fungal spores are the most resistant to ultraviolet rays, followed by bacterial spores, and the worst are reproductive-type microorganisms. Generally, bacterial spores are 2-7 times more resistant than their propagules.

There are also differences in the resistance to ultraviolet rays between different strains of the same species, different cultures of the same bacteria and different generations. [The number of microorganisms, the influence of suspended carriers and organic matter] Experiments have shown that the more bacteria that are contaminated, the greater the dose of ultraviolet radiation required. Bacteria attached to dust and suspended in the air are more resistant than bacteria liquid aerosols, because the penetration of ultraviolet rays is poor, air dust can absorb ultraviolet rays and reduce the sterilization rate, when the air contains 800-900 dust particles. cm3, the bactericidal efficiency can be reduced by 20%-30%; the presence of peptone, eggs, milk, blood, serum, etc. can increase the resistance of microorganisms to ultraviolet rays, because adding organic solvents to DNA or methylthymine solutions can make For base stacking, Wacker et al. studied the effect of different organic solvents on the formation of thymine dimers, and found that the greater the non-polarity, the smaller the dimerization.

[Affecting temperature] Most microorganisms (except Micrococcus) are very sensitive to ultraviolet radiation at low temperatures, because under this condition, the number of thymine dimers is significantly reduced, and the accumulation of thymine photoproducts will affect the growth of microorganisms. Repair, and temperature changes also affect the intensity of UV rays. If the temperature is too high or too low, it will affect the disinfection effect. Generally, the appropriate temperature is 20-40°C7, and some people think that the appropriate temperature is 10-25°C. 【Moderate effect】 There is no consensus on the effect of humidity on ultraviolet sterilization.

Ri2leyr believes that when the relative humidity is above 60%-70%, the killing rate of microorganisms will drop sharply, the most suitable is 40%-60%, and more than 80% may even have an anti-activation effect. When the relative humidity increases from 33% to 56%, the bactericidal efficiency can be reduced to the original 1.3. Others think that the impact of humidity on the sterilization rate may be manifested in three aspects: ① Due to the high relative humidity, the particles in the air increase and are easy to capture during sampling, which makes the sterilization effect appear to decline.

②The increase of particles weakens the penetration of radiation into cells, thus reducing the killing effect. ③When the relative humidity is 60%-70%, the water content of bacteria in the air is 30g.100g bacteria, which is called the critical water content. Ultraviolet radiation energy transfer can destroy the conjugation relationship of bacterial macromolecules. This effect is likely to occur in bacteria with critical water content and dehydration. Therefore, the sterilization efficiency of ultraviolet rays is generally low under high humidity conditions.

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