In the sterilization method of food industry water, the traditional method is to use chlorine-containing bactericide and heat sterilization. In addition, processes such as ozone treatment, ultraviolet radiation, and membrane (UF/MF) treatment are also used. These methods have their own advantages and disadvantages. After studying their nature, scope of application and precautions, they can be used flexibly according to the specific situation.
Ozone sterilization
1. Ozone disinfection mechanism and disinfection characteristics.
The decomposition of ozone gas produces new ecological oxygen and oxygen. New ecological oxygen can act on cell walls and cell membranes, such as bacteria and viruses, and react with the double bonds of lipids (lipid compounds). In this process, the cell membrane will be destroyed, and the enzyme will also be destroyed, resulting in a bactericidal effect.
The ozone fungicide with a concentration of 0.3~0.5mg/L is used to sterilize the spores of Bacillus. Lactic acid bacteria have weak resistance to ozone. Reports show that most of the bacteria in the initial 2.3~5.6×109/mL, within 30 seconds of ozone treatment, died.
The bactericidal effect of ozone varies greatly depending on the cell wall or cell membrane, and the type of microorganisms.
It takes a long time to treat the spores and yeast of Bacillus with ozone, but if the ozone concentration is increased, the reaction time can be shortened appropriately. In fact, the ozone concentration and contact reaction time can be determined according to the bacterial species, and can also be selected appropriately.
Carry out ozone sterilization according to drinking water standards, the contact reaction time can reach 5~8 minutes, the ozone concentration at the outlet of the ozone generator is above 0.4mg/L (injection rate 2~3mg/L), in most cases the above Conditions are used as operational management indicators. In the same system, the ozone injection rate should be increased to 5mg/L, and in the water treated in this way, bacteria usually cannot survive.
2. The ozone sterilization method in water is not only a sterilization equipment, but a sterilization system.
In order to build this system, the following points should be noted.
(a) Choose an ozone source that can produce stable ozone and make it full of vitality. In recent years, the research progress and technical level of ozone biological activity have been significantly improved. There are ozone generators on the market, and various models are available, such as silent discharge type, homopolar plate type, ceramic surface discharge type and so on. From small machines of 15g/h to large machines of 40kg/h, PSA oxygenator can be used to assemble a series.
(b) Refining of ozone raw materials: In addition to small ozone equipment used to produce ozone or cold storage, industrial-scale ozone biomass must also be air-purified and used as ozone raw materials to achieve dust removal and dehumidification. Generally speaking, the ozone concentration generated by the use of electrostatic discharge ozone is 1 to 3% when air is used as the raw material, and 2 to 6% when oxygen is used as the raw material. If the purification process is not perfect, it is not only the production of ozone. The efficiency is low, and the unpurified parts of the raw materials enter the ozone treatment water system and become nitrogen oxides.
The ozone sterilization method is used in the food production water, and the ozone raw material should be pure oxygen or PSA oxygen generator.
(c) Contact reaction time between water and ozone: The amount of ozone injected and the contact reaction time are determined by the type of microorganisms to be sterilized and the target sterilization rate. These factors include construction costs.
(d) Ozone concentration management: In order to make ozone sterilization work reliably, the ozone injection concentration and ozone solubility must be monitored and controlled within an appropriate range. In addition to the high-precision continuous ozone concentration meter, an inexpensive handheld ozone concentration meter has also been developed. Therefore, it is necessary to regularly monitor the ozone concentration and remedy it. In the disinfection process, the ozone in the water will inevitably be discharged out of the system, so it must be treated with harm to make the ozone emission lower than the allowable concentration.
2. Ultraviolet radiation disinfection method.
UV sterilization mechanism and characteristics of sterilization technology.
Ultraviolet rays with a wavelength of 200~290mm can be irradiated through the cell membrane of bacteria or viruses, causing damage to the control gene phenomenon and biological function nucleic acid (DNA), causing it to lose the ability to reproduce, thereby achieving sterilization.
Nucleic acid (DNA) is especially easy to absorb under the ultraviolet radiation of 250~260mm wavelength. Therefore, ultraviolet rays of this wavelength have a strong bactericidal effect. Sterilization is carried out based on the amount of ultraviolet radiation required to kill the microorganisms, without any change in water quality, and instantaneous sterilization in a very short time, with good effects. In addition, the treatment process is completed on a straight tube circulation machine.
As for ultraviolet disinfection, the ratio of the disinfection capacity to the ultraviolet radiation in the treated water is mw·s/cm^2 (ultraviolet disinfection intensity [mw/cm^2×time]). The amount of ultraviolet radiation is related to the sterilization rate.
The sensitivity of various microorganisms to ultraviolet rays varies from species to species. According to the factory test results of Bacillus (including B.subtlis), under the irradiation of D10=12.5mw·s/cm^2, the bactericidal effect can reach 99.5%. Therefore, the design lighting power of the actual device is equal to D10×4, that is, 50mw·s/cm^2.
Use occasions and precautions for ultraviolet sterilization
1. Selection of ultraviolet disinfection equipment: When choosing ultraviolet disinfection equipment, the amount of ozone generated should be used as the standard, and when choosing ultraviolet disinfection equipment, the amount of water treated should be used as the standard. The lighting intensity of disinfection lamps decays with the extension of use time. Therefore, the selection of the required amount of ultraviolet radiation should be based on the service life of the lamps.
2. The characteristics of the water to be treated: using ultraviolet sterilization method, according to the amount of ultraviolet radiation required by the bacteria in the water to be treated, it can play its role initially. Therefore, it is a difficult problem to treat the transmittance in water with ultraviolet light. Especially for water or sugar liquid containing a mixture, when selecting the required amount of ultraviolet radiation, the ultraviolet attenuation factor of the water (solution) to be treated should be considered.
3. Temperature characteristics: Generally, low-pressure mercury lamps are used. Under the ambient temperature of 40~50℃, the ultraviolet lamp has the highest exposure rate. When the water temperature is low, the sterilization effect is poor, which should be considered.
