For its strong oxidizing ability, ozone is applied in many fields such as object surface sterilization, environmental air purification and water treatment, etc. Among them, ozone air purification can be divided into air sterilization, odor removal and the treatment for certain air pollutants. Today, in this blog, we will mainly look at what ozone can do in air sterilization, odor removal and the treatment for nitrogen oxides.
Air sterilization is an important aspect of ozone air purification. Ozone’s role in air sterilization is enormous. In the food processing industry, the presence of microorganisms in the air can cause premature ripening of fruits and vegetables. Ozone can control such process. Ozone treatment of the air can also slow the spoilage of ready-to-eat foods. In food processing workshops, ozone at a concentration of 0.5-1 ppm can kill more than 80% of the bacteria and viruses in the air. In cold storage, effective sterilization requires an ozone concentration at 6-10 ppm, and the environment to be treated needs to be closed for more than 24 hours. Ozone in this case can kill 90% of bacteria and more than 80% of mold. In the storage of fruits and vegetables, the use of ozone at 2-3 ppm can inhibit the growth of mold, which can double their shelf life.
In a hospital environment, ozone can quickly disinfect large amounts of air in a large space, oxidizing microbes such as bacteria and viruses.
According to statistics, at room temperature and conventional humidity, ozone can achieve a killing rate of 99.9% of pseudomonas aeruginosa in 30 minutes. Ozone can also kill more than 99% of Escherichia coli and Staphylococcus aureus. For HbsAg (hepatitis B surface antigen), HAAg (hepatitis A virus antigen) and poliomyelitis virus, ozone’s killing rates can all reach over 99%, or even 100%. This works well in hospitals where there are lots of people in waiting rooms and treatment rooms. When ozone is used for air sterilization, it needs to be ensured that ozone gas can be kept in a certain space for more than 30 minutes. And after the process, there should be an air ventilation period for 30-45 minutes to ensure the diffusion of ozone gas. But in the case of some resistant viruses or bacterial spores, ozone treatment time needs to be appropriately extended. Ozone can be very efficient for ordinary sterilization operations.
Ultraviolet ray is also a commonly used sterilization means. But the problem with using UV light is that for the effective sterilization of the air, it needs to be turned on with no person in. And for a good sterilization effect, it needs to be turned on often. This is not appropriate for the working environment of the hospital during the daytime. And it is impossible to effectively sterilize areas that do not receive ultraviolet light.
In chemical-sensitive food production facilities such as milk production enterprises, ozone can be used to efficiently sterilize the air within the environment, thus avoiding the use of other chemicals. We have covered this topic in our previous blog Ozone Application in Dairy Farms and Milk Products.
In the above, we have introduced the role of ozone in air sterilization. Next, we’ll talk about another type of problems that ozone air purification addresses – odors.
Odors in the air are caused by the odorous organic compounds in the air. They can be VOC (volatile organic compounds), H2S, or even VFA (volatile fatty acid), etc. Odorous air mainly comes from kitchens, food factories, breweries, spice manufacturers and wastewater treatment plants.
VOC are odorous compounds too. They refer to a class of organic compounds whose saturated vapor pressure is greater than 133.22 Pa at room temperature. VOC can be aromatic hydrocarbons, aldehydes and others. Common VOC are formaldehyde, benzene, acetone, skarole, xylene and limonene, etc. We focused on VOC because although they have different chemical properties, they may cause a variety of environmental or health problems. The reason why they are relevant with our life is that they exist extensively in all sorts of interior decoration material. They may cause serious indoor air pollution. This is also why their use in pharmaceutical, paints, coating and textile industries has been severely limited. We have covered the introduction of VOC in detail in a previous blog post. For more details, visit VOC Removal with Ozone.
Hydrogen sulfide (H2S) in the air comes mainly from sulfur compounds present in large quantities in the environment of food processing enterprises and wastewater treatment plants. Hydrogen sulfide is a toxic gas that smells like rotten eggs. In breweries and biogas production enterprises, hydrogen sulfide is mainly produced due to the anaerobic reactions in the facilities like bioreactors and digesters. Even at a concentration at 0.07 mg/m3, hydrogen sulfide dissolved in water will be enough to change the taste of the water, and a concentration at 0.15 mg/m3 will affect the growth of fish.
The good news is that ozone has a great decomposition ability for the above mentioned VOC and hydrogen sulfide. By breaking down their molecular structures, ozone can fundamentally change their chemical property and thereby effectively remove them. Ozone odor removal is not only suitable for industrial environment, but also widely used in kitchen and bathroom odor removal, furniture and clothing odor removal, and others.
Treatment for Nitrogen Oxides
Besides VOC and odor removal, the power of ozone air purification is also reflected in the treatment of nitrogen oxides. Nitrogen oxides mainly come from the burning of fossil fuels like coal, petrol, natural gas, etc. Vehicles exhaust is also a significant source of nitrogen oxides in the air. They are in many kinds, and the most common ones are nitric oxide (NO) and nitrogen dioxide (NO2). If they are preset in the air in abundance, there will be health concerns. They mainly harm people’s nervous system. Inhaling a large amount of nitrogen oxides can cause central nervous paralysis, memory loss and even life-threatening injuries. If it gets into the lungs, nitrogen oxides can cause respiratory discomfort, coughing and, in severe cases, bronchitis or emphysema.
Nitrogen oxides mainly come from the burning of fossil fuels such as coal, oil and natural gas both in industrial circumstances and our everyday life. In order to solve the problem of nitrogen oxide emissions, one of the most effective solutions will be the denitrification treatment.
Previously, denitrification of nitrogen oxides can be mainly divided into selective catalytic reduction and selective non-catalytic reduction. Both the two solutions have their limitations. Selective catalytic reduction needs to be carried out at temperatures up to 400-500℃. It also requires a high consumption of catalysts and the cooperation with other equipment. So, the financial cost will be high. In the selective non-catalytic reduction process, the reaction temperature needed will be up to 1000℃. And also a large quantity of catalysts will be consumed. The drawback is that the processing efficiency of this reaction is as low as 40%. Due to their own shortcomings, these two methods are difficult to meet the demand for denitration of waste gas in many enterprises.
In recent years, ozone has been gaining more and more attention for the denitrification of flue gas. It has gradually entered the mature application stage. Ozone can not only remove high concentration of nitrogen oxide pollutants, but also have certain removal ability of mercury and other heavy metals existed in flue gas. In terms of compatibility with other treatment equipment, the introduction of ozone will not affect the normal operation of the existed equipment. The replacement of traditional denitration equipment can be easily achieved. The petrochemical industry has a great demand for flue gas denitrification. And ozone treatment has been widely applied in this industry and achieved favorable results.
In the above, we introduced the role of ozone in air sterilization, odor removal and treatment for nitrogen oxides. The advantages of ozone air purification are also reflected in the on-site generation of the gas and no storage or handling of hazardous chemicals required. Ozone, in the form of a gas, can easily reach places inaccessible for normal wiping work. In terms of time, the process of ozone air purification and subsequent ventilation takes just over an hour. There will be no complex operation steps. Ozone air purification does not produce any harmful residue. The excessive ozone remained will soon be converted into oxygen which is certainly harmless. For more details about ozone, just go to our previous blog: An Introduction of Ozone.