Posts Tagged ‘air disinfection’

Why do we need air disinfection? (3)

September 2, 2010 Leave a comment
Procedure for air disinfection using ozone
In order to test for the effectiveness of ozone in reducing airborne bacteria, a conference room with area about 12m2 was selected for testing. As high level of ozone is required to kill viruses, bacteria and spores, the disinfection process was carried out when humans, animals and plants were evacuated.
Depends on the size of the room, an ozone generator (PIE Ozonation) with 2g/hr output was chosen. The capacity of the chosen ozone generator has the ability to maintain high concentration of ozone (0.5 – 5 ppm) inside. Circulation fan was placed in the room to ensure good distribution of ozone. After closing all the windows and doors, the ozone generator was turned on by remote device located outside to begin ozonation process. Concentration of ozone was monitored using a digital ozone sensor (Ecosensor). Different levels of ozone (0.5, 2.5 and 5 ppm) were tested to determine the optimal value for killing as much microorganisms as possible. After turning off the ozone generator, ozone level began to drop as it was undergoing self-decomposition to oxygen.
For safety reason, no people should enter the room until the level of residual ozone is below 0.02 ppm. In general, ozone concentration drops to below 0.02 ppm in a hour after ozonation, therefore people should wait for at least one hour (after turning off the generator) before entering the “ozonated” room.
The total airborne bacteria in the conference room was measured before and after each ozonation. Measurement was carried out using an Andersen N-6 single-stage sampler with Tryptone Soya Agar (Oxoid) in petri dish. 283L of air was taken for each sampling. The petri dish was incubated at 35oC for 48 hrs before counting. The disinfection efficiency of ozonation at different concentration was tabulated in Table 1.
Table 1. Reduction of Airborne Bacteria after Ozonation

Ozone conc.

0.5 ppm

2.5 ppm

5 ppm

Before Ozonation

592 CFU/m3 

612 CFU/m3 

552 CFU/m3 

After Ozonation

169 CFU/m3 

42 CFU/m3 

57 CFU/m3 

Reduction %




The results show that ozone is effective in reducing airborne bacteria. At higher ozone level, the sanitizing effect increased. Over 90% of airborne bacteria could be reduced at 2.5 ppm concentration. Further increase of ozone concentration to 5 ppm does not beneficial in bacteria reduction percentage.
Unlike laboratory experiments conducted by Kowalski et al (1) that could remove 99.99% airborne bacteria after ozonation, the best reduction percentage in our case was around 93% only. High removal percentage could not be achieved because the conference room was not 100% sealed. Doors should be opened briefly during each air sampling (for placing a new agar dish on the sampler) and air exchange from outside was unavoidable.
For safety reason, excessive high concentration ozone should be avoided and the lowest ozone concentration that could kill most of the microorganisms should be selected as optimum. Depends on the contamination level, 0.5 – 2.5 ppm ozone level is adequate for air disinfection.


Experimental data shows that ozone is effective in reducing airborne bacteria of unoccupied room. Over 90% of airborne bacteria could be reduced after ozonation. As viruses are generally more susceptible to ozone than bacteria, it could assume that all viruses are killed if large percentage of airborne bacteria are removed. Ozone is a gas that has good penetration capacity and powerful oxidizing power, thus its disinfection efficiency is superior to UV radiation and HEPA filter. As ozone disinfection is conducted in unoccupied room only and all the residual ozone will be decomposed after the treatment, ozone toxicity to human is therefore not a concern. Given the advantages of strong oxidizing power, good penetration capacity and no harmful residues left after the treatment, ozone is recommended to be used in disinfection of SARS-contaminated environments.


Why do we need air disinfection? (2)

September 2, 2010 Leave a comment
Disinfection capacity of ozone
Ozone (O3) is an unstable gas comprising three atoms of oxygen. It is unstable because the gas will readily degrade back to its stable state, diatomic oxygen (O2) with the formation of free oxygen atoms or free radicals. The free oxygen atoms or radicals are highly reactive and they will oxidize almost anything (including viruses, bacteria, organic and inorganic compounds) in contacts, making ozone an enormously powerful disinfectant and oxidizer.
In fact, ozone is a much stronger oxidizer than other common disinfectants such as chlorine and hypochlorite. The usage of chlorine or hypochlorite in many countries has been decreased significantly due to the possibility formation of carcinogenic by-products such as trihalomethanes (THM) during the disinfection process. In contrast, ozone disinfection does not produce any harmful residues, and all the residual ozone will be converted back to oxygen within a short time. Ozone is therefore considered as an environmentally friendly disinfectant.

Figure 1 shows a typical curve (concentration vs. time) during ozonation process. As shown in the figure, the ozone concentration raise very slowly in the initial period (the first few minutes). The delay in building up the ozone  concentration is probably due to the consumption of ozone for oxidizing pollutants (including bacteria and viruses) in the initial period. After oxidizing the major pollutants, ozone concentration inside the room raise rapidly up to the desired level. To ensure entire room disinfection, high level of ozone was maintained for 30 minutes. When ozone generator was off, the ozone concentration dropped gradually as ozone converting back to oxygen.
Given its superior strength and effectiveness as an oxidant and biocide, ozone becomes one of the dominant water treatment technologies in Europe and America. But its application in air disinfection is not as popular as water due to the concern on ozone’s toxicity. Ozone with concentration higher than 1 ppm has adverse effects on human health and the use of ozone for air disinfection is generally not recommended if people are around. Therefore, air disinfection using ozone should be restricted to unoccupied room only.

Why do we need air disinfection? (1)

September 2, 2010 Leave a comment
Technologies for air disinfection
The most common air disinfection method is using ultraviolet (UV) radiation. UV radiation (UV-C) kills bacteria and viruses by damaging the DNA/RNA of the cells of microorganisms. However, UV radiation could only disinfect air close to the lamps as UV light has limited penetration capacity. In case of SARS contaminated room, UV disinfection alone is not adequate to provide virus-free environment for us.
Another well-known air cleaning method is to employ High Efficiency Particulate Air (HEPA) filter. HEPA filter can capture particulate sizes down to 0.3 microns, and so bacteria with size larger than 0.3 microns could be trapped in the filter. Although HEPA filters are effective in reducing airborne bacteria  in air, it is not effective to remove viruses, which are nanometer (10-9 m) in size. Also, air must pass through the filter in order for it to be cleaned. Hence HEPA filters can only clean air that is within a short distance of the HEPA unit. These drawbacks make HEPA filters become an unsatisfactory candidate for disinfection of SARS contaminated areas.
Chemical disinfectants could also be used for air disinfection, usually by means of vaporizing or spraying. However, these chemical disinfectants are usually difficult to decompose, leaving toxic chemical residues that are hazardous to human health.
Ozone is a well-known powerful oxidizer which could kill microorganisms effectively. Ozone applications in water and wastewater treatments are well-documented and it is widely used by most of the modern cities. Although studies for using ozone to disinfect air are relatively limited, experimental results (2,3) indicate that ozone could also be an effective air disinfectant as in water. For example, Kowalski et al (2) investigated the bactericidal effects of high ozone concentrations on E. coli and S. aureus and concluded that more than 99.99% death rate was achieved for both species after ozonation.
In addition to the strong oxidizing power of ozone, properties of ozone also help it to be an ideal aerial disinfectant. In contrast to UV radiation and HEPA filter, ozone is a gas that could penetrate to every corners of the room, thus it could disinfect the entire room effectively. As ozone is unstable, it is readily converted back to oxygen, leaving no harmful residual ozone after disinfection.
Although ozone is success as an aerial disinfectant in laboratory experiments (1), its effectiveness in real situation needs to be further explored. In this article, the effectiveness of ozone in disinfection of a conference room will be evaluated and discussed.


Poultry ozone applications

September 1, 2010 Leave a comment

Ozone is used in the poultry industry as air and water treatments for the storage, incubation of eggs and breeding of healthy birds. Ozone being an effective oxidant, it is mostly used for processing, storage and transport of poultry and meat products. Ozonated water is used to feed the birds as drinking water, wash and sterilize meat and equipments to kill harmful pathogen.

Ozone – Air treatment

  • Ozone oxidizes ammoniacal gases, methane and carbon dioxide, creating a healthier environment for the birds and the staff working in the poultry
  • Ozone is more effective than other air disinfecting systems such as chemical fogging and UV light.
  • In growing birds, ozone in the pens as a gas reduces the amount of bacteria and thus reducing the spread of infection and viruses thereby increasing their health and even weight by up to 18%. Ozone application helps to improve their skin colour.
  • Ozone is more effective than formaldehyde in disinfecting Poultry sheds and requires no dormant period in which the sheds have to remain evacuated. Immediately after disinfecting by ozone at high concentrations, the shed is ventilated and can be inhabited by the birds and staff safely. Unlike formaldehyde, ozone is non-carcinogenic.
  • Hatching hens which are kept under ozonized conditions show an increase in the amount of eggs they lay, and a stronger consistency of the egg shell, because of the corresponding decrease in pathogenic illness and prevention of a toxic build up of disinfectant chemicals. Ozone is used to disinfect incubation rooms and chambers, in the place of chemicals which cause a toxic build-up on the egg shell surfaces and weaken the immune system of the birds.

Ozone in drinking water

Drinking water for poultry is an important dietary requirement. Under normal conditions, birds will consume, approximately, double the quantity as food on weight basis

Poor water quality, can retard growth, curtail egg production, or produce lower egg quality. Feed

conversion has been positively correlated to the presence of sulfate and copper concentrations in the water and Ozone effectively oxidize them and can be easily removed by filtration.

Benefits of ozone in drinking water

  • It reduces waterborne pathogens and prevents development of resistance by pathogen
  • It helps to accelerate weight gain by the birds
  • It improves feed conversion and increased layer output
  • It helps to increase  the dissolved oxygen in water which helps the birds to tolerate heat

Ozone – Water treatment for washing Poultry carcasses, equipments and Cold Storage.

  • Ozonated water is effective as a disinfectant for poultry carcasses without loss of colour and flavour
  • Ozonated water kills instantly more than 5 log units of Salmonella typhirium and Escherichia coli cells, as well as 4,5 log units of Candida albicans and Zygosaccraomyces bacilli.
  • It has been proved that Staphylococcus colonise on de feathering machinery have become endemic with poultry processing plants, and become resistant to normal cleaning and disinfecting, including chlorine. Ozone has got the property of killing and destroying those bacteria effectively
  • Ozone during refrigerated storage of poultry has a pronounced effect on flora causing deteriorations and consequently prolongs the shelf life of poultry in cold storage