**5.4 Antibacterial filters**

Antibacterial filters are prepared by incorporating a bactericidal substance in the filter media. However, doubts remain regarding the effectiveness of these filters. One type is prepared by simply spraying the additive onto the surface of the filter medium, and therefore effective coverage is often not achieved, and not all of the filter layers will kill bacteria. A second type is prepared by application of a bacteriostatic agent, which does not kill the bacteria and may indeed promote the development of drug resistance among the bacteria. A third type may generate certain gaseous substances or odors that are potentially harmful to humans. Furthermore, it should be emphasized that it is difficult to capture bacteria on the windward side of the HEPA filters fabricated from inorganic materials, into which

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*Impact of Air-Conditioning Filters on Microbial Growth and Indoor Air Pollution*

incorporating inorganic nanoparticles and natural plant extracts [25].

the bacteria may even penetrate. However, these microorganisms are only likely to survive under suitable conditions of temperature and humidity. Accordingly, the efficacy of these antibacterial filters remains inconclusive, and ASHRAE has recommended that HVAC systems incorporating antibacterial filters should be used with caution, so as not to produce any additional chemical pollution within

Although air filters often show excellent removal efficiency with regard to pathogens, the captured microorganism can remain viable within the filter and subsequently grow and become re-dispersed in the air flow, thereby generating a secondary source of pollutants and unpleasant odors. In an effort to resolve this issue, a large number of studies have been conducted with the objective of improving the effectiveness of air filters with antibacterial properties, and some of these studies have demonstrated that such air filters can be successfully prepared by

Kim [26] also evaluated the efficacies of various functional filters coated with antimicrobial chemicals in deactivating representative microorganisms on filters or as bioaerosols. Specifically, they examined the effectiveness of functional filters coated with different chemicals, including ginkgo and sumac; Ag-apatite and guanidine phosphate; SiO2, ZnO, and Al2O3; and zeolite, using a model ventilation system to evaluate the efficiency in which bacteria (*Escherichia coli* and *Legionella pneumophila*), bacterial spores (*Bacillus subtilis* spore), and viruses (MS2 bacteriophage) were removed. Their result showed that although the functional filters could facilitate the biological removal of various bioaerosols, physical removal was minimal. Appropriate use of chemical-coated filter materials could reduce exposure

Electrostatic filters: Static electricity attracts dirt and dust to vertical and overhead surfaces. The static is often generated when two surfaces rub together and are then separated. Electrostatic filters generate a static electrical charge on all particles in the air that passes through eight filter layers. The discharged particles are then attracted to collector plates with an opposite electrical charge. These filters have the

High-efficiency particulate air filters: HEPA filters have a strong particletrapping capacity that facilitates the removal of a high percentage (99.97%) of airborne particles that pass through an air purifier and accordingly meet US government standards. This contrasts with the 60–90% efficiency of medium filters [27]. Furthermore, HEPA filters perform significantly better than electrostatic air cleaners, in which filtering is based on ionic processes. HEPA filters are therefore often used in medical facilities and in households in which the residents suffer from

Photocatalysts are nanoscale metal oxide materials (commonly titanium dioxide) that are applied to substrate surfaces, forming a film after drying under the action of light. They have a strong catalytic degradation function and can be used to degrade hazardous atmospheric gases. They can also be used to effectively kill a variety of bacteria, with an antibacterial rate of 99.99%. Furthermore, toxins released during the degradation of bacteria and fungi can be rendered harmless. These catalysts also have a range of other properties, including deodorant and dirt

*DOI: http://dx.doi.org/10.5772/intechopen.88548*

indoor environments [24].

to these agents.

severe allergies.

removal functions.

**5.5 Electrostatic and HEPA filters**

advantage of being washable.

**5.6 Microbial filtration efficiency of HEPA filters**

#### *Impact of Air-Conditioning Filters on Microbial Growth and Indoor Air Pollution DOI: http://dx.doi.org/10.5772/intechopen.88548*

the bacteria may even penetrate. However, these microorganisms are only likely to survive under suitable conditions of temperature and humidity. Accordingly, the efficacy of these antibacterial filters remains inconclusive, and ASHRAE has recommended that HVAC systems incorporating antibacterial filters should be used with caution, so as not to produce any additional chemical pollution within indoor environments [24].

Although air filters often show excellent removal efficiency with regard to pathogens, the captured microorganism can remain viable within the filter and subsequently grow and become re-dispersed in the air flow, thereby generating a secondary source of pollutants and unpleasant odors. In an effort to resolve this issue, a large number of studies have been conducted with the objective of improving the effectiveness of air filters with antibacterial properties, and some of these studies have demonstrated that such air filters can be successfully prepared by incorporating inorganic nanoparticles and natural plant extracts [25].

Kim [26] also evaluated the efficacies of various functional filters coated with antimicrobial chemicals in deactivating representative microorganisms on filters or as bioaerosols. Specifically, they examined the effectiveness of functional filters coated with different chemicals, including ginkgo and sumac; Ag-apatite and guanidine phosphate; SiO2, ZnO, and Al2O3; and zeolite, using a model ventilation system to evaluate the efficiency in which bacteria (*Escherichia coli* and *Legionella pneumophila*), bacterial spores (*Bacillus subtilis* spore), and viruses (MS2 bacteriophage) were removed. Their result showed that although the functional filters could facilitate the biological removal of various bioaerosols, physical removal was minimal. Appropriate use of chemical-coated filter materials could reduce exposure to these agents.
