**7.2 Microbial colonization of the types of filters commonly used in airconditioning systems**

Microorganisms that are captured by filters can thrive on the filters and can potentially be released into the air, thereby resulting in sick building syndrome [67]. Furthermore, it has been determined that the number of microbes found in indoor air is less than that colonizing the surface of filters used in air-conditioning systems [68]. Foarde [69] and Kowalski [68] examined the efficiency of these systems and provided solutions for the HEPA filters. In addition, they noted that the tested filter samples trapped *Bacillus subtilis*, with efficiencies ranging from 19 to 100%, whereas in contrast the efficiency in trapping viruses was low, ranging from 0.7 to 20%.

Al-Abkari [17] examined the ability of microorganisms (bacteria and fungi) to degrade various types of filter commonly used in air-conditioning systems,

**199**

**Figure 15.**

*(c) HEPA.*

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

namely, sponge, polyester, HEPA, and the environmental conditions, such as dust, temperature, and moisture, which enable these organisms to take refuge, grow, and reproduce. The results indicated that the growth of bacterial strains was dependent on the filter media containing a carbon source. The average of bacterial moist mass loading on different filters was found to be positively related to the length of incubation period (1, 2, and 3 months), with weights reaching 0.061, 0.09, and 0.101 g after incubations for 1, 2, and 3 months, respectively. Furthermore, it was found that the average microbial mass detected on sponge filters (0.177 g) was larger than

*The mycelial growth and conidia of Cladosporium sp. on the studied filters: (a) sponge, (b) polyester, and* 

Generally, it was observed that the average of moist weights of bacterial mass on all filters increases with an increase in the length of the incubation period, with recorded averages of (0.134, 0.169, and 0.228 g) and (0.019, 0.024, and 0.03 g) and (0.031, 0.035, and 0.046 g) for sponge, polyester, and HEPA filters, respectively. In contrast, it was found that the moist mass of microbial growth on culture medium lacking a carbon source remained essentially constant with increasing incubation time, with values of 0.023, 0.023, and 0.028 g; 0.03, 0.035, and 0.039 g; and 0.163,

0.171, and 0.162 g) for sponge, polyester, and HEPA filters, respectively. With regard to the growth of fungal strains, when these were grown in a medium containing a carbon source, the average moist fungal mass loading on different filters showed a positive relationship with incubation period (1, 2, and 3 months), with weights reaching 0.87, 0.118, and 0.142 g, respectively. Similar to bacterial growth, the average weight of fungal biomass growing on sponge filters (0.257 g) was larger than that on polyester (0.072 g) and HEPA (0.047 g). The weight of fungal mass on polyester and HEPA filters was 0.05, 0.082, and 0.085 g

that on either polyester (0.024 g) or HEPA (0.037 g).

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

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

#### **Figure 15.**

*Low-temperature Technologies*

Comparatively, the bacterial mass recorded on polyester and HEPA reached 0.024 and 0.037 gm, respectively, and the corresponding fungal mass on these filters was 0.072 and 0.047 gm, respectively. Douwes [65] isolated polysaccharide compounds known to be excreted by various fungi that grow on dust in residential homes, and the detection of these compounds is accordingly consid-

*The mycelial growth of Rhizoctonia sp. on the studied filters: (a) sponge, (b) polyester, and (c) HEPA.*

Moray and Williams [66] performed direct microscopic observations of the porous soft filters typically used in air-conditioning systems and accordingly identified pollen grains, cellulose fibers, synthetic fibers, decayed plant leaves, hairs, parts of insects, dust, mites, and numerous organic compounds, all of which can

Microorganisms that are captured by filters can thrive on the filters and can potentially be released into the air, thereby resulting in sick building syndrome [67]. Furthermore, it has been determined that the number of microbes found in indoor air is less than that colonizing the surface of filters used in air-conditioning systems [68]. Foarde [69] and Kowalski [68] examined the efficiency of these systems and provided solutions for the HEPA filters. In addition, they noted that the tested filter samples trapped *Bacillus subtilis*, with efficiencies ranging from 19 to 100%, whereas in contrast the efficiency in trapping viruses was low, ranging

Al-Abkari [17] examined the ability of microorganisms (bacteria and fungi) to degrade various types of filter commonly used in air-conditioning systems,

**7.2 Microbial colonization of the types of filters commonly used in air-**

ered to be a good indicator of the presence of these fungi.

provide a refuge for microbes.

**Figure 14.**

**conditioning systems**

**198**

from 0.7 to 20%.

*The mycelial growth and conidia of Cladosporium sp. on the studied filters: (a) sponge, (b) polyester, and (c) HEPA.*

namely, sponge, polyester, HEPA, and the environmental conditions, such as dust, temperature, and moisture, which enable these organisms to take refuge, grow, and reproduce. The results indicated that the growth of bacterial strains was dependent on the filter media containing a carbon source. The average of bacterial moist mass loading on different filters was found to be positively related to the length of incubation period (1, 2, and 3 months), with weights reaching 0.061, 0.09, and 0.101 g after incubations for 1, 2, and 3 months, respectively. Furthermore, it was found that the average microbial mass detected on sponge filters (0.177 g) was larger than that on either polyester (0.024 g) or HEPA (0.037 g).

Generally, it was observed that the average of moist weights of bacterial mass on all filters increases with an increase in the length of the incubation period, with recorded averages of (0.134, 0.169, and 0.228 g) and (0.019, 0.024, and 0.03 g) and (0.031, 0.035, and 0.046 g) for sponge, polyester, and HEPA filters, respectively. In contrast, it was found that the moist mass of microbial growth on culture medium lacking a carbon source remained essentially constant with increasing incubation time, with values of 0.023, 0.023, and 0.028 g; 0.03, 0.035, and 0.039 g; and 0.163, 0.171, and 0.162 g) for sponge, polyester, and HEPA filters, respectively.

With regard to the growth of fungal strains, when these were grown in a medium containing a carbon source, the average moist fungal mass loading on different filters showed a positive relationship with incubation period (1, 2, and 3 months), with weights reaching 0.87, 0.118, and 0.142 g, respectively. Similar to bacterial growth, the average weight of fungal biomass growing on sponge filters (0.257 g) was larger than that on polyester (0.072 g) and HEPA (0.047 g). The weight of fungal mass on polyester and HEPA filters was 0.05, 0.082, and 0.085 g and 0.022, 0.04, and 0.078 g, respectively. Notably, however, fungal growth on sponge filters increased with increasing incubation time, reaching 0.181 and 0.324 g, following incubation for 1 and 2 months, respectively, whereas after incubation for 3 months, it had decreased to 0.265 g.
