Survival of bacterial and mold spores in air filter media

The present study deals with the survival of bacterial and mold spores (B. subtilis, A. niger) in new and used air filter media. In an filtration test unit samples of different filter media were challenged with specific micro bial aerosols and the viability or survival of the microorganisms collected in the filter media was studied. No notable decline or increase in the via bility of B. subtilis in new or used filter samples was observed within 5 d ays. No differences were observed when filter media were either continuousl y exposed to air flow or stored under static conditions. No influence of re lative humidity (RH = 30-85%) on the viability of B. subtilis spores was de tected as well. Under ideal humidity conditions (RH, 98%) no bacterial grow th occurred within all the investigated filter media which is due to the la ck of nutrients. Similar results were obtained when employing A. niger spor es at low relative humidities (RH < 35%). However, in two new filter media the viability declined notably at high relative humidity (RH > 85%). This t rend is attributed to the combined effect of spore rehydration and diffusio n of fiber substances into the spores which rendered the spores prone to ai r flow and air toxics. Under static conditions in a climatic chamber (RH > 98%) abundant mold growth occurred in two filter media. The results indicat e that atmospheric dust deposited in air filters may serve as nutrient for molds if humidity is sufficient and filters are not exposed to an air flow. (C) 2000 Elsevier Science Ltd. All rights reserved.