VIABILITY OF BACTERIA IN UNUSED AIR FILTER MEDIA

Different experimental techniques were applied to determine the effect s of different air filter media on the viability of bacteria. Rinse su spensions of unused filter media were employed in standard inhibition tests to determine the effects of filter ingredients on bacterial grow th under ideal nutritional conditions. Furthermore, a new test procedu re was proposed and validated to determine the survival of viable micr oorganisms in fibrous air filters as a function of different parameter s. Samples of filter media were challenged with microbial aerosols in an experimental set-up designed for measuring the collection efficienc ies of fibrous filters. The loaded filter samples were then challenged with clean air under controlled conditions for a definite time span a nd numbers of viable microorganisms in the filter media were determine d as colony forming units. The filter samples were retrieved from unus ed filter media usually employed in common air conditioning and ventil ation systems. Under ideal nutritional and moisture conditions, growth of investigated microorganisms in nutrient broth and on nutrient agar was not inhibited by the inclusion of filter samples or rinse solutio ns of different filters in the growth medium with one exception. M. lu teus and E. coli collected in air filter media and exposed to low air humidity (RH = 30-60%) showed a decline in their viability as a functi on of time (within 1 h). The decline rate was dependent on the type of bacteria employed and also the filter material itself. (C) 1997 Elsev ier Science Ltd.