AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Toilet Plume Droplet Nuclei Aerosol Production and Bowl Clearance during Sequential Flushes
DAVID L. JOHNSON, Robert A. Lynch, Jacob F. Jones, Kenneth R. Mead, Deborah V.L. Hirst, Dept Occup/Envir Health, Univ OK HSC
Abstract Number: 27 Working Group: Health Related Aerosols
Abstract Background. Toilets will generate bioaerosols for several flushes following contamination. Bowl water will remain contaminated even after several flushes, possibly due to bowl wall particle adhesion. This study compares droplet nuclei “bioaerosol” generation and bowl water clearance for three modern siphonic toilet types during sequential flushes after an initial seeding.
Methods. Three siphonic toilet types were seeded with 0.25 µm fluorescent polymer microspheres as microbe surrogates. The toilets had similar flush and bowl water volumes but different flush energies. Bowl water was seeded prior to the first flush only and a water sample collected before the first flush. The toilet was flushed and airborne particles sampled onto 0.2µm pore size MCE filters for 30 minutes beginning 15 minutes after the flush, using 4 open-face cassettes mounted 2 and 5 feet high on the water closet side walls. A water sample was collected and cassettes changed between flushes. Water samples were filtered, and air and water filters counted via fluorescent microscopy. Air samples were collected over 4 sequential flushes and water samples over up to 24 flushes.
Results. All toilets exhibited clearances of 3+ log bowl water concentration reductions with the 1st flush, 1-2 logs with the 2nd flush, and less than 1 log thereafter. Post-flush #3 the clearances were extremely gradual. Air concentrations did not decrease in proportion to water concentration, spanning 2 orders of magnitude compared to a span of 6 o.m. in bowl water concentration. These findings were consistent with previous reports for 3-7 flushes using microbes Surfactant addition after 24 flushes boosted the bowl water concentration.
Conclusions. Particle adhesion to and re-release from bowl water surfaces was demonstrated, with substantial bowl contamination remaining for at least 24 flushes.