A comparative evaluation of bioaerosols between gravity and vacuum toilets

Toilet flushing is known to generate and disperse bioaerosols which can contaminate surfaces in the washroom and increase the risk of infections through contact with the contaminated surfaces or inhalation of these bioaerosols. Whilst this phenomenon is well known for gravity toilets, vacuum toilets have been hypothesized not to generate bioaerosols and have been tagged as more sanitary compared to the gravity toilet. This study investigates whether a vacuum toilet produces bioaerosols and how the bioaerosols and particle concentrations of a vacuum and a gravity toilet differ from each other. The study further looks into the reasons and behaviour of the measured concentrations based on the main difference between the toilets - their flushing mechanism. Experiments were conducted in a warehouse-office building using two identical toilet cubicles with dimensions of 1.5 meters by 1.17 meters which were constructed for the purposes of this study. 12 experimental conditions this were framed around two main toilet-use scenarios; using the toilet during an incidence of diarrhea and using the toilet when there was no diarrhea (faecal matter of solid consistency). Faecal matter was not used in this study; rather, Escherichia coli bacteria, an indicator organism for faecal contamination on surfaces and in toilet water was used in seeding the toilet bowls to represent the experimental conditions in the study. The bioaerosol concentrations in this study were measured according to the ACGIH and ASTM standards. Particle concentrations were measured using an optical particle counter. Based on the results of this study, it can be concluded that, gravity toilets produce bioaerosols via visible splashes or overspray when faecal matter of loose or solid consistency is flushed with the lid open, but a vacuum toilet would not produce bioaerosols or visible splashes under the same conditions