Experimental study on droplet and bioaerosol emissions from flushing a squat toilet

Abstract

Toilet flushing can produce pathogen-laden aerosols and may pose a serious concern for the transmission of diseases. The emission of bioaerosols from flushing a squat toilet has not been thoroughly examined in the literature. In this study, we conducted pilot measurements to quantify the emission of airborne microorganisms during the flushing of a squat toilet. A full-scale custom-built squat toilet with a typical flushing system was designed and built. The aerosolized droplets and microbes emitted after a single flushing were measured and quantified. Three bacteria (Escherichia coli, Pseudomonas alcaligenes, and Salmonella enterica) and two viruses (bacteriophage MS2 and P22) were tested. The results suggest that a single flush can generate a large number of small droplets in the air. The total emission number of droplets within 0.3–10 μm per flush was 5.72 × 105±1.93 × 105 of which 96 % were smaller than 2 μm. We observed a linear correlation between the number of emitted bioaerosols and the amount of microorganisms introduced into the toilet bowl. The quantified data also shows that flushing-induced airborne microorganism emission strength (a normalized parameter) varied significantly with the sizes of microorganisms. Overall, the emission strengths of viruses were significantly higher than those of the tested bacteria. The mean emission strength of P22 and MS2 per flush was 33.5 times higher than the average emission strength of the three tested bacteria. This work provides valuable data on the bioaerosol emission by flushing a squat toilet, which is essential for developing control measures and evaluating the risk of pathogen exposure.