馬桶沖水過程中微粒產生的評估與控制

Abstract

一款設計不良的馬桶可能成為疫情傳播的助手。 在SARS、COVID-19疫情爆發前，呼吸道傳染病常被認為主要藉由咳嗽、打噴嚏、呼吸及說話方式進行傳播，隨著許多研究證明了馬桶能在沖水過程中將病原體氣膠化後，有關馬桶與呼吸道傳染病間的關係才逐漸受到重視，然而，目前多數的研究主要以馬桶產生微粒之特性、影響微粒產生的因子以及所產生微粒與傳染病間的關係進行探討，反而較少針對產生源與相關控制手段進行探討，因此，本研究以職業衛生的基本工作，評估與控制馬桶逸散微粒的問題，在現有馬桶的基礎之下，透過調整影響微粒產生的參數與加裝微粒防制設備，來減少微粒的逸散，並降低使用馬桶後暴露於疾病的風險。

由於目前尚未有一套統一量測馬桶產生微粒的方法，在實驗上，本研究於一般室內環境中建立一套不受背景微粒干擾且能快速量測市售馬桶微粒排放與逸散的方法。在量測上，本研究使用自來水重複進行沖洗，並以沖水所產生的液滴微粒特性進一步探討。而在量測微粒的基本特性上，使用光學式粒徑分析儀與凝結式微粒計數器分別量測0.3～10 μm微粒之粒徑濃度分布，以及小於1 μm微粒之總微粒數。而本研究主要針對市售六款馬桶進行測量，並探討不同沖洗參數(沖水量、水流方式、沖洗時間、沖洗機制)條件下對於微粒逸散的影響，接著會針對目前市售馬桶清潔產品對於微粒排放的影響進行評估。在量測完微粒的基本排放特性後，針對市售馬桶蓋與脫臭馬桶蓋進行量測與探討(馬桶蓋的效果、抽氣流量的影響)，最後藉由將一系列測試(抽氣流量、氣罩外型、抽氣面積)所收集到的參數整理後，將市售馬桶蓋進行改良並探討其效果。

結果顯示，沖水後馬桶產生微粒的主要過程是沖水時，由於水柱撞擊液面後導致大量空氣與水在快速混合後產生大量的氣泡破裂，進而有大量的液滴微粒產生；目前市售馬桶在單次沖洗所排放的微粒量上皆落在105 #/Flush，並且會受到不同的沖洗條件(水量、沖洗能量、入水角度)而有所影響；在微粒的基本特性上，乾燥微粒的中位數粒徑為0.2 μm、初始液滴的中位粒徑為2.84 μm；在馬桶清潔劑的使用上則會增加液滴微粒的排放量；而市售馬桶蓋在防止微粒逸散上約有85%的效果，其主要原因在於馬桶蓋與馬桶座間存在間隙問題，導致微粒能逸散環境；而市售抽氣脫臭馬桶蓋因為所使用的活性碳濾材無法補集沖水時所產生的微粒，反而會導致馬桶盆內的微粒快速逸散至環境。最後，經過一系列的測試後，目前共研發兩款有效控制微粒逸散的馬桶蓋原型，並且皆能在沖水後1.5分鐘內有效移除99%殘留於馬桶盆內的微粒。

因此，就研究結果可發現，在微粒逸散上，運用工程控制的角度，針對沖水所產生的微粒進行主動式收集，能有效解決微粒逸散至環境的問題；而在未來的馬桶設計上，若能有效防止沖水過程中大量氣泡的產生，將能根本減少液滴微粒的形成。

A poorly designed toilet may facilitate the spread of epidemics. After the outbreak of SARS and COVID-19, numerous studies have demonstrated that toilets can aerosolize pathogens during flushing. Nevertheless, most existing research is more focused on the characteristics of particles, the influence factors of particle generation, and the relationship between the particles and infectious diseases. In contrast, fewer studies used source control or engineering control to decrease particle generation. Therefore, this study aims to experimentally investigate the particle characteristics, generation mechanisms, and influencing factors of droplet particles generated by various flushing toilets. Then, design and evaluate methods that can eliminate the generation or emission of droplet particles from toilets.

Due to the lack of a standardized method for measuring particles generated by toilet flushing. This study established a method without interference from background particles and could rapidly measure particles generated from toilet flushing and evaluate the effectiveness of toilet lids in preventing particle leakage. This study used tap water for repeated flushing and further discussed the characteristics of droplet particles generated from toilet flushing. To measure the basic characteristics of particles, a Condensation Particle Counter and an Optical Particle Sizer were used to monitor the particle size distribution in the size range of 0.3～10 μm and the total count of particles with diameters less than 1 μm, respectively. This study used six commercial toilets to measure and discuss the effects of different flushing parameters (flush volume, angle of water entry into the bowl, flush duration, flushing mechanism) on particle generation. Then, the impact of commercial toilet cleaning products on particle generation, and the effectiveness of preventive particle leakage on the commercial toilet lid were also assessed and discussed. Finally, some parameters would be collected from a series of tests (exhaust airflow, hood shape, exhaust area), and these parameters would be used to modify the commercial toilet lids and then evaluate their effectiveness.

The results indicated that the primary particle generation process during toilet flushing was the rapid mixing of air and water inside the toilet bowl, and it would produce a large number of bubble bursts and droplet particles. The count of particles generated from commercial toilets was about 10⁵ #/flush and would be affected by different flushing conditions (water volume, flushing energy, and water entry angle). The count median diameter of particles and initial droplets was 0.2 μm and 2.84 μm. The toilet bowl cleaner would increase the generation of droplet particles. The commercial toilet lids could provide 85% effectiveness in preventing particle leakage from toilet bowl. However, there were gaps between the toilet lid and seat, resulted in particles leakage into the environment. For deodorizing toilet lids, particles could rapidly leaked into the environment because the activated carbon could not capture particles generated during flushing. Finally, two prototype toilet lids were developed, and both could effectively remove 99% of particles remaining in the toilet bowl within 1.5 minutes after flushing.

Therefore, using engineering controls to actively collect the particles generated during flushing can effectively address the issue of particle emission into the environment. For future toilet designs, it can fundamentally reduce the generation of droplet particles by effectively preventing the generation of large bubbles during the flushing process.