Influence of seasons and sites on bioaerosols in indoor wastewater treatment plants and proposal for air quality indicators

During wastewater treatment, bioaerosols are generated and, can either remain in suspension for several hours or settle on surfaces and workers may be exposed. The presence of pathogens in the air could contribute to an increased frequency of gastrointestinal or respiratory illness amongst workers. Due to harsh winter conditions in Eastern Canada, many of the steps in the wastewater treatment process occur indoors, leading to a greater risk of significant occupational exposure especially if there is inadequate ventilation or a lack of personal protection. This work has used stationary sampling at various indoor wastewater treatment steps both in winter and summer. Bioaerosols were evaluated using both culture and molecular methods along with ventilation characterization. Endotoxins were quantified, as well as total cultivable and gram-negative bacteria and pathogen indicators using qPCR. This study highlights the presence of potential pathogens at all steps in the treatment process, which may represent a potential occupational hazard. Comparisons between summer and winter data suggest that water temperature is an important factor for microbial activity and suggest that increasing the rate of air changes per hour in summer would be beneficial to reduce the concentration of bioaerosols during this time of the year. The screening, grit/FOGs removal and biofiltration were the most bioaerosol-loaded sites. Based on strong correlations, we suggest the reconsideration of exposure limits in WWTPs. Workers should be encouraged to use personal respiratory protection to limit the risk of health problems, especially during long-term work. <i>Implications:</i> The work presented herein showcases significant correlations between concentrations of endotoxins, cultivable bacteria, gram-negative bacteria, and total bacteria by qPCR from air collected in indoor wastewater treatment plants. These correlations lead us to propose new limit of exposure values, revisited to fit the endotoxin exposure limits recommendations. The results can serve as guidelines for future proposals for air quality indicators.

在污水处理过程中会产生生物气溶胶（bioaerosols），此类气溶胶既可悬浮数小时之久，也可沉降至物体表面，进而使作业人员面临暴露风险。空气中存在的病原体可能会提升作业人员罹患胃肠道或呼吸道疾病的概率。由于加拿大东部冬季气候严苛，污水处理流程的多数环节均在室内开展，若通风条件不足或未配备个人防护装备，则作业人员面临显著职业暴露的风险会进一步升高。本研究在冬、夏两季分别对多个室内污水处理环节开展定点采样，同时结合培养法与分子生物学方法对生物气溶胶进行检测，并对通风情况开展表征分析。本研究通过定量聚合酶链式反应（qPCR）对细菌内毒素、总可培养菌、革兰氏阴性菌及病原体指示物进行定量检测。研究证实，污水处理流程的所有环节均存在潜在病原体，这可能构成潜在的职业健康危害。冬夏两季的数据对比结果显示，水温是影响微生物活性的重要因素；同时研究表明，夏季提升每小时换气次数，有助于降低该时段内生物气溶胶的浓度。筛分工序、砂砾/油脂（FOGs）去除工序以及生物过滤工序是生物气溶胶负载量最高的作业点位。基于显著的相关性结果，本研究建议重新审视污水处理厂（WWTPs）的暴露限值标准。应鼓励作业人员佩戴个人呼吸防护装备以降低健康风险，尤其在长期作业场景中。*研究意义：* 本研究通过对室内污水处理厂采集的空气样本进行分析，证实了通过qPCR检测得到的细菌内毒素、可培养菌、革兰氏阴性菌与总细菌的浓度之间存在显著相关性。基于上述相关性，本研究提出了适配现有细菌内毒素暴露限值建议的全新暴露限值标准。本研究结果可为未来空气质量指示物相关标准的制定提供参考依据。