Greywater (GW), domestic wastewater excluding the streams generated by toilets and kitchens, can serve as an alternative water source. The main options for GW reuse are toilet flushing and garden irrigation, both generating aerosols. These may transmit inhalable pathogens like Legionella and present a potential health risk. This study quantified the health risk that may arise from inhalation of Legionella-contaminated aerosols due to non-potable GW reuse. Data on Legionella concentrations in potable water and GW was collected. Then, Quantitative Microbial Risk Assessment (QMRA) was performed for two possible exposure scenarios: garden irrigation and toilet flushing. This was performed while considering Legionella seasonality. In order to determine the safety of GW reuse regarding Legionella transmission, the obtained results were compared with estimated tolerable risk levels of infection and of disease. Both limits were expressed as Disability-Adjusted Life Years index (DALY) being 10^-4 and 10^-5, respectively. The QMRA revealed that the annual risk associated with reuse of treated and chlorinated GW for garden irrigation and toilet flushing was not significantly higher than the risk associated with using potable water for the same two purposes. In all studied scenarios, the health risk stemming from reusing treated and chlorinated GW was acceptable regarding Legionella infection. In contrast, reuse of untreated or treated but unchlorinated grey-water should not be practiced, as these are associated with significantly higher health risks.

中文翻译：

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中水回用-评估肺炎军团菌引起的健康风险

除厕所和厨房产生的水流以外，生活用水Greywater（GW）可以作为替代水源。GW重用的主要选择是冲厕和花园灌溉，两者都会产生气溶胶。这些可能传播可吸入的病原体，例如军团菌，并存在潜在的健康风险。这项研究量化了由于非饮用水GW的重复使用而吸入军团菌污染的气雾可能产生的健康风险。收集了饮用水和GW中军团菌浓度的数据。然后，针对两种可能的暴露情况进行了定量微生物风险评估（QMRA）：花园灌溉和厕所冲水。这是在考虑军团菌时进行的季节性。为了确定有关军团菌传播的重用GW的安全性，将获得的结果与估计的感染和疾病的可承受风险水平进行比较。这两个限制分别表示为10 ^-4和10 ^-5的残疾调整生命年指数（DALY）。QMRA揭示，与处理过的和氯化的GW重复用于花园灌溉和厕所冲洗相关的年度风险并不显着高于出于相同的两个目的而使用饮用水的相关风险。在所有研究方案中，对于军团菌，因重复使用经处理和氯化的GW而产生的健康风险是可以接受的感染。相比之下，未经处理的或未经处理但未氯化的灰水不应该再利用，因为它们与健康风险显着相关。