AbstractThis study was carried out to evaluate the effect of natural ventilation and intermittent pumping events in hydrogen sulfide and methane dynamics, in terms of system operation and risk of gas exposure. Work was conducted in a full scale gravity sewer downstream of pumping stations, in Portugal. Different ventilation rates and locations were assessed, as well as H2S removal rates and potential exposure risk, through the opening of distinct manhole covers. Increased ventilation, resulting from opening of one manhole cover, saw a 38% increase in average pipe air velocity peaks, doubling the estimated rate of air turnovers per day, accompanied by an increase of nearly 20% in H2S average removal rate. Simultaneous opening of two manhole covers induced similar airflow rates through the vent stack, but different rates throughout the pipe. H2S removal rates were also found to differ, according to location of open manholes, but also initial H2S headspace concentration. Under more unfavourable conditions, natural ventilation did not suffice in attaining recommended safety concentrations, regardless of number and location of open manhole covers. H2S concentrations above defined thresholds were verified for all studied setups. Headspace oxygen concentrations below an 18.5% asphyxiation threshold also occasionally occurred, even at manholes immediately downstream of ventilation point.

中文翻译：

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通风对硫化氢暴露和重力下水道排放的影响

摘要本研究的目的是评估自然通风和间歇泵送事件对硫化氢和甲烷动力学在系统运行和气体暴露风险方面的影响。工作是在葡萄牙泵站下游的全尺寸重力下水道中进行的。通过打开不同的井盖，评估不同的通风率和位置，以及硫化氢去除率和潜在暴露风险。由于打开一个井盖而增加了通风，平均管道风速峰值增加了 38%，使每天的空气周转率估计增加了一倍，同时 H2S 平均去除率增加了近 20%。同时打开两个井盖会导致通过通风管的气流速率相似，但整个管道的气流速率不同。还发现 H2S 去除率因开放检修孔的位置以及初始 H2S 顶空浓度而异。在更不利的条件下，无论打开的井盖的数量和位置如何，自然通风都不足以达到建议的安全浓度。所有研究设置均验证了 H2S 浓度高于定义的阈值。顶空氧气浓度低于 18.5% 窒息阈值的情况也偶尔发生，甚至在通风点下游的检修孔处也是如此。