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首页> 外文期刊>Journal of Environmental Science and Health >Aeration prevents methyl mercury production in dental wastewater
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Aeration prevents methyl mercury production in dental wastewater

机译：曝气可防止牙科废水中产生甲基汞

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Although research has demonstrated that Hg is methylated in the reducing conditions of the dental clinic wastewater collection system, studies are inconclusive as to whether further methylation occurs in the aeration basin of activated sludge wastewater treatment plant (WWTP) which typically treats this waste. Given the high levels of methyl Hg reported in dental wastewater (DWW), it is important to determine whether additional methylation occurs once it enters the WWTP. To achieve this objective, we incubated DWW under conditions designed to mimic the oxidized conditions of the activated sludge aeration basin in a WWTP. Duplicate bioreactors were charged with raw DWW collected from a 12-chair dental clinic and incubated both with and without aeration. Aeration was continued for 15 days, consistent with the typical mean cell residence time (MCRT) necessary for both heterotrophic carbon oxidation (typically 5-6 days) and nitrification (typically 12-15 days), thus ensuring that incubation time exceeded those for most conceivable MCRTs used in the activated sludge process. Results demonstrate a rapid increase in pH concomitant with an increase in dissolved oxygen (DO) to near saturation in the aerated reactor. The non-aerated reactor remained low or at zero DO due to low surface reaeration coupled with the high levels of organic matter. The rate of mercury methylation increased in the unaearated reactors rapidly upon incubation, reaching highest levels when DO was at the lowest levels during the experiment. In great contrast, methyl mercury levels were much lower and net mercury methylation does not appear to occur at any significant rate under aeration. These results imply that although some mercury methylation may occur in the sewer collection system (or anaerobic digesters), net methylation is unlikely to occur in the aeration basin in activated sludge WWTPs, and thus methyl Hg influent levels from DWW represent an upper bound on effluent levels.
机译：尽管研究表明，汞可在牙科诊所废水收集系统的还原条件下被甲基化，但对于通常处理该废物的活性污泥废水处理厂（WWTP）的曝气池中是否会发生进一步的甲基化，尚无定论。考虑到牙科废水（DWW）中甲基汞的含量很高，因此重要的是确定一旦进入废水处理厂，是否还会发生其他甲基化。为了实现此目标，我们在设计为模拟污水处理厂中活性污泥曝气池的氧化条件的条件下孵育了DWW。一式两份的生物反应器中装有从12个椅子的牙科诊所收集的原始DWW，并在有充气和无充气条件下进行温育。持续通气15天，这与异养碳氧化（通常5-6天）和硝化（通常12-15天）所需的典型平均细胞停留时间（MCRT）一致，从而确保了大多数培养时间都超过了活性污泥工艺中可使用的MCRT。结果表明，在充气反应器中，pH值迅速升高，同时溶解氧（DO）升高至接近饱和。由于低表面反应和高水平的有机物，未充气的反应堆保持较低或为零的溶解氧。孵育后，未安装反应器中的汞甲基化速率迅速增加，在实验过程中当DO处于最低水平时达到最高水平。与之形成鲜明对比的是，在曝气条件下，甲基汞的水平要低得多，并且净汞甲基化似乎没有任何显着的发生。这些结果表明，尽管下水道收集系统（或厌氧消化池）中可能会发生一些汞甲基化，但活性污泥污水处理厂的曝气池中不太可能发生净甲基化，因此DWW中的甲基汞进水量代表了污水的上限。水平。

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