Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 100085, Beijing, China.
Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 100085, Beijing, China; Beijing Climate Change Response Research and Education Center, Beijing University of Civil Engineering and Architecture, Beijing 100044, China.
Water Res. 2024 Nov 15;266:122364. doi: 10.1016/j.watres.2024.122364. Epub 2024 Sep 1.
Odorous dioxanes and dioxolanes, a class of cyclic acetals often produced as byproducts in polyester resin manufacturing, are problematic in drinking water treatment due to their low odor thresholds and resistance to conventional treatment technology. Our research focuses on the removal of ten dioxane/dioxolane compounds through oxidation and adsorption processes, exploring the key molecular properties that govern the treatmentability. We discovered that both chlorination and permanganate oxidation were largely ineffective at degrading cyclic acetals, achieving less than 20% removal even at high applicable doses. Conversely, powdered activated carbon (PAC) adsorption proved to be a more effective method, with a removal of > 90% at a PAC dosage of 10 mg/L for seven out of ten compounds. The presence of natural organic matter (NOM) reduced PAC adsorbability for all odorants, but the deterioration level substantially varied and mostly affected by structural flexibility as indicated by the number of rotatable bonds. The results of both the experimental investigation and molecular simulation corroborated the hypothesis that more rotatable bonds (from one to three here) are indicative of greater structural flexibility, which in consequence determines the susceptibility of cyclic acetals to NOM competitive adsorption. Increased structural flexibility could facilitate greater entry into silt-like micropores or achieve preferential adsorption sites with more compatible morphology against NOM competition. When pre-oxidation (chlorination and permanganate oxidation) and adsorption were applied sequentially, additional low molecular weight NOM components produced by pre-oxidation resulted in intensified NOM competition and decreased odorant adsorbability. If this combination is inevitably required for algae and odorant control, it would be beneficial to utilize a wise screen for oxidants and a reduced oxidant dose (less than 2 mg/L) to mitigate the deterioration of odorant adsorption. This study elucidates the roles of structural flexibility in influencing the treatability of dioxanes and dioxolanes, extending beyond the solely well-established effects of hydrophobicity. It also presents rational practice guidelines for the combination of pre-oxidation and adsorption in addressing odor incidents associated with dioxane and dioxolane compounds.
含臭味的二恶烷和二氧五环，是一类环状缩醛，通常作为聚酯树脂制造的副产物产生，由于其低气味阈值和对传统处理技术的抗性，在饮用水处理中存在问题。我们的研究重点是通过氧化和吸附过程去除十种二恶烷/二氧五环化合物，探索控制可处理性的关键分子特性。我们发现，即使在高适用剂量下，氯化和高锰酸盐氧化对环状缩醛的降解作用也很小，降解率均小于 20%。相比之下，粉末状活性炭（PAC）吸附被证明是一种更有效的方法，十种化合物中有七种在 PAC 剂量为 10mg/L 时的去除率超过 90%。天然有机物（NOM）的存在降低了所有气味物质的 PAC 吸附性，但劣化程度差异很大，主要受结构灵活性的影响，这里由可旋转键的数量表示。实验研究和分子模拟的结果都证实了这样的假设，即更多的可旋转键（这里从一个到三个）表明结构灵活性更大，这反过来又决定了环状缩醛对 NOM 竞争吸附的敏感性。增加的结构灵活性可以更容易地进入类似淤泥的微孔中，或者通过与 NOM 竞争具有更兼容形态的优先吸附位置。当预氧化（氯化和高锰酸盐氧化）和吸附依次进行时，预氧化产生的低分子量 NOM 成分会导致 NOM 竞争加剧，并降低气味物质的吸附性。如果为了控制藻类和气味必须组合使用这两种方法，那么明智地筛选氧化剂并减少氧化剂剂量（小于 2mg/L）以减轻气味物质吸附的恶化是有益的。本研究阐明了结构灵活性在影响二恶烷和二氧五环可处理性方面的作用，超出了仅仅是既定的疏水性的影响。它还为处理与二恶烷和二氧五环化合物相关的气味事件时预氧化和吸附的组合提供了合理的实践指导原则。
