Cleaning water with mud: clay minerals producing reactive oxidizing species

我们理所当然地认为，高质量的饮用水直接送到我们的家里，我们产生的废水经过处理，达到可以安全排放到环境中的水平。然而，水处理涉及以化学品和能源的形式进行密集投入，以将有机污染物转化为无害的形式，并摧毁有害微生物，使水处理成为一个经济和环境代价高昂的过程。在拟议的研究中，我们将探索一种储量丰富且成本低廉的天然材料粘土矿物是否能够可持续地产生活性氧化物种，用于水处理中的高级氧化。这种方法不需要化学或能源投入，因此将对环境的负面影响降至最低，并使低收入国家也能负担得起高级氧化。我们认为，含铁粘土矿物在与氧气反应时会产生一系列活性氧化物种，类似于已知的溶解亚铁。然而，在粘土矿物的结构中使用铁是可靠和重复地在需要氧化的部位再生氧化反应性的关键，从而设计出可持续的高级氧化工艺。在这项研究中，我们将为基于含铁粘土矿物的高级氧化提供概念证明，并将具体研究(1)含铁粘土矿物在氧气存在下是否氧化污染物和灭活微生物；(2)在反应过程中产生哪些活性氧化物种，是否形成与粘土矿物表面结合的任何物种；(3)粘土矿物的氧化活性如何可持续地再生。在第一步，我们将通过监测模型有机污染物的氧化和微生物的生存来探索粘土矿物系统中的氧化反应活性。将对不同的粘土矿物进行筛选，以确定粘土矿物性质对其氧化活性的影响，并确定最有希望进行进一步研究的粘土矿物。为了确定在反应过程中产生了哪些活性氧化物种，我们将使用特定的探针化合物，这些化合物只与可能形成的不同活性氧化物种中的一种反应。在其他实验中，粘土矿物将通过半透膜从特定的探针化合物中分离出来，使我们能够识别活性氧化物种是否与粘土矿物表面结合。这些实验结果将证明含铁粘土矿物高级氧化在消毒和污染物氧化方面的有效性。在最后的一系列实验中，我们将评估如何可靠和重复地再生含铁粘土矿物的氧化活性。为此，我们将从批量实验开始，在这些实验中，粘土矿物的反应性将通过化学物质实现再循环，然后我们将把同样的方法应用于柱子实验。接下来，将使用特定微生物的活动来重新生成粘土矿物的氧化活性，最后将只管理水流和柱饱和度，以展示如何使用含铁粘土矿物进行可持续的高级氧化。在这项研究中，我们的目标是证明可以使用一种通常被称为“泥”的天然材料来实现水处理的高级氧化，以及如何可持续地管理和应用这种高级氧化过程来进行水处理或土壤和沉积物修复。预期结果将为确定可应用于高收入、中等收入和低收入国家的新的、本质上可持续的水处理工艺指明前进方向。

We take for granted that high quality drinking water is delivered directly to our home and that the wastewater we produce is treated to a level where it is safe to be released into the environment. Water treatment involves, however, intense inputs in the form of chemicals and energy to transform organic contaminants into a harmless form and to destroy harmful microbes, making water treatment a financially and environmentally costly process. In the proposed research, we will explore whether an abundant and low-cost natural material, clay minerals, can sustainably generate reactive oxidizing species for advanced oxidation in water treatment. This approach would need no chemical or energy input and would therefore minimize negative environmental impacts as well as make advanced oxidation affordable also for low-income countries.We suggest that ferrous iron-containing clay minerals can produce a series of reactive oxidizing species during the reaction with oxygen, similar to what is known for dissolved ferrous iron. Using iron in the structure of clay minerals is, however, key to reliable and repeated regeneration of oxidizing reactivity at the site where oxidation is needed and thus to designing a sustainable advanced oxidation process. In this research, we will provide a proof of concept for advanced oxidation based on iron-bearing clay minerals and will specifically investigate (1) whether ferrous iron-containing clay minerals oxidize contaminants and inactivate microbes in the presence of oxygen;(2) which reactive oxidizing species is produced during the reaction and whether any species bound to the clay mineral surface are formed, and(3) how the oxidative reactivity of clay minerals can be sustainably regenerated.In a first step, we will thus probe for oxidative reactivity in our clay mineral systems by monitoring the oxidation of model organic contaminants and the viability of microbial organisms. Different clay minerals will be screened to determine the effect of clay mineral properties on their oxidative reactivity and to identify the most promising clay mineral for further investigation. To identify which reactive oxidizing species is produced during the reaction, we will then use specific probe compounds that will react with only one of the different reactive oxidizing species that could potentially form. In additional experiments, clay minerals will be separated from the specific probe compounds by means of semipermeable membranes, allowing us to identify whether reactive oxidizing species are bound to the clay mineral surface. The results from these experiments will demonstrate the effectiveness of iron-bearing clay mineral-based advanced oxidation for disinfection and contaminant oxidation. In a last series of experiments, we will assess how we can reliably and repeatedly regenerate the oxidative reactivity of iron-bearing clay minerals. To this end, we will start with batch experiments in which the re-cycling of clay mineral reactivity will be achieved with chemicals and we will then apply the same approach to column experiments. Next, the activity of specific microbes will be used to regenerate the oxidative reactivity of clay minerals and finally only water flow and column saturation will be managed to show how iron-bearing clay minerals can be used for sustainable advanced oxidation.In this research, we aim to demonstrate that advanced oxidation for water treatment can be implemented using a natural material often referred to as "mud" and how this advanced oxidation process can be managed and applied sustainably for water treatment or soil and sediment remediation. The expected results will illustrate a way forward to identifying new and intrinsically sustainable water treatment processes that could be applied in high-, middle, and low-income countries.