Cleaning water with mud: clay minerals producing reactive oxidizing species

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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.