Fate of pyrene on mineral surfaces during thermal remediation as a function of temperature.

There is evidence that contaminants can transform at the elevated temperatures of thermal remediation; however, the contribution of redox active minerals to transformation has not been investigated. Three redox active minerals (i.e., birnessite (MnO2), magnetite (Fe3O4), and hematite (Fe2O3)) and one redox inactive mineral (Ottawa sand (SiO2)) were spiked with pyrene and thermally treated. Under dry, anoxic conditions, 100%, 75% ± 3%, 70% ± 15%, and 14% ± 28% of the initial pyrene mass was removed with birnessite, magnetite, hematite, and Ottawa sand, respectively, after treatment at 250 °C for 30 min. Under wet, oxic conditions, 92% ± 8%, 86% ± 12%, 79% ± 4%, and 42% ± 7% was removed for the same minerals, respectively, after treatment at only 150 °C for 30 min. Baseline studies with Ottawa sand resulted in volatilization alone of pyrene with no transformation observed. Increased pyrene loading was used to evaluate potential transformation pathways based on identified by-products, demonstrating that both oxidative and reductive pathways were operative depending on the conditions. Reaction products in the presence of redox active minerals indicate transformation was dominated by reduction via hydrogenation in dry experiments, and by oxidation via hydroxyl radicals in wet experiments. The latter was unexpected, because only low hydroxyl radical concentrations have been detected in mineral-water systems at ambient temperature. These results indicate that understanding dominant reaction pathways and products is advantageous for the design of efficient and safe thermally enhanced treatment systems.

Water Treatment: Are Membranes the Panacea?

Alongside the rising global water demand, continued stress on current water supplies has sparked interest in using nontraditional source waters for energy, agriculture, industry, and domestic needs. Membrane technologies have emerged as one of the most promising approaches to achieve water security, but implementation of membrane processes for increasingly complex waters remains a challenge. The technical feasibility of membrane processes replacing conventional treatment of alternative water supplies (e.g., wastewater, seawater, and produced water) is considered in the context of typical and emerging water quality goals. This review considers the effectiveness of current technologies (both conventional and membrane based), as well as the potential for recent advancements in membrane research to achieve these water quality goals. We envision the future of water treatment to integrate advanced membranes (e.g., mixed-matrix membranes, block copolymers) into smart treatment trains that achieve several goals, including fit-for-purpose water generation, resource recovery, and energy conservation.