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Optimized iron-biochar composites for degrading halogenated compounds in environmental media: synthesis strategies and reaction mechanisms

Applicant Dr. Anett Georgi
Subject Area Technical Chemistry
Solid State and Surface Chemistry, Material Synthesis
Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
Term from 2018 to 2022
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 392011053
 
Final Report Year 2023

Final Report Abstract

Due to the increasing water shortage, it will become increasingly important to remediate contaminated water resources in the future. Care should be taken to ensure that sustainable principles are applied both in the remediation process and in the production of the materials required for this purpose. The in-situ remediation of contaminated groundwater using fine-grained activated carbon or iron-carbon composites represents an innovative and low-impact remediation method without any excavation of contaminated soil and water. The particles are simply injected into the subsoil in the form of aqueous suspensions and, once deposited on the sediment, form a reactive zone that effectively stops the further spread of the pollutants with the groundwater. The activated carbon used in this process has so far been obtained by grinding commercial activated carbon, which in Germany is often produced from fossil and imported raw materials (e.g. hard coal). It is also not possible to control the particle morphology and the surface properties in this process. In this project, alternative synthesis routes for fine-grained activated carbon as well as iron-carbon composites based on hydrothermal carbonization (HTC) were developed. The HTC process has the advantage that colloidal particles can be produced from renewable raw materials and the morphology of the particles can be controlled. In a subsequent pyrolysis step, the pore system and surface properties of the generated activated carbon and the Fe0 content of the generated Fe/C composite were optimized. In the first part of the project, the synthesis of the fine-grained particles was developed starting from household sugar and a stabilizer with the aim of maximizing the yield and adapting the pore system to various pollutants. The product was extensively characterized in terms of pore size distribution, surface properties and suspension stability. It was shown to have excellent sorption properties for various halogenated organic groundwater contaminants such as per- and polyfluorinated alkyl substances (PFAS). In the second part of the project, the synthesis of an Fe/C composite material was investigated starting from different iron- and carbon-containing feedstocks. Iron and sodium gluconate proved to be particularly promising. The iron content and thus the colloidal and reactive properties of the product were optimized by adjusting the HTC process and subsequent thermal activation. The composite was shown to degrade chloroform as model substance for chlorinated organic groundwater pollutants. By incorporating low amounts of palladium into a Pd/Fe/C composit, nearly complete degradation into chlorine-free products and strongly increased reactivity was achieved. The products developed have application potential in various areas of water treatment, in particular in soil and groundwater remediation, but also in an urban context as filter materials for stormwater infiltration or in the tertiary treatment stage of wastewater treatment plants.

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