Redox Properties and Reactivity of Sorbed Natural Organic Matter

• Applicant: Professor Dr. Stefan Haderlein, since 6/2018
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 338519729

Natural organic matter (NOM) is a major diver of biogeochemical redox processes in soils aquifers. The prominent role of NOM in electron transfer reactions arises from is its ability to act as redox buffer as well as an electron shuttle, enhancing reactions between bulk electron donors and acceptors. Although in natural porous media a major fraction of NOM is present in sorbed state, the effect of redox properties (i.e., the electron exchange capacities and the redox state) on NOM sorption to minerals has not been addressed nor the effect of sorption on the redox properties of sorbed NOM. We hypothesize that the redox properties of adsorbed NOM will differ from those of the same type of NOM in the absence of sorbing surfaces. The research proposed here aims at quantifying these changes to provide the basis for a mechanistic understanding of how sorption processes control redox properties and biogeochemical functions of NOM in aqueous systems. Since sorption of NOM also determines the fraction of mobile and immobilized NOM and their respective redox properties, a detailed insight is needed in order to assess which part of NOM will be available and active for processes such as pollutant transformation, microbial respiration or electron shuttling. We suggest to study experimentally the mechanisms in detail that determine the redox properties and redox state of sorbed NOM. Thus, we propose to address the following major research questions in this proposal: - How does sorption of NOM to solid surfaces per se (i.e., in the absence of electron transfer) change its redox properties (electron accepting/donating capacity, redox state, EH distribution, redox mediation capacity)? - How does the redox state of NOM influence its sorption behavior? - How does electron transfer between the sorbent and NOM change the redox properties of sorbed NOM? - How do bulk properties and pretreatment of NOM (origin, aromaticity, acid/base chemistry) affect sorption and electron transfer processes altogether? To this end, we will study experimentally and systematically the mechanisms that determine the redox properties and redox state of sorbed NOM in laboratory batch experiments at environmentally relevant conditions using novel electrochemical techniques and a range of NOM samples and minerals. As NOM coatings are ubiquitous in aquatic systems answers to these questions will allow us to develop a much deeper understanding of heterogeneous redox processes in the subsurface and are a prerequisite for development of quantitative models for predicting biogeochemical processes at the mineral-water interface.

• DFG Programme: Research Grants
• Ehemalige Antragstellerin: Dr. Silvia Orsetti, until 6/2018