The design of a permeable iron wall depends to a great
extent on the transformation kinetics of the chlorinated
compounds. Therefore these degradation kinetics of TCE
and cis-DCE with commercial iron and their dependence on
the properties of the compounds and on the experimental
conditions were studied in mixed-batch and column
experiments. Since our data cannot sufficiently be described
by a pseudo-first-order kinetics, we successfully applied
an enhanced model accounting for both zero- and first-order
kinetics. The fitted kinetic parameters, however, were
found to depend on the experimental conditions and compound
properties, which is interpreted in terms of different rate-limiting processes. The zero-order rate constant turned
out to be twice as high for cis-DCE as for TCE in both
experimental systems. Despite its slower transformation
without transport control, the first-order rate constant was
about 4 times higher for TCE than for cis-DCE in the mixed-batch vials. We attribute this to the lower water solubility
and thus higher sorptivity of TCE at the polished iron surface.
In the column experiments, transformation without
transport control was twice as fast as in the batch
experiments for both compounds. cis-DCE was degraded
faster than TCE in the zero- and first-order region. At higher
influent concentrations, the zero- and first-order rate
constant of TCE decreased, which we assume to be due
to the buildup of iron oxides, and transport to the reactive
sites was found to depend a little on flow velocity. Due
to the slow first-order kinetics of both compounds, we assume
diffusion within micropores to be rate-limiting in flow-through systems. These variations in the kinetic parameters
of the combined zero- and first-order model suggest that
transport and sorption to reactive sites contribute to kinetic
control of the degradation of chlorinated ethenes in
addition to charge-transfer processes.
New techniques and methods for energy storage are required for the transition to a renewable power supply, termed ''Energiewende'' in Germany. Energy storage in the geological subsurface provides large potential capacities to bridge temporal gaps between periods of production of solar or wind power and consumer demand and may also help to relieve the power grids. Storage options include storage of synthetic methane, hydrogen or compressed air in salt caverns or porous formations as well as heat storage in porous formations. In the ANGUS? project, heat and gas storage in porous media and salt caverns and aspects of their use on subsurface spatial planning concepts are investigated. The optimal dimensioning of storage sites, the achievable charging and discharging rates and the effective storage capacity as well as the induced thermal, hydraulic, mechanical, geochemical and microbial effects are studied. The geological structures, the surface energy infrastructure and the governing processes are parameterized, using either literature data or own experimental studies. Numerical modeling tools are developed for the simulation of realistically defined synthetic storage scenarios. The feasible dimensioning of storage applications is assessed in sitespecific numerical scenario analyses, and the related spatial extents and time scales of induced effects connected with the respective storage application are quantified. Additionally, geophysical monitoring methods, which allow for a better spatial resolution of the storage operation, induced effects or leakages, are evaluated based on these scenario simulations. Methods for the assessment of such subsurface geological storage sites are thus developed, which account for the spatial extension of the subsurface operation itself as well as its induced effects and the spatial requirements of adequate monitoring methods.
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