Removal of Volatile Organic Compounds in Vertical Flow Filters: Predictions from Reactive Transport Modeling

Vertical flow filters are containers filled with porous medium that are recharged from top and drained at the bottom, and are operated at partly saturated conditions. They have recently been suggested as treatment technology for groundwater containing volatile organic compounds (VOCs). Numerical reactive transport simulations were performed to investigate the relevance of different filter operation modes on biodegradation and/or volatilization of the contaminants and to evaluate the potential limitation of such remediation mean due to volatile emissions. On the basis of the data from a pilot‐scale vertical flow filter intermittently fed with domestic waste water, model predictions on the system’s performance for the treatment of contaminated groundwater were derived. These simulations considered the transport and aerobic degradation of ammonium and two VOCs, benzene and methyl tertiary butyl ether (MTBE). In addition, the advective‐diffusive gas‐phase transport of volatile compounds as well as oxygen was simulated. Model predictions addressed the influence of depth and frequency of the intermittent groundwater injection, degradation rate kinetics, and the composition of the filter material. Simulation results show that for unfavorable operation conditions significant VOC emissions have to be considered and that operation modes limiting VOC emissions may limit aerobic biodegradation. However, a suitable combination of injection depth and composition of the filter material does facilitate high biodegradation rates while only little VOC emissions take place. Using such optimized operation modes would allow using vertical flow filter systems as remediation technology suitable for groundwater contaminated with volatile compounds.     

Computationally efficient stochastic optimization using multiple realizations

The presented study is concerned with computationally efficient methods for solving stochastic optimization problems involving multiple equally probable realizations of uncertain parameters. A new and straightforward technique is introduced that is based on dynamically ordering the stack of realizations during the search procedure. The rationale is that a small number of critical realizations govern the output of a reliability-based objective function. By utilizing a problem, which is typical to designing a water supply well field, several variants of this “stack ordering” approach are tested. The results are statistically assessed, in terms of optimality and nominal reliability. This study demonstrates that the simple ordering of a given number of 500 realizations while applying an evolutionary search algorithm can save about half of the model runs without compromising the optimization procedure. More advanced variants of stack ordering can, if properly configured, save up to more than 97% of the computational effort that would be required if the entire number of realizations were considered. The findings herein are promising for similar problems of water management and reliability-based design in general, and particularly for non-convex problems that require heuristic search techniques.     

Towards solution of the pulsar problem

The 24-year-old pulsar problem is reconsidered. New results are obtained by replacing the assumption of steady-state discharges near the polar caps by oscillatory discharges, and by creating the neutral-excess pair plasma via inverse-Compton collisions rather than via curvature radiation. As a result, the electrons and positrons which compose the pulsar wind have different bulk velocities and an oscillating space density, and (strong) coherent curvature radiation is implied (without invoking the excitation of instabilities, and contrary to existing proofs of its impossibility). The magnetospheres of young pulsars are likely to have considerable higher-order multipole components, in particular octupole. Radiation transfer through the pulsar magnetosphere results in fan beams whose polarization is dictated by the bottom of the radiation zone, hence, looks like curvature radiation from dipole-like polar caps.Wind generation depends mainly on the quantityB² which takes similar values for the ms pulsars; the latter compensate for (somewhat) weaker fields by wider polar caps and smaller curvature radii.     

Integrated geothermal modeling on different scales in the Northeast German basin

Geothermal modeling is an important part of large-scale basin studies. Based on a new 3D structural model of the Northeast German basin, the present day regional geothermal field is modeled. Range and regional trend of the modeled temperature values are in agreement with the published data. Due to the high spatial resolution, the calculated temperature distribution provides additional information with respect to areas where no measured data is available. The results are used as input and boundary parameters for small-scale models of geothermal energy production. In general, in many regions not enough data is available to define all necessary physical or chemical parameters for modeling. In this context, data obtained from the large-scale model help to constrain unknown parameters. Subsequently, the small-scale model is used to simulate various production schemes focusing on enhanced predictions with respect to the possible lifetime of such installations. The simulation results also show the need for elaborated models if reliable predictions of the temperature evolution are required.     

Vesteris Seamount: An enigma in the Greenland Basin

Vesteris Seamount is a solitary submarine volcano located at 73°30 N, 9°10W in the Greenland Basin. Steeply rising from a base depth of 3100 m to a minimum depth of ~ 130 m and striking 030°/210°, the feature lies ~ 300 km east of the east Greenland margin on an otherwise nearly flat and featureless seafloor. The main body of the seamount appears to have been formed episodically, the last of which culminated about 110 000 years ago. Subsequent, lower intensity volcanic activity continued sporadically until about 25 000 years ago, as evidenced by ash layers found in cores near the base of the feature. The smoothed surfaces at the summit make it likely that the seamount actually broached the surface during the Weichselian glacial period, between 8000 and 13 000 years ago. Two multibeam bathymetric investigations aboardPFS Polarstern during ARKTIS II/4 (1984) and ARKTIS VII/1 (1990), combined with geologic sampling, single-channel seismic profiling and underwater television coverage, have resulted in a new interpretation of both the morphology and origins of the seamount. Data collected aboardPolarstern from ARKTIS II/4 (1984) have been previously reported by Hempelet al. (1991), however, when combined with the ARKTIS VII/1 (1990) data set, a more detailed interpretation of the morphology and structure was feasible. This included the elongated shape of the feature and showed the existence of several small volcanic cones on the seamount flanks.The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged.     

Ein einfaches,universelles Gerät für luftelektrische Messungen und seine Anwendungsmöglichkeiten

Zusammenfassung Es wird ein einfaches Gerät für luftelektrische Untersuchungen beschrieben, das folgende Messungen bzw. Registrierungen auszuführen gestattet: 1) Registrierung des luftelektrischen Antennenstromes (Vertikalstrom); 2) Registrierung des luftelektrischen Feldes nach einer «halbstatischen» Methode; 3) Registrierung bzw. Zählung rascher zeitlicher Aenderungen des statischen Feldes (Feldsprünge bei el. Entladungen in der Atmosphäre). Die Anordnung besteht aus einem besonders konstruierten Röhrenvoltmeter, dessen Gehäuse Anzeigegerät und Stromversorgungen vercinigt. Die verschiedenen Fehlergrenzen der Messmethode werden eingehend dis kutiert. Das Gerät eignet sich zur Messung der Feldstärke bis ± 1500 V/m. Ein Einfluss der Windegeschwindigkeit auf die Feldanzeige besteht nach eingehenden Untersuchungen nicht. Zehntägige Anschlussregistrierungen im Erdmagnetischen Observatorium in Fürstenfeldbruck mit demBenndorf- Elektrometer erbrachten völlige Kurvengleichkeit der beiden Geräte. Einige Messbeispiele führen die Anwendungsmöglichkeiten des Gerätes vor Augen. Die gleichzeitige Registrierung des luftelektrischen Feldes an mehreren Stationen erbrachte sehr gute Uebercinstimmung im Kurvenverlauf, der durch die jcweiligen meteorologischen Verhältnisse bedingt war. Die Darstellung der mittleren Tagesgänge der Monate von 1949 und 1950 schliesst sich an.

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Summary A simple apparatus is described for measuring and recording the following data: 1) Vertical atmospheric current; 2) Atmospheric potential gradient (using a «half-static» method); 3) Frequency und shape of fast changes of the atmospheric potential gradient (at times of electric discharges in the atmosphere). The apparatus consists of a specially divised tube-voltmeter, combining current supply and reading instrument in one housing. Various error limits of the method are discussed. Potential gradients may be measured up to ±1500 volts per meter. Special investigations showed the wind velocity to have no influence on the measurements. 10 days' comparative records of this apparatus and theBenndorf-elektrometer of the Fürstenfeldbruck Geomagnetic Observatory showed complete identity of curves. Several examples of results obtained with the new intrument are given. Simultaneous records of atmospheric potential gradients at various places showed good agreement of curves obtained under similar meteorological conditions. Graphs of average daily variations during the months of 1949 and 1950 are also given.

     

The legacy of the NE German Basin — reactivation by compressional buckling

In contrast to previously published models for the area, the seismic reflection Moho is essentially flat beneath the NE German Basin along the DEKORP deep seismic profile Basin'96. This raises the question, whether the present structure of the crust and flat Moho reflect the initial formation of the basin or modification by more recent processes. A 2D flexural model, developed for a thin elastic plate, is presented together with lithospheric strength profiles calculated along the BASIN 9601 reflection seismic line. The analysis shows a southward decrease of lithospheric strength below the Basin, with a lithospheric decoupling between the crust and the mantle. The modelling supports the hypothesis that the present Moho topography is caused by flexural buckling which caused subsidence of the NE German Basin during the Upper Cretaceous–Early Cenozoic inversion event. This suggests that the basin is in isostatic disequilibrium, and that compressive stresses are required to keep the present basin geometry.