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While a high content of reclaimed asphalt in road construction is targeted, recycled bitumen has often undergone chemical and physical damages characterized as ageing. This can be counteracted with additives denoted as rejuvenators and by controlling the heating process during mix production. This study investigated the surface and base layers of three asphalt variants with different levels of reclaimed asphalt and rejuvenator. Asphalt samples were heated either through conventional heat conduction or through dielectrical heating using radio waves. Bitumen analyses included Ring-and-Ball, Needle Penetration, Dynamic Shear Rheometry and Fourier-Transform Infrared Spectroscopy while asphalt performance was assessed by Cyclic Indirect Tensile Test. Ageing indicators were derived and correlated quantitatively, revealing high correlation among bitumen analysis results and lower correlation of asphalt analysis results. Some of the test methods explicitly supported the hypothesis that radio wave heating may induce a lower ageing than conventional heating combined with rejuvenation.

Die Feintrocknung spielt eine Schlüsselrolle für den Einsatz und insbesondere die Einspeisung von Wasserstoff in die Erdgasinfrastruktur. Zur thermischen Regenerierung des Trockenmittels können Radiowellen für eine direkte dielektrische Erwärmung des Schüttbettes eingesetzt werden. In Abhängigkeit von den verwendeten Zeolithen, NaX oder NaY, sind dabei sowohl eine homogene Erwärmung als auch eine selektive Erwärmung der wasserbeladenen Trockenmittelschüttungen möglich. Nach entsprechenden Tests steht nunmehr ein einsatzfähiger druckfester Prototyp für die Wasserstofftrocknung zur Verfügung.

Selective measurement of hydrogen in the natural gas grid as large transport and storage infrastructure is a crucial requirement for establishing a hydrogen economy. Cost-effective sensors must face mainly two critical conditions: (i) absence of oxygen contents capable for ensuring the sensor function and (ii) presence of a large surplus of another reducing gas, methane. The developed Pt/TiO2 sensor is based on the combination of the catalytic spillover effect and an impedance measurement. It allows hydrogen detection in a wide concentration range and it is specific for hydrogen while other gases such as methane or carbon dioxide behave like inert gases. The sensor curve with decreasing relative sensitivity for higher hydrogen concentrations and the temperature dependence of the sensor effect are in agreement with the spillover-based sensor principle, where hydrogen is activated on Pt and then spills over onto the TiO2 where it acts as electron donor.

Carbon coatings are synthesized on various solids via hydrothermal carbonization as a green and environmental-friendly method. The coatings can be produced on various solid substrates independent of their shape and surface properties by application of stirring during the reaction. Coatings on stainless steel felt and mesh as well as on ceramic tubes were further investigated. In their raw state, the coatings obtained have a high content of various oxygen-containing functional groups, and are somewhat lacking in surface area. However, thermal treatment creates porosity (up to 500 m2 g-1 specific surface area) and reduces oxygen content and density of functional groups. The heat-treated carbonaceous materials can be used as cost-efficient adsorbents in water treatment systems for adsorption of organic pollutants, with the option for regeneration through electro-thermal heating.

Reductive catalytic conversion of DDT (p,p′-dichlorodiphenyltrichloroethane) was studied under ambient conditions in a hydrogen atmosphere using platinum and palladium deposited on several supports, in particular on porous alumina and silica. Almost complete hydrodechlorination and hydrogenation of DDT and its dehydrochlorination byproduct DDE (p,p′-dichlorodiphenyldichloroethene), leading to the formation of diphenylethane (with Pd) and dicyclohexylethane (with Pt), were observed at ambient temperature within minutes or hours. Rapid hydrodechlorination also takes place after depositing DDT and the metal component on separate particles and mixing them mechanically. This long-range reactivity can be explained either by a fast surface diffusion of DDT or DDE, or by hydrogen spillover. Irrespective of the mechanism, the reactivity thus bridges the barrier across solid particle interfaces. Most findings indicate the fast diffusion of target compounds as dominant mechanism for the observed long-range reactivity.

Mit Erwärmung durch Radiowellen Holzschädlinge bekämpfen: Im Rahmen eines von der Deutschen Bundesstiftung Umwelt im Netzwerk RWTec geförderten Forschungsprojekts [1] entwickelten das Helmholtz-Zentrum für Umweltforschung (UFZ) und die Hochschule für Technik, Wirtschaft und Kultur (HTWK) Leipzig in Zusammenarbeit mit Praxispartnern ein Verfahren, mit dem durch eine kontrollierte Erwärmung Holzschädlinge abgetötet werden können. In der Regel sind dabei Temperaturen von 55 °C bis 60 °C ausreichend. Der Einsatz wurde an unterschiedlichen Objekten erfolgreich demonstriert, wobei das Einsatzpotenzial von der Sanierung von Dachstühlen bis zur Behandlung von wertvollen Kunstgegenständen reicht.

[EN] For drying building structures, dielectric heating using RF energy (13.56 MHz) is an efficient and fast alternative to conventional heating methods relying solely on heat transfer from the surface to the interior of the masonry. Another innovative application of volumetric RF heating is chemical-free pest control in wood-based materials. For such applications where the RF systems often cannot be completely shielded, the propagation or coupling of the electromagnetic waves into wires that are placed inside the field cannot be neglected which represents a certain risk. Depending on the different electromagnetic coupling mechanisms, several interference signals can be generated. In order to protect electrical equipment in the surrounding, these interferences have to be significantly reduced by electrical filters. For this purpose, a cost-effective and robust measuring concept was developed. With the help of this system, the common mode (iCM) interference could be identified as the dominant part and the differential mode (iDM) interference as a minor disturbance. Based on the experimental evaluation, a cost-effective filter for the respective disturbance was constructed and successfully tested.

[EN] For drying building structures, dielectric heating using RF energy (13.56 MHz) is an efficient and fast alternative to conventional heating methods relying solely on heat transfer from the surface to the interior of the masonry. Another innovative application of volumetric RF heating is chemical-free pest control in wood-based materials. For such applications where the RF systems often cannot be completely shielded, the propagation or coupling of the electromagnetic waves into wires that are placed inside the field cannot be neglected which represents a certain risk. Depending on the different electromagnetic coupling mechanisms, several interference signals can be generated. In order to protect electrical equipment in the surrounding, these interferences have to be significantly reduced by electrical filters. For this purpose, a cost-effective and robust measuring concept was developed. With the help of this system, the common mode (iCM) interference could be identified as the dominant part and the differential mode (iDM) interference as a minor disturbance. Based on the experimental evaluation, a cost-effective filter for the respective disturbance was constructed and successfully tested.

[EN] For drying building structures, dielectric heating using RF energy (13.56 MHz) is an efficient and fast alternative to conventional heating methods relying solely on heat transfer from the surface to the interior of the masonry. Another innovative application of volumetric RF heating is chemical-free pest control in wood-based materials. For such applications where the RF systems often cannot be completely shielded, the propagation or coupling of the electromagnetic waves into wires that are placed inside the field cannot be neglected which represents a certain risk. Depending on the different electromagnetic coupling mechanisms, several interference signals can be generated. In order to protect electrical equipment in the surrounding, these interferences have to be significantly reduced by electrical filters. For this purpose, a cost-effective and robust measuring concept was developed. With the help of this system, the common mode (iCM) interference could be identified as the dominant part and the differential mode (iDM) interference as a minor disturbance. Based on the experimental evaluation, a cost-effective filter for the respective disturbance was constructed and successfully tested.

[EN] For drying building structures, dielectric heating using RF energy (13.56 MHz) is an efficient and fast alternative to conventional heating methods relying solely on heat transfer from the surface to the interior of the masonry. Another innovative application of volumetric RF heating is chemical-free pest control in wood-based materials. For such applications where the RF systems often cannot be completely shielded, the propagation or coupling of the electromagnetic waves into wires that are placed inside the field cannot be neglected which represents a certain risk. Depending on the different electromagnetic coupling mechanisms, several interference signals can be generated. In order to protect electrical equipment in the surrounding, these interferences have to be significantly reduced by electrical filters. For this purpose, a cost-effective and robust measuring concept was developed. With the help of this system, the common mode (iCM) interference could be identified as the dominant part and the differential mode (iDM) interference as a minor disturbance. Based on the experimental evaluation, a cost-effective filter for the respective disturbance was constructed and successfully tested.

The non‐thermal plasma (NTP) technique was shown to be a method to improve indoor air quality. In particular in kitchens, odorous emissions can be removed by NTP. A combined concept of adsorption of volatile organic compounds (VOC) and plasma regeneration of the adsorber was tested in adsorption‐regeneration‐adsorption cycles. As reference VOC, 2‐methylthiophene, 2‐methylpyrazine, 2‐acetylthiazole, nonanal and trans‐2‐nonenal were used in humid air streams. These odorous compounds are emitted during cooking and frying processes. The adsorption‐regeneration concept was also tested during a simulated frying process with garlic in rape oil. A hydrophobic zeolite was chosen as adsorber material and placed directly into the discharge zone of a plasma reactor.

Purpose The aim of this study was to prove that radio-frequency (RF) energy with 13.56 MHz can be used for heating building structures in a controlled manner exploiting the advantage that homogeneous heating with sufficient penetration depths can be achieved. Design/methodology/approach Because parallel electrodes on both sides of the heated structure cannot be used in many practical applications, two special electrode designs have been developed by modeling the field distribution and energy absorption and by carrying out test experiments to validate the simulation results. Findings One solution is based on a two-dimensional surface capacitor providing certain penetration depths and being especially suitable for treating thin structures such as wooden parquet floor. Such an arrangement can be particularly used for pest control even when sensitive surfaces have to be protected. The other solution uses a capacitive coupling between the grounded shielding and an electrode or an equivalent structure (e.g. moist soil) at the other side of the masonry to establish a sufficiently strong electrical field between a “hot” electrode on the side of the shielding and the coupled rear electrode. Originality/value Both solutions significantly enhance the application potential of RF heating. &nbsp

Decontamination of air or other gas streams loaded with low VOC concentrations is a prevalent task for adsorption using zeolites. Emphasizing the importance of adsorber selection, several zeolites varying in type, Si/Al ratio and provider were tested for toluene as representative organic target compound and water as adsorbate both in single and competing adsorption studies. In some cases, the toluene breakthrough is mainly caused by water-driven desorption. It was shown that for adsorption capacity, kinetics and competition behavior not only type and Si/Al ratio of the zeolite are important but also producer-specific parameters such as crystallinity, binder type and content which are usually not explicitly documented. This study offers a basis for the selection of adsorber materials for treatment of gas streams with significant water contents.

Non-thermal plasma technique can be a method to improve indoor air quality. In particular in cuisines, odorous emissions can be removed by non-thermal plasmas. In this study 2-methylthiophene, 2-methylpyrazine, 2-acetylthiazole, nonanal and trans-2-nonenal were used as target compounds in concentrations in the low ppmv range. These odorous compounds are emitted during cooking and frying processes. The oxidation of these target compounds as multi-component mixture in a non-thermal gas-phase plasma was studied in dry mixtures of argon and oxygen and in humid air. Complete oxidation of the odorous compounds to COX was achieved in both atmospheres. The energy efficiency was higher in the dry mixture of argon and oxygen, whereas the selectivity of the oxidation towards carbon dioxide was significantly higher in humid air. The main products of plasma treatment were identified as CO, CO2 and polymeric deposits. Some minor organic intermediates in the pptv range were also identified. Although odor carriers could be completely degraded and the concentrations of potentially harmful organic byproducts were several orders of magnitude below critical values, high ozone and CO emissions during plasma operation are critical for indoor application of non-thermal plasma as stand-alone technique. The combination with a catalytic step, either as in-plasma or post-plasma catalysis, might be a promising approach to tackle this problem.

Thermal pest control with hot air is widely accepted as an alternative to chemical methods. However, it requires relatively long treatment times due to the low thermal conductivity of wood. Direct dielectric heating applying radio waves or microwaves has the advantage of a more homogeneous heating. However, sound experimental data on this technique are rare at present. Therefore, thermal treatment of wood-destroying insects with radio waves and microwaves was studied with two model pests, Anobium punctatum and Hylotrupes bajulus, and with Tenebrio molitor as reference. It was shown that a secure elimination of pests can be achieved by temperatures above 55°C; the corresponding treatment time was in the range of a few minutes. Temperature profiles were more homogeneous when applying radio waves.

Dielectric heating with radio waves (RW) and microwaves (MW) are alternatives to treatments with hazardous chemicals or hot air for pest control. In particular, RW can be used to heat up bulky materials with larger size (in the meter range) homogeneously and smoothly in order to eliminate embedded pest organisms. Dielectric heating, in principle, enables selective overheating of certain materials in a heterogeneous mixture. This unique feature of electromagnetic heating methods, in contrast to techniques being based on thermal conduction, is caused by significant differences in the dielectric properties of pest organisms and matrix materials. The present study proves unambiguously that selective heating of cylindrical pest organisms in wood matrices occurs under defined conditions. The selective heating effect strongly depends on the orientation of the pest organisms in the electric field. For a parallel alignment, maximum overheating factors (ratio of adiabatic local heating rates) of 2 to 3 were determined experimentally. In case of a perpendicular alignment, no overheating was detected. A simulation of electric field and power loss density distributions in pest organisms and in their vicinity in the wood matrix, using a finite element method, can qualitatively explain the experimental results. According to the simulation, the overheating occurs not directly within the pest organism but in the wood matrix in the vicinity on both ends of the cylinder-shaped pest organism

Heat treatment of concrete during the early stages of hydration using the new radio wave technology enables a uniform energy supply at distinct rates under steady, closed-loop temperature control. This precise control of temperature makes it possible to implement accurately and uniformly any heat treatment regime based on existing or future guidelines over the entire volume of a concrete element. The article at hand presents this new technology briefly and focuses on the issue of possible delayed ettringite formation which might compromise concrete durability. By means of ESEM- and XRD-analysis the influence of the different heat treatment temperatures on the concrete microstructure could be comprehensively investigated. It was found that a maximum temperature of 60 °C should not be exceeded because higher temperatures cause severe delayed ettringite formation. Dielectric heating as such had no additional influence on microstructural damage, especially on the extent of the formation of delayed ettringite.

The application of radio waves with a frequency of 13.56 MHz on electrolyte solutions in a capillary reactor led to the formation of reactive hydrogen and oxygen species and finally to molecular oxygen and hydrogen. This process of water splitting can be principally used for the elimination of hazardous chemicals in water. Two compounds, namely perfluorooctanoic acid (PFOA) and tetrahydrofuran, were converted using this process. Their main decomposition products were highly volatile and therefore transferred to a gas phase, where they could be identified by GC-MS analyses. It is remarkable that the chemical reactions could benefit from both the oxidizing and reducing species formed in the plasma process, which takes place in gas bubbles saturated with water vapor. The breaking of C–C and C–F bonds was proven in the case of PFOA, probably initiated by electron impacts and radical reactions.

For mitigation of the impact on flood-damaged cultural heritage buildings and sites, solely conservation-compatible and noninvasive strategies can be applied. All procedures have to take into account not only the specific situation after flooding but also the material properties and the characteristics of the artwork related to the building. After a heavy flooding event damaging the monastery Marienthal in Germany demonstration studies were proceeded to evaluate heritage-adequate treatment strategies for the drying of a decorated chapel. To respect and preserve the original gypsum stucco interior drying in certain temperature limits had to be respected. Particularly, direct volumetric heating methods were employed working with electromagnetic waves in the frequency ranges of either microwaves or radio waves. The studies comprised heating tests on site and experiments on a heritage-representative masonry specimen. It could be shown that the removal of water could be significantly enhanced by both techniques. Radio wave heating was demonstrated to allow a more homogeneous and better controlled treatment in comparison to microwave application, which is especially relevant in case of sensitive materials such as gypsum. With respecting that limits the techniques can be applied in combination with efficient removal of moisture from the ambient air by ventilation in order to reduce the drying time thus limiting subsequent damage of the heritage building.

By means of radio-wave technology it is possible to allow the uniform, rapid and accurate, temperature-controlled heating of fresh concrete. This results in the significantly accelerated release of hydration heat. The heat release from this second source can be easily compensated by the temperature-controlled reduction of RF energy input. The consequences are accelerated hydration and higher early-age compressive strength. Early-age concrete, heat-treated by radio waves, have a denser microstructure with a higher gel-pore content and more C-S-H phases than untreated concrete. When cured at the maximum temperature of 80 °C, secondary ettringite can be formed in concrete, whereas this is not the case for the treatment temperatures of 40 °C and 60 °C. At the age of 28 d, heat-treated concretes exhibit a looser microstructure than does untreated concrete. Larger portlandite crystals and secondary ettringite are its characteristic features as a consequence of the much faster reaction rates in the early-age concrete. This results in lower values of the compressive strength of the heat-treated concrete.

Zur wirtschaftlichen Herstellung von industriell gefertigten Betonbauteilen werden geringe Taktzeiten angestrebt, um die Formen und Schalungen möglichst schnell wiederverwenden zu können. Dafür ist es notwendig, dass der Beton eine hohe Frühfestigkeit entwickelt, um die nötige Ausschalfestigkeit zu erreichen. Um den Hydratationsprozess schneller ablaufen zu lassen, kann einerseits ein Beton mit hohem Zementanteil oder mit einer hohen Zementfestigkeitsklasse verwendet werden, andererseits kann der Frischbeton erwärmt werden. Gegenstand dieses Artikels ist, ein Verfahren zur Wärmebehandlung von Frischbeton vorzustellen, welches eine energieeffiziente, temperaturgesteuerte Erwärmung möglich macht. Durch das elektromagnetische Feld bei der Radiowellen-Technologie wird der Frischbeton dielektrisch erwärmt, was eine homogene Temperaturerhöhung bewirkt. Durch die Kopplung von Temperaturmessung und Energieeintrag können vorher definierte Temperaturkennlinien und Maximaltemperaturen eingehalten werden, eine genaue Temperatursteuerung wird gewährleistet. Ziel der Untersuchungen zur Wärmebehandlung von Frischbeton mit der Radiowellen-Technologie ist, Aussagen über Temperatursteuerung, Homogenität und energetischen Wirkungsgrad zu treffen. Weiterhin werden die Auswirkungen der dielektrischen Erwärmung auf die Früh- und Endfestigkeit geklärt und es wird die Strukturentwicklung im Beton beschrieben. Die Struktur des wärmebehandelten Betons wird mit verschiedenen Methoden bestimmt, um ein möglichst detailliertes Bild zu bekommen. Zur Charakterisierung der Gefügemorphologie des Betons werden Messungen zur Porengrößenverteilung mit der Quecksilberporosimetrie sowie mikroskopische Untersuchungen mit dem Rasterelektronenmikroskop (ESEM) herangezogen.Radio wave technology used for heat treatment of fresh concreteThe economical production of industrially-produced concrete elements aims for low cycle times in order to be able to reuse the forms and form-works as soon as possible. Therefo

Die thermische Bekämpfung von Holzschädlingen erfordert wegen der geringen Wärmeleitfähigkeit von Holz lange Behandlungszeiten und kann zur Rissbildung führen. Hier wurde die thermische Behandlung mittels Radio- und Mikrowellen untersucht. Die direkte, dielektrische Erwärmung hat den Vorteil einer größeren Homogenität der Aufheizung. Die mit Radiowellen erzielten Temperaturprofile waren homogener als die mit Mikrowellen realisierten. Untersuchungen zeigten, dass die Abtötung nicht auf die direkte Einwirkung von elektromagnetischen Feldern, sondern auf die Temperaturerhöhung zurückzuführen ist.Thermal pest control requires long treatment times due to the low thermal conductivity of wood and may lead to the formation of cracks. Here, the thermal treatment with radio waves as well as microwaves has been studied. The direct dielectric heating has the advantage of a good homogeneity. The obtained temperature profiles for radio waves were more homogeneous compared to microwaves. Detailed studies showed that elimination of pests was not related to the application of the electromagnetic field itself, but due to the temperature increase.

CO2 emissions, energy costs and cement consumption in the precast industry can be lowered substantially with the aid of high-frequency heat treatment, an innovative procedure for the controlled heating of fresh concrete. This procedure generates a second internal heat source, alongside hydration heat, by employing radio wave technology (the operating principle is similar to that of microwaves) during the concrete curing process, thereby accelerating hardening considerably.

Mithilfe der Hochfrequenz-Wärmebehandlung, einem neuartigen Verfahren zur kontrollierten Erwärmung von Frischbeton, können CO2- Emissionen, Energiekosten und Zementverbrauch in der Fertigteilindustrie deutlich gesenkt werden. Dieses Verfahren erzeugt unter Nutzung der Radiowellen-Technologie (mit einem Funktionsprinzip ähnlich dem einer Mikrowelle) während der Betonerhärtung neben der Hydrata­tionswärme eine zweite innere Wärmequelle und beschleunigt so die Aushärtung deutlich.

A dynamic phenomenon of selective dielectric heating using radio-frequency energy is used to establish a continuous process for the elimination of organic pollutants from contaminated gas streams. The process consists of two phases characterized by adsorption and by regeneration utilizing in situ catalytic oxidation. The thermal regeneration of the packed bed is started by a so-called thermo-chromatographic pulse, i.e. a combined water/temperature pulse moving through the reactor with a packed bed containing both an adsorber and a catalytically active component (NaY zeolite and Pt, respectively). The pronounced temperature pulse is formed due to the strongly enhanced absorption of electromagnetic energy within a water pulse. This can be explained by the complex dependency of the energy absorption on both local moisture content and local temperature of the zeolite. As a result, the previously adsorbed organic contaminants are desorbed and, simultaneously, the catalyst is thermally activated leading to total oxidation of the released hydrocarbons. Thus, the gas stream can be permanently cleaned employing only one packed bed reactor. This has been demonstrated for various experimental conditions.

The influence of low-frequency (50 Hz) resistive and high-frequency (13.56 MHz, radio-frequency) dielectric heating in comparison to conventional heating on the microbial degradation of pollutants in soil was studied. The investigation of the biodegradation of model substances (benzoic acid, acetic acid, glucose, sodium acetate) added to a standard soil showed no significant influence of the electrical heating methods when compared withsamples heated to the same temperature in a water bath. Therefore, a hindrance of the microbial degradation could be excluded as it was done for soil respiration in a previous study. This finding is especially relevant for the application of these electrical heating methods for thermally enhanced soil bioremediation as an option for making in situ or ex situ clean-up processes more efficient.

The influence of electrical heating on microbiological processes in soil has been studied to evaluate the potential for enhancing biodegradation of pollutants by controlling the temperature. A frequency of 50 Hz (power line frequency) was applied for resistive heating. Dielectric heating was realized using a frequency of 13.56 MHz (radio frequency). Both techniques were compared with conventional heating in a water bath. For experimentsin laboratory and full scale, a model soil and a contaminated original soil were used. It was shown that under conditions capable for heating soil to 35 °C or even 60 °C, soil respiration as a measure for microbial activity was not hindered by electrical heating when temperature and moisture content were comparable with conventional heating. The variations of soil respiration were reversible upon temperature changes. Under certain conditions, periodical fluctuations of microbiological activity were observed. Several possible explanations including chronobiology are discussed without being able to provide an unambiguous interpretation for this effect.

Applying a new experimental design with a capillary glass reactor and plate electrodes outside of the reactor allowed the initiation of discharges in aqueous electrolytes under the influence of a radio-frequency (RF) electromagnetic field.This study focused on the mechanism leading to the initiation of such discharges in the restriction of a glass tube. The light emission correlated with discharges was analysed with optical emission spectroscopy. Electrons with energies between 20 and 45 eV were responsible for the dissociation of water molecules into (excited) OH, H and O radicals. Current–voltage characteristics were measured before and under discharge conditions. Modelling of the experimental setup and simulation of electrical field strength distribution support the hypothesis of the origin of discharges in general and experimental findings such as ring-shaped discharges and a minimum solution conductivity of about 1 S m−1 required for discharge initiation with RF voltages of 2 kV.

By utilizing the specific influence of water adsorption on the dielectric loss factor and,consequently, selective heating of the zeolite NaY in a radio-frequency (RF) electromagnetic field,a hot zone moving through the packed bed can be realized initiated by water injection. While theeffect of water adsorption on RF heating and the phenomenon of the thermo-chromatographicpulse (TCP) itself were described in a previous paper, the present study presents a detailedmodel for the description and explanation of this effect. It involves the complex dependence ofdielectric loss on temperature and moisture content, a diffusion model considering both hoppingand Knudsen mechanisms and a power balance for a representative segment of the packed bed.The developed model was successfully applied to adequately describe various experimentalsituations observed for selective RF heating in a NaY zeolite bed.

In situ radio-frequency heating (ISRFH) combined with soil vapor extraction was demonstrated at a contaminated field site of a former hydrotreatment plant in Zeitz near Leipzig. The project was carried out in several phases including cold soil vapor extraction for comparison. During the test, a soil volume of about 300 m3 was heated to an average temperature of 54 °C. As expected, the extraction rate for hydrocarbons (especially the main contaminant benzene) was markedly enhanced by soil heating. Furthermore, microbial degradation of organic compounds was supported. Although a total amount of approximately 1.4 t of hydrocarbons was removed from the soil, the demonstration project was not aimed at complete remediation of the site. Conditions limiting the extent of cleanup are discussed in detail and conclusions for an efficient application of ISRFH in soil remediation are derived whereas experiences from other sites are also implied.

A new type of water dissociation at ambient pressure initiated by the irradiation of aqueous electrolytes using an electromagnetic field with a frequency of 13.56 MHz is described in this study. A special reactor design allows the use of ex situ electrodes to form in situ electrical discharges in water vapour bubbles. The observed formation of molecular hydrogen (H2) and oxygen (O2) combined with the emission of light ('burning water' phenomenon) originates from a non-thermal plasma in water vapour bubbles. The influences of type of electrolyte, its concentration, pH value and external RF voltage on the gas formation rate as well as on the gas composition are presented.

In situ radio-frequency heating (ISRFH) was successfully applied during remediation of a former petrol station. Using a three-electrode array in combination with extraction wells for soil vapor extraction (SVE), pollution consisting mainly of benzene, toluene, ethylbenzene, xylenes, and mineral oil hydrocarbons (in total about 1100 kg) was eliminated from a chalk soil in the unsaturated zone. Specially designed rod electrodes allowed selective heating of a volume of approximately 480 m3, at a defined depth, to a mean temperature of about 50 °C. The heating drastically increased the extraction rates. After switching off ISRFH, SVE remained highly efficient for some weeks due to the heat-retaining properties of the soil. Comparison of an optimized regime of ISRFH/SVE with conventional “cold” SVE showed a reduction of remediation time by about 80 % while keeping the total energy consumption almost constant.

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In the present study, the astonishing influence of water dosage on a purged dry packed bed of NaY zeolite in the presence of an electric field with a frequency of 13.56 MHz was investigated. The injection of a small amount of water to the inlet of the bed led to pronounced selective heating of the inlet zone by more than 150 K. Thus, water represented a very effective coupling medium for dielectric heating. The selectively heated zone then slowly moved through the whole packed bed and a water pulse finally left the zeolite. This effect correlated with a coupled water and heat flux was called thermo-chromatographic pulse (TCP) emphasizing its analogy to chromatography. The phenomenon could not be performed by using conventional (convective) or microwave heating. It was demonstrated under various conditions and explained by a new model based on own experimental results as well as data from literature. The model will be the objective of a forthcoming publication.

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Direct dielectric heating with radio-frequency (RF) electromagnetic fields is used to optimize a variety of processes in environmental technology, namely soil remediation by soil vapor extraction or biodegradation, adsorptive-catalytic off-gas treatment, thermal regeneration of drying agents in biogas or natural gas treatment and decontamination and/or drying of brickwork.

The transport diffusivity of the paramagnetic molecule 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) was measured by monitoring its influence on the NMR transverse relaxation time (T2) on surrounding water protons - also known as paramagnetic relaxation enhancement (PRE). Due to the nature of the PRE effect, few paramagnetic molecules are able to simultaneously reduce the T2 of many NMR active nuclei, which represents a significant gain in sensitivity. In an aqueous solution, the minimal detectable TEMPO concentration was around 70 ppm. The value of the diffusivity was estimated by fitting the relaxation data, collected as a function of time, with the appropriate solutions of the second Fick’s law in respect to the corresponding sample geometry and dimensions. Considering the experimentally determined TEMPO relaxivity in water (“TEMPO-water relaxivity”; RTEMPO = (1.05 ± 0.12) × 10–3 ppm–1 s–1), the obtained diffusion coefficients (D) of TEMPO in homogeneous solution and in a water saturated sand column (Dbulk = (6.7 ± 0.4) × 10–10 m2 s–1 and Dsand = (1.4 ± 0.5) × 10–10 m2 s–1, respectively) are in good agreement with the expected values (literature values: Dbulk = 6.6 × 10–10 m2 s–1, 1.3 × 10–10 m2 s–1 < Dsand < 2.3 × 10–10 m2 s–1). This new approach enables one to determine the diffusivity of paramagnetic molecules in homogeneous (aqueous solution) and porous media with basic NMR equipment, at low concentrations and in a noninvasive manner.

In situ electrical heating of soil was studied applying different frequencies: low-frequency energy for resistive heating and radio-frequency energy for dielectric heating. Steep temperature gradients were observed for each heating mode under the condition of the coexistence of saturated and unsaturated soil zones. By combining the two heating modes, this undesired effect can be avoided, thus allowing efficient soil remediation especially when organic phases are accumulated at the capillary fringe. A parallel application of both frequencies was demonstrated as the most suitable method to reduce temperature gradients. By using electronic filters, both electric fields can be established by only one electrode array. This innovative concept is especially applicable for optimizing thermal remediation of light non-aqueous phase liquid contaminations or realizing thermally-enhanced electrokinetic removal of heavy metals.

Radio-frequency heating to enhance soil decontamination requires adjusted solutions for the electrode design depending on scale and remediation technique. Parallel plate electrodes provide widely homogeneous field and temperature distributions and are, therefore, most suitable for supporting biodegradation processes. For thermally enhanced soil vapor extraction, certain temperature gradients can be accepted and, therefore, the less-demanding geometry of rod-shaped electrodes is usually applied. For electrode lengths of some meters, a design with an air gap has to be used in order to focus heating to the desired depth. Perforated rod electrodes may be simultaneously employed as extraction wells. Placing an oxidation catalyst in situ within the electrodes is an option for handling of highly loaded air flows. Coaxial antenna may be utilized to selectively heat soil compartments far from the surface of the soil.