A boundary value problem of heat transfer within DBD-based plasma jet setups.

We claim an analytical solution for the thermal boundary value problem that arises in DBD-based plasma jet systems as a preliminary and consistent approach to a simplified geometry. This approach involves the outline of a coaxial plasma jet reactor and the consideration of the heat transfer to the reactor solids, namely, the dielectric barrier and the grounded electrode. The non-homogeneous initial and boundary value thermal problem is solved analytically, while a simple cut-off technique is applied to deal with the appearance of infinite series relationships, being the outcome of merging dual expressions. The results are also implemented numerically, supporting the analytical solution, while a Finite Integration Technique (FIT) is used for the validation. Both the analytical and numerical data reveal the temperature pattern at the cross-section of the solids in perfect agreement. This analytical approach could be of importance for the optimization of plasma jet systems employed in tailored applications where temperature-sensitive materials are involved, like in plasma biomedicine.

Biosolids: The Trojan horse or the beautiful Helen for soil fertilization?

The simultaneous requirement to manage resources and wastes in more rational way has meant that many communities worldwide have begun to search for long-term alternative solutions. Reuse and recovery of biosolids is considered to be a constant solution of circular sustainability, as waste disposal without further reuse background like fertilizer is no longer an alternative to be promoted. There have been developed many treatment methods over the years for the stabilization and sanitization of biosolids. However, the literature concludes that none of them is fully integrated by meeting all the basic criteria. Each method has its Achilles heel, and the appropriateness of the method lies in what is the goal each time. There are conventional methods with positive reciprocity in terms of sustainability, reuse indicators and technological maturity, but have high risk of microorganisms' reappearance. New advanced sustainable technologies, such as cold plasma, need to be further studied to apply on a large scale. The reuse of biosolids as construction materials is also discussed in the context of circular economy. Biosolids reuse and management legislation frame need to be revised, as a directive adopted 30 years ago does not fully meet communities' current needs.

Modelling the electric field in reactors yielding cold atmospheric-pressure plasma jets.

The behavior of the electric field in Cold Atmospheric-Pressure Plasma jets (CAPP jets) is important in many applications related to fundamental science and engineering, since it provides crucial information related to the characteristics of plasma. To this end, this study is focused on the analytic computation of the electric field in a standard plasma reactor system (in the absence of any space charge), considering the two principal configurations of either one-electrode or two-electrodes around a dielectric tube. The latter is considered of minor contribution to the field calculation that embodies the working gas, being an assumption for the current research. Our analytical technique employs the cylindrical geometry, properly adjusted to the plasma jet system, whereas handy subdomains separate the area of electric activity. Henceforth, we adapt the classical Maxwell's potential theory for the calculation of the electric field, wherein standard Laplace's equations are solved, supplemented by the appropriate boundary conditions and the limiting conduct at the exit of the nozzle. The theoretical approach matches the expected physics and captures the corresponding essential features in a fully three-dimensional fashion via the derivation of closed-form expressions for the related electrostatic fields as infinite series expansions of cylindrical harmonic eigenfunctions. The feasibility of our method for both cases of the described experimental setup is eventually demonstrated by efficiently incorporating the necessary numerical implementation of the obtained formulae. The analytical model is benchmarked against reported numerical results, whereas discrepancies are commented and prospective work is discussed.

Sanitary effect of FE-DBD cold plasma in ambient air on sewage biosolids.

Sewage sludge is treated by means of cold plasma and stabilization in terms of biological load deactivation is achieved. The plasma is produced by floating electrode dielectric barrier discharge operating with air under atmospheric pressure conditions. The process is presented in detail and the discharge is characterized electrically. Additionally, simulation of the thermal flow inside the process chamber is implemented, using computational fluid dynamics. Deactivation of the serotypes S. Paratyphi B., S. Livingstone, S. Mbandaka and S. Typhimurium, and Escherichia coli and Coliforms, is hereby claimed. The process involves mean electrical power in the range of tens of watts, treatment time in the scale of minutes, and maximum instantaneous temperature <400 K. The present work is a preliminary contribution towards the promotion of advanced methods for the pro-ecological management of biosolids, according to European Regulations.

Automated electrostatic probe device of high resolution and accuracy.

In this work, an automated apparatus for driving single electrostatic probes and acquiring the plasma-related data has been designed and fabricated. The voltage range of the present system is ±110 V with an adjustable voltage step as low as 3 mV. Voltage and current measurements are carried out with high resolution and high accuracy circuits, both based on 16 bit analog-to-digital converters. The code embedded in a micro-controller, schedules the operation of the device and transfers the experimental data to a personal computer. The modular design of the system makes possible its modification and thus increases its adaptability to different plasma setups. Finally, the reliable operation of the entire device is confirmed by tests in Electron Cyclotron Resonance plasma.