A commercial air-fed and piezoelectric-driven plasma pen (piezobrush ^® , relyon plasma GmbH, Regensburg, Germany) including three different nozzles was investigated for its suitability as a medical plasma device. In this regard, potential risk factors for human health, which originate from gas temperature, thermal output, patient leakage current, ultraviolet radiation and gas emissions, were assessed according to DIN SPEC 91315:2016–06. As a result, safe treatment distances were determined for each nozzle. The antimicrobial efficacy was investigated subsequently by inhibition zone assays with five different clinical relevant microorganisms. All results were compared to an approved medical plasma source fed with argon (kINPen ^® MED, neoplas tools GmbH, Greifswald, Germany). It was observed that the antimicrobial efficacy differs not only between the two devices as a result from different feed gases, but also between the nozzles. This could be traced back to a different plasma chemistry, which accompanying Fourier-transform infrared absorption spectroscopy suggests. The measured physical properties of the piezoelectric plasma pen at the determined operating parameters do not show human health risks. Due to its distinct antimicrobial efficacy, the piezoelectric plasma pen shows a high potential for a medical application.

A non-thermal plasma source based on a surface dielectric barrier discharge (DBD) is developed for purification of recirculating air in operating theatres in hospitals. This is a challenging application due to high flow rates, short treatment times and the low threshold for ozone in the ventilated air. Therefore, the surface DBD was enhanced in order to generate an ionic wind, which can deflect and thus, filter out airborne microorganisms. Electrical and gas diagnostics as well as microbiological experiments were performed in a downscaled plasma source under variation of various electrical parameters, but application-oriented airflow velocity and humidity. The dependence of electrical power and ozone concentration as well as charged particles in the plasma treated air on frequency, voltage and relative humidity is presented and discussed. The presence of humidity causes a more conductive dielectric surface and thus a weaker plasma formation, especially at low frequency. The airborne test bacteria, Escherichia coli , showed significant effect to plasma treatment (up to 20% reduction) and to plasma with ionic wind (up to 90% removal); especially a configuration with 70% removal and an accompanying ozone concentration of only 360 ppb is promising for future application.

In the field of bioeconomy, biological materials are used as resource for a wide field of application, such as manufacturing of pharmaceutical products or fine chemicals and processes, e.g., aqua cultures, or mussel farming. Resources may be, amongst others, microorganisms, land plants, but also agricultural residues. To access these resources, technologies are necessary. Many methods already exist, but are accompanied by drawbacks on several levels. High-energy input, detrimental effects caused by heat or chemical impact, generation of toxic by-products, or incomplete extraction/purification are often observed for these standard methods. With physical plasmas, an interesting alternative has been developed to address several aspects from those drawbacks. Plasmas are effective against cell walls of microorganisms, such as microalgae, but also in the valorisation of manure for biogas production, or in the recycling of (waste) water. The unique characteristics of a plasma help to extract compounds from these materials due to shockwaves, which are generated during plasma generation. Also, the production of reactive oxygen and nitrogen species (RONS) are the decisive agents for the degradation of pollutant in water. Here, we review possible fields of application for physical plasmas in the frame of bioeconomy.

A recently proposed pulsed in-liquid microwave plasma pretreatment aiming for biomass disintegration and methane yield enhancement in subsequent anaerobic digestion was further studied and optimized experimentally. A water-based, transparent, highly viscous, sodium carboxylmethyl cellulose solution was used as the treatment model and enabled a systematic quantification of the ignitability of the discharge depending on operational, geometric and substrate parameters. Higher conductivity and initial viscosity along with more powerful pulses and a small microwave antenna cross section promoted the built-up of an initial vapor bubble and hence a fast, efficient and reliable plasma ignition. The observed large viscosity reduction of the model indicated its disintegration and was found to originate from the production of hydrogen peroxide and subsequent advanced oxidation processes. The release of tungsten, copper and zinc due to erosion of the microwave antenna led to additional catalytic effects. Subsequently, the geometry of the coaxial antenna and the shape of the MW pulses were optimized for the most effective and energy-efficient disintegration of the cellulose model, which aligned with the most efficient ignition and hydrogen peroxide production. The best-performing configuration compromised the newly introduced small tungsten coaxial antenna and microwave pulses of 2 kW and 4.6 ms power and length, respectively (10% duty cycle). These findings represent not only an improved understanding of the proposed plasma biomass pretreatment, but also directly led to an improved technical implementation. A sophisticated application on actual biomass substrates in future work was therefore prepared.

Desktop laser cutters are an affordable and flexible rapid-prototyping tool, but some materials cannot be safely processed. Among them is polyvinyl chloride (PVC), which users usually cannot distinguish from other, unproblematic plastics. Therefore, an identification system for PVC applicable in a low-cost laser cutter has been developed. For the first time, this approach makes use of the laser-ablative sound generated by a low-power laser diode. Using a capacitor microphone, a preprocessing algorithm and a very simple neural network, black PVC could be detected with absolute reliability under ideal conditions. With ambient noise, the accuracy dropped to 80%. A different color of the material did not influence the accuracy to detect PVC, but a susceptibility of the method against a color change was found for other materials. The ablation characteristics for different materials were recorded using a fast-framing camera to get a better insight into the mechanisms behind the investigated process. Although there is still potential for improvements, the presented method was found to be promising to enhance the safety of future desktop laser cutters.

Various studies have proposed using plasma treatment prior to anaerobic digestion to enhance the degradation of organic dry residue (oDR) and increase biogas production. This disintegration process also significantly affects phosphorus release by disrupting cell walls. Several studies show that the driving disintegration process through plasma implementation occurs due to the production of hydrogen peroxide. Since targeted plasma treatment is still technically demanding, this study proposes to estimate the related P release by applying defined hydrogen peroxide dosage to the test medium. Here, the approach was implemented on washed activated sludge (WWAS) in batch tests using H₂O₂ at two different temperatures: 20 °C and 60 °C. Results show only heating treatment mobilised approximately 23% P as PO₄-P, while only 9% P was mobilised by applying 3.4 g H₂O₂ / g DR at 20 °C. The reason behind this scenario is the low reactivity of H₂O₂ as catalase is active at ambient temperature, which also caused only 3% COD solubilisation. However, complete COD solubilisation was achieved by applying similar dosage of H₂O₂ at 60 °C. In this treatment condition, dissolved P mobilisation increased to 40% while PO₄-P mobilisation reduced by 11%. The reduction of PO₄-P can be occurred by parallel formation of P related precipitants, since metal ions like Ca and Mg released in this study. Additionally, the oxidation of ammonia to nitrate is also observed, resulting in lower pH (4.41). Also, the oxidation of Fe²⁺ to Fe³⁺ could cause FePO₄ precipitation. These observed effects are probably transferrable to activated sludge from other wastewater treatment plants (WWTPs). Summarizing these effects, high temperature developed in intense wet plasma treatment can prevent the intended P recovery from the wet sludge phase or sludge liquor.