Anaerobic digestion (AD) is a biological process that breaks down organic matter in the absence of oxygen, producing biogas and nutrient-rich digestate. Various reactor designs and mixing strategies are well-established in AD processes, each with their own advantages and benefits. The presented study summarizes and investigates the state of the art of AD in domestic wastewater treatment plants (WWTPs) in an Austrian alpine region, with a primary focus on finding similarities among the most efficient plants regarding digester design, mixing approaches, and biogas production. By combining surveys and detailed field studies in cooperation with 34 WWTPs, the study provides a comprehensive overview of common AD practices, reactor shapes, and inherent mixing methods, highlighting their potential regarding energetic efficiency and biogas production. The results of the survey reveal qualitative trends in efficient AD design alongside detailed quantitative data derived from the supervised in-field optimization studies. Notably, one of the studies demonstrated energetic savings of 52% with no decrease in biogas production, achieved by transitioning from gas injection to mechanical agitation. Redundant impeller-based overmixing was also practically investigated and demonstrated in another field study. After optimization, the adaptations also resulted in energy savings of 30%, still proving sufficient substrate mixing with biomethane potential analysis. In conclusion, this research emphasizes the economic and environmental importance of energy-refined practices and optimized processes while highlighting the sustainability of AD, particularly for large domestic WWTPs but also for different comparable applications.

The dewatering of substrates is one of the key tasks in the handling of material flows in a circular economy. Besides belt filters, sedimenters, and decanters, screw presses are frequently used to reduce the water content of substrates. However, screw presses available on the market are usually designed for high throughputs (>5 m³/h). The dewatering of smaller feed rates (<1 m³/h), however, requires more compact solutions. For this reason, a compact screw press (short screw length), which is normally used in agriculture for cow manure dewatering, was investigated in this work, as there exist no publications on this type of compact screw press. A mobile test setup was developed and loaded with different material such as digested sludge from a wastewater treatment plant, commercially available potting soil, wood shavings, and biological waste. The dry matter content of the feed material, the feed material itself, the screw rotational speed, and the weight setting (pressure) at the back plate were varied, and the effects on the dewatering result were recorded. A significant influence on the dewatering result was found for the weight setting, the type of substrate (particle size), and the dry substance content of the feed material. The tests confirmed that the compact screw press separator is suitable for the dewatering of wood shavings and biological waste (with an increase in dry matter percentage of up to 7.7%). The direct dewatering of potting soil and digested sludge is not possible and can only be implemented by using structural support material. This study fills the gap between published work on large screw presses and potentially new application fields of compact screw press manure separators, which, until now, have only been used in agriculture.

Despite the high number of scientific publications on related topics, such as sustainability, pollution control, etc., research on microplastic (MP) is still in its infancy. To advance the quality of future MP investigations, scientists have recently called for harmonization regarding the definition and categorization of MP, as well as for consensus in sampling and investigations methodologies. The application of standardized and fully characterized MP particles, which are commercially available on a large scale but rarely characterized by manufacturers, could add another piece to that mosaic. This publication aims to introduce ten low-priced MP powders that can be used as reference particles in future MP studies. The physical parameters shape, particle density and particle size distribution were examined, and results compared to technical information reports and data sheets, available. Particle densities were almost in line with the manufacturer’s information. However, significant leaks could be revealed for particle size specifications, thus underlining the demand for an accurate description of the particle size distribution, e.g., D₅₀ or D₉₀.

Coandă effect screen structures are used to protect hydropower turbines in mountainous regions from impurities of different sizes. To save time during the design phase, computational fluid dynamics simulations (CFD) can support experimental investigations. Experimental investigations and 2D CFD simulations are performed on the base of the Coandă effect screen structure. Flow rates of 7 m³/h, 8 m³/h, and 9 m³/h are simulated, captured by a camera system in the experiments, and compared. In the experimental setting, the fill level of the Coandă rake is measured. For comparison, the RMSE of the y-position fill level is computed between simulation and measurement. Furthermore, the mass flow balance, $\mathsf{\Pi }$, is evaluated. The RMSE of the y-direction fill level between simulation and measurement is on average 2.1 mm and 4.4 mm for the lower CFD level and the higher CFD level, respectively. Experiments show an average 6.72% higher Π. The reason for this is that 2D CFD does not consider the surface tension of the borders. In the diverted flow region, the flow field based on experiments appears less viscous than in the simulations. CFD simulations are an appropriate tool to support the design process of Coandă effect screens, especially for fill level determination. The validated CFD code can reduce the cost and time of experiments to design future Coandă effect screen structures.