## 2 Special Issue Findings  
A summary of the accepted manuscripts with their main contributions is presented below. 1. The first contribution included in this Special Issue was submitted by [PERSON]; [PERSON]; and [PERSON], from the University of Stuttgart, Institute of Combustion and Power Plant Technology, Germany [2]. In this work, sewage sludge gasification was investigated using a 20 kW bubbling fluidised bed test facility (see Figure 1). Steam and oxygen were used as gasification agents, and in situ generated sewage sludge ash was applied as bed material. The influence of the main operating parameters such as gasification temperature, oxygen ratio, steam to carbon ratio, and fluidisation velocity on the composition of the produced raw gas (CO, H\({}_{2}\), CO\({}_{2}\), H\({}_{2}\)S, CH\({}_{4}\), C\({}_{x}\)H\({}_{y}\), COS, NH\({}_{3}\), and tar) was determined. The authors found that the raw gas had high H\({}_{2}\) and CO concentrations of up to 0.37 m\({}^{3}\)/m\({}^{3}\) and 0.18 m\({}^{3}\)/m\({}^{3}\), respectively, making it suitable for the synthesis of fuels and chemicals. By adjusting the steam-to-carbon ratio (by the water gas shift reaction), the H\({}_{2}\)/CO ratio of the syngas could be targeted for different synthesis products such as synthetic natural gas (H\({}_{2}\)/CO = 3) or Fischer-Tropsch products (H\({}_{2}\)/CO = 2). The analysis of the bed ash showed that the cadmium and mercury content was drastically reduced by the gasification process. Ash is appropriate as a secondary raw material to produce phosphorus or phosphate fertilisers. 2. The second article, which was written by [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; and [PERSON], from the VSB-Technical University of Ostrava, Czech Republic, dealt with the thermochemical utilisation of sewage sludge based on thermogravimetric analysis (TGA) [3]. Since sewage sludge is difficult to use as a feedstock due to its high moisture and ash content, its energy utilisation is increased by adding suitable waste materials (various types of plastics, used tires, and paper waste). Fifty-five waste mixtures were prepared in different volume ratios, a visual comparison was made, and high and low calorific values were measured. It was found that thermoplastics with sewage sludge and low-density polyethylene with sewage sludge had the lowest residual masses and the highest weight loss rates. Higher pyrolysis temperatures have always resulted in higher gas  
Figure 1: Schematic flow diagram of 20 kW fluidised bed gasification facility at the University of Stuttgart [2]. volume yields, as observed in many previous studies, e.g., [4]. The authors claimed that the highest average mass yield was reached in the pyrolysis of plastics. The most suitable material and temperature combinations to produce pyrolysis oils and gases were the blends of thermoplastics with sewage sludge and low-density polyethylene with sewage sludge. 3. Solar absorption cooling systems are more advantageous than other cooling systems such as vapour compression because the peak cooling load nearly coincides with the available solar energy. The most common working fluid pairs are water/lithium bromide (H\({}_{2}\)O-LiBr) (water as refrigerant and lithium bromide as a solvent, especially for air conditioning and process cooling) and ammonia/water (NH\({}_{3}\)-H\({}_{2}\)O) (ammonia as refrigerant and water as a solvent, especially for frozen food applications). The authors of the third article ([PERSON]; [PERSON]; and [PERSON], from the Technical University of Darmstadt, Germany) carried out a thermo-economic analysis to compare different configurations of solar absorption cooling systems used for thermal cooling processes [5]. While the first solar absorption cooling system used H\({}_{2}\)O-LiBr as the working fluid pair, the second absorption cooling system adopted NH\({}_{3}\)-H\({}_{2}\)O. Parabolic trough collectors and evacuated tube collectors were applied under the same operating conditions as a source of thermal energy for both systems.