## 2 Materials and Methods
During each cycle, the temperature ranged from \(-\)30 \({}^{\circ}\)C (simulating winter conditions) to \(+\)35 \({}^{\circ}\)C (simulating summer conditions), with a complete cycle lasting 10 days. To model seasonal variations, the chamber's relative humidity was adjusted between 60% and 90%:  
At low temperatures (\(-\)30 \({}^{\circ}\)C), the relative humidity was set to 60%, which corresponded to typical winter conditions in the mid-latitudes of Russia. As the temperatures rose to \(+\)35 \({}^{\circ}\)C, the humidity was increased to 90%, which simulated the high humidity typical of summer. Additionally, sludge samples were subjected to ultraviolet (UV) irradiation to replicate the seasonal solar radiation levels typical of this region. The UV intensity was varied from 0.5 mW/cm\({}^{2}\) to 1.5 mW/cm\({}^{2}\):  
* 0.5 mW/cm\({}^{2}\) at lower temperatures, which reflected the reduced solar activity during winter. * 1.5 mW/cm\({}^{2}\) at higher temperatures, which represented the peak summer solar radiation levels. UV irradiation was applied for a simulated daylight period of 12 h to account for the daily fluctuations in solar exposure. This comprehensive configuration of the climate chamber parameters enabled a realistic simulation of mid-latitude Russian seasonal conditions. Consequently, this study could closely examine the impact of temperature fluctuations, humidity changes, and UV irradiation on the drying processes, biochemical transformations, and microbial activity within the wastewater sludge. Heating phase: Lasting several days, this phase involved rapid microbial population growth as the microorganisms decomposed the soluble and easily degradable substances, such as simple sugars and carbohydrates, followed by more complex compounds, like cellulose, hemicellulose, and proteins. The temperature rose to approximately 40 \({}^{\circ}\)C, and the pH became acidic due to the formation of organic acids. Thermophilic phase: Characterized by temperatures exceeding 40 \({}^{\circ}\)C, this phase saw mesophilic microorganisms replaced by thermophiles. There was accelerated decomposition of proteins, fats, and complex carbohydrates, and the pH became alkaline due to ammonia release during protein degradation. Upon reaching around 55 \({}^{\circ}\)C, most pathogens were eliminated, and the substrate was sterilized. This phase typically lasted from several days to one or two weeks. Cooling phase: As easily degradable substances diminished and metabolic activities decreased, the temperature began to drop. The pH remained alkaline. Thermophilic fungi and actinomycetes actively broke down polysaccharides, hemicellulose, and cellulose into monosaccharides, which were then utilized by a diverse range of microorganisms. This phase lasted up to one or two weeks, and the temperatures fell to 35-40 \({}^{\circ}\)C, which allowed mesophilic microorganisms to dominate. Organic matter was transformed into humus-like substances through complex reactions between lignin residues and decomposed proteins. The final pH was weakly alkaline, and invertebrates, such as earthworms and beetles emerged, where they actively processed the substrate. Aeration of the sludge was carried out mechanically by mixing once a day. It is well known that the aeration mechanism significantly influences both the temperature profile and the duration of the process [38]. Since this study was conducted under laboratory conditions with small volumes of sludge, implementing a pneumatic aeration system proved challenging. Nevertheless, some studies were related to the regulation of aeration intensity based on biological oxygen consumption or oxygen concentration in the exhaust gases [39; 40]. A total of eight samples were analyzed for each type of sludge. Each sample was measured in two parallel measurements, with the results averaged. The averaged results were subjected to statistical analysis to identify any outliers beyond the 1.5 interquartile range using boxplots.