# Drying Characteristics of Chicken Manure Under a Variable Temperature Process
## 3 Results and Discussion
### Drying Characteristics at Different Moisture Content Nodes  
In this set of experiments, an air velocity of 1.2 m/s was sustained, and the temperature was increased to 55 \({}^{\circ}\)C when the moisture content dropped to 35%, 40%, 45%, 50%, and 55%, respectively. The experimental results (Figure 9) show that the drying time gradually decreased with increasing moisture content nodes, with a successive reduction of 0.5 h, 1.2 h, 2.5 h, and 5 h as the moisture content nodes increased. This trend can be explained by the fact that as the moisture content nodes increased, the transition to the second drying stage occurred earlier, and the drying rate remained consistently high during the second drying stage. Furthermore, it was observed that when the moisture content node was below 45%, the influence of the moisture content nodes on drying time diminished. The drying times at the moisture content levels of 35% and 40% did not show a significant difference (\(p>0.05\)). A possible explanation for this phenomenon is that when the moisture content approaches 30%, the remaining water in the chicken manure primarily exists as bound water. This observation aligns with the conclusions presented in Section 3.1. The energy consumption of each group is shown in Figure 10, with values of 2.69, 2.41, 2.30, 2.24, and 2.39 kWh, respectively. The experimental results reveal that when the moisture content node was set at 35%, the energy consumption was the highest. This occurred because a lower moisture content node extended the drying time in the first stage, leading to increased fan energy consumption. Additionally, when the moisture content node was set at 55%, the energy consumption was higher than that observed in experimental groups with moisture nodes of 40-50%. This result can be attributed to the larger amount of water that needed to be removed during the second drying stage, and the higher the moisture content nodes, the longer the second drying stage. At the same time, it can be seen from the changing trend of the bar chart that the influence of water content nodes on energy consumption is similar to that of drying temperature in the second stage. This result also indirectly shows that the energy consumption in the variable-temperature drying process is related to the drying time required for the two drying stages. Analyses of Figure 11 showed that the total nitrogen loss gradually decreased as the moisture content node increased. For every 5% increase in the moisture content node, the total nitrogen loss decreased by 2.5%, 2.8%, 3.2%, and 3.5%, respectively. This trend was directly related to the drying time of the first stage. When the moisture content node was set higher, the drying time of the first stage became shorter. During the early drying stage, the water content of chicken manure is high, and the drying temperature is relatively low,  
Figure 9: Effect of moisture content nodes on drying time of the variable temperature process. Notes: Different letters (a, b, c, d) are significant (\(p<0.05\)). The same letters are not significant. which creates favorable conditions for microbial activity and the degradation of organic matter [4]. A shorter first-stage drying time results in lower uric acid degradation and reduced production of NH\({}_{4}\)-N. In contrast, during the second drying stage, the temperature is high, which accelerates the dehydration rate of chicken manure and shortens the drying time. These conditions are not conducive to microbial activity or further hydrolysis of organic nitrogen. Consequently, the degradation of organic nitrogen and the generation of NH\({}_{4}\)-N during this stage are negligible [27]. Therefore, a higher moisture content node results in less NH\({}_{4}\)-N generation and lower NH\({}_{4}\)-N volatilization throughout the drying process [6]. In the actual production process, reducing the fermentation time and retention time of chicken manure can reduce nitrogen loss in the chicken manure drying process.