# Feedback Characterization for Enhanced Heat Recovery from Composing Processes: A Review
## 3 Results and Discussion
### Chemical and Physical Properties
Non-agricultural feedstocks had a relatively consistent mean bulk density of 528.57 kg/m\({}^{3}\), with a maximum of 600 kg/m\({}^{3}\). The findings indicate that plant-based materials have higher variability in bulk density with a coefficient of variation of 0.46, which may potentially cause fluctuations in composting efficiency. In contrast, animal-derived and non-agricultural feedstock materials exhibit more consistent bulk densities with a coefficient of variation of 0.19 and 0.06, respectively, supporting better oxygen availability and microbial activity and ensuring more efficient biodegradation and heat production. pH is an important parameter during the composting process, directly affecting microbial growth, enzyme function, and nutrient availability. The optimum pH for microbial growth rate and degradation activity is in the 7-8 range [28], at which the maximum thermophilic activity and organic matter degradation occur with the release of heat. The pH for animal-derived materials measured during the study ranged between 5.35 and 8.50, with an average of 7.46, which is within the range for adequate and effective microbial activities for composting. On the opposite end, the mean pH for plant-based materials was 6.38 with a range of 5.35-7.50. Since some of the materials were below the optimal range, it could limit the efficiency of microbial actions. A mean pH of 5.75 was obtained from non-agricultural feedstocks, which falls out of the optimal range, meaning that some adjustments will be necessary to enhance the activity of the microbes and the overall effectiveness of any aerobic process. Animal-derived materials have a mean pH within the optimum range of 7-8 and therefore support optimal microbial growth and microbial degradation activities, which enhance composting and heat production. Materials with plant-based and non-agricultural feedstocks that have lower pH values may require adjustments to achieve optimal microbial activity and ensure consistent aerobic biodegradation. These findings back the theory that the physical and chemical properties influence microorganism activity and the degradability of materials for composting as well as heat generation. Animal-based materials consistently prove to be optimal for composting due to their composition of lignin and other elements like cellulose and hemicellulose along with bulk density and pH levels. Conversely, plant-based materials exhibit a range of variability that may result in inconsistent microbial activity and heat generation. As for the case of the non-agricultural feedstocks, the analysis showed bulk density stability but revealed a lack of detailed information regarding cellulose and hemicellulose content. Furthermore, its low pH value may require some modifications in order to optimize the work of the microbes. It is crucial to monitor and make changes, especially when dealing with plant-based and non-agricultural feedstock materials, to maintain consistent performance and maximize heat recovery in their respective aerobic processes.