## 1 Introduction  
The poultry-processing industry is one of the largest and fastest growing segments in global livestock production, driven by the increasing demand for protein-rich diets, advancements in poultry nutrition, and its status as the most economical source of animal-based protein [1]. The two major byproducts of poultry production are feather and bone wastes, with a total estimated 25 million tons generated globally each year. Most of this waste is currently disposed of in landfills or incinerated, processes that are both costly and environmentally damaging [2, 3]. Poultry feathers and bones present significant challenges for integration into production flows due to their unique composition and structural properties. Feathers are primarily composed of keratin--a tough, fibrous protein that is highly resistant to natural degradation and difficult to break down and utilize in standard processing or recycling systems [3]. Similarly, bones are primarily composed of calcium phosphate and collagen, which are dense and require specialized processing to recycle effectively [4]. Common waste-management practices of raw poultry residues, such as land application, can spread pathogens, produce phytotoxic substances, cause air pollution, and emit greenhouse gases. Excessive land application may also lead to nitrate contamination of groundwater, posing health risks such as respiratory disorders and cancer in humans, as well as fetal loss in cattle [5]. The environmental concerns mentioned above have prompted a search for alternative waste-disposal methods to replace conventional practices. Various approaches for managing poultry industry waste have been explored, including composting (aerobic digestion), anaerobic digestion, and direct incineration [6; 7; 8]. However, composting has several drawbacks, such as a loss of nitrogen and essential nutrients, high equipment and labor costs, unpleasant odors, and the need for significant land area [9]. Slaughterhouse waste, in particular, is often challenging for anaerobic digestion due to its high protein and fat content, which can lead to the formation of byproducts during anaerobic breakdown that are toxic and inhibit the activity of anaerobic microorganisms at elevated concentrations [10]. One promising solution for managing poultry waste is transforming it into a valuable soil amendment through thermochemical processes. This process uses thermal decomposition of organic materials in an oxygen-free environment to convert poultry byproducts into biochar, tar, and gas [11; 12; 13]. Poultry feathers, mainly made of keratin, and bones, abundant in calcium phosphate, can be transformed into nutrient-dense biochar that supports soil fertility [14; 15]. Having an increased calcium and phosphorus content, chicken bones could be a useful raw material to use in producing biochar. The resultant product is an effective soil amendment due to its composition [16]. The chemical breakdown of animal bones to produce soil amendments may reduce reliance on natural resources [17]. Numerous studies have examined the pyrolysis process to repurpose chicken bones, with primary goals centered on analyzing the structure of biochar and the composition of bio-oil generated from animal-based waste [18]. The muffle combustion chamber, which operates at temperatures between 300 and 1000 \({}^{\circ}\)C, is the most widely used reactor for this kind of operation. The main goal when performing pyrolysis of waste materials is to produce high-quality solid byproducts such as biochar. Biochar shows promising qualities for use as a fertilizer [19; 20], an adsorbent, or as catalyst. These studies primarily investigate the transformation processes of poultry waste into biochar; however, details regarding the use of biochar in agriculture are less thoroughly documented. Key factors influencing the pyrolysis process and the composition of its products include particle dimensions, reactor construction, residence time, gas-solid flow direction, temperature, heating rates, and nitrogen flow.