Food waste, particularly animal-derived waste, presents a significant challenge globally, prompting the need for sustainable management strategies. In 2022, the amount of food waste per capita reached 131 kg/capita in the EU (European Union), which is why the search for environmentally friendly ways to manage food waste through thermochemical conversion processes has gained momentum in recent years. Animal-derived waste is a good source of organic matter (proteins, lipids, and polysaccharides) and mineral compounds (calcium phosphate, mostly hydroxyapatite). This composition makes animal-derived waste valuable for the extraction of chemical compounds, such as hydroxyapatite (HAp), which constitutes up to 70 wt% of animal bones; keratin; collagen; and hyaluronic acid (HA), to produce pharmaceutical, medical, or industrial by-products. The thermochemical conversion of chicken bones through pyrolysis and gasification creates a new opportunity to valorize this type of waste by reintroducing valuable by-products into the economy and thus achieving sustainable waste management objectives. The results of this study showcase the multiple applications of the pyrolysis of chicken bone waste products (as adsorbents in aqueous mediums, catalysts, fertilizers, and biomedical applications) and the necessity of a better exploration of the gasification process of chicken bone waste. Therefore, this study explores the properties of animal-derived waste and discusses the pyrolysis and gasification of chicken bone waste, the influence of process conditions on product yields, and the catalytic enhancement of these thermochemical processes.

Worldwide, the waste generated by the food industry sector is expected to increase due to demographic extension and consumer-driven society effect. One type of this waste is represented by animal bone. This study explores the valorization of biochar obtained from chicken bone waste (CBW) pyrolysis at 500–700 °C. The biochar obtained at 700 °C showed better characteristics, such as higher porosity, specific surface area and dielectric proprieties. Further on, the biochar was activated through microwave (MW) treatment to improve its structure and morphology. The activated biochar was investigated as microwave susceptor material and catalyst support for microwave-assisted pyrolysis of low-density polyethylene (LDPE) packaging waste. Compared to common microwave susceptors, the activated biochar proved good microwave absorption capabilities, reaching temperatures of 450 °C. Additionally, the biochar was used as catalyst support, doped with silicon, titanium, and zinc oxides with applications in plastic pyrolysis. As catalyst in microwave-assisted pyrolysis (MAP) of LDPE, it enhanced the gas yield of the process, obtaining a pyro-gas composition rich in hydrogen (43%). These findings prove the dual functionality of the CBW-derived biochar, providing a new sustainable solution for converting chicken bone and plastic waste into value-added products. Graphical abstract

Animal-derived waste poses significant disposal and environmental challenges, yet its organic and mineral-rich composition offers opportunities for energy recovery through thermochemical valorization. Chicken bone waste (CBW), a byproduct of the poultry industry, was selected as a feedstock for conversion into energy. In this study, CBW was first processed via pyrolysis to produce a carbon-rich char, which was subsequently gasified with air at 700 °C in a lab-scale fixed-bed batch reactor to generate synthesis gas (syngas). The resulting syngas was rich in carbon monoxide (~43.5 % CO), carbon dioxide (~39.2 % CO₂), and moderate hydrogen fraction (~14.0% H₂). It exhibited a higher heating value (HHV) of approximately 25.87 MJ/kg, and the gasification achieved a cold-gas efficiency of ~54.6%, suggesting that over half of the feedstock’s energy content was recovered in gaseous form. Based on these results, a conceptual pilot-scale system was analyzed, comprising a 100 kg/h gasifier and a 15.36 kWe syngas turbine for power generation. Under the stated assumptions, the techno-economic analysis demonstrated economic viability for syngas utilization as an energy source, with net present value (NPV) ≈ 28554 € and internal rate of return (IRR) ≈ 15.3%. Sensitivity analyses were performed to capture the impact of technical and market variability. Increasing the syngas LHV (8.98–11.67 MJ/Nm³) enhanced NPV linearly. Improving electric turbine efficiency (30–40 %) produced the strongest effect, increasing NPV to ≈ 58700 € and IRR to ≈ 21 %, while reducing discounted payback period (DPP) to ≈ 6 years. Electricity price variation (0.09–0.15 €/kWh) identified a break-even tariff of ≈ 0.106 €/kWh, above which profitability rapidly improved. Overall, air gasification of CBW-derived biochar was shown to efficiently produce high-quality syngas for power generation. This waste-to-energy pathway is energy-efficient and economically viable, illustrating a practical approach to circular economic goals through the valorization of animal-derived waste.

This study investigates the synergistic processing of chicken bone waste through a novel combination of advanced ultrasound-assisted enzymatic pretreatment and fast pyrolysis conditions (500-900 °C, ∼100 °C/min). The higher process temperature inhibits CO₂, and promotes ≥ C₂, CH₄, CO and H₂. The pyrolysis gas energetic potential reaches a maximum of 33 MJ/Nm³, thus can serve as biofuel. The bio-oil derived from the pyrolysis of feedstock, whether pretreated by classical or enzymatic methods, yields rich in N-heterocycles. At ≥ 700 °C, bio-oil contains more heterocyclic compounds and hydrocarbons. Pyrolysis of enzymatically pretreated feedstock results in higher concentrations of pyrrole and pyrrolo[1,2-a]pyrazine-1,4-dione, hexahydro, which are valuable for the synthesis of organonitrogen compounds relevant to the agriculture, pharmaceutical and advanced materials industries. The H/C < 0.7 and O/C < 0.28 ratios, together with the phosphorus content, indicated a stable high-quality biochar. The increase of process temperature decreases biochar yield, doubles ash content, promotes density and improves thermal stability. The total heat absorbed increases from 22 kJ (500 °C) to 39 kJ (900 °C), indicating a moderate energy demand for pyrolysis. This synergistic processing promotes sustainable poultry waste management and facilitates the circular utilisation of bio-based, compound-oriented products, for their potential use as renewable gases, green chemicals and functional biochar.