Valorization of poultry litter through biochar production: Linking feedstock chemistry, pyrolysis conditions, and application performance for the Canadian poultry industry.

The Canadian poultry industry generates large quantities of poultry litter rich in carbon, nitrogen, phosphorus, and mineral constituents, creating both environmental challenges and opportunities for resource recovery. Pyrolysis has emerged as a promising pathway to valorize poultry litter into biochar, enabling waste stabilization, nutrient management, and carbon sequestration. This review critically synthesizes around 160 studies to evaluate how feedstock properties and pyrolysis conditions govern the physicochemical characteristics and functional performance of poultry litter-derived biochars. A key outcome of this review is the identification of seven distinct application domains for poultry litter biochars: carbon sequestration, heavy metal adsorption, agricultural soil amendment, CO2 adsorption, supercapacitors, nitrogen compound adsorption/desorption, and composting. By systematically linking raw feedstock properties to biochar structure and reactivity, the review demonstrates that poultry litter biochars exhibit strong decoupling between physical surface area and chemical or mineral functionality. Despite persistently low specific surface areas, these biochars exhibit effective nutrient retention and contaminant immobilization, driven by mineral phases, alkalinity, and surface chemistry. Increasing pyrolysis temperature enhances carbon stability but introduces trade-offs through nitrogen loss and reduced nutrient availability, while chemical activation fundamentally transforms poultry biochars into carbon-dominated materials suitable for advanced energy and adsorption applications. This review uniquely categorizes poultry litter-derived biochar applications into seven functional domains and demonstrates that performance is primarily governed by mineral-organic interactions rather than surface area alone. These insights provide an application-oriented framework for deploying poultry litter biochars in support of sustainable waste management and circular nutrient strategies within the Canadian poultry sector.