Comparative assessment of biochar reactor technologies for biomass conversion: Design, performance, and application suitability

The effectiveness of biochar for ecological restoration, toxicity remediation and carbon sequestration are fundamentally dependent on the biochar production technology. This review provides a systematic comparison of thermochemical conversion techniques such as pyrolysis (slow, rotary kiln, auger-based), gasification (downdraft and fluidized bed) and hydrothermal carbonization (HTC). Key performance metrics such as temperature profile, residence time, emissions regulation, and scalability are evaluated alongside critical biochar qualities such as surface area, porosity, fixed carbon content, cation exchange capacity, and polycyclic aromatic hydrocarbon. Priority has been given to aligning the biochar produced from each reactor with their respective environmental applications based on the biochar functions, such as nutrient retention, pH adjustment, and carbon fixation. The reactor performances have been summarized in context with production capacity, capital cost, and other variables related to system selection. The review uniquely integrates technical, environmental, and agronomic factors to propose a decision framework that aligns biochar production technologies with appropriate feedstocks, logistical settings, and long-term sustainability goals. In conclusion, this interdisciplinary approach fills a gap in literature by linking reactor engineering with functional outcomes in land management and climate resilience.