Technical Feasibility of Producing and Utilizing Livestock Manure-Derived Biochar for Soil Carbon Sequestration in South Korea: A Review

In Korea, policy efforts are being made to achieve carbon neutrality in the agricultural sector by promoting the production and utilization of livestock manure-derived biochar. Recently, new quality standards for livestock manure biochar have been introduced. However, some of the produced biochar does not meet the criteria required for soil carbon sequestration. In this study, a literature review evaluated the technical feasibility of livestock manure biochar to support its industrial utilization and activation. This study performed a literature review to comparatively assess the physicochemical properties of woody, herbaceous, and livestock manure biomass, and to evaluate the quality standards of biochar derived from these feedstocks through pyrolysis and hydrothermal carbonization (HTC). According to an analysis of previous studies, the carbon content of woody biochar produced by pyrolysis ranged from 46.3% to 93.5% (n = 29), with average H/C and O/C molar ratios of 0.49 and 0.09, respectively. Herbaceous biochar exhibited a carbon content ranging from 26.1% to 83.8% (n = 34), with mean H/C and O/C molar ratios of 0.48 and 0.28, respectively. Thus, most woody and herbaceous biochars met the biochar quality criteria (H/C < 0.7, O/C < 0.4). In contrast, manure-derived biochar demonstrated a comparatively lower carbon content, ranging from 29.0% to 44.6% (n = 21). The average H/C molar ratio for manure-derived biochar was higher at 0.60, and 73% of samples exceeded the established quality threshold for H/C (<0.7). Hydrothermal carbonization (HTC), which is suitable for high-moisture feedstocks such as manure, yields hydrochar with an average H/C ratio of 1.01, indicating lower aromaticity and reduced carbon stability, thereby limiting its potential for long-term carbon sequestration. These findings underscore the necessity for region-specific standards and further investigation into the properties of manure-derived biochar to promote sustainable soil carbon sequestration practices.