Understanding the physicochemical structure of biochar affected by feedstock, pyrolysis conditions, and post-pyrolysis modification methods – A meta-analysis

The impact of feedstock type, pyrolysis conditions, and post-pyrolysis modifications on the physicochemical properties of biochar has not been systematically evaluated. To this, a comprehensive meta-analysis was conducted to assess the impact of 17 effective variables including three groups of modification techniques (acidic, alkalic, H 2 O 2 , metal oxides , microbial, organic acids, physical, soil mineral), pyrolysis temperature (<400, 400–550, >550 °C), and feedstocks (herbaceous, hull, manure, nut, straw, wood). Also, 26 properties of the biochar were identified as being impacted; some of the most important among them are pH, cation exchange capacity (CEC), ash content (AC), specific surface area (SSA), carbonization (H/C), and surface functional groups (SFGs). The CEC of biochar modified by acidic, and soil mineral treatment significantly increased by 44.8 % and 48.5 %. The H/C ratio of biochar decreased in alkalic modification with a negative effect size of 7.2 %. Soil minerals, metal oxides, and alkalic modifications resulted in a positive change in AC with a 20.9 %, 15.7 %, and 13.6 % increase. Also, the highest SSA of modified biochar was observed when acidic and H 2 O 2 modification methods were applied, with 57.1 % and 53.4 % effect sizes. Further, high pyrolysis temperature (>550 °C) aided in significantly increasing SSA and SFGs on modified biochar. Overall, the strong association of acidic modifiers, high pyrolysis temperature, and high lignin-based feedstock could contribute to high SSA, SFGs, and absorption efficiency of biochar. This meta-analysis establishes a robust comparative framework, advancing the precision of biochar modification strategies to maximize physicochemical properties for improved environmental remediation. • Alkalic and H 2 O 2 showed the highest APD with values of 9.3 %, and 6.4 %. • The highest O C, OH-C and C-O-C compounds were obtained with acidic and H 2 O 2 . • Alkalic modification caused a negative effect size in FC with 5.8 % decrease. • Micropore volume notably decreased from 32.8 % in <400 °C to 11.9 % in >550 °C. • The highest CEC (49 %) was obtained from straw-based feedstocks.