Discrepancies in measurement methods for biochar's heavy metal adsorption performance caused by its dissolved organic...

Biochar demonstrates significant potential as a sustainable adsorbent for heavy metals (HMs) remediation, yet methodological discrepancies in measuring adsorption capacity (qₓ) undermine performance comparability. This study demonstrates that filter membrane specifications critically affect the measured adsorption capacity of biochar due to differential retention of biochar-derived dissolved organic matter (BDOM)-HM complexes, highlighting concerns regarding the lack of filter membrane standardization. Adsorption experiments showed that smaller filter membranes resulted in higher measured adsorption capacities, with Cu(II) in reed biochar exhibiting a coefficient of variation (CV) of 55.4 %. Spectroscopic analyses confirmed that protein-like components in BDOM mostly account for the discrepancies. Crucially, reed biochar (RB) exhibited 4-10 times higher protein-like components (78 % vs. 7-19 % in other feedstocks), directly correlating with its markedly elevated CV. To address these challenges, the study recommends bypassing filtration and instead assessing adsorption capacity based on the difference in free heavy metal ion concentrations before and after adsorption, ensuring more accurate assessments of biochar performance. Additionally, the ion-selective electrode (ISE) is proposed as a potential alternative method. This study underscores the necessity of addressing biases in traditional methods to ensure accurate evaluations of biochar's environmental applications.