Transport of biochar colloids in saturated porous media in the presence of humic substances or proteins

• Published in: Environmental pollution (1987) Vol. 246; pp. 855 - 863
• Main Authors: Yang, Wen, Bradford, Scott A., Wang, Yang, Sharma, Prabhakar, Shang, Jianying, Li, Baoguo
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.03.2019
• Subjects: Colloidal biochar particle; Dissolved organic matter; Humic acid; Protein; Dissolved organic matter; Colloidal biochar particle; Humic acid; Protein
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2018.12.075

Application of biochar in the field has received considerable attention in recent years, but there is still little known about the fate and transport of biochar colloids (BCs) in the subsurface. Natural organic matter (NOM), which mainly consists of humic substance (HS) and proteins, is ubiquitous in the natural environment and its dissolved fraction is active and mobile. In this study, the transport of BCs in saturated porous media has been examined in the presence of two HS (humic and fulvic acids) and two proteins. Bull serum albumin (BSA) and Cytochrome c (Cyt) were selected to present the negatively and positively charged protein, respectively. At low and high salt concentration and different pH conditions, the transport of BCs was strongly promoted by HS. HS significantly increased the mobility of BCs in porous media under both low and high salt conditions due to the enhanced electrostatic repulsion and modification of surface roughness and charge heterogeneity. While BC mobility in porous media was suppressed by both BSA and Cyt in the low salt solution, the presence of BSA largely promoted and Cyt slightly enhanced the transport of BCs in high salt solutions. BSA and Cyt adsorption onto BC surface decreased the negative charge of BC and resulted in a less repulsive interaction in low salt solutions. In high salt solutions, the adsorbed BSA layers disaggregated BCs and reduced the strength of the interaction between BC and the sand. Adsorbed Cyt on BCs caused more attractive patches between BC and sand surface, and greater retention than BSA. [Display omitted] •Humic substances (HSs) increased the transport of biochar colloids (BCs).•Proteins decreased BC mobility at low salt solution due to less negative charge.•Negatively charged protein enhanced BC transport at high IS via disaggregation.•Positively charged protein increased BC retention by attractive patch interaction.•Surface roughness and charge heterogeneity strongly affect BC retention. Humic substances and proteins present in the environment showed distinct impacts on BC mobility, which have implications for the risk assessment of biochar application.