Understanding activation effects on low-temperature biochar for optimization of herbicide sorption

Authors: GAMIZ, BEATRIZ - Instituto De Recursos Naturales Y Agrobiologia De Sevilla (IRNAS-CSIC); HALL, KATHLEEN - Minnesota Department Of Agriculture; Spokas, Kurt; COX, LUCIA - Instituto De Recursos Naturales Y Agrobiologia De Sevilla (IRNAS-CSIC)

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2019
Publication Date: 9/27/2019
Citation: Gamiz, B., Hall, K., Spokas, K.A., Cox, L. 2019. Understanding activation effects on low-temperature biochar for optimization of herbicide sorption. Agronomy. 9(10):588. https://doi.org/10.3390/agronomy9100588.
DOI: https://doi.org/10.3390/agronomy9100588

Interpretive Summary: We need to understand the mechanisms on how biochar sorbs agrochemicals in order to optimize their use to combat off-site herbicide transport. This work investigates the effects of hydrogen peroxide treatment of a low-temperature (350°C) grape wood biochar. We observed that this chemical treatment exposed new additional pores and increased its surface area, as well as increasing its oxygen content. We also determined that the activated biochar sorbed more water vapor than the untreated biochar. Two different herbicides were examined for their sorption behavior with different chemistries, an organic acid (cyhalofop-butyl) and a clomazone is a non-ionizable organic compound. The activation of biochar resulted in a higher removal of the organic acid (cyhalofop-butyl), but no differences were observed in the sorption of the non-ionizable compound (clomazone). Results from this study suggest that hydrogen peroxide activation treatments on low-temperature biochars may improve the removal of organic acid herbicides but are of little value in optimizing the removal of polar, non-ionizable agrochemicals. These results highlight the need to understand the mechanisms of herbicide sorption to biochar to optimize biochar’s capacity. These results are significant to farmers and policy makers and will assist scientists and engineers in understanding the potential pathways for improved mechanisms of biochar’s chemical sorption behavior.

Technical Abstract: Activation treatments are often used as a means of increasing a biochar’s sorption capacity for agrochemical compounds but can also provide valuable insight into sorption mechanisms. This work investigates the effects of H2O2 activation on a low-temperature (350°C) grape wood biochar, evaluates subsequent changes to the removal efficiency (RE) of cyhalofop and clomazone, and elucidates potential sorption mechanisms. Activation by H2O2 decreased the biochar pH, ash content, and C content. Additionally, the biochar O content and surface area increased following activation, and FTIR data suggested a slight increase in surface O groups and a decrease in aliphatic C. Cyhalofop RE significantly increased following activation, while clomazone RE was unchanged. The increased sorption of cyhalofop was attributed to pH effects and charge-based interactions with biochar O moieties. Results from this study suggest that H2O2 activation treatments on low-temperature biochars may improve the removal of organic acid herbicides, but are of little value in optimizing the removal of polar, non-ionizable herbicides.