Feedstock selection influences performance and mechanism of DNA adsorption onto biochar

Authors: Schmidt, Michael; RUPP, SIERRA - University Of California, Riverside; Ashworth, Daniel; PHAN, DUC - University Of California, Riverside; BHATTACHARJEE, ANANDA - University Of South Florida; Ferreira, Jorge; MEN, YUJIE - University Of California, Riverside; Ibekwe, Abasiofiok

Submitted to: Environmental Nanotechnology, Monitoring and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2025
Publication Date: 1/14/2025
Citation: Schmidt, M.P., Rupp, S., Ashworth, D.J., Phan, D., Bhattacharjee, A., Ferreira, J.F., Men, Y., Ibekwe, A.M. 2025. Feedstock selection influences performance and mechanism of DNA adsorption onto biochar. Environmental Research. 23(2025). https://doi.org/10.1016/j.enmm.2025.101040.
DOI: https://doi.org/10.1016/j.enmm.2025.101040

Interpretive Summary: Agricultural irrigation accounts for roughly 70% of freshwater consumption worldwide. As water resources globally become more stressed due to increased demand and future climate uncertainty, alternative water sources are receiving greater attention as irrigation water sources. One widely available source of water is treated wastewater, which provides a steady source of nutrient-rich water for irrigating crops. Treated wastewater, however, contains trace levels of antibiotic resistance genes that may promote antibiotic resistance in plants, livestock and humans. Biochar, a material formed from pyrolyzing biomass feedstock, represents a possible adsorbent for antibiotic removal from wastewater streams and, thus, a potential mitigation strategy for antibiotic resistance risk. Here we study biochars from different byproduct feedstock sources (manure, black mustard, orange peel, macadamia nut shell and pine pellet) to understand how feedstock selection impacts removal of genes from wastewater. We found that feedstock impacted the performance of DNA adsorption from solution as well as the mechanism by which it occurs. Overall, we found that black mustard showed the best performance. This indicates that this prevalent invasive species and agricultural byproduct may be a particularly suitable feedstock as a value added biochar for water treatment. These results demonstrate the capacity of biochar materials for removing antibiotics from water and show potential for developing a biochar-based water treatment system in the future.

Technical Abstract: Antibiotic-resistance genes (ARGs) in wastewater may promote antibiotic resistance in consumers of crops irrigated with wastewater. Removal of DNA from wastewater may therefore mitigate potential environmental risks associated with irrigation and environmental release of recycled wastewater. Although biochar adsorbents are a potentially cost-effective mitigation strategy for removing DNA from water, biochar feedstock influence on performance has not been studied across a range of feedstock classes. Our objective was to produce biochar from 5 distinct feedstocks (manure (MN), black mustard (Brassica nigra) (MU), orange peel (OP), pine pellet (PP) and macadamia nutshell (MNS)) at a fixed pyrolysis temperature of 500°C, characterize biochars and relate characteristics to DNA adsorption at pH = 7.0. Adsorption reached equilibrium within two hours and kinetics were fit by the pseudo-second order model. Adsorption rates increased from MNS, PP, OP, MN to MU. Adsorption isotherms fit the Freundlich model, with affinities increasing from PP, MNS, OP, MN to MU. DNA adsorption on all biochars increased with solution ionic strength from I = 0 – 0.10 M except for MN. Addition of Ca2+ resulted in increased adsorption for biochars at I = 0.01 and 0.10 M, except for MN, which increased only with I = 0.10 M. Lower sensitivity of DNA adsorption on MN biochar to ionic conditions relative to other biochars indicates a different mechanism may control adsorption on MN. The high ash content of MN biochar may favor direct coordination of DNA to ash mineral particles compared to p-p interactions likely driving DNA adsorption to biochars higher in structural carbon. These findings help to understand how feedstock-driven variability in biochars translates to DNA removal from water and will assist researchers and stakeholders in determining the most suitable feedstocks for this purpose.