Performance of acid- and base-modified biochars for the removal of antibiotics from water under dynamic conditions

Authors: Ashworth, Daniel; Schmidt, Michael - Mike; Ibekwe, Abasiofiok - Mark

Submitted to: Journal of Environmental Chemical Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2023
Publication Date: 12/2/2023
Citation: Ashworth, D.J., Schmidt, M.P., Ibekwe, A.M. 2023. Performance of acid- and base-modified biochars for the removal of antibiotics from water under dynamic conditions. Journal of Environmental Chemical Engineering. 11:111616. https://doi.org/10.1016/j.jece.2023.111616.
DOI: https://doi.org/10.1016/j.jece.2023.111616

Interpretive Summary: The human use of antibiotics for medicinal purposes leads to their presence in treated municipal wastewater (TMW) because conventional wastewater treatment plants are not designed to remove such contaminants effectively. Subsequent polishing of TMW is therefore desirable to limit the loading of soils with antibiotic compounds when TMW is used for agricultural irrigation. An effective approach to polishing is to chemically adsorb the compounds in filtration systems where TMW is passed through a sand/biochar medium. Biochar has a high capacity to adsorb such contaminants owing to its physical and chemical characteristics, which can be manipulated by modifying the biochar using acid and base treatment. In this work we used columns of sand/biochar to study the retention of three antibiotics, trimethoprim (TMP), sulfamethoxazole (SMZ), and sulfapyridine (SPD), on acid- and base-modified biochars derived from dairy manure and rice husk. TMP was completely removed from water by all biochars. SMZ retention was best at low pH, i.e., in acid modified biochars. SPD retention was best in cases where the biochar surface area was largest, which was found in the acid-modified dairy manure biochar and the base-modified rice husk biochar. The findings indicate that acid or base modification of biochars may improve retention of certain antibiotics under dynamic conditions. Therefore, biochar-based polishing systems comprising such biochars may offer potential in mitigating the spread of antibiotics and antibiotic resistance in agricultural settings.

Technical Abstract: The increased recycling of treated municipal wastewater (TMW) to agricultural land is potentially hampered by the presence of antibiotic compounds, which may lead to the spread of antibiotic resistance. Biochar-based adsorption has been widely assessed as a means of polishing TMW to remove antibiotics prior to use; however, relatively little is known about how acid and base modification of biochar impacts its antibiotic retention capabilities, especially under the dynamic (flow-through) conditions inherent in proposed polishing systems. Using small columns of sand mixed with dairy manure or rice husk biochars modified with acid or base, the retention of trimethoprim (TMP), sulfamethoxazole (SMZ), and sulfapyridine (SPD) was assessed. For SMZ and SPD, retention by the columns was consistently markedly lower than that measured in batch studies, indicating that equilibrium data may overestimate the retention of more realistic (dynamic) systems. TMP was completely retained by all biochars under both batch and column conditions. In columns, SMZ retention was strongly controlled by its pH-dependent speciation (greater retention at low pH, i.e., in acid modified biochars). SPD retention was strongly controlled by biochar surface area, which was markedly increased in the acid-modified dairy manure biochar and the base-modified rice husk biochar. The findings indicate that acid or base modification of certain biochars may improve retention of sulfonamide antibiotics (which are known to be particularly difficult to remove from TMW) even under dynamic conditions. Biochar-based polishing systems comprising such biochars may offer potential in mitigating the spread of antibiotics and antibiotic resistance in agricultural settings.