Biochar-based filtration effectively removes trimethoprim from synthetic treated municipal wastewater but may introduce antibiotic resistance genes to agricultural soil via irrigation

Authors: PHAN, DUC - University Of California, Riverside; BHATTACHARJEE, ANANDA - University Of South Florida; Ibekwe, Abasiofiok; Schmidt, Michael; Skaggs, Todd; Ashworth, Daniel

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/6/2025
Publication Date: 5/21/2025
Citation: Phan, D., Bhattacharjee, A., Ibekwe, A.M., Schmidt, M.P., Skaggs, T.H., Ashworth, D.J. 2025. Biochar-based filtration effectively removes trimethoprim from synthetic treated municipal wastewater but may introduce antibiotic resistance genes to agricultural soil via irrigation. Presented ar the Association of Environmental Engineering and Science Professors Research and Education Conference, May 20-22, 2025, Durham, NC.

Interpretive Summary:

Technical Abstract: Using treated municipal wastewater (TMW) as an agricultural irrigation water source can help reduce stress on freshwater sources. However, conventional municipal wastewater treatment is not typically effective in removing traces of emerging contaminants, such as antibiotics. Therefore, using TMW for crop production could expose agricultural environments to antibiotics and antibiotic resistance genes (ARGs), ultimately impacting human health. In this study, we investigated two filtration systems, conventional sand and sand mixed with 2% (w/w) dairy manure biochar, for the removal of the common antibiotic trimethoprim (TMP) from synthetic TMW. The efficacy of these two systems as well as bacterial 16S and ARGs were evaluated during 74 days of operation (the first 24 days operated with DI water) without backwashing. While the performance of the sand filtration system ultimately declined to 20–40% TMP removal efficiency, the sand/biochar filtration system maintained >94% TMP removal efficiency over the course of the study. Bacterial cells (indicated by the 16S rRNA gene) and ARGs were detected in the effluent of both systems after several weeks of operation, raising concerns about water quality for long-term use without backwashing. In subsequent microcosm studies, the influent (synthetic TMW with and without TMP spike) and effluents from these two filtration systems were utilized as irrigation water for agricultural soil containing earthworms. The results indicate that the sand/biochar filtration system helped reduce the spread of TMP into the agricultural soil via irrigation and has the potential to reduce the development of ARGs over time. However, long-term operation of the filtration systems could introduce ARGs to the treated water. Thus, backwashing is needed with an improved design for the filtration system. With the current design, results from the irrigation of water to agricultural soil for three weeks showed that the system effectively reduced the development of several ARGs that need a short period of time to develop (e.g., ttgA, ttgB). Overall, this study not only offers a potential strategy for mitigating antibiotic spread and antibiotic resistance development in TMW-irrigated agricultural environments but also suggests the importance of design and operational management of sand and sand/biochar-based filtration systems for agricultural water quality improvement.