Assessing the inhibition potential of azole compounds to biological nitrogen removal processes in wastewater treatment

Highlights

	● Acute inhibition of azoles in biological nitrogen removal processes was evaluated.
	● The granular structure did not protect Anammox bacteria from azole inhibition.
	● Azoles mainly inhibited ammonium oxidation process in nitrification.
	● The nitrification is more sensitive to azoles than Anammox and denitrification.
	● Azole inhibition mechanisms in biological nitrogen removal processes were discussed.

Abstract

As emerging organic contaminants (EOCs), azoles have been detected in various environments. However, comprehensive information on the impact of azoles on biological nitrogen removal (BNR) processes in wastewater treatment is limited, particularly regarding the denitrification process. This study aims to investigate the short-term (< 24 h) inhibitory potentials of ten azole compounds on major BNR processes, including nitrification, denitrification, and anaerobic ammonium oxidation (Anammox). At 6 mg/L, pyrazole (PA), triazole (TA), benzotriazole (BTA), and methyl-benzotriazole (MBTA) caused over 90% inhibition of nitrification activity. In comparison, denitrifiers exhibited greater resistance to these azoles, with calculated half-maximal inhibitory concentrations (IC₅₀) of 126, 520, 412, and 152 mg/L, respectively. Regarding Anammox, the calculated IC₅₀ was 20 mg/L for BTA and 18 mg/L for MBTA, while PA and TA showed no significant inhibition (< 20%) at concentrations up to 250 mg/L. The granular structure of Anammox sludge did not exhibit additional protection from the inhibition. The ammonium oxidizing process in nitrification showed the highest sensitivity to tested azoles. The results are expected to aid in evaluating the stability of BNR processes for treating azole-containing wastewater and in developing effective strategies to protect BNR systems from disruptions caused by azoles.

Graphical abstract

Keywords

Emerging organic contaminants / BNR / Anammox / Nitrification / Denitrification / Toxicity

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CRediT Authorship Contribution Statement

Xiaojue Chen: Investigation, Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Validation, Visualization, Writing -original draft, Writing-review & editing. Emily A. Speierman: Conceptualization, Writing-review & editing. Liu Jiang: Conceptualization, Writing-review & editing. Khashayar Aghilinasrollahabadi: Investigation, Writing-review & editing. Camila A. Proano: Investigation, Writing-review & editing. Marya O. Anderson: Conceptualization, Writing-review & editing. Guangbin Li: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Writing-review & editing.

Conflict of interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors thank Dr. Caroline Nguyen and Mr. Yerman Saavedra (Washington Suburban Sanitary Commission, WSSC Water, USA) for providing the assistant in collecting sludge samples for the inhibition bioassays. This material is based upon work supported by the National Science Foundation (USA) under Grant No. 2327516. This work was supported by the Faculty-Student Research Award and Grand Challenge Grant from the University of Maryland, USA.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at https://doi.org/10.1007/s11783-025-1985-8 and is accessible for authorized users.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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