# Population dynamics of ammonium oxidizing and heterotrophic bacteria in a nitrifying consortium fed with ammonium and benzotriazole

## TL;DR

This study examines how ammonium-oxidizing and heterotrophic bacteria in wastewater sludge change when exposed to ammonium and benzotriazole.

## Contribution

The study reveals how microbial community shifts correlate with the simultaneous oxidation of ammonium and biotransformation of benzotriazole.

## Key findings

- Nitrosomonadaceae family became dominant when benzotriazole was added.
- Nitrosomonas mobilis and unassigned Nitrosomonas OTUs increased during benzotriazole exposure.
- Higher microbial diversity in cycle 47 correlated with benzotriazole biodegradation ability.

## Abstract

Nitrifying sludge used in biological wastewater treatment contain ammonium oxidizing bacteria (AOB) and heterotrophic bacteria that can enable the simultaneous removal of contaminants. The population dynamics of a nitrifying consortium was assessed in a sequencing batch reactor (SBR) fed with ammonium (cycles 1-130) and benzotriazole (BT) (cycles 40–130). Diversity of the identified AOB and heterotrophs could be associated with the capacity of the sludge for carrying out simultaneously ammonium oxidation and BT biotransformation processes. Thirty-nine OTU’s constituted the bacterial core of the consortium with an abundance higher than 58% of the total population along the experimentation where Nitrosomonadaceae family became dominant during cycles with BT addition. Nitrosomonas mobilis and thirteen unassigned OTUs of Nitrosomonas genus increased their relative abundance during BT exposure, suggesting their participation in both ammonium oxidation and BT cometabolic biodegradation. The acquirement of metabolic ability of the sludge for biodegrading BT in cycle 47 could also be associated with the highest diversity and richness of species detected during this cycle and the abundance increase of twelve identified heterotrophic bacteria. Results showed that the changes in metabolic capacities of the sludge for carrying out two efficient oxidizing processes reflected the changes in microbial community composition along the SBR operation.

The online version contains supplementary material available at 10.1007/s11274-025-04578-2.