Inhibition and acclimation of nitrifiers exposed to erythromycin

• Erythromycin was found to have an apparent adverse effect on nitrification process.
• Nitrite-oxidizing bacteria were more sensitive than ammonia-oxidizing bacteria.
• The major removal route for erythromycin was by adsorption than biodegradation.
• Erythromycin decreased bacterial diversity in the sludge after long-term exposure.

The influence of erythromycin on ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) was investigated using batch and continuous experiments. During the batch experiments, the impact of erythromycin was strictly dose-dependent for AOB and NOB. The continuous addition of 1 mg/L of erythromycin in the long-term exposure experiment made NOB to be sensitive whereas AOB to be minimally sensitive. After a prolonged exposure to concentration, even up to 50 mg/L both NOB and AOB become insensitive to increases in erythromycin. From the seven dosage levels, between 54.3% and 69.1% of erythromycin was removed by adsorption and the percentage of nitrifiers in the microbial community increased from 39.8% to 55.6%.