Effect of a Subinhibitory Benzalkonium Chloride Concentration on the Development of Antibiotic Resistance and the Performance of Activated Sludge Semicontinuous Reactors

In recent years, the use of disinfectants, such as benzalkonium chloride (BAC), has increased. BAC may alter the normal performance of biological wastewater treatment systems and promote resistance to human-use antibiotics. Thus, the present work aimed to study the effect of BAC on the performance of an activated sludge reactor and the change in the resistance of the biomass to BAC and to three antibiotics. Acclimation to BAC lasted 2 weeks. Then, the biomass could remove BAC within the first 4 h. BAC did not affect the performance of the reactor in terms of oxygen consumed (OC), biomass concentration, or carbon removal. According to OC data, BAC was completely oxidized. Thus, BAC could not be a carbon source for biomass growth under the tested conditions. The minimum inhibitory concentration (MIC) of BAC corresponding to native sludge was higher than the tested initial BAC concentration, confirming that a BAC subinhibitory concentration was tested. The acclimation to BAC was also evidenced through the increase in the BAC-MIC. BAC also increased the MIC corresponding to ampicillin. The MIC corresponding to cephalexin was higher than the highest tested concentration. Finally, activated sludge was highly sensitive to ciprofloxacin.