Removal of Ampicillin with Nitrifying Cultures in a SBR Reactor

Abstract

The presence of antibiotics in wastewater discharges significantly affects the environment, mainly due to the generation of bacterial populations with multiple antibiotic resistances. The cometabolic capacity of nitrifying sludge to simultaneously remove ammonium (NH₄⁺) and emerging organic contaminants (EOCs), including antibiotics, has been reported. In the present study, the removal capacity of 50 mg ampicillin (AMP)/L by nitrifying cultures associated with biosorption and biotransformation processes was evaluated in a sequencing batch reactor (SBR) system. The contribution of nitrifying enzymes (ammonium monooxygenase (AMO) and nitrite oxidoreductase (NOR)) and β-lactamases in AMP biodegradation was evaluated using specific inhibitors in batch cultures. AMP was 100% eliminated after 5 h since the first cycle of operation. The sludge maintained its ammonium oxidizing capacity with the total consumption of 102.0 ± 2.5 mg NH₄⁺-N/L in 9 h, however, the addition of AMP altered the nitrite-oxidizing process of nitrification, recovering 30 cycles later at both physiological and kinetic level. The kinetic activity of the nitrifying sludge improved along the operating cycles for both AMP removal and nitrification processes. The elimination of 24% AMP was attributed to the biosorption process and 76% to biotransformation, wherein the AMO enzyme contributed 95% to its biodegradation. Finally, the repeated exposure of the sludge to AMP for 72 operating cycles (36 days) was not sufficient to detect β-lactamase activity. The cometabolic ability of ammonium-oxidizing bacteria for biodegrading AMP could be employed for bioremediation of wastewater.

Keywords: Ampicillin; Biosorption; Cometabolic biodegradation; Nitrifying sludge; Sequencing batch reactor.

Fig. 1

Kinetic profiles of AMP removal in the SBR reactor. Cycles 16–45 (blue diamond), cycles 46–75 (orange triangle), and cycles 76–87 (green circle)

Fig. 2

Kinetic profiles of AMP removal in serological bottles (average data obtained in triplicate batch experiments with biomass collected from the SBR at cycles 17, 52, or 87). a Abiotic process (green circle), biosorption process (pink square), biosorption and biotransformation processes (blue triangle). b Contribution assays of nitrifying enzymes and bacterial resistance with enzymatic inhibitors: control cultures without inhibitors (yellow diamond), allylthiourea (AMO) (green triangle), sodium chlorate (NOR) (violet square), sulbactam (β-lactamases) (red circle)

Fig. 3

Nitrifying performance of the sludge during the AMP addition in the SBR reactor: a ammonium consumption profiles; b nitrite formation profiles; c nitrate formation profiles. Cycles 1–15 (control without AMP addition) (blue circle), cycles 16–45 (orange diamond), cycles 46–75 (green triangle), and cycles 76–87 (pink square)