Respirometric activities of unacclimatized Enterobacter aerogenes and mixed culture bacteria in sequencing batch reactor systems in response to acrylamide and its biodegradation products

The acute effects of acrylamide and its biodegradation products on the respiration activities of microbes during wastewater treatment are not well understood. Herein, unacclimatized mixed culture bacteria and Enterobacter aerogenes from two aerobic treatment systems, Activated Sludge (AS) and Integrated Fixed Film Activated Sludge (IFAS) both of which were sequencing batch reactors (SBR), were studied for their response to acrylamide. Respiration activities and biodegradation rates were determined by both the OxiTop respirometer and batch studies. The experimental results revealed that E. aerogenes in the AS system quickly removed both acrylamide and acrylic acid without the need of an acclimation period, but required two hours for removing acrylic acid in the IFAS system. The mixed culture bacteria in both AS and IFAS systems required 2 hours to acclimatize with acrylamide and 1 hour for acrylic acid, respectively. Acrylic acid was initially polymerized to produce acrylic acid polymer or reacted with ammonia to form acrylamide, resulting in the reduced acrylamide biodegradation rate. Both E. aerogenes and mixed culture bacteria from the AS systems could simultaneously biodegrade acrylamide and acrylic acid whereas only acrylamide was biodegraded by both cultures in the IFAS systems due to the limitation of acrylic acid diffusion. The results also indicated that ammonia inhibited the acrylamide biodegradation by both E. aerogenes and mixed culture bacteria from the AS systems. The unacclimatized E. aerogenes and mixed culture bacteria from the AS systems showed superior performances compared to the ones from the IFAS systems.