Assessment of toxicity and kinetic effects of erythromycin on activated sludge consortium by fast respirometry method

Background: The present study aimed to assess the acute impact of erythromycin (ERY) as an inhibitor on peptone mixture utilization of activated sludge (AS) consortium. Methods: For this purpose, the inhibition of oxygen consumption was used based on the ISO 8192:2007 procedure. In this method, the AS consortium (10-day age) was extracted from labscale membrane bioreactor, then, percentage inhibition for total, heterotrophic, and nitrifying microorganisms, in separate batch respirometric tests were calculated in the absence and presence of Nallylthiourea (ATU) as a specifc Nitrifcation inhibitor. Results: The obtained data showed that the height of oxygen uptake rate (OUR) profles and amount of oxygen consumption reduced with increasing ERY dose. The halfmaximal effective concentration (EC 50) of ERY for heterotrophic and nitrifer microorganisms were 269.4 and 1243.1 mg/L, respectively. In Run 1, the kinetic coeffcients bH, fA,H, YH, and µH were calculated as 2.61 d^-1, 0.44, 0.4945 mg VSS/mg COD, and 0.047 d^-1, respectively. Also, for maximum ERY concentration (1000 mg/L), the kinetic coeffcients bH., fA,H, YH, and µH were calculated as 2.27 d^-1, 0.3, 0.4983 mg VSS/mg COD, and 0.0049 d^-1, respectively. Conclusion: The fndings showed that the inhibitory impact of ERY was observed as a decrease in the amount of oxygen consumption by OUR profles in rapid respirometric method (ISO 8192), which offered a novel insight for the acute inhibitory impact of this antibiotic. Also, chemical oxygen demand (COD) as an overall substrate parameter is most helpful in interpreting the behavior and the metabolic functions of AS systems.