Chronic impact of sulfamethoxazole: how does process kinetics relate to metabolic activity and composition of enriched nitrifying microbial culture?

Abstract

BACKGROUND This study investigated utilization kinetics of ammonia‐nitrogen induced by chronic sulfamethoxazole (SMX) exposure on biomass with an enriched nitrifying community. A lab‐scale activated sludge system was supplied with 100 mg COD L‐1 of peptone mixture and 50 mg N L‐1 of ammonia nitrogen at a SRT of 15 days. At steady‐state, the reactor was operated with additional daily SMX dosing of 50 mg L‐1 for 35 days. Profiles of oxygen uptake rates and nitrogen fractions obtained in respirometric/batch experiments were used for estimation of nitrification kinetics. RESULTS Acute inhibitory impact of SMX was expressed with high levels of half saturation constants and endogenous decay rates. After 35 days, half saturation constants significantly increased while higher active biomass fractions and recovered endogenous decay rates were estimated. At the end of the acclimation phase, 92% nitrification was achieved with 10 mg L‐1 SMX utilization. CONCLUSION Interpretation of modeling results with the outcomes of molecular analysis facilitated explanation of autotrophic/heterotrophic bacteria behavior in the course of SMX exposure. Removal of SMX may be attributed to co‐metabolism with ammonia oxidation and/or activity of SMX utilizing heterotrophic bacteria. © 2017 Society of Chemical Industry

Significance of enriched culture on the assessment of the acute inhibitory impact of sulfamethoxazole on nitrifying biomass

“…The same results were also reported in earlier studies. 1,26 It is interesting to note that the study by Pala-Ozkok, 54 where the experiment was conducted with conventional culture, also confirmed the same results, substantiating the suitability of the peptone mixture for this type of experimental evaluation. The table also lists the results of another study that was conducted with a COD/N ratio of 10 and only indicated a slight inhibition on the growth rate of AOBs and a variation of the endogenous decay coefficient, b H , between 0.10-0.20/day.…”

“…74,75 The study on the chronic impact of SMX basically involved observing the response of an enriched culture developed and sustained at steady-state to a continuous feeding of 50 mg/L of SMX for a period of 36 days, which was more than twice the sludge age selected for reactor operation. 26 Table 7 outlines the corresponding process kinetics obtained by means of model calibration of OUR profiles at different key steps along the observation period together with acute impact results of 50 mg/L SMX in this study. Run (2) related to the first day of SMX feeding, which replicated the acute exposure results in this study: competitive inhibition with markedly higher values for half saturation coefficients, K NH and K NO , and increased endogenous decay coefficients for both nitrifier fractions.…”

“…1,24,25 Lately, this approach was extensively utilized to determine the adverse effects of inhibitory substances on the nitrification kinetics under different conditions. 2,26 This study selected sulfamethoxazole (SMX), a well-known antibiotic, for the evaluation of its inhibitory impact on enriched microbial culture; SMX is a member of the sulfonamide family, covering 16-21% of antibiotic demand for human consumption. 27 It has attracted extensive research efforts exploring the conditions favoring its biodegradation, [28][29][30][31][32] as well as its inhibitory action on heterotrophic growth, nitrification, and endogenous decay.…”

“…33,34 Chronic impact of SMX was also investigated on the process kinetics and microbial composition of enriched nitrifying microbial culture. 26,35 This study evaluated, for the first time, the kinetic behavior of a similar enriched nitrifying culture under acute exposure to varying concentrations of SMX. It should be noted that chronic and acute exposure to an inhibitor define equally valuable but totally different conditions for the affected microbial culture, both from a scientific and practical perspective; 33,36,37 While the chronic impact would provide a much better perception on adaptation, resistance, and possible shifts in the biomass composition, the acute exposure would better reflect the impairment of metabolic reactions under the effect of a pulse inhibitor discharge (possibly at high concentrations).…”

Appraisal of Super-Fast Membrane Bioreactors by MASM—A New Activated Sludge Model for Membrane Filtration

“…Before the simulation, the model was calibrated with the oxygen uptake rate (OUR) profiles generated with the selected wastewater. In previous studies, the standard deviation of the OUR measurements was assessed as 3%, a level, which is the same as that of COD analysis [48].…”