Saturation Constant Research Articles

A simple equation to quantify the effect of frequency of light/dark cycles on the photosynthetic response of microalgae under intermittent light

Accurately assessing the influence of light/dark changes on the productivity of microalgal cultures is currently a complicated task that requires the use of a set of differential equations. A simple, algebraic equation that allows quantifying the effect of the frequency of light on the photosynthetic response of microalgae under varying light is presented and evaluated. The equation was derived from a particular case of the mechanistic model proposed by Camacho Rubio et al. (2003) [1]. The algebraic equation is demonstrated in this work to be a rapid method that allows characterizing the dynamic photosynthetic response of Muriellopsis sp. The parameters obtained using this method (Pmax = 8.22·10−7 mol O2 g−1 s−1, α = 1.82·10−4 mol photon m−2 s−1, β = 15.3 s−1, κ = 0.0402, at 25 °C, where Pmax is the maximum rate of photosynthesis, α is the saturation constant, β is the characteristic frequency and κ is a shape factor of the photosynthesis-irradiance curve) are very close to the values obtained using the original model proposed by Camacho Rubio et al., which is based on differential equations. The proposed new equation requires a reduced set of experiments that can be carried out under easy-to-attain conditions (continuous light and short flashes), and a straightforward, subsequent calculation of the dynamic parameters of photosynthesis. It can be used as a time-saving, efficient method to optimize the light regime for microalgal production.

Effect of operating parameters on the performance of wastewater treatment plant (Case study: The south of Tehran wastewater treatment)

Despite the fact that there are wastewater treatment plants (WWTPs) currently operational across Iran and great advances have been made in this area, there are still problems in the design, construction, and operation of WWTPs with large nonlinear systems, varying flow rates, and pollution charges. The objective of this study was to investigate the effect of operating parameters including the return activated sludge (RAS) ratio, internal recycle (IR) ratio and dissolved oxygen (DO) concentration in an activated sludge system for the Modules 5&6 of the Southern Tehran WWTP. This study designed and simulated a plant based on the activated sludge model No.1 (ASM1) to determine the factors affecting wastewater treatment systems; then, the kinetic parameters were measured. The kinetic parameters such as the yield coefficient (Y), decay coefficient (Kd), maximum specific growth rate (K), and saturation constant (Ks) were in the range of 0.303-0.331g/g, 0.030-0.033d-1, 1.65-1.93d-1 and 37.6-44.92mg/l, respectively. The RAS ratios, IR ratios, and DO concentration varied from 0.2 to 2, 1 to 3.5, and 0.27 to 3.54 mg/l, respectively. The amount of RAS had the greatest impact on the effluent. The amounts of IR and DO concentration had no significant effect on the concentration of the five-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), and total suspended solids (TSS) in the effluent. After the RAS, the amount of IR had the most direct effect on reducing the effluent total nitrogen (TN) concentration. As a result, the overall removal efficiency increased up to 75% when the IR rate was 200% of the influent flow rate, the RAS rate was 90% of the influent flow rate, and the DO concentration in the first aeration unit was 2 mg/l considering the aeration cost. Therefore, proper operating parameters can provide the best quality of effluent that meets environmental standards.

Inhibitory Kinetics of Free Ammonia (FA) on Ammonia-oxidizing Bacteria (AOB)

In this study, a sequencing batch reactor (SBR) was operated to investigate the inhibitory kinetics of free ammonia (FA) on ammonia-oxidizing bacteria (AOB). At the beginning of the experiment, FA concentrations in influent were altered to achieve stable short-cut nitrification and enrich AOB. Nitritation sludge was then employed to study variations in the specific nitrite production rate (SNiPR) during the ammonia oxidation process of batch tests. Furthermore, a kinetic model of FA inhibition on AOB activity was fitted for statistical analysis. Results showed that SNiPR increased rapidly with increase in FA concentration (0.7 mg·L-1 ≤ FA ≤ 50.2 mg·L-1) but decreased with an increase in FA concentration (FA ≥ 50.2 mg·L-1). SNiPR was maintained at 0 g·(g·d)-1 when FA concentration was higher than 687.1 mg·L-1, implying that AOB activity was completely inhibited. Statistical analysis showed that, compared to Haldane, Edwards-1#, Edwards-2#, and Luong inhibition kinetics models, the Aiba model was the most suitable for describing the inhibitory effect of FA on AOB activity. The statistical constants, i.e., residual square sum (RSS) correlation coefficient (R2), F value of the fitting equation, and confidence degree (P) were 0.005, 0.932, 181.7, and 1.06×10-9, respectively. The dynamic constant values, i.e., maximum specific nitrite production rate (rmax), half saturation constant (KS), and inhibition constant (KI) were 0.37 g·(g·d)-1, 11.78 mg·L-1, and 153.74 mg·L-1, respectively.

Liquid state bioconversion continuous bioreactor of sewage sludge treatment: Determination and evaluation of mixed fungi growth kinetics

Abstract Liquid state bioconversion (LSB), a bioremediation and biodewatering process was applied for sewage sludge treatment in this study. The LSB process is a non-hazardous, safer and environmentally friendlier method for ultimate sludge management and disposal compared to the other available technologies. The system presented in this study was developed by using mixed fungi of Aspergillus niger and Penicillium corylophilum to treat sewage sludge in a LSB bioreactor. This research was conducted in order to study the LSB process on continuous system in terms of kinetic coefficients determination. For the continuous LSB process, a mathematical model was developed from the basic principles of material balance based on Monod equation. By investigating the kinetics of substrate utilisation and biomass growth, the kinetic coefficients of growth yield coefficient (Y), specific microorganism decay rate (Kd), half saturation constant (Ks) and maximum specific growth rate (μmax) were found to be 0.79 g VSS g COD−1, 0.012 day−1, 1.78 g COD L−1 and 0.357 day−1, respectively.

Structural elucidation and magnetic behaviour evaluation of gallium substituted garnet ferrites

Impact of gallium (Ga) on structural, morphological and magnetic properties of yttrium iron garnet (YIG) nano-sized ferrites with nominal composition (Y3GaxFe5-xO12, where x = 0.00, 0.40, 0.80, 1.20, 1.60) has been investigated. The samples were prepared via sol-gel auto combustion route. XRD (X-ray diffraction), FESEM (field emission scanning electron microscopy) and VSM (vibrating sample magnetometer) were used to unfold the structural, morphological and magnetic properties of Ga substituted YIG ferrites. Single phase structure of all samples was confirmed through XRD. Cations distribution such as site radii, hopping bond length, shared and unshared edges of the Ga substituted YIG ferrites were also determined. Physical properties such as X-ray density (Dxrd), bulk density (Dbulk), porosity and lattice parameters were found to increase with increasing Ga concentration. FESEM images represented well crystallized and homogenous grains for YIG whereas porous structures were found for Ga substituted ferrites. The grain size of these samples was found in the nano regime (40–86 nm). Magnetic properties such as magnetic saturation, coercivity, remanence, initial permeability, Bohr magneton and anisotropy constant (K) were calculated from hysteresis loops. However, Yafet and Kittle (Y-K) angles were also calculated. Y-K angles were increased with Ga concentration in YIG nano-sized ferrites. Low coercivity and moderate magnetization suggested the use of these ferrites for electromagnetic microwave absorption and frequency agile antenna for wireless communication. Furthermore, the range of operated frequency in microwave region of these nanoferrites suggests the use of these ferrites for high frequency (S and C bands) applications.

Physical insights of ultrasound-assisted ethanol production from composite feedstock of invasive weeds

Invasive weeds ubiquitously found in terrestrial and aquatic ecosystems form potential feedstock for lignocellulosic ethanol production. The present study has reported a bioprocess for production of ethanol using mixed feedstock of 8 invasive weeds found in India. The feedstock was subjected to pretreatment comprising dilute acid hydrolysis (for hydrolysis of hemicellulosic fraction), alkaline delignification and enzymatic hydrolysis of cellulosic fraction. Pentose-rich and hexose-rich hydrolyzates obtained from pretreatment were fermented separately using microbial cultures of S. cerevisiae and C. shehatae. Fermentation mixture was sonicated at 35 kHz at 10% duty cycle. The time profiles of total reducing sugars, ethanol and biomass was fitted to a kinetic model using Genetic Algorithm. Sonication boosted the kinetics of fermentation 2-fold. The net bioethanol yield of the process was ∼220 g/kg raw biomass (with contributions of 86.8 and 133 g/kg raw biomass from pentose and hexose fermentations, respectively). Comparative evaluation of parameters of kinetic model under control and test conditions revealed several beneficial influences of sonication on both pentose and hexose fermentation systems such as faster transport of nutrients, substrate and products across cell membrane, rise in Monod saturation constant for substrate with concurrent reduction in substrate inhibition, and reduction of energy requirements for cell maintenance. Flow cytometry analysis of native and ultrasound-treated cells revealed no adverse influence of sonication on cell viability.

Mathematical modelling of flat plate biofilm photobioreactors with circular and rectangular configurations

Flat plate photobioreactors (FPPBRs) using bacterial biofilm have gained much recent attention due to operational ease, improved light conversion efficiency and reduction of process cost, particularly in hydrogen production. In this study, two comprehensive mathematical models, one explaining the dynamics of a batch type FPPBR used for the development of biofilm and the other a deterministic model (both temporal and spatial) to predict the performance of a continuous FPPBR using Rhodopseudomonas sp. have been developed for both circular and rectangular configurations. The system equations have been solved using MATLAB 2013. From batch studies, the maximum specific growth rate and half saturation constant for the microorganism have been determined to be 0.07 h−1 and 1.946 g l−1 respectively. An “Instantaneous attachment and proliferation” mechanism has been proposed to explain the behaviour of biofilm right from the early stage of attachment to the reversal from attached to planktonic state. The flow patterns of substrate medium through the biofilm have been generated using COMSOL Multiphysics software. From the perspective of the hydrogen yield, the models predict that the FPPBR geometry plays a crucial role by demonstrating the superior performance of the circular reactor in comparison to the rectangular counterpart. It is expected that the mathematical models developed here will help in the design, scale-up and control of FPPBRs to be used particularly for hydrogen production using suitable microorganisms.

Methane hydrate formation in mixed-size porous media with gas circulation: Effects of sediment properties on gas consumption, hydrate saturation and rate constant

Being a promising potential source for natural gas, methane hydrate (MH) is attracting increasing interest due to its great amount and diverse geographic distribution. The formation of MH is significantly influenced by the properties of sediment media such as porosity and permeability. In this study, in order to have a better understanding on the relationship between MH formation behavior and sediment properties, as well as to synthesize representative hydrate samples, MH was formed in six different sets of mixed-size porous media composed of clay, silt and fine sand, with saline water and circulating methane gas to reflect MH formation with free methane flux in marine sediment. The sediment composition, experimental pressure (15 MPa) and temperature (286.2 K) were chosen based on the SH2 drilling site in the Shenhu area in South China Sea. A two-stage growing behavior was observed for all systems. The gas consumption and hydrate formation rate exhibited positive relations with the permeability and porosity of the sediments. Furthermore, hydrates were found to be preferably formed in the bottom layer of the sediment, which could be attributed to the drastic drop of permeability at the early stage of hydrate formation. Lastly, the hydrate formation rate constant was calculated based on the intrinsic kinetic model and found to be a good reflection of the mass transfer properties of different porous media.

Light Is More Important Than Nutrient Ratios of Fertilization for Cymodocea nodosa Seedling Development.

Restoration of seagrass beds through seedlings is an alternative to the transplantation of adult plants that reduces the impact over donor areas and increases the genetic variability of restored meadows. To improve the use of Cymodocea nodosa seedlings, obtained from seeds germinated in vitro, in restoration programs, we investigated the ammonium and phosphate uptake rates of seedlings, and the synergistic effects of light levels (20 and 200 μmol quanta m-2 s-1) and different nitrogen to phosphorus molar ratios (40 μM N:10 μM P, 25 μM N:25 μM P, and 10 μM N:40 μM P) on the photosynthetic activity and growth of seedlings. The nutrient content of seedlings was also compared to the seed nutrient reserves to assess the relative importance of external nutrient uptake for seedling development. Eighty two percent of the seeds germinated after 48 days at a mean rate of 1.5 seeds per day. All seedlings under all treatments survived and grew during the 4 weeks of the experiment. Seedlings of C. nodosa acquired ammonium and phosphate from the incubation media while still attached to the seed, at rates of about twice of adult plants. The relevance of external nutrient uptake was further highlighted by the observation that seedlings’ tissues were richer in nitrogen and phosphorus than non-germinated seeds. The uptake of ammonium followed saturation kinetics with a half saturation constant of 32 μM whereas the uptake of phosphate increased linearly with nutrient concentration within the range tested (5 – 100 μM). Light was more important than the nutrient ratio of fertilization for the successful development of the young seedlings. The seedlings’ photosynthetic and growth rates were about 20% higher in the high light treatment, whereas different nitrogen to phosphorus ratios did not significantly affect growth. The photosynthetic responses of the seedlings to changes in the light level and their capacity to use external nutrient sources showed that seedlings of C. nodosa have the ability to rapidly acclimate to the surrounding light and nutrient environment while still attached to the seeds. C. nodosa seedlings experiencing fertilization under low light levels showed slightly enhanced growth if nourished with a balanced formulation, whereas a slight increase in growth was also observed with unbalanced formulations under a higher light level. Our results highlight the importance of high light availability at the seedling restoration sites.

The effect of calcium on biofilm formation in dairy wastewater

Abstract Biofilm formation in dairy wastewater system irrigation pipes can reduce treatment capacity, increasing maintenance and cleaning costs. Understanding the effect of different components in the wastewater on growth and yield of bacteria present could help prevent excessive build-up of biofilms. This study investigated, in aerobic and anaerobic conditions, the effect of calcium, sodium and magnesium concentrations on growth rates, yields and saturation constants of four known biofilm forming bacteria associated with the blockage of an irrigation system. The ions tested (Ca2+, Mg2+, Na+) varied growth rates with biofilm growth in the presence of calcium being significantly slower (P < 0.05) than planktonic growth in sodium. Along with the slower growth, the addition of Ca2+ (up to 0.1 M) increased biofilm formation while addition over 0.5 M prevented biofilm formation. Knowing the nutritional requirements of the bacteria and the effects of the ions will be useful in predicting the growth, development and strategies in controlling biofilm formation in dairy wastewater.

Development of a Novel Kinetic Model for Cocoa Fermentation Applying the Evolutionary Optimization Approach

Abstract Traditional Mexican cocoa fermentation performed in batch was studied by applying kinetic modelling with experimental validation. Similar microbiological behaviour was observed up to 60 h, with a temperature increase at 72 h that remained constant (50 °C) until 156 h. Metabolite-production kinetics (ethanol and acetic acid) from degradable mucilage (glucose) was explored. Exploration involved applying different combinations of unstructured growth models, in order to consider the effect of temperature when predicting the concentration of metabolites in these microorganisms. Two methods were used to optimize model parameters: the Levenberg–Marquardt optimization approach and Genetic Algorithms (GAs). GAs which could be used to scale up the fermentation process indicated the applicability of this model for predicting fermentation quality. The maximum specific rate average for μmax and saturation constant (Ks) were 0.0961 h−1 and 1.4 mg/g m.s., respectively. The results obtained indicate the expediency of this technique for future application in the design and control of batch fermentation.

Inhibitory Effects of Cyanide on the Activity of Granular Starch Hydrolyzing Enzyme (GSHE) during Hydrolysis of Cassava (Manihot Esculenta Crantz) Starch

The kinetics and inhibitory effects of cyanide on the granular starch hydrolyzing enzyme (GSHE) activity during hydrolysis of cassava (Manihot esculenta Crantz) starch at low temperature were studied. The substrates included native cassava starch at various concentrations (100-400 g/L) and native cassava starches with added cyanide at various concentrations (50-150 mg/kg), while the concentration of enzyme was 1.5% (w/w). A decrease in reducing sugar concentration during hydrolysis of cassava starch indicated that the cyanide reduced the enzyme activity. Lineweaver-Burk plot of Michaelis-Menten equation was used to study the inhibition kinetics. The maximum velocity (Vmax) value was higher for native cassava starch than that of native cassava starch with added cyanides. The presence of cyanide was found to reduce the Vmax values. No significant different of the saturation constant (Km) value between native cassava starch and native cassava starch with added cyanides was observed. Based on the inhibition type analysis, the effect of cyanide in the cassava starch can be classified as a noncompetitive inhibition, with the Ki value of 0.33 mg/L.

Growth Kinetics for Microalgae Grown in Palm Oil Mill Effluent (POME) medium at various CO2 Levels

This paper sought to find the growth kinetic data of maximum specific growth rate (μmax) and substrate saturation constant (KS) for a microalgal reaction system over various dissolved CO2 levels (0.04, 0.1, 0.3, 0.5, 0.8, 1.0, 5.0, 10.0% v/v) at a constant sparging rate of 1.2 vvm, by using logistic model and Monod kinetics. The reaction system consisted of microalgae growing in palm oil mill effluent (POME) medium in 1 L flask with constant light illumination and sparged with the specified CO2 gas mixture. It is found from the experimental works that the values of μmax and KS to be at 0.04958 h-1 and 0.03523% (v/v) respectively. The results also showed that utilizing CO2 levels (v/v) in the sparging gas mixture more than 1% (v/v) would not improve microalgae growth significantly as expressed in the values of specific growth rate µ. These data and information are critically important for bioreactor scaling up purposes, especially bioreactor system dedicated for microalgae products and CO2 sequestration.

Out-of-time-order correlators in finite open systems

We study out-of-time-order correlators (OTOCs) of the form for a quantum system weakly coupled to a dissipative environment. Such an open system may serve as a model of, e.g., a small region in a disordered interacting medium coupled to the rest of this medium considered as an environment. We demonstrate that for a system with discrete energy levels the OTOC saturates exponentially ∝Σa i e -t/τi + const to a constant value at t → ∞, in contrast with quantum-chaotic systems which exhibit exponential growth of OTOCs. Focusing on the case of a two-level system, we calculate microscopically the decay times τ i and the value of the saturation constant. Because some OTOCs are immune to dephasing processes and some are not, such correlators may decay on two sets of parametrically different time scales related to inelastic transitions between the system levels and to pure dephasing processes, respectively. In the case of a classical environment, the evolution of the OTOC can be mapped onto the evolution of the density matrix of two systems coupled to the same dissipative environment.

An Integrated Response of Trichodesmium erythraeum IMS101 Growth and Photo-Physiology to Iron, CO2, and Light Intensity.

We have assessed how varying CO2 (180, 380, and 720 μatm) and growth light intensity (40 and 400 μmol photons m−2 s−1) affected Trichodesmium erythraeum IMS101 growth and photophysiology over free iron (Fe′) concentrations between 20 and 9,600 pM. We found significant iron dependencies of growth rate and the initial slope and maximal relative PSII electron transport rates (rPm). Under iron-limiting concentrations, high-light increased growth rates and rPm; possibly indicating a lower allocation of resources to iron-containing photosynthetic proteins. Higher CO2 increased growth rates across all iron concentrations, enabled growth to occur at lower Fe′ concentrations, increased rPm and lowered the iron half saturation constants for growth (Km). We attribute these CO2 responses to the operation of the CCM and the ATP spent/saved for CO2 uptake and transport at low and high CO2, respectively. It seems reasonable to conclude that T. erythraeum IMS101 can exhibit a high degree of phenotypic plasticity in response to CO2, light intensity and iron-limitation. These results are important given predictions of increased dissolved CO2 and water column stratification (i.e., higher light exposures) over the coming decades.

Kinetic evaluation on cell growth and biosynthesis of polyhydroxybutyrate (PHB) by Bacillus safensis EBT1 from sugarcane bagasse

Polyhydroxybutyrate (PHB), a biodegradable polymer (an intracellular product) was produced using Bacillus safensis EBT1. A kinetic model that describes microbial growth, biopolymer production and substrate consumption was used to predict the performance of batch fermentation of Bacillus safensis EBT1. The experimental data were fitted with modified logistic equation. The specific growth rate (μmax) and half saturation constant (Ks) values for the models such as Monod, Contois and Herbert were found to be 0.16, 0.15, 0.13 h−1 and 79.51, 68.19, 43.39 g/L respectively. Leudeking-Piret kinetics indicated that PHB formation in this study as growth associated. The recovered polymer was characterized using Transmission Electron Microscopy, Differential Scanning Calorimetry, Thermogravimetry analysis and Nuclear Magnetic Resonance. The PHB produced was used to synthesize nanoparticles using modified nano-precipitation method.

Trait selection and co-existence of phytoplankton in partially mixed systems: Trait based modelling and potential of an aggregated approach.

Trait selection and co-existence in phytoplankton communities in partially mixed water columns is investigated using trait based modelling. In the models employed, trait selection results from phytoplankton competition for two limiting resources, light and nutrients. The study employs spatially resolved models, in which the phytoplankton community is represented as a large number of trait-groups characterized by fixed trait combinations (trade-offs). Results from the trait-group resolving model (RM) are compared to results from an aggregated trait based model with adaptive traits (AM). Differences in specific production resulting from a trade-off between the half saturation constants of light and nutrients are sufficient to support evolutionary stable co-existence confirming that co-existence does not require differences in resource consumption. If abiotic conditions lead to the selection of a single trait group in RM, AM provides excellent approximations of the development of total biomass, average community trait and trait variance in the phytoplankton community. However, if selection leads to bimodal trait distributions, e.g. to co-existence of two trait groups (or species), functionally important properties of the phytoplankton community cannot be adequately represented by the aggregated information provided by AM. Because the increase in variance due to the development of bimodal trait distributions cannot be distinguished from an increase in variance due to an increase in trait diversity, the development of trait variance in AM models is not a reliable measure of trait diversity. Furthermore, AM may not provide reliable simulations of trophic interactions if the performance of the consumers depends on the traits of their resources. However, AM may support exploration of the consequences of environmental conditions and of the parameterization of species for co-existence within communities.

Biodegradation of 2-chloro-4-nitrophenol via a hydroxyquinol pathway by a Gram-negative bacterium, Cupriavidus sp. strain CNP-8

Cupriavidus sp. strain CNP-8 isolated from a pesticide-contaminated soil was able to utilize 2-chloro-4-nitrophenol (2C4NP) as a sole source of carbon, nitrogen and energy, together with the release of nitrite and chloride ions. It could degrade 2C4NP at temperatures from 20 to 40 °C and at pH values from 5 to 10, and degrade 2C4NP as high as 1.6 mM. Kinetics assay showed that biodegradation of 2C4NP followed Haldane substrate inhibition model, with the maximum specific growth rate (μmax) of 0.148/h, half saturation constant (Ks) of 0.022 mM and substrate inhibition constant (Ki) of 0.72 mM. Strain CNP-8 was proposed to degrade 2C4NP with hydroxyquinol (1,2,4-benzenetriol, BT) as the ring-cleavage substrate. The 2C4NP catabolic pathway in strain CNP-8 is significant from those reported in other Gram-negative 2C4NP utilizers. Enzymatic assay indicated that the monooxygenase initiating 2C4NP catabolism had different substrates specificity compared with previously reported 2C4NP monooxygenations. Capillary assays showed that strain CNP-8 exhibited metabolism-dependent chemotactic response toward 2C4NP at the optimum concentration of 0.5 mM with a maximum chemotaxis index of 37.5. Furthermore, microcosm studies demonstrated that strain CNP-8, especially the pre-induced cells, could remove 2C4NP rapidly from the 2C4NP-contaminated soil. Considering its adaptability to pH and temperature fluctuations and great degradation efficiency against 2C4NP, strain CNP-8 could be a promising candidate for the bioremediation of 2C4NP-contaminated sites.

Performance of Halomonas sp. to reduce hexavalent chromium in batch and continuous fixed film reactor

The performance of fixed film bioreactor on bioreduction of Cr(VI) was evaluated. The reactor was operated under batch and continuous mode. Influent contained glucose as the single carbon source. The maximum specific growth rate obtained was 7.16 mg L−1. The half saturation constant for COD was 475 mg L−1. The yield coefficient was found to be 0.209. A maximum biomass of 457 h−1 was obtained for Cr(VI) free cells. Both the reactor performed better under an hydraulic retention time of 24 h. Near complete reduction of Cr(VI) was reported for an initial Cr(VI) concentration of 10 and 20 mg L−1. The maximum number of suspended cells reported was 4.3 × 1014 at an Cr(VI) loading rate of 240 mg L−1day−1. The maximum amount of attached and suspended cells reported was 2013 and 238 mg. A maximum COD reduction of 84.1% was reported. The lag period for growth of cells under a Cr(VI) load ranging up to 40 mg L−1 was 3 h.

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

AbstractBACKGROUNDThis 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.RESULTSAcute 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.CONCLUSIONInterpretation 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