Andrews Equation Research Articles

Pseudomonas aeruginosa based concurrent degradation of beta-cypermethrin and metabolite 3-phenoxybenzaldehyde, and its bioremediation efficacy in contaminated soils

Beta-cypermethrin is one of the widely used pyrethroid insecticides, and problems associated with the accumulation of its residues have aroused public attention. Thus, there is an urgent need to effectively remove the beta-cypermethrin that is present in the environment. Biodegradation is considered a cost-effective and environmentally friendly method for removing pesticide residues. However, the beta-cypermethrin-degrading microbes that are currently available are not optimal. In this study, Pseudomonas aeruginosa PAO1 was capable of efficiently degrading beta-cypermethrin and its major metabolite 3-phenoxybenzaldehyde in water/soil environments. Strain PAO1 could remove 91.4% of beta-cypermethrin (50 mg/L) in mineral salt medium within 120 h. At the same time, it also possesses a significant ability to metabolize 3-phenoxybenzaldehyde—a toxic intermediate of beta-cypermethrin. The Andrews equation showed that the maximum substrate utilization concentrations of beta-cypermethrin and 3-phenoxybenzaldehyde by PAO1 were 65.3558 and 49.6808 mg/L, respectively. Box–Behnken design-based response surface methodology revealed optimum conditions for the PAO1 strain-based degradation of beta-cypermethrin as temperature 30.6 °C, pH 7.7, and 0.2 g/L inoculum size. The results of soil remediation experiments showed that indigenous micro-organisms helped to promote the biodegradation of beta-cypermethrin in soil, and beta-cypermethrin half-life in non-sterilized soil was 6.84 days. The bacterium transformed beta-cypermethrin to produce five possible metabolites, including 3-phenoxybenzyl alcohol, methyl 2-(4-hydroxyphenoxy)benzoate, diisobutyl phthalate, 3,5-dimethoxyphenol, and 2,2-dimethyl-1-(4-phenoxyphenyl)propanone. Among them, methyl 2-(4-hydroxyphenoxy)benzoate and 3,5-dimethoxyphenol were first identified as the intermediate products during the beta-cypermethrin degradation. In addition, we propose a degradation pathway for beta-cypermethrin that is metabolized by strain PAO1. Beta-cypermethrin could be biotransformed firstly by hydrolysis of its carboxylester linkage, followed by cleavage of the diaryl bond and subsequent metabolism. Based on the above results, P. aeruginosa PAO1 could be a potent candidate for the beta-cypermethrin-contaminated environmental bioremediation.

Novel mechanism and degradation kinetics of allethrin using Bacillus megaterium strain HLJ7 in contaminated soil/water environments

As a common pyrethroid insecticide, allethrin is widely used for various purposes in agriculture and home applications. At present, allethrin residues have been frequently detected worldwide, yet little is known about the kinetics and degradation mechanisms of this insecticide. In this study, a highly efficient allethrin-degrading bacterium, Bacillus megaterium strain HLJ7, was obtained through enrichment culture technology. Strain HLJ7 can remove 96.5% of 50 mg L−1 allethrin in minimal medium within 11 days. The first-order kinetic analysis of degradation demonstrated that the half-life of allethrin degradation by strain HLJ7 was 3.56 days, which was significantly shorter than the 55.89 days of the control. The Box–Behnken design of the response surface method optimized the degradation conditions for strain HLJ7: temperature 32.18 °C, pH value 7.52, and inoculation amount 1.31 × 107 CFU mL−1. Using Andrews equation, the optimal concentration of strain HLJ7 to metabolize allethrin was determined to be 21.15 mg L−1, and the maximum specific degradation rate (qmax), half-rate constant (Ks) and inhibition coefficient (Ki) were calculated to be 1.80 d−1, 1.85 mg L−1 and 68.13 mg L−1, respectively. Gas chromatography-mass spectrometry identified five intermediate metabolites, suggesting that allethrin could be degraded firstly by cleavage of its carboxylester bond, followed by degradation of the five-carbon ring and subsequent metabolism. The results of soil remediation experiments showed that strain HLJ7 has excellent bioremediation potential in the soils. After 15 days of treatment, about 70.8% of the initial allethrin (50 mg kg−1) was removed and converted into nontoxic intermediate metabolites, and its half-life was significantly reduced in the soils. Taken together, these findings shed light on the degradation mechanisms of allethrin and also highlight the promising potentials of B. megaterium HLJ7 in bioremediation of allethrin-comtaminated environment.

Effect of Nickel as Stress Factor on Phenol Biodegradation by Stenotrophomonas maltophilia KB2.

This study focuses on the phenol biodegradation kinetics by Stenotrophomonas maltophilia KB2 in a nickel-contaminated medium. Initial tests proved that a nickel concentration of 33.3 mg·L−1 caused a cessation of bacterial growth. The experiments were conducted in a batch bioreactor in several series: without nickel, at constant nickel concentration and at varying metal concentrations (1.67–13.33 g·m−3). For a constant Ni2+ concentration (1.67 or 3.33 g·m−3), a comparable bacterial growth rate was obtained regardless of the initial phenol concentration (50–300 g·m−3). The dependence µ = f (S0) at constant Ni2+ concentration was very well described by the Monod equations. The created varying nickel concentrations experimental database was used to estimate the parameters of selected mathematical models, and the analysis included different methods of determining metal inhibition constant KIM. Each model showed a very good fit with the experimental data (R2 values were higher than 0.9). The best agreement (R2 = 0.995) was achieved using a modified Andrews equation, which considers the metal influence and substrate inhibition. Therefore, kinetic equation parameters were estimated: µmax = 1.584 h−1, KS = 185.367 g·m−3, KIS = 106.137 g·m−3, KIM = 1.249 g·m−3 and n = 1.0706.

Peculiarities of the Kinetics of 2-Nitrophenol Removal by the Native Culture of Microbial Biomass

In the processes of water purification from organic matter, the biomass of biological activated carbon (BAC) can be used independently (separately from the carrier). In the present work, the enriched culture of microorganisms of biofilm biomass capable of effectively removing xenobiotics from more concentrated water solutions (45 mg/dm3) was obtained using the biofilm washed from the BAC laboratory filter, which has been used for several years for filtering 2-nitrophenol (NP) aqueous solution at a low concentration (8 ± 2 mg/dm3). The procedure of progressive adaptation, including moderate aeration, the stage of endogenous respiration and the elements of anaerobic system, was aimed at obtaining a specialized culture of microorganisms with enhanced survival rate, which would be able to increase the rate of NP destruction with each cycle of adaptation, to provide complete extraction of organic substrates and to prevent the accumulation of excessive concentrations of nitrates. The need of enriched biomass for the treatment of BAC regeneration wastewater arises occasionally. Hence, it is highly important to know the peculiarities of kinetics of biomass transition from the state of “maintenance” into the active state sufficient for effective destruction of the higher levels of xenobiotics, as well as the influence of additional substrates and biomass carriers on these processes. In the present work we have studied the effect of NP concentration, the NP/biomass concentration ratio and the form of biomass on the kinetics of xenobiotic extraction in a batch anaerobic process. Mathematical formulation of experimental data was performed in accordance with the Monod and Haldane/Andrews growth kinetics. During the progressive increase in the initial NP concentration (from 45–50 to 200 mg/dm3) based on the kinetic coefficients of the Haldane–Andrews equation, there was a change in the internal fermentative properties of microbial culture. The increase in specialization of the biomass is represented by a formal decrease in the values of the half-saturation constant Ks and an increase in the concentration inhibition constant Ki indicating the ability of the culture to adapt to assimilation of enhanced xenobiotic concentrations. The enriched native biomass adapted to 200 mg/dm3 of NP was effectively used for utilization of the waste from chemical regeneration of a laboratory BAC filter. Transition to the anoxic mode as the final stage of regeneration activated the groups of microorganisms capable of using nitrates as a terminal electron acceptor.

Performance of several Saccharomyces strains for the alcoholic fermentation of sugar-sweetened high-strength wastewaters: Comparative analysis and kinetic modelling

This work focuses on the performance of ten commercial Saccharomyces yeast strains in the batch alcoholic fermentation of sugars contained in selected industrial wastewaters from the soft drink industry. Fermentation has been applied successfully to treat these effluents prior to their disposal. Although many strains were investigated, similar behaviour was observed between all of the Saccharomyces strains tested. When media were inoculated with 2gL−1 of yeast, all strains were able to completely consume the available sugars in less than 14h. Thus, any of the strains studied in this work could be used in non-conventional wastewater treatment processes based on alcoholic fermentation. However, ethanol production varied between strains, and these differences could be significant from a production point of view. Saccharomyces bayanus produced the most ethanol, with a mean yield of 0.44gethanolgsugarconsumed−1 and an ethanol specific production rate of 5.96gethanol (Lh)−1. As the assayed soft drinks wastewaters contain about 105gsugar/L of fermentable sugars, the concentration of ethanol achieved after the fermentations process was 46.2gethanol/L. A rigorous kinetic modelling methodology was used to model the Saccharomyces bayanus fermentation process. The kinetic model included coupled mass balances and a minimal number of parameters. A simple unstructured model based on the Andrews equation (substrate inhibition) was developed. This model satisfactorily described biomass growth, sugar consumption and bioethanol production. In addition to providing insights into the fermentative performance of potentially relevant strains, this work can facilitate the design of large-scale ethanol production processes that use wastewaters from the sugar-sweetened beverage industry as feedstock.

Characterization of naphthalene degradation by Streptomyces sp. QWE-5 isolated from active sludge

A bacterial strain, QWE-5, which utilized naphthalene as its sole carbon and energy source, was isolated and identified as Streptomyces sp. It was a Gram-positive, spore-forming bacterium with a flagellum, with whole, smooth, convex and wet colonies. The optimal temperature and pH for QWE-5 were 35 °C and 7.0, respectively. The QWE-5 strain was capable of completely degrading naphthalene at a concentration as high as 100 mg/L. At initial naphthalene concentrations of 10, 20, 50, 80 and 100 mg/L, complete degradation was achieved within 32, 56, 96, 120 and 144 h, respectively. Kinetics of naphthalene degradation was described using the Andrews equation. The kinetic parameters were as follows: qmax (maximum specific degradation rate) = 1.56 h⁻¹, Ks (half-rate constant) = 60.34 mg/L, and KI (substrate-inhibition constant) = 81.76 mg/L. Metabolic intermediates were identified by gas chromatography and mass spectrometry, allowing a new degradation pathway for naphthalene to be proposed. In this pathway, monooxygenation of naphthalene yielded naphthalen-1-ol. Further degradation by Streptomyces sp. QWE-5 produced acetophenone, followed by adipic acid, which was produced as a combination of decarboxylation and hydroxylation processes.

An Evaluation of Kinetic Parameters and Mass Transfer Coefficient in the Biodesulfurization of Natural Gas

Biodesulfurization of natural gas in a batch culture was investigated. The microorganisms used for the removal of hydrogen sulfide were isolated from a local hot spring. The experiments were conducted with natural gas initial pressures of 1 to 1.8 atm. The kinetic parameters and mass transfer coefficients were determined. With gas pressure of 1.2 atm, maximum cell dry weight of 3.136 g.l−1 and mass transfer coefficient of 0.023 h−1 were obtained. The kinetic model was growth dependent. Andrew's equation predicted the inhibition constant; as the gas pressure increased the inhibition coefficient increased. The maximum specific growth rate (μmax) for Andrew's model was 0.176 h−1.

Kinetic analysis of biohydrogen production from complex dairy wastewater under optimized condition

Present work describes a kinetic analysis of various aspects of biohydrogen production in batch test using optimized conditions obtained previously. Monod model and Logistic equation have been used to find growth kinetic parameters in batch test under uncontrolled pH. The values of μm, Ks, and Xm were 0.64 h−1, 15.89 g-COD L−1, and 7.26 g-VSS L−1, respectively. Modified Leudeking-Piret and Michaelis–Menten equation corroborates a flux of energy to hydrogen production pathway and energy sufficiency in the system. Modified Gompertz equation illustrates that the overall rate and hydrogen yield at 15 g-COD L−1 was higher compared to a dark fermentation of other wastewaters. Besides, Andrew's equation also suggests that since the higher value of KI (19.95 g-COD L−1), k (255 mL h−1 L−1) was not inhibited at high S. The experimental results implied that the entire products during the fermentation process were growth and substrate degradation associated. The result also confirms that the acetate and butyrate were substantially used for hydrogen production in acidogenic metabolism under uncontrolled pH.

The Influence of Glucose on Growth and Lipid Production under Heterotrophic and Mixotrophic Conditions for Monoraphidium sp. FXY-10

The impact of glucose on the growth under heterotrophic and mixotrophic conditions for Monoraphidium sp. FXY-10 as well as its lipid content was investigated through the Andrew equation. The results demonstrated that the subsaturation constant of Monoraphidium sp. FXY-10 under heterotrophic condition to glucose was smaller than that of Monoraphidium sp. FXY-10 under mixotrophic condition, indicating that Monoraphidium sp. FXY-10 is more sensitive to glucose under heterotrophic condition. Furthermore, the biomass productivity, lipid productivity and lipid content of Monoraphidium sp. FXY-10 all reached the peak at 10 g L-1 of glucose concentration under both heterotrophic and mixotrophic conditions. Compared with other Chlorella sp., the Monoraphidium sp. FXY-10 represented higher lipid productivity (131.79 mg L-1 d-1).

The Kinetics of Ethanol Production from Cane Molasses by Saccharomyces cerevisiae in a Batch Bioreactor

The present study was aimed at achieving a better understanding about fermentation condition by Saccharomyces cerevisiae with cane molasses for bioethanol production. The biosynthesis of ethanol was conducted via S. cerevisiae from cane molasses at pH 4.5 and 30°C. The fermentation was carried out in triplicate with various feed concentrations of molasses for S. cerevisiae in a batch bioreactor. S. cerevisiae produced ethanol at 9.3 ± 1.8 g/l with a biomass yield of 0.57 g/g after 36 h. The kinetic of growth dependence on molasses was represented by Andrew equation to predict the inhibition constant in the cultures media.

Biodegradation of 3,4-Dichloroaniline by a Novel Myroides odoratimimus Strain LWD09 with Moderate Salinity Tolerance

A Gram-negative bacterium strain LWD09, capable of growing aerobically on 3,4-dichloroaniline (DCA) as the sole carbon and energy source, was isolated from the farm field. This bacterium was identified as Myroides odoratimimus strain by morphological, physiological, and biochemical characteristics as well as 16S rDNA sequence. Analysis of culture pH, temperature, cells growth, and DCA concentration demonstrated that strain LWD09 could effectively degrade DCA without a lag phase. The kinetics of DCA degradation was well described using the Andrews equation, and the kinetic parameters were as follows: q max = 1.74 h−1, K s = 43.5 mg L−1, and K i = 230.3 mg L−1. In addition, strain LWD09 was found to be moderately halophilic and showed the highest power of DCA degradation in 5% NaCl (w/w, %). With initial concentrations of 30, 100, and 200 mg L−1, 100%, 80.4%, and 33.2% of DCA were transformed after 96 h in 5% NaCl, respectively. These results suggest that strain LWD09 has the potential to degrade DCA in saline wastewater. To date, this is the first report on the degradation of DCA by a M. odoratimimus strain with moderate salinity tolerance.

Biodegradation of beta-cypermethrin and 3-phenoxybenzoic acid by a novel Ochrobactrum lupini DG-S-01

A newly isolated bacterium DG-S-01 from activated sludge utilized beta-cypermethrin (beta-CP) and its major metabolite 3-phenoxybenzoic acid (3-PBA) as sole carbon and energy source for growth in mineral salt medium (MSM). Based on the morphology, physio-biochemical characteristics, and 16S rDNA sequence analysis, DG-S-01 was identified as Ochrobactrum lupini. DG-S-01 effectively degraded beta-CP with total inocula biomass A590nm=0.1–0.8, at 20–40°C, pH 5–9, initial beta-CP 50–400mgL−1 and metabolized to yield 3-PBA leading to complete degradation. Andrews equation was used to describe the special degradation rate at different initial concentrations. Degradation rate parameters qmax, Ks and Ki were determined to be 1.14d−1, 52.06mgL−1 and 142.80mgL−1, respectively. Maximum degradation was observed at 30°C and pH 7.0. Degradation of beta-CP was accelerated when MSM was supplemented with glucose, beef extract and yeast extract. Studies on biodegradation in liquid medium showed that over 90% of the initial dose of beta-CP (50mgL−1) was degraded under the optimal conditions within 5d. Moreover, the strain also degraded beta-cyfluthrin, fenpropathrin, cyhalothrin and deltamethrin. These results reveal that DG-S-01 may possess potential to be used in bioremediation of pyrethroid-contaminated environment.

Aerobic biodegradation of nitrobenzene by a defined microbial consortium immobilized in polyurethane foam

An aerobic microbial consortium constructed by the combination of Rhodotorula mucilaginosa Z1, Streptomyces albidoflavus Z2 and Micrococcus luteus Z3 was immobilized in polyurethane foam and its ability to degrade nitrobenzene was investigated. Batch experimental results showed that polyurethane-foam-immobilized cells (PFIC) more efficiently degrade 200–400 mg l−1 nitrobenzene than freely suspended cells (FSC). Kinetics of nitrobenzene degradation by PFIC was well described by the Andrews equation. Compared with FSC, PFIC exhibited better reusability (over 100 times) and tolerated higher shock-loadings of nitrobenzene (1,000 mg l−1). Moreover, In the presence of salinity (≤5% NaCl, w/v), phenol (≤150 mg l−1) and aniline (≤50 mg l−1), respectively, degradation efficiency of nitrobenzene by PFIC reached over 95%. Even in the presence of both 100 mg l−1 phenol and 50 mg l−1 aniline, over 75% nitrobenzene was removed by PFIC in 36 h. Therefore, the immobilization of the defined consortium in polyurethane foam has application potential for removing nitrobenzene in industrial wastewater treatment system.

Aerobic degradation of 2-picolinic acid by a nitrobenzene-assimilating strain: Streptomyces sp. Z2

Streptomyces sp. Z2 was isolated from nitrobenzene contaminated activated sludge, which utilized nitrobenzene as a sole source of carbon, nitrogen, and energy under aerobic condition. It was found that besides nitrobenzene strain Z2 can degrade 2-picolinic acid. Strain Z2 completely degraded 2-picolinic acid with initial concentration of 500 mg/L, 1000 mg/L, 1500 mg/L, 2000 mg/L, 2500 mg/L, and 3000 mg/L within 36 h, 50 h, 72 h, 100 h, 136 h, and 180 h, respectively. Kinetics of 2-picolinic acid degradation was described using the Andrews equation. The kinetic parameters were as follows: q max = 3.81 h −1, K s = 83.10 mg/L, and K i = 252.11 mg/L. During the biodegradation process, Z2 transformed 2-picolinic acid into a product which was identified as 6-hydroxy picolinic acid by UV–vis spectrometry, 1H nuclear magnetic resonance spectroscopy, and mass spectrometry. 6-Hydroxy picolinic acid was then cleaved and mineralized with release of ammonia.

Isolation and characterization of a novel nitrobenzene-degrading bacterium with high salinity tolerance: Micrococcus luteus

Strain Z3 was isolated from nitrobenzene-contaminated sludge. Strain Z3 was able to utilize nitrobenzene as a sole source of carbon, nitrogen and energy under aerobic condition. Based on the morphology, physiological biochemical characteristics, and 16S rDNA sequence, strain Z3 was identified as Micrococcus luteus. Strain Z3 completely degraded nitrobenzene with initial concentration of 100, 150, 200, and 250 mg L −1 within 70, 96, 120 and 196 h, respectively. Kinetics of nitrobenzene degradation was described using the Andrews equation. The kinetic parameters were as follows: q max = 1.19 h −1, K s = 29.11 mg L −1, and K i = 94.00 mg L −1. Strain Z3 had a high salinity tolerance. It degraded 200 mg L −1 nitrobenzene completely in 5% NaCl (w/w%). Strain Z3 therefore could be an excellent candidate for the bio-treatment of nitrobenzene industrial wastewaters with high salinity. This is the first report on the degradation of nitrobenzene by M. luteus and the degradation of nitrobenzene achieved in such a high salinity.

Isolation and characterization of a nitrobenzene degrading yeast strain from activated sludge

Strain Z1 was isolated from nitrobenzene-contaminated sludge. Strain Z1 was able to utilize nitrobenzene as a sole source of carbon, nitrogen, and energy under aerobic condition. Based on the morphology, physiological biochemical characteristics, and 26S rDNA D1/D2 domain sequence, strain Z1 was identified as Rhodotorula mucilaginosa. Strain Z1 mineralized up to 450 mg L −1 nitrobenzene. Kinetics of nitrobenzene degradation was described using the Andrews equation. The kinetic parameters were as follows: q max = 1.50 h −1, K s = 31.31 mg L −1, and K i = 101.34 mg L −1. Strain Z1 had a high-salinity tolerance. It degraded nitrobenzene effectively in 5% NaCl (quality concentration). Even in the presence of aniline or phenol, strain Z1 degraded nitrobenzene efficiently. Strain Z1 therefore could be an excellent candidate for the bio-treatment of nitrobenzene industrial wastewaters.

Anaerobic digestion of cattail with rumen culture in the presence of heavy metals

The anaerobic digestion of cattail by rumen cultures in the presence of Cu(II), Cd(II) or Cr(VI) was investigated in this study. Three cases were respectively observed for the different metal dosages: promoted cattail degradation and methane production at a low heavy metal concentration, e.g., Cu(II) 2.4 mg/l, Cd(II) 1.6 mg/l, Cr(VI) 4.0 mg/l; reduced cattail degradation efficiency and methane production at a middle metal level; a severe inhibition to the cattail degradation at a high heavy metal dosage. The inhibition kinetics of Cu(II) on the digestion of cattail by rumen cultures was also analyzed and a simplified Andrews equation was used to describe such an inhibition. The inhibition constants for Cu(II) on the degradation of cattail, production of volatile fatty acids and formation of methane were estimated as 7.4, 9.5 and 6.4 mg/l, respectively. Comparative experimental results suggest that the order of toxicity degree of the tested metals on the rumen cultures was: Cd(II) > Cu(II) > Cr(VI).

Ethanol and acetate production from synthesis gas via fermentation processes using anaerobic bacterium, Clostridium ljungdahlii

Synthesis gas was used to produce ethanol and acetate via fermentation processes. A strict autotrophic bacterium, Clostridium ljungdahlii, was grown on syngas to investigate production of acetate and ethanol. The experiments were conducted with various initial total pressures of syngas at 0.8–1.8 atm with 0.2 intervals. Formation of acetate was almost the same for all initial pressures as well as cell concentrations. Ethanol concentration was promoted by hydrogen and carbon dioxide in the culture media. Maximum acetate production (1.3 g l −1) was obtained at syngas total pressures of 1.4 atm. However, maximum ethanol concentration of 0.6 g l −1 was obtained with the syngas total pressures of 1.6 and 1.8 atm. The cell and product yields were 0.3 g cell g −1 CO and 0.41 g products g −1 CO, respectively. The product ratio of ethanol and acetate was 0.54 g ethanol g −1 acetate at syngas total pressures of 1.6 and 1.8 atm. In this study, a novel prediction was introduced which proposes the death phase of bacteria. Based on predicted model fitted with experimental data, the maximum cell dry weight ( x m), inhibition constant ( k) and maximum specific growth rate were 1.2 g l −1, 0.003 h −1 and 0.07 h −1, respectively. The kinetic of growth-dependence on CO was represented by Andrew equation to predict inhibition constant in the cultures media. The inhibition constant was obtained at 2 mmol CO l −1.

Rate of ammonia oxidation in a synthetic saline wastewater by a nitrifying mixed‐culture

AbstractMost of the kinetic studies on nitrification have been performed in diluted salts medium. In this work, the ammonia oxidation rate (AOR) was determined by respirometry at different ammonia (0.01 and 33.5 mg N‐NH3 L−1), nitrite (0–450 mg N‐NO2− L−1) and nitrate (0 and 275 mg N‐NO3− L−1) concentrations in a saline medium at 30 °C and pH 7.5. Sodium azide was used to uncouple the ammonia and nitrite oxidation, so as to measure independently the AOR. It was determined that ammonia causes substrate inhibition and that nitrite and nitrate exhibit product inhibition upon the AOR. The effects of ammonia, nitrite and nitrate were represented by the Andrews equation (maximal ammonia oxidation rate, rAOMAX, = 43.2 [mg N‐NH3 (g VSSAO h)−1]; half saturation constant, KSAO, = 0.11 mg N‐NH3 L−1; inhibition constant KIAO, = 7.65 mg N‐NH3 L−1), by the non‐competitive inhibition model (inhibition constant, KINI, = 176 mg N‐NO2− L−1) and by the partially competitive inhibition model (inhibition constant, KINA, = 3.3 mg N‐NO3− L−1; α factor = 0.24), respectively. The rAOMAX value is smaller, and the KSAO value larger, than the values reported in diluted salts medium; the KIAO value is comparable to those reported. Process simulations with the kinetic model in batch nitrifying reactors showed that the inhibitory effects of nitrite and nitrate are significant for initial ammonia concentrations larger than 100 mg N‐NH4+ L−1. Copyright © 2005 Society of Chemical Industry

Kinetics of inhibition in the biodegradation of monoaromatic hydrocarbons in presence of heavy metals

The toxicity and inhibitory effects of heavy metals such as cadmium, nickel and zinc on alkylbenzene removal were evaluated with a Bacillus strain. The kinetics of alkylbenzene biodegradation with the different heavy metals at various concentrations were modeled using the Andrews equation which yielded a good fit between model and experimental data. Additional experiments undertaken with a Pseudomonas sp. in presence of nickel confirmed a good fit between experimental data and the Andrews model for this strain as well. The heavy metals inhibition constants ( K i) were calculated for different combinations of volatile organic compounds (VOC) and heavy metals. The present approach provides a method for evaluating and quantifying the inhibition effect of heavy metals on the biodegradtion of pollutants by specific microbial strains.