Biodegradation kinetics of monoterpenes in liquid and soil-slurry systems

Batch experiments were conducted to evaluate the biodegradation rates of limonene, α-pinene, γ-terpinene, terpinolene and α-terpineol at 23 °C under aerobic conditions. Biodegradation was demonstrated by the depletion of monoterpene mass, CO₂ production and a corresponding increase in biomass. Monoterpene degradation in liquid cultures devoid of soil followed Monod kinetics. The maximum specific growth rate (μ_max) was 0.02 h⁻¹ and 0.06 h⁻¹ and the half-velocity constant (K _s ) varied from 32 mg/l to 3 mg/l for the limonene and α-terpineol respectively. The recovery of monoterpenes by solvent extraction from autoclaved and azide-amended soil-slurry samples decreased over time and ranged from 69% to 73% for 120 h of incubation period. Although a significant fraction of monoterpene hydrocarbon could not be extracted, mineralization of these compounds in the soil-slurry systems took place, as shown by CO₂ production. The soil-normalized degradation rates for the hydrocarbon monoterpenes ranged from 0.6 μg g⁻¹ h⁻¹ to 2.1 μg g⁻¹ h⁻¹. A kinetic model – which combined monoterpene biodegradation in the liquid phase and net desorption – was developed and applied to data obtained from soil-slurry assays. Received: 10 September 1996 / Received revision: 16 December 1996 / Accepted: 10 January 1997     

Biodegradation kinetics of naphthalene in nonaqueous phase liquid-water mixed batch systems: comparison of model predictions and experimental results

A model is formulated to describe dissolution of naphthalene from an insoluble nonaqueous phase liquid (NAPL) and its subsequent biodegradation in the aqueous phase in completely mixed batch reactors. The physicochemical processes of equilibrium partitioning and mass transfer of naphthalene between the NAPL and aqueous phases were incorporated into the model. Biodegradation kinetics were described by Monod's microbial growth kinetic model, modified to account for the inhibitory effects of 1,2-naphthoquinone formed during naphthalene degradation under certain conditions. System parameters and biokinetic coefficients pertinent to the NAPL-water systems were determined either by direct measurement or from nonlinear regression of the naphthalene mineralization profiles obtained from batch reactor tests with two-component NAPLs comprised of naphthalene and heptamethylnonane. The NAPLs contained substantial mass of naphthalene, and naphthalene biodegradation kinetics were evaluated over the time required for near complete depletion of naphthalene from the NAPL. Model predictions of naphthalene mineralization time profiles compared favorably to the general trends observed in the data obtained from laboratory experiments with the two-component NAPL, as well as with two coal tars obtained from the subsurface at contaminated sites and composed of many different PAHs (polycyclic aromatic hydrocarbon compounds). The effects of varying the NAPL mass and the naphthalene mole fractions in the NAPL are discussed. It was observed that the time to achieve a given percent removal of naphthalene does not change significantly with the initial mass of naphthalene in a fixed volume of the NAPL. Significant changes in the mineralization profiles are observed when the volume (and mass) of NAPL in the system is changed.     

Biodegradation of azo and anthraquinone dyes in continuous systems

The purpose is to develop a complete microbiological model system for the treatment of wastewater from textile mills in developing countries. Artificial wastewater was treated by microorganisms growing on wood shavings from Norway spruce during unsterile conditions. The microorganisms were inoculated from forest residues. Mixtures of the azo dyes Reactive Black 5 and Reactive Red 2 were degraded in batch as well as continuous experiments. Reactive Red 2 mixed with the anthraquinone dye Reactive Blue 4 was also treated in the continuous system. The system consisted of three reservoirs - the first two with an anaerobic environment and the third with an aerobic. The dye concentrations were 200 mg l⁻¹ of each dye in the continuous system and the retention time was approximately 4 days and 20 h per reservoir. Samples from the process were analysed with spectrophotometer and LC/MS to monitor the degradation process. 86-90% of the colour was removed after a treatment of 4 days and 23 h in the continuous process. Two metabolites were found in the outlets of reactors one and two, but they were degraded to below the detection limit in the aerobic reactor.     

Biodegradation and kinetics of aerobic granules under high organic loading rates in sequencing batch reactor

Biodegradation, kinetics, and microbial diversity of aerobic granules were investigated under a high range of organic loading rate 6.0 to 12.0 kg chemical oxygen demand (COD) m⁻³ day⁻¹ in a sequencing batch reactor. The selection and enriching of different bacterial species under different organic loading rates had an important effect on the characteristics and performance of the mature aerobic granules and caused the difference on granular biodegradation and kinetic behaviors. Good granular characteristics and performance were presented at steady state under various organic loading rates. Larger and denser aerobic granules were developed and stabilized at relatively higher organic loading rates with decreased bioactivity in terms of specific oxygen utilization rate and specific growth rate (μ _overall) or solid retention time. The decrease of bioactivity was helpful to maintain granule stability under high organic loading rates and improve reactor operation. The corresponding biokinetic coefficients of endogenous decay rate (k _d), observed yield (Y _obs), and theoretical yield (Y) were measured and calculated in this study. As the increase of organic loading rate, a decreased net sludge production (Y _obs) is associated with an increased solid retention time, while k _d and Y changed insignificantly and can be regarded as constants under different organic loading rates.     

Inhibition of jack bean urease by 1,4-benzoquinone and 2,5-dimethyl-1,4-benzoquinone. Evaluation of the inhibition mechanism

1,4-benzoquinone (BQ) and 2,5-dimethyl-1,4-benzoquinone (DMBQ) were studied as inhibitors of jack bean urease in 50 mM phosphate buffer, pH 7.0. The mechanisms of inhibition were evaluated by progress curves studies and steady-state approach to data achieved by preincubation of the enzyme with the inhibitor. The obtained reaction progress curves were time-dependent and characteristic of slow-binding inhibition. The effects of different concentrations of BQ and DMBQ on the initial and steady-state velocities as well as the apparent first-order velocity constants obeyed the relationships of two-step enzyme-inhibitor interaction, qualified as mechanism B. The rapid formation of an initial BQ-urease complex with an inhibition constant of Ki = 0.031 mM was followed by a slow isomerization into the final BQ-urease complex with the overall inhibition constant of Ki* = 4.5 x 10(-5) mM. The respective inhibition constants for DMBQ were Ki = 0.42 mM, Ki* = 1.2 x 10(-3) mM. The rate constants of the inhibitor-urease isomerization indicated that forward processes were rapid in contrast to slow reverse reactions. The overall inhibition constants obtained by the steady-state analysis were found to be 5.1 x 10(-5) mM for BQ and 0.98 x 10(-3) mM for DMBQ. BQ was found to be a much stronger inhibitor of urease than DMBQ. A test, based on reaction with L-cysteine, confirmed the essential role of the sulfhydryl group in the inhibition of urease by BQ and DMBQ.     

Inhibition of Jack Bean Urease by 1,4-benzoquinone and 2,5-dimethyl-1,4-benzoquinone. Evaluation of the Inhibition Mechanism

1,4-benzoquinone (BQ) and 2,5-dimethyl-1,4-benzoquinone (DMBQ) were studied as inhibitors of jack bean urease in 50 mM phosphate buffer, pH 7.0. The mechanisms of inhibition were evaluated by progress curves studies and steady-state approach to data achieved by preincubation of the enzyme with the inhibitor. The obtained reaction progress curves were time-dependent and characteristic of slow-binding inhibition. The effects of different concentrations of BQ and DMBQ on the initial and steady-state velocities as well as the apparent first-order velocity constants obeyed the relationships of two-step enzyme-inhibitor interaction, qualified as mechanism B. The rapid formation of an initial BQ-urease complex with an inhibition constant of K i =0.031 mM was followed by a slow isomerization into the final BQ-urease complex with the overall inhibition constant of K*_i=4.5 × 10 ^?5 mM. The respective inhibition constants for DMBQ were K i =0.42 mM, K*_i =1.2 × 10 ^?3 mM. The rate constants of the inhibitor-urease isomerization indicated that forward processes were rapid in contrast to slow reverse reactions. The overall inhibition constants obtained by the steady-state analysis were found to be 5.1 × 10 ^?5 mM for BQ and 0.98 × 10 ^?3 mM for DMBQ. BQ was found to be a much stronger inhibitor of urease than DMBQ. A test, based on reaction with L-cysteine, confirmed the essential role of the sulfhydryl group in the inhibition of urease by BQ and DMBQ.     

Protein targets of 1,4-benzoquinone and 1,4-naphthoquinone in human bronchial epithelial cells

Many aspects of the toxicity of xenobiotic compounds have been attributed to the consequences of covalent modification of specific proteins, but the nature and specificity of protein targets for classes of electrophilic toxins remain largely uncharacterized. For inhaled toxicants, the point of exposure or absorption lies with epithelial cells lining the pulmonary tree. In this study, abundant proteins in human bronchial epithelial cells that are arylated in vitro by two quinonoid compounds, 1,4-benzoquinone (BQ) and 1,4-naphthoquinone (NQ) have been detected using (14)C-labeled quinones and two-dimensional gel electrophoresis. These proteins were identified using matrix assisted laser desorption/ionization mass spectrometry for tryptic mass mapping followed by sequence database searching. Corroborative identification of protein targets was obtained from the apparent isoelectric points, molecular weights, and the use of antibody probes. There were subtle differences in the protein targets of BQ and NQ, but both associated with the following abundant proteins, nucleophosmin, galectin-1, probable protein disulfide isomerase, protein disulfide isomerase, 60 kDa heat shock protein, mitochondrial stress-70 protein, epithelial cell marker protein, and S100-type calcium binding protein A14. We further delineate the properties of these proteins that make them preferred targets and the evidence these adducts present for delivery of these quinones to subcellular compartments.     

Efficiency of copper removal by Sargassum sinicola in batch and continuous systems

The efficiency of batch and continuous systems of copper removal by Sargassum sinicola was studied. The effects of flow rate, initial metal concentration, and bed density on the capacity of the continuous system were also recorded. In batch systems, the maximum biosorption capacity was calculated as 49.63?±?0.88 mg g^?1; in the continuous system, under the following conditions: flow rate of 10 mL min^?1, initial solution of 200 mg Cu L^?1, bed density of 150 g L^?1, and higher copper removal of 62.39?±?1.91 mg g^?1 was achieved. The Thomas model can be used to predict the breakthrough curves, but it underestimated breakthrough time.     

Biodegradation of 4-nitrophenol in a two-phase sequencing batch reactor: concept demonstration,kinetics and modelling

The objectives of this work were to demonstrate the potential of a two-phase sequencing batch reactor in degrading xenobiotics and to evaluate the kinetic parameters leading to a mathematical model of the system. 4-Nitrophenol (4NP), a typical representative of substituted phenols, was selected as the target xenobiotic; this compound has never been remediated in a two-phase bioreactor before. Partition tests were conducted to determine the most appropriate partitioning solvent, and among the three investigated solvents (1-undecanol, 2-undecanone and oleyl alcohol), 2-undecanone was chosen because of its favourable partition coefficient and its negligible emulsion-forming tendencies. Moreover, the selected solvent showed satisfactory biocompatibility characteristics with respect to the biomass, with only minor effects on the intrinsic microbial kinetics. Kinetic tests were then performed in a sequencing batch reactor (2-l volume) operated in both conventional one- and two-phase configurations, with the two-phase system showing a significant improvement in the process kinetics in terms of reduced inhibition and increased maximum removal rate. The obtained kinetic parameters suggest that the two-phase sequencing batch system may find full-scale application, as the maximum removal rate k _max (~3 mg 4NP mgVSS⁻¹ day⁻¹) is of the same order of magnitude of heterotrophic bacteria operating in wastewater treatment plants.     

1,4-benzoquinone attracts males of Rhizotrogus vernus Germ

Two candidate attractants, phenol and 1,4-benzoquinone, a synthetic mixture of typical compounds from green-leaf odours [(Z)-3-hexenyl acetate: (Z)-3-hexen-1-ol: benzaldehyde: (E)-2-hexen-1-ol: 1-hexanol; 100:20:10:1:1] and freshly damaged oak leaves were screened for field attractancy in funnel traps in Hungary. Males of two Rhizotrogus spp. (Coleoptera, Scarabaeidae, Melolonthinae), R. aestivus 01. and R. vernus Germ. were caught in larger numbers. While R. aestivus catches were probably chance captures, male R. vernus was significantly attracted to the baits containing 1,4-benzoquinone. This compound represents a promising basis for the development of a monitoring trap for R. vernus.     

Growth and physiology of a yeast cultivated in batch and continuous culture systems

Inoculum size has been found to affect significantly the maximum attainable specific growth rate during batch cultivation ofCandida utilis. Lower inoculum size resulted in an increased growth rate and relatively longer lag. The culture is found to be most active in the beginning of the exponential phase as regards its RNA synthesis rate. Batch data were used for predicting the conditions of the yeast population in single-stage continuous culture system. Predicted and the experimental values showed a reasonable agreement. In single-stage chemostat the physiology of the yeast was studied on the basis RNA, DNA and protein synthesis rates at various growth rates. The results indicate that the productivity of cells and the rate of synthesis of macromolecules is highest at the dilution rate values of 0.33 to 0.35 hr⁻¹. In order to attain so-called unrestricted conditions of growth a pluristage pluristream continuous system was employed. It is assumed that under such conditions the specific growth rate and the synthetic activity of yeasts may reach its maximum on a given medium. The results presented do not show such conditions of growth under the experimental conditions employed (D ₁=0.35 hr⁻¹ andD ₂=0.2 to 1.7 hr⁻¹) withCandida utilis cultivated on beet molasses medium. Second stage of a two-stage two-stream continuous system is constantly fed with the cells from the foregoing stage; this category of cells on entering the new conditions of the second stage is expected to show some adaptation period. Experiments are reported to this effect.     

Characterization of 1,4-benzoquinone reductase from bovine liver

1,4-Benzoquinone reductase was purified to electrophoretic homogeneity from bovine liver, and the purified enzyme found to have a molecular mass of 29 kDa, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme exhibited pH optimum between 8.0 and 8.5. The apparentK _m for 1,4-benzoquinone was 1.643 mM, and the apparent Km for NADH was 1.837 mM. Various divalent cations, such as Hg²⁺, Cu²⁺, and Zn²⁺, exhibited strong inhibitory effects. The enzyme activity was also strongly inhibited by quercetin, dicumarol, and benzoic acid. Incubation of the enzyme withN-bromosuccinimide and pyridoxal 5′-phosphate led to inhibitions of 100% and 99%, respectively. Accordingly, these results suggest that tryptophan and lysine residues are involved at or near the active sites of the enzyme.     

Biodegradation kinetics of poly(3-hydroxybutyrate)-based biopolymer systems

The aim of this study was to evaluate and to compare the long-term kinetics curves of biodegradation of poly(3-hydroxybutyrate) (PHB), its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and a PHB/polylactic acid composite. The total weight loss and the change of average viscosity molecular weight were used as the parameters reflecting the biodegradation degree. The rate of biodegradation was analyzed in vitro in the presence of lipase and in vivo after film implantation in animal tissues. The morphology of the PHB film surface was studied by the atomic force microscopy technique. It was shown that PHB biodegradation involves both polymer hydrolysis and its enzymatic biodegradation. The results obtained in this study can be used for the development of various PHB-based medical devices.     

Growth and product inhibition kinetics of T-cell hybridomas producing lymphokines in batch and continuous culture.

The kinetics of growth and lymphokine formation by T-cell hybridomas were investigated in batch and continuous culture. Product inhibitions by ammonia and lactic acid were considered in the proposed model and experimental data were used to determine the kinetic and inhibition constants. The effect of dilution rate on specific substrate consumption and product formation rates was investigated.     

Biodegradation kinetics of LAS in river water

This article reports the biodegradation kinetics of linear alkylbenzene sulfonates (LAS) in river water. The authors used the ‘river die-away' test method and high performance liquid chromatography to monitor LAS concentrations as functions of time in a series of tests systems. Controlled variables included initial LAS concentrations and incubation temperature. The kinetic parameters computed from the experimental data demonstrated strong correlations (r²>0.99) with theoretical values computed from the kinetic model presented in this paper. The proposed model accurately predicts concentrations of non-biodegradable substrate and the maximum specific microbial growth rate.     

Prediction of continuous reactors performance based on batch reactor deactivation kinetics data of immobilized lipase

Experiments on deactivation kinetics of immobilized lipase enzyme fromCandida cylindracea were performed in stirred batch reactor using rice bran oil as the substrate and temperature as the deactivation parameter. The data were fitted in first order deactivation model. The effect of temperature on deactivation rate was represented by Arrhenius equation. Theoretical equations were developed based on pseudo-steady state approximation and Michaelis-Menten rate expression to predict the time course of conversion due to enzyme deactivation and apparent half-life of the immobilized enzyme activity in PFR and CSTR under constant feed rate policy for no diffusion limitation and diffusion limitation of first order. Stability of enzyme in these continuous reactors was predicted and factors affecting the stability were analyzed.     

Vancomycin production in batch and continuous culture

Production of the glycopeptide antibiotic vancomycin by two Amycolatopsis orientalis strains was examined in batch shake flask culture in a semidefined medium with peptone as the nitrogen source. Different growth and production profiles were observed with the two strains; specific production (Y(p/x)) was threefold higher with strain ATCC 19795 than with strain NCIMB 12945. A defined medium with amino acids as the nitrogen source was developed by use of the Plackett-Burman statistical screening method. This technique identified certain amino acids (glycine, phenylalanine, tyrosine, and arginine) that gave significant increased specific production, whereas phosphate was identified as inhibitory for high specific vancomycin production. Experiments made with the improved medium and strain ATCC 19795 showed that vancomycin production kinetics were either growth dissociated or growth associated, depending on the amino acid concentration. In chemostat culture at a constant dilution rate (0.087 h(-1)), specific vancomycin production rate (q(vancomycin)) decreased linearly as the medium phosphate concentration was increased from 2 to 8 mM. In both phosphate and glucose limited chemostats, q(vancomycin) was a function of specific growth rate; the maximum value was observed at D = 0.087 h(-1) (52% of the maximum specific growth rate). Under phosphate limited growth conditions, q(vancomycin) was threefold higher (0.37 mg/g dry weight/h) than under glucose limitation (0.12 mg/g dry weight/h). (c) 1996 John Wiley & Sons, Inc.     

Deacetylation of cephalosporins in batch and continuous reactors

We wish to report here the principal observations and conclusions concerning the deacetylation of three substrates, 7-ACA¹), cephalosporin C and 2-methoxyethyl acetate by the immobilized esterase from B. subtilis (Konecny and Voser, 1977) in three types of reactors: A stirred tank and recirculation reactor, both operated in the batch mode under pH-stat conditions, and a continuous packed bed, operated with excess buffer in the feed. The results, formulated in terms of simple empirical equations, are discussed in relation to the choice of carriers, reactor efficiency, scale up and other factors governing the choice of reactor. Certain general considerations apply to all reactions which generate acid and involve a catalyst whose activity and life are adversely effected by low pH.