Decreased citrate improves iron availability from infant formula: application of an in vitro digestion/Caco-2 cell culture model

The characteristics of microbial growth and kinetics of DBP biodegradation was studied in a continuous culture system using DBP as a sole source of carbon. The results showed that, at high substrate concentration, the microbial growth was inhibited by DBP, and can be described by the Haldane model. Kinetic parameters based on Haldane substrate inhibition were evaluated. The values were mu(m) = 0.38 h-1, Ki = 86 mg/l, Ks = 28 mg/l. The DBP concentration to avoid substrate inhibition was inferred theoretically and determined to be 49 mg/L.     

Arsenite Oxidation by Batch Cultures of Thiomonas Arsenivorans Strain b6

Arsenite [As(III)] oxidation by Thiomonas arsenivorans Strain b6 was investigated in batch reactors at pH 6 and 30°C over As(III) concentrations ranging from 10 to 1,000 mg/L in the absence of added organic carbon. Strain b6 completely oxidized As(III) to arsenate [As(V)] during exponential growth phase for lower levels of As(III) concentrations ( ≤ 100?mg/L). At higher levels of 500 and 1,000 mg/L, As(III) oxidation was observed mostly in the exponential phase but continued into the stationary phase of growth. The Haldane substrate inhibition model was used to estimate biokinetic parameters for As(III) oxidation. The best fit parameters of half saturation constant Ks = 33.2±1.87?mg/L, maximum specific substrate utilization rate k = (0.85±0.18)-mg As(III)/mg dry cell weight/h, substrate inhibition coefficient Ki = 602.4±33.6?mg/L, yield coefficient Y = (0.088±0.0048)-mg cell dry weight/mg As(III), and endogenous decay coefficient kd = 0.006±0.002?h?1 were obtained using the Adams-Bashforth-Moulton algorithm and nonlinear regression technique. Sensitivity analysis revealed that Y and Ki are the most sensitive to model predictions, while kd is the least sensitive to model simulation at both low and high concentrations of As(III).     

Empirical Model and Kinetic Behavior of Thermophilic Composting of Vegetable Waste

Laboratory-scale temperature-controlled reactors were used to generate experimental data of thermophilic composting of vegetable waste. By fitting in experimental data of thermophilic composting, the obtained empirical model (also verified by F-test) appeared to be a quadratic form. The empirical model can be used to predict operating conditions (ratio of predried vegetable waste to rice husks, aeration rate, and reaction temperature and time) for thermophilic composting of vegetable waste in the subtropical region. Moreover, an innovative method for investigating kinetic behavior of thermophilic composting (an exoenzyme-catalyzed reaction followed by a multienzyme-catalyzed reaction) is proposed. The two biochemical reactions of thermophilic composting of vegetable waste followed Monod-type kinetics with the specific substrate utilization rate constants k1 and k2 of 0.026 and 4.5 mg COD∕mg VSS∕day, respectively. Accordingly, the exoenzyme-catalyzed reaction kinetically controls the overall process of thermophilic composting of vegetable waste.     

Verification of Anaerobic Biofilm Model for Phenol Degradation with Sulfate Reduction

A mathematical model was developed to describe phenol degradation with sulfate reduction in an anaerobic biofilm process. The model incorporates the mechanisms of diffusive mass transport and Monod kinetics. The model was solved using a combination of the orthogonal collocation method and Gear's method. A pilot-scale column reactor was conducted to verify the model. The batch kinetic tests were independently conducted to determine nine biokinetic coefficients used in the model while shear loss and initial thickness of the biofilm were assumed so that the model simulated the substrate concentration results very well. The removal efficiencies for phenol and sulfate are 98 and 88%, respectively. At a steady-state condition, the experimental data of phenol and sulfate concentrations were higher than those obtained from the model. The reason was that the effect of shear loss became significant as the biofilm grew thicker. The higher shear loss resulted in the more-suspended biomass. The suspended biomass decomposed and released soluble microbial products which increased the substrate effluent concentrations. The procedures presented in this paper could be employed for the design of anaerobic biofilm reactor systems for the biodegradation of multiple substrates.     

Design Model for COD Removal in Constructed Wetlands Based on Biofilm Activity

Current design criteria for free-water-surface constructed wetlands are based on either empirical relationships or first-order reaction rates and do not emphasize the microbial activity. This study was conducted to evaluate the role of biofilm bacteria present in free-water-surface constructed wetland beds in the removal of organic matter. A kinetic model incorporating the biofilm kinetics and dispersion number was proposed to predict chemical oxygen demand removal in free-water-surface constructed wetlands. The model parameters were determined from laboratory experiments and from the literature. The proposed kinetic model satisfactorily predicted chemical oxygen demand removal efficiencies in a pilot-scale constructed wetland unit located in the tropics. A design chart and a design example based on the kinetic model are given.     

Modeling Cr(VI) Reduction and Phenol Degradation in a Coculture Biofilm Reactor

A transient-state model was developed to simulate simultaneous Cr(VI) reduction and phenol degradation by a coculture of Cr(VI)-reducing/phenol-degrading bacteria growing on glass bead surfaces in a fixed-film bioreactor. The coculture consisted of the Cr(VI) reducers, Escherichia coli ATCC 33456, and the phenol degraders, Pseudomonas putida DMP-1. Phenol was supplied as the sole added carbon source and electron donor. The model simulated cell growth kinetics with E. coli utilizing metabolites formed from phenol degradation in P. putida as carbon sources. Substrate utilization and Cr(VI) reduction in the fixed-film bioreactor was represented by a system of (second-order) partial differential equations (PDEs). The PDE system was solved by the fourth-order Runge–Kutta method adjusted for mass transport resistance by the second-order Crank–Nicholson and backward Euler methods. A heuristic procedure, genetic search algorithm, was used to optimize the model against experimental data. The model predicted effluent concentration with 98.6% confidence for Cr(VI), 93.4% confidence for phenol, and 88.3% confidence for metabolites. Parameters determined showed higher Cr(VI) and phenol removal kinetics in the biofilm system than previously observed in batch systems.     

Biodegradation of Mixtures of Phenolic Compounds in an Upward-Flow Anaerobic Sludge Blanket Reactor

The anaerobic biodegradability of mixtures of phenolic compounds was studied under continuous and batch systems. Continuous experiments were carried out in up-flow anaerobic sludge bed (UASB) reactors degrading a mixture of phenol and p-cresol as the main carbon and energy sources. The total chemical oxygen demand (COD) removal above 90% was achieved even at organic loading rates as high as 7 kg COD/m3/day. Batch experiments were conducted with mixtures of phenolic compounds (phenol, p-cresol, and o-cresol) to determine the specific biodegradation rates using unadapted and adapted anaerobic granular sludge. Phenol and p-cresol were mineralized by adapted sludge with rates several orders of magnitude higher than unadapted sludge. Additionally, an UASB reactor was operated with the mixture phenol, p-cresol, and o-cresol. After 54 days of operation, 80% of o-cresol (supplied at 132 mg/L) was eliminated. The phenol biodegradation was not affected by the presence of o-cresol. These results demonstrate that major phenolic components in petrochemical effluents can be biodegraded simultaneously during anaerobic treatment.     

Sludge Blanket Height and Flow Pattern in UASB Reactors: Temperature Effects

Two upflow anaerobic sludge blanket (UASB) reactors were operated for approximately 900?days to examine the feasibility of treating municipal wastewater under low temperature conditions. In this paper, a modified solid distribution model has been formulated by incorporating the variation of biogas production rate with a change in temperature. It was found that the model simulated the solid distribution well as confirmed by experimental observations of solid profile along the height of the reactor. Mathematical analysis of tracer curves indicated the presence of a mixed type of flow pattern in the sludge-bed zone of the reactor. It was found that the dead-zone and bypass flow fraction were impacted by the change in operating temperatures.     

Mass Transfer Effects on Kinetics of Dibromoethane Reduction by Zero-Valent Iron in Packed-Bed Reactors

Mass transfer effects on the kinetics of 1,2-dibromoethane (EDB) reduction by zero-valent iron (ZVI) in batch reactors, a laboratory scale packed-bed reactor, and a pilot scale packed-bed reactor are described. EDB was debrominated by ZVI to ethylene and bromide. EDB sorption to the cast iron surface was nonlinear and was described by a Langmuir equation. Laboratory scale column studies showed a nonlinear dependence of EDB removal on flow rate and initial EDB concentration. A nonequilibrium model of EDB sorption and reaction dependent on mass transfer was constructed using the laboratory scale data. The model was verified using data from a larger pilot scale packed-bed reactor that was used to remove EDB from contaminated groundwater. The data showed two distinct removal processes, an initial rapid phase dominated by mass transfer followed by a slower phase where surface reactions dominated. The model successfully predicted the transition from mass transfer controlled to surface reaction controlled conditions in the pilot scale data.     

Nitrifying Biomass Acclimation to High Ammonia Concentration

Selection, acclimation, and kinetic characterization of a nitrifying microflora chosen from natural sources and capable of degrading total ammonia nitrogen (TAN) at high concentration was performed. The inocula of animal manure and of marine sediments were selected due to their nitrate production (55.8 mg N/L?day) and tolerance to salinity (16 g Cl?/L). An acclimation continuous culture was made using TAN up to 1,000 mg N/L and nitrogen load rate of 250 to 1,000 mg N/L?day. The TAN degradation rate after acclimation reached 0.16 mg N/mg VSS?h (VSS=volatile suspended solids) at a feed concentration of 1,000 mg N/L; the ammonia-oxidizing population increased from 60 to 77% whereas nitrite-oxidizing bacteria decreased from 40 to 23%. The following substrate-inhibition Haldane parameters were determined: rTAN,max = 0.21 and 0.19 mg N/mg VSS?h; Ks = 3.0 and 4.8 mg NH3-N/L; Ki = 22.4 and 35.6 mg NH3-N/L for sludge before and after acclimation, respectively. Differences between rTAN,max values were not statistically significant with a confidence limit of 95%, whereas Ks and Ki differences were significant, showing a better tolerance to higher ammonium concentrations.     

The genus Myxidium (Protozoa: Myxosporida) in macrourid fishes

A physical model approach was used to investigate cholesterol gallstone dissolution kinetics in simulated bile. Critical experimental and theoretical investigations simulating in vivo conditions showed that, in the bile acid-lecithin solutions, there is a significant interfacial barrier for both cholesterol gallstone and cholesterol monohydrate pellet dissolution. In the present study, the rotating-disk dissolution method and the accompanying Levich theory were applied to assess the contributions of the diffusion convection mass transfer resistance and of the interfacial barrier to the overall kinetics. Cholesterol dissolution rates in bile acid solutions were about 2-20 times slower than diffusion-controlled rates depending upon the degree of agitation. As found in previous studies, these rates in the presence of sufficient concentrations of dissolution accelerators approached the theoretical diffusion-convection-controlled rates. To account for the much slower dissolution rates in bile acid-lecithin solutions, two possible kinetic interpretations were investigated. The first is based upon slow crystal-micellar solution interfacial kinetics, and the second is based upon a slow rate of cholesterol solubilization in the aqueous diffusion layer. For the latter, an analytical mathematical solution was obtained.     

Flow Distribution Parameters in Relation to Flow Resistance in an Upflow Anaerobic Sludge Blanket Reactor System

The use of flow resistance in the distribution of flows is well known in traditional hydraulics. To evenly distributed flows, flow resistance forms the basis of flow distribution in pipes connected in parallel. Flow distribution in different zones of upflow anaerobic sludge blanket (UASB) reactors is well documented in existing literature, and so far modeling of flow distribution parameters, i.e., the fraction of inflow entering into the bed, the fraction of flow bypassing over the bed and entering into the blanket, and the fraction of inflow to the bed entering into the blanket, has remained empirical in nature. The role of flow resistance in the distribution of flows in UASB reactor systems is still unexplained. In this study, some of the available data on flow distribution parameters are analyzed to assess if there is any correlation between these parameters and flow resistance. It is found that with an increase in flow resistance in the UASB reactor system, the magnitude of short-circuiting flows at the reactor bed increases. Also, the flow distribution at the blanket and settler levels of UASB reactor systems is related to parameters influencing flow resistance. Some of the functional forms derived in this study are expected to form the basis for representing flow distribution in the simulation studies of UASB reactor performance.     

Kinetics of Liquid-Phase Hydrogenation of Toluene Catalyzed by Hydrogen Storage Alloy MlNi_5

Asacleanandhigh efficiencyenergyresource ,hydrogenisthoughttobethemostpromisingsubstituteoffossilfuels .Storingandutilizingtheenergybyus ingthehydrogenasenergycarrieristhemostfavor ablemethodtosolvetheenergycrisis ,whichattractsthefocusoftheworld .Therehavebeenconsiderableprogressesinthetechnologyofhydrogen energyinre centyears .Reillyetal .[1] firstproposedtheconceptofthemetalhydrideslurryin 1 980s ,inwhichthede formationorruptureofthevesselsduetotheparticlepulverizationandthepoorheattransfer…     

Interfacial catalysis by human 85 kDa cytosolic phospholipase A2 on anionic vesicles in the scooting mode

Analysis of phospholipases A2 on model phospholipid bilayers in which enzyme is essentially irreversibly bound at the lipid-water interface, termed "scooting mode", is a useful tool for studying the kinetic properties of interfacial enzymes. It is shown that human cytosolic 85 kDa phospholipase A2 (cPLA2) hydrolyzes sn-2-arachidonyl-containing phospholipids or the gamma-linolenoyl ester of 7-hydroxycoumarin (GLU) dispersed in vesicles of 1,2-dioleoyl-sn-glycero-3-phosphomethanol (L-DOPM) in the scooting mode. Trapping of cPLA2 on L-DOPM vesicles is rapid and independent of product formation. Slowing of cPLA2-catalyzed hydrolysis of substrates present in phosphatidylmethanol and phosphatidylcholine vesicles is primarily due to apparent inactivation rather than to substrate depletion. cPLA2 phosphorylated on serine 505 by mitogen-activated protein kinase displays a 30% increase in the rate of sn-2-arachidonylphosphatidylcholine hydrolysis in the scooting mode compared to that of the nonphosphorylated enzyme. Kinetic parameters of cPLA2 acting on a variety of different phosphatidylmethanol vesicles were evaluated, and the results are discussed in terms of active site affinities for substrates and of lateral organization of substrates in the bilayer. A key result is that the sigmoidal kinetics reported previously using 1,2-dimyristoyl-sn-glycero-3-phosphomethanol (DMPM) vesicles are most prominent near the phase transition temperature of DMPM. No sigmoidal kinetics was observed using L-DOPM vesicles. The results of kinetic experiments and the behavior of a fluorescent substrate analog are consistent with nonideal mixing of substrate in DMPM vesicles, but not in L-DOPM vesicles, suggesting that apparent saturation and sigmoidal kinetics are more a result of nonideal mixing of substrate in DMPM vesicles than of active site binding of substrate. The fluorescence assay described using L-DOPM/GLU vesicles is useful for evaluating the interfacial behavior of cPLA2, including its substrate preferences and the effect of active site-directed inhibitors.     

Effect of Aeration on the Quality of Effluent from UASB Reactor Treating Sewage

The treatment of effluent of pilot- and full-scale upflow anaerobic sludge blanket (UASB) reactors operating at steady state was studied in an aeration-settling system. The fine pore submerged diffusers were used to aerate the effluent of UASB reactors under different operating conditions. Forty to 55% of the biochemical oxygen demand (BOD) and the chemical oxygen demand (COD) removal efficiencies were achieved by the direct aeration of the UASB effluent in the laboratory. The maximum removal efficiencies were achieved at 30?min hydraulic retention time (HRT) and a dissolved oxygen (DO) of 5–6??mg/L or high KLa (vigorous aeration). Batch experiments on nitrogen purging and the aeration of sulfides, volatile organic compounds (VOCs), and nonpurgeable organic carbons (NPOCs) were performed to ascertain the mechanism of BOD/COD removal. During aeration, BOD and COD were reduced by the stripping of H2S and VOCs and by the chemical oxidation of total sulfides and organic carbon. The stripping and chemical oxidation depended on the HRT and DO. The performance of a full-scale surface aeration system was compared to the performance of a pilot-scale diffused aeration system. Final sedimentation was effective only in removing the solids from the effluent of the aeration system. The results were confirmed by organic mass balance.     

Incorporating Both Physical and Kinetic Limitations in Quantifying Dissolved Oxygen Flux to Aquatic Sediments

Traditionally, dissolved oxygen (DO) fluxes have been calculated using the thin-film theory with DO microstructure data in systems characterized by fine sediments and low velocities. However, recent experimental evidence of fluctuating DO concentrations near the sediment-water interface suggests that turbulence and coherent motions control the mass transfer, and the surface renewal theory gives a more mechanistic model for quantifying fluxes. Both models involve quantifying the mass transfer coefficient (k) and the relevant concentration difference (ΔC). This study compared several empirical models for quantifying k based on both thin-film and surface renewal theories, as well as presents a new method for quantifying ΔC (dynamic approach) that is consistent with the observed DO concentration fluctuations near the interface. Data were used from a series of flume experiments that includes both physical and kinetic uptake limitations of the flux. Results indicated that methods for quantifying k and ΔC using the surface renewal theory better estimated the DO flux across a range of fluid-flow conditions.     

Modeling Water Treatment Chemical Disinfection Kinetics

Various empirical and probabilistic kinetic inactivation models that can be used to assist in the design and analysis of potable water disinfection systems were reviewed. Models were derived for both disinfectant demand-free and demand conditions. Ozone was used to inactivate heterotrophic plate count bacteria that were grown in natural water under low nutrient conditions and enumerated using R2A agar at 20°C for 7 days. Experiments were conducted at 22°C in 0.05 M (pH 6.9) phosphate buffer in bench-scale, batch 250 mL reactors. This disinfection data set, characterized by tailing-off behavior, was used to assess Chick–Watson, Hom-type, Rational, Hom–Power law, and Selleck model fit to the observed logarithmic survival ratios. It was found that the Chick–Watson model did not adequately represent the ozone disinfection kinetics. A Hom-type model incorporating a first-order disappearance term for ozone residual was found to best describe the observed inactivation of heterotrophic plate count bacteria. Named the incomplete gamma Hom model, it was found to be a robust kinetic model. The proposed incomplete gamma Hom model can be used to generate simple design charts for a wide range of disinfectant types, organisms, and conditions, as an aid to the design of water disinfection systems.     

Fate of Anionic Surfactants in a 38?ML/Day UASB-Based Municipal Wastewater Treatment Plant: Case Study

The outcome of a 15-month monitoring study (August 2004–October 2005) on the anionic surfactants (AS), at the 38?ML/day up-flow anaerobic sludge blanket (UASB)-based sewage treatment plant (STP) is described. The average removal of AS was only around 57%. Appreciable concentration of AS was being discharged to the watercourse (average 2.41?mg/L; range 0.63–5.16?mg/L). On an average dried sludge contained 1,560?mg?AS?kg?1 dry weight. Mass balance indicated that, AS load of the orders of 23 and 33% is removed by adsorption in UASB reactors and polishing ponds (PP), respectively. Biodegradation of AS under anaerobic conditions in UASB reactors and PP does not seem to take place. In the sludge stream, appreciable biodegradation ( ≈ 70%) of adsorbed AS under aerobic conditions on the sludge drying beds takes place. If influent AS mass flux is normalized to 100?units, than 43 and 7?units are discharged with treated effluent and dried sludge, respectively, whereas 33 and 16?units are adsorbed/settled in PP and aerobically biodegrade on sludge drying beds, respectively.     

Effects of Stressed Loading on Startup and Granulation in Upflow Anaerobic Sludge Blanket Reactors

The successful operation of an upflow anaerobic sludge blanket (UASB) process depends on the formation of settleable and active granular sludge. As the anaerobic bacteria are slow-growing microorganisms, a common problem encountered in UASB operation is the long startup period and the development of biogranules. In the present study, an unconventional approach to accelerate startup and granulation processes in UASB reactors has been developed by stressing the organic loading rate (OLR) without having to reach steady-state conditions. Three UASB reactors treating a synthetic feed with chemical oxygen demand (COD) of 2,500 mg/L, at a mesophilic temprature of 35°C were studied. One reactor (R1) served as a control, while the other two (R2 and R3) were operated at different stress levels upon reaching COD removal efficiency of 75 and 85%, respectively. Experimental results indicated that under stressed loading conditions, the startup, and granule development were accelerated by 45 and 33%, respectively, along with the formation of granules of superior characteristics without deteriorating loading capacity. The operating time to reach designated OLRs was also shortened by at least 30 days in the stressed reactors. The results presented indicate that the unconventional startup approach could offer a practical solution for the inherent long start-up in UASB systems with concomitant saving in time and cost.     

Interaction between the antibiotic spiramycin and a ribosomal complex active in peptide bond formation

The inhibition of peptide bond formation by spiramycin was studied in an in vitro system derived from Escherichia coli. Peptide bonds are formed between puromycin (S) and Ac-Phe-tRNA, which is a component of complex C, i.e., of the [Ac-Phe-tRNA-70S ribosome-poly(U)] complex, according to the puromycin reaction: C+S (Ks)<==>CS (k3)==>C'+P [Synetos, D., & Coutsogeorgopoulos, C. (1987) Biochim. Biophys. Acta 923, 275-285]. It is shown that spiramycin (A) reacts with complex C and forms the spiramycin complex C*A, which is inactive toward puromycin. C*A is the tightest complex formed between complex C and any of a number of antibiotics, such as chloramphenicol, blasticidin S, lincomycin, or sparsomycin. C*A remains stable following gel chromatography on Sephadex G-200 and sucrose gradient ultracentrifugation. Detailed kinetic study suggests that C*A is formed in a variation of a two-step mechanism in which the initial encounter complex CA is kinetically insignificant and C*A is the product of a conformational change of complex CA according to the equation, C+A (kassoc)<==>(kdissoc) C*A. The rate constants of this reaction (spiramycin reaction) are kassoc = 3.0 x 10(4) M-1 s-1 and kdissoc = 5.0 x 10(-5) s-1. Such values allow the classification of spiramycin as a slow-binding, slowly reversible inhibitor; they also lead to the calculation of an apparent overall dissociation constant equal to 1.8 nM for the C*A complex. Furthermore, they render spiramycin a useful tool in the study of antibiotic action on protein synthesis in vitro. Thus, the spiramycin reaction, in conjunction with the puromycin reaction, is applied (i) to detect a strong preincubation effect exerted by chloramphenicol and lincomycin (this effect constitutes further evidence that these two antibiotics combine with complex C as slow-binding inhibitors) and (ii) to determine the rate constant for the regeneration (k7 = 2.0 x 10(-3) s-1) of complex C from the sparsomycin complex C*I [Theocharis, D. A., & Coutsogeorgopoulos, C. (1992) Biochemistry 31, 5861-5868] according to the equation, C+I (Ki)<==>CI (k6)<==>(k7) C*I. The determination of k7 enables us to calculate the apparent association rate constant of sparsomycin, (k7/Ki') = 1.0 x 10(5) M-1 s-1, where Ki' = Ki(k7/k6 + k7). It is also shown that Ac-Phe-tRNA bound to the sparsomycin complex C*I is protected against attack by hydroxylamine.(ABSTRACT TRUNCATED AT 400 WORDS)