Mutual Inhibition Effect Research Articles

Comparison of water-soluble organic matter (WSOM)-containing and WSOM-free biochars for simultaneous sorption of lead and cadmium

The effects of individual biochar constituents and natural environmental media on the immobilization behaviors and chemical activities of toxic heavy metals are still poorly understood. In this work, the physicochemical properties of raw corn straw (CS) and CS-derived biochar materials as well as their sorption abilities and retention mechanisms for lead (Pb) and cadmium (Cd) were evaluated by combining batch experiments and spectral approaches. According to the spectral analysis results and single variable principle, the setting of biochars after soaking in solution as the control group was suggested when evaluating their retention mechanisms for Pb and Cd. The rising of ionic strength did not apparently affect the immobilization of Pb by biochar prepared at 500 °C (i.e., CB500) and Pb/Cd by water-soluble organic matter (WSOM)-free CB500 (i.e., DCB500), while slightly inhibited the sorption of Cd by CB500. Pb and Cd exhibited a mutual inhibition effect on their sorption trends with a higher sorption preference of Pb. The dominant fixation mechanism of Pb by CB500 and DCB500 was identified to be mineral precipitation. In contrast, the main sorption mechanism of Cd changed from mineral precipitation in the single-metal system to surface complexation in the binary-metal system. The sorption ratios of Pb and Cd on CB500 were comparable to those on DCB500 with the coexistence of mixed natural organic matters (NOM) and ferrihydrite. The current experimental findings suggested that DCB500 was a suitable remediation agent for regulating the migration behaviors of toxic Pb and Cd in acidic and NOM-rich soil and water systems.

The effect of the elderly and child care on household carbon emissions

The aim of this work is to investigate the different implications in terms of the elderly and child care on household carbon emissions in China. We estimate the effect of family structure on household carbon emissions in the 2018 China Family Panel Studies (CFPS), by means of the STIRPAT model. The results indicate that significant differences exist between the effect of the elderly and child care on each household's carbon emissions. Moreover, there is a negative effect between the elderly and household carbon emissions with an elasticity coefficient of −0.029, and a positive effect between children and household carbon emissions with an elasticity coefficient of 0.008. Interestingly, the elderly and children have an interactive effect on carbon emissions except for housing carbon emissions. To be specific, the elderly and child care have a mutual inhibition effect on the health carbon emissions of household, whereas they have a mutually reinforcing effect on other carbon emissions. Low carbon emissions paths in household should be urgently explored, and deliberate policy action is required to achieve carbon emissions reduction.

Pungency Perception and the Interaction with Basic Taste Sensations: An Overview.

The perception of pungency can be attributed to the combination of pain and heat, and it has critical impacts on food flavor and food consumption preferences. Many studies have reported a variety of pungent ingredients with different Scoville heat units (SHU), and the mechanism of pungent perception was revealed in vivo and in vitro. The worldwide use of spices containing pungent ingredients has led to an increasing awareness of their effects on basic tastes. However, the interaction between basic tastes and pungency perception based on structure-activity relationship, taste perception mechanism and neurotransmission lacks review and summary, considering its brighter prospects in food flavor. Thus, in this review, common pungency substances and pungency evaluation methods, and the mechanism of pungency perception is presented, and the interaction between basic tastes and pungency perception and the possible factors of their interaction are reviewed in detail. Pungent stimuli are mainly transduced through transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential fixed hormone isoform (TRPA1) activated by stimulants. Using modern detection techniques combined with sensory standards, different substances produce different degrees of pungent stimulation, ranging from 104 to 107 SHU/g. Pungent stimuli can affect taste receptor or channel protein conformation and regulate taste bud cell sensitivity by producing neurotransmission products. The products of neurotransmission and taste receptor cell activation in turn act on taste perception. When there are simultaneous effects of taste perception, pungency stimulation may enhance the perception of salty at a certain concentration, with a mutual inhibition effect with sour, sweet, and bitter taste, while its interaction with umami taste is not obvious. However, due to the complexity of perception and the uncertainty of many perceptual receptors or channels, the current studies of interactions are still controversial. Based on the understanding of the mechanism and influencing factors, the availability of pungency substances is proposed in the perspective of food industry in order to achieve new development.

Runoff and Infiltration responses of revegetated slopes to clipping management on the northern Loess Plateau

Large-scale vegetation restoration can reduce local watershed water yield, limit vegetation establishment and subsequent growth, and influence regional ecosystem functions. Clipping management by reducing aboveground parts of grassland was gradually recommended and adopted in Grain-for-Green project management to offset these additional issues. Thus, scientific evaluation of the effectiveness of clipping management on infiltration and runoff processes is necessary for maintaining the stability of the surface water system and the sustainability of vegetation restoration in semi-arid regions. A field simulated rainfall experiment was conducted with four managed clipping grasslands (mainly bunge needlegrass and Stipa grandis), including no clipping, light clipping, heavy clipping, and complete clipping under three slope gradients (10, 20, and 30°) and three rainfall intensities (60, 90, and 120 mm/h) to explore the mechanism of runoff and infiltration responses to clipping using structural equation modeling and variation partitioning based on an SCS-CN model. The results showed the runoff coefficient of the light clipping, heavy clipping, and complete clipping plots were 1.33, 2.22, and 4.22 times that of the no clipping plot. The light clipping, heavy clipping, and complete clipping plots decreased the infiltration coefficients by 0%, 5%, and 26% relative to the no clipping plot. Rainfall intensity dominated runoff and infiltration amounts, and clipping intensity's total effect was stronger than slope gradient. Clipping intensity and slope gradient were more influential on runoff with increasing rainfall intensity. The mutual inhibition effect was between clipping intensity and slope gradient on runoff. In order to maintain the sustainability of restoration, a 25–50% vegetation coverage after clipping maximizes the benefits of increasing runoff and maintaining enough soil water supply that prevents possible soil drought. We propose that future vegetation restoration policies should evaluate the appropriate clipping intensity; meanwhile, local physiographic and climate conditions should be considered. These findings may offer guidance for the development of measures for runoff regulation and ecosystem functions of the watershed during vegetation restoration on the northern Loess Plateau.

The reaction behaviors of acetonitrile and ethyl acetate simultaneous degradation over Cu–Ce/ZSM–5 catalyst

Aiming at the coexistence of pollutants in the actual industrial process, the catalytic oxidation of acetonitrile and ethyl acetate mixture on the Cu–Ce/ZSM–5 catalyst was studied. The mutual inhibition effect during catalytic removal of acetonitrile and ethyl acetate mixture was observed. Acetonitrile showed a more obvious inhibitory effect on the conversion of ethyl acetate, and the introduction of ethyl acetate reduced the N2 selectivity of acetonitrile oxidation. The simulation results demonstrated acetonitrile could be preferentially adsorbed on Cu center of the catalyst surface, leading to significant inhibition of the initial conversion of ethyl acetate. In addition, the coexistence of ethyl acetate would weaken the hydrolysis of acetonitrile to generate carboxylic acid and –NHx species. As such, no enough adsorbed NHx species could be used to reduce the NOx produced by excessive oxidation of acetonitrile, resulting in a decreased in N2 selectivity. This study could provide reference on the application of catalysts for cyanide–containing waste gas degradation.

Free and Bound Phenolics of Laird Lentil (Lens culinaris) Hulls and the Anti-inflammatory Activity of their Digestive Products via Crosstalk between NF-κB and Keap1-Nrf2 Signaling Pathways in HT-29 Cells.

Polyphenol-rich Laird lentil hulls are a byproduct of lentil processing. In the present study, free and bound polyphenols in lentil hulls were analyzed with UHPLC-LTQ-OrbiTrap-MS2, and the anti-inflammatory mechanism of their digestive products was explored based on the NF-κB and Keap1-Nrf2 signaling pathways in the HT-29 cell model. In summary, a total of 27 polyphenols and 5 nonphenolic constituents were identified in free and bound fractions, and among them, catechin glucoside, kaempferol tetraglucoside, procyanidin dimer, and dihydroxybenzoic acid-O-dipentoside were the main polyphenols in the digestive products. These digestive products could reduce inflammatory mediators and exert anti-inflammatory activity by inhibiting NF-κB and activating Keap1-Nrf2 signaling pathways, and there was crosstalk between them, which was a mutual inhibition effect. The results show that polyphenols in lentil hulls are a good source of anti-inflammatory ingredients and have a promising development potential.

Molecular dynamics study on coupled ion transport in aluminium-doped cement-based materials: effect of concentration

The mutual inhibition effect of transport of sulfate and chloride in concrete specimens was determined in a macroscopic experiment. A higher concentration of sulfate has a better inhibition effect on chloride transport and the opposite is also true. In this paper, molecular dynamics (MD) simulation was performed to explore the effect of concentration (0, 0.5, 1.0 mol/l) on the transport of mixed solutions (sodium chloride (NaCl) and sodium sulfate (Na2SO4)) in the main hydration products of aluminium-doped cement-based materials (i.e. calcium–aluminium–silicate–hydrate (C–A–S–H) gel). Sulfate was found to promote the aggregation of other ions to form ion clusters, which can reduce the effective width of the channel entrance and create a ‘necking’ effect, thus reducing the overall transport rate of the solution. With the increase of sodium chloride concentration, sulfate ions in the mixed solution can adsorb more Na+ and Cl− ions, and then form larger ion clusters to block the nanopores. Moreover, with increasing sodium sulfate concentration, a higher amount of sulfate ions existing in the solution makes it possible to form more ion clusters. The results can provide a reasonable nanoscale explanation for macroscopic experiment.

Mutual inhibition effect of sulfur compounds in the hydrodesulfurization of thiophene, 2-ethylthiophene and benzothiophene ternary mixture

The hydrodesulphurization of a model component and equimolar ternary mixture of thiophene, 2-ethylthiophene and benzothiophene over sulphided CoMo/γ-Al2O3 and CoMo/γ-Al2O3-Nb2O5 catalysts were investigated in a fixed bed flow reactor. The catalysts were prepared by incipient wetness impregnation method and characterized by textural characteristics, total acidity and chemical species present on the catalysts surface. The characterization results showed that both CoMo/γ-Al2O3-Nb2O5 and sulphided CoMo/γ-Al2O3 catalysts exhibit a mesoporous structure with cylindrical pores open at both ends, evidenced by the IV type adsorption–desorption isotherm with a H1 hysteresis loop and have an average pore diameter between 3 and 4 nm. The chemical species present on the catalysts surface evaluated by XPS indicated that Co2+ and Mo4+ species are present in the sulfide form on both catalysts surfaces. In addition, there are also found oxidic species arising from incomplete reduction and sulphidation. The presence of niobium oxide in the catalytic support had a positive effect in leading to higher specific surface area (170 m2/g) and total acidity (0.421 meq/g) compared with CoMo/γ-Al2O3 catalyst (140 m2/g and 0.283 meq/g) respectively. The evaluation results from the hydrodesulfurization showed that CoMo/γ-Al2O3-Nb2O5 catalyst had a higher activity in hydrodesulphurization process of thiophene, 2-ethylthiophene and benzothiophene. The CoMo/γ-Al2O3-Nb2O5 catalyst eliminated sulfur from the single component feed (corresponding to 2380 ppm S) and reduced below 10 ppm, for the feed consisting in the equimolar ternary mixture of thiophene, 2-ethylthiophene and benzothiophene (2380 ppm S). The reactivity of thiophen compounds was reduced due to competitive adsorption. It was observed that benzothiophene inhibits the transformation of thiophene and 2-ethylthiophene. A mutual inhibition effect between sulfur compounds was also observed when thiophene, 2-ethylthiophene and benzothiophene were combined and tested over the CoMo/γ-Al2O3 catalyst. The inhibition effect had a lower intensity by introducing Nb2O5 in the catalyst support.

Mutual inhibition effect of hydrogen and ammonia in oxidation processes and the role of ammonia as “strong” collider in third-molecular reactions

Ammonia/hydrogen interaction in oxidation chemistry has been extensively valued for traditional flames, while no-experimental evidences have been provided at lower temperatures, relevant for MILD combustion. Herein, ter-molecular reactions play a fundamental role, boosted by “strong” colliders (CO2, H2O). H2O “strong” collider nature derives from its polar nature. Ammonia exhibits a polar behavior similar to water. Given this background, the aim of this work is to value the “strong” collisional nature of ammonia through experimental tests in a Jet Stirred Flow Reactor for H2–O2/Ar or N2 mixtures in presence of H2O or NH3. Results show NH3 inhibits H2 reactivity more than H2O. Numerical analyses suggest a hydrogen/ammonia mutual inhibiting effect under MILD conditions. Simulations are very sensitive to the declaration of NH3 third-body collisional efficiencies in third-molecular reactions in detailed kinetic mechanisms. These effects may infer the possibility to develop economic hydrogen transport/store systems while minimizing ammonia production costs.

A numerical model predicting indoor volatile organic compound Volatile Organic Compounds emissions from multiple building materials.

There have been many studies on the model of volatile organic compound (VOC) emissions from individual dry building material and have been validated in the chamber. Actually, VOC emitted from multiple dry building materials simultaneously indoor. The concentration of VOC indoor increases and will inhibit the VOC emission of dry building materials indoor. This paper developed a new model predicting indoor VOC concentrations caused by simultaneous emissions from multiple dry building materials, with a consideration of impact from dynamic VOC concentrations on the emission rate. The model has been used to predict the VOC emissions from a combination of medium-density fiberboard (MDF) and consolidated compound floor (CCF) simultaneously. The study demonstrated a good prediction performance of the newly proposed model, against field experimental data. The study also showed that when multiple dry building materials emit pollutants in a common space, a mutual inhibition effect could be observed. Furthermore, when multiple dry building materials emit VOC simultaneously, the change of VOC concentrations in the air followed the trends of VOC emissions from building materials with higher initial concentration (C0), diffusion coefficient (Dm), and the partition coefficient (Kma).

Theoretical study on simultaneous removal of SO2, NO, and Hg0 over graphene: competitive adsorption and adsorption type change.

In this work, the influence of competitive adsorption and the change of charge transfer for simultaneous adsorption removal of SO2, NO, and Hg0 over graphene were investigated using density functional theory method. The results showed that all the adsorptive effect of SO2, NO, and Hg0 were caused by physical interaction. The adsorptive energy of SO2 was the highest, and the adsorptive energy of Hg0 was the lowest. SO2 could be preferentially adsorbed and removed. NO/SO2 and Hg0 had the mutual promotion effect for simultaneous adsorption over graphene surface. SO2 and NO had the mutual inhibition effect for simultaneous adsorption over graphene surface. Compared with single molecular adsorption, the adsorption type of bi-molecular adsorption did not change. However, the simultaneous adsorption changed the adsorption type of Hg0+ SO2+ NO to chemical adsorption due to the interaction among Hg0, SO2, and NO. As such, this study provides a theoretical insight for future application and development. Graphical abstractNO/SO2 and Hg0 had the mutual promotion effect for simultaneous adsorption. SO2 and NO had the mutual inhibition effect for simultaneous adsorption.

Click chemistry improved wet adhesion strength of mussel-inspired citrate-based antimicrobial bioadhesives.

For the first time, a convenient copper-catalyzed azide-alkyne cycloaddition (CuAAC, click chemistry) was successfully introduced into injectable citrate-based mussel-inspired bioadhesives (iCMBAs, iCs) to improve both cohesive and wet adhesive strengths and elongate the degradation time, providing numerous advantages in surgical applications. The major challenge in developing such adhesives was the mutual inhibition effect between the oxidant used for crosslinking catechol groups and the Cu(II) reductant used for CuAAC, which was successfully minimized by adding a biocompatible buffering agent typically used in cell culture, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES), as a copper chelating agent. Among the investigated formulations, the highest adhesion strength achieved (223.11±15.94kPa) was around 13 times higher than that of a commercially available fibrin glue (15.4±2.8kPa). In addition, dual-crosslinked (i.e. click crosslinking and mussel-inspired crosslinking) iCMBAs still preserved considerable antibacterial and antifungal capabilities that are beneficial for the bioadhesives used as hemostatic adhesives or sealants for wound management.

Mutual inhibition of insulin signaling and PHLPP-1 determines cardioprotective efficiency of Akt in aged heart.

Insulin protects cardiomyocytes from myocardial ischemia/reperfusion (MI/R) injury through activating Akt. However, phosphatase PHLPP-1 (PH domain leucine-rich repeat protein phosphatase-1) dephosphorylates and inactivates Akt. The balanced competitive interaction of insulin and PHLPP-1 has not been directly examined. In this study, we have identified the effect of mutual inhibition of insulin signaling and PHLPP-1 on the cardioprotective efficiency of Akt in aged heart. Young (3 mon) and aged (20 mon) Sprague Dawley (SD) rats were subjected to MI/R in vivo. The PHLPP-1 level was higher in aged vs. young hearts at base. But, insulin treatment failed to decrease PHLPP-1 level during reperfusion in the aged hearts. Consequently, the cardioprotection of insulin-induced Akt activation was impaired in aged hearts, resulting in more susceptible to MI/R injury. In cultured rat ventricular myocytes, PHLPP-1 knockdown significantly enhanced insulin-induced Akt phosphorylation and reduced simulated hypoxia/reoxygenation-induced apoptosis. Contrary, PHLPP-1 overexpression terminated Akt phosphorylation and deteriorated myocytes apoptosis. Using in vivo aged animal models, we confirmed that cardiac PHLPP-1 knockdown or enhanced insulin sensitivity by exercise training dramatically increased insulin-induced Akt phosphorylation. Specifically, MI/R-induced cardiomyocyte apoptosis and infarct size were decreased and cardiac function was increased. More importantly, we found that insulin regulated the degradation of PHLPP-1 and insulin treatment could enhance the binding between PHLPP-1 and β-transducin repeat-containing protein (β-TrCP) to target for ubiquitin-dependent degradation. Altogether, we have identified a new mechanism by which insulin suppresses PHLPP-1 to enhance Akt activation. But, aged heart possesses lower insulin effectiveness and fails to decrease PHLPP-1 during MI/R, which subsequently limited Akt activity and cardioprotection. PHLPP-1 could be a promising therapeutic interventional target for elderly ischemic heart disease patients.

Preparation and Crystallization Property of Ternary Composites of WBG/AA-RCC/PP

A series of ternary composites of WBG/AA-RCC/PP were prepared and their crystallization behaviors were investigated by XRD and DSC. The results indicate that WBG and AA-RCC affect the crystallization of PP matrix with a mutual inhibition effect. This effect is enhanced with increasing content of WBG and induces the growth ofβ2crystal. AA-RCC promotes the heterogeneous nucleation ofαcrystal and offers a template forαcrystal growth along a specific lattice plane and promotes the epitaxial crystallization of PP matrix, while the specific arrangedαcrystal could induce the formation ofβcrystal.

Methane–benzene binary mixture destruction in a reverse flow catalytic reactor

An experimental study of methane–benzene binary mixture purification in a bench-scale reverse flow reactor is carried out. Results for catalytic oxidation of the two hydrocarbons with remarkably discrepant chemical properties show that autothermal catalytic combustion of very lean combustible concentration can be achieved with periodic feed reversal. Benzene is well removed, but methane conversion is relatively low and mainly determined by the thermal level of the reactor. If methane is added as auxiliary fuel to maintain autothermal operation when the volatile organic compound (VOC) concentration in the contaminated air is too low, an excess amount is needed. The influences of gas superficial velocity, cycle period, and methane-to-benzene ratio are discussed. A mathematical model is developed and solved using a FORTRAN code, with good correspondence being observed between the two approaches. Results of experimental and numerical study indicate that, during catalytic oxidation of lean VOCs in reverse flow reactor, the mutual inhibition effect between different kinds of hydrocarbon can be neglected.

Mutual Inhibition of RecQ Molecules in DNA Unwinding

Helicases make conformational changes and mechanical movements through hydrolysis of NTP to unwind duplex DNA (or RNA). Most helicases require a single-stranded overhang for loading onto the duplex DNA substrates. Some helicases have been observed to exhibit an enhanced unwinding efficiency with increasing length of the single-stranded DNA tail both by preventing reannealing of the unwound DNA and by compensating for premature dissociation of the leading monomers. Here we report a previously unknown mutual inhibition of neighboring monomers in DNA unwinding by the monomeric Escherichia coli RecQ helicase. With single molecule fluorescence resonance energy transfer microscopy, we observed that the unwinding initiation of RecQ at saturating concentrations was more delayed for a long rather than a short tailed DNA. In stopped-flow kinetic studies under both single and multiple turnover conditions, the unwinding efficiency decreased with increasing enzyme concentration for long tailed substrates. In addition, preincubation of RecQ and DNA in the presence of 5'-adenylyl-beta,gamma-imidodiphosphate was observed to alleviate the inhibition. We propose that the mutual inhibition effect results from a forced closure of cleft between the two RecA-like domains of a leading monomer by a trailing one, hence the forward movements of both monomers are stalled by prohibition of ATP binding to the leading one. This effect represents direct evidence for the relative movements of the two RecA-like domains of RecQ in DNA unwinding. It may occur for all superfamily I and II helicases possessing two RecA-like domains.

ANÁLISE DE CRESCIMENTO EM CAPIM-TANZÂNIA NOS SISTEMAS DE PLANTIO SOLTEIRO E CONSÓRCIO COM LEGUMINOSAS

This work aimed to evaluate the effect of the competition in the growth of the forage grasses Panicum maximum to Tanzânia cv. and two legumies forages Stylosanthes guianensis cv. Mineirao and Neonotonia wightii cv. Common, in the single and mixed crop systems. The experiment was carried out in a randomized block design with four replications and the treatments were: Tanzânia grass in a single crop system; Tanzânia grass in a mixed crop system with the Perennial Soy and Tanzânia grass in a mixed crop system with Stilozantes. Considering that maximum TCC (kg.ha-1.dia-1) of Tanzânia they were obtained 84 DAE, to leaf area index (IAF) observed in this same date correspond to great IAF. What demonstrates that the mixed crop didn’t affect the cycle of the grass, but yes in what it’s refers to the values obtained for TCC and IAF. The low value observed for Tanzania in the mixed crop with Perennial Soy evidences the effect of mutual inhibition. This way, in relation to TCC and MS, the low values observed to Tanzania in the mixed crop with Perennial Soy suggest suppress effect, promoted by this leguminous plant forage. KEY-WORDS: Absolute growth rate (TCC), leaf area index (IAF), Neonotonia wightii, Panicum maximum, Stylosanthes guianensis.

Predicting stability of mixed microbial cultures from single species experiments: 1. Phenomenological model

The growth of mixed microbial cultures on mixtures of substrates is a fundamental problem of both theoretical and practical interest. On the one hand, the literature is abundant with experimental studies of mixed-substrate phenomena [T. Egli, The ecological and physiological significance of the growth of heterotrophic microorganisms with mixtures of substrates, Adv. Microbiol. Ecol. 14 (1995) 305–386]. On the other hand, a number of mathematical models of mixed-substrate growth have been analyzed in the last three decades. These models typically assume specific kinetic expressions for substrate uptake and biomass growth rates and their predictions are formulated in terms of parameters of the model. In this work, we formulate and analyze a general mathematical model of mixed microbial growth on mixtures of substitutable substrates. Using this model, we study the effect of mutual inhibition of substrate uptake rates on the stability of the equilibria of the model. Specifically, we address the following question: How much of the dynamics exhibited by two competing species can be inferred from single species data? We provide geometric criteria for stability of various types of equilibria corresponding to non-competitive exclusion, competitive exclusion, and coexistence of two competing species in terms of growth isoclines and consumption curves. A growth isocline is a curve in the plane of substrate concentrations corresponding to the zero net growth of a given species. In [G.T. Reeves, A. Narang, S.S. Pilyugin, Growth of mixed cultures on mixtures of substitutable substrates: The operating diagram for a structured model, J. Theor. Biol. 226 (2004) 143–157], we introduced consumption curves as sets of all possible combinations of substrate concentrations corresponding to balanced growth of a single microbial species. Both types of curves can be obtained in single species experiments.

Mutual catalyst inhibition in the chromium(VI)–copper(II)–hydrogen peroxide reacting system

Cr(VI) and Cu(II) are both efficient catalysts for the decomposition of H2O2. However, in their joint presence, the two catalysts exert a mutual inhibition effect on the catalytic activity of the other, and the study of these inhibition effects has provided important information on the mechanisms of the Cr(VI)/H2O2 and Cu(II)/H2O2 reactions. The inhibition effect produced by Cr(VI) on the catalytic activity of Cu(II) is the more pronounced (a [Cr(VI)]/[Cu(II)] ratio as low as 2×10-4 is enough to provoke a 10% decrease in the decomposition rate), the limit being around 90% inhibition. On the contrary, higher concentrations of Cu(II) are necessary to produce a noticeable inhibition on the catalytic effect of Cr(VI), the limit being 50% inhibition. Besides, Cu(II) prevents the reduction of Cr(VI) to Cr(III) by H2O2, so that when [Cu(II)] is high enough the catalyst Cr(VI) is recovered unaltered at the end of the reaction. The inhibition effect produced by Cu(II) on the Cr(VI)/H2O2 reaction can be ascribed to its ability to catalyze the dismutation of superoxide free radicals, thus preventing the reduction of Cr(V) to Cr(IV) provoked by them, whereas the inhibition effect produced by Cr(VI) on the Cu(II)/H2O2 reaction can be ascribed to its ability to act as an oxidative scavenger for Cu(I), thus preventing its participation as the initiator of a free-radical chain mechanism leading to the decomposition of H2O2.

Inhibition kinetics for propionate degradation using propionate-enriched mixed cultures

To study propionate inhibition kinetics, seed cultures for the experiment were obtained from a propionate-enriched steady-state anaerobic Master Culture Reactor (MCR) operated under a semi-continuous mode for over six months. The MCR received a loading of 1.0 g propionate COD/l-day and was maintained at a temperature of 35±1°C. Tests using serum bottle reactors consisted of four phases. Phase I tests were conducted for measurement of anaerobic gas production as a screening step for a wide range of propionate concentrations. Phase II was a repeat of phase I but with more frequent sampling and detailed analysis of components in the liquid sample using gas chromatography. In phase III, different concentrations of acetate were added along with 1.0 g propionate COD/l to observe acetate inhibition of propionate degradation. Finally in phase IV, different concentrations of propionate were added along with 100 and 200 mg acetate/l to confirm the effect of mutual inhibition. Biokinetic and inhibition coefficients were obtained using models of Monod, Haldane, and Han and Levenspiel through the use of non-linear curve fitting technique. Results showed that the values of kp, maximum propionate utilization rate, and Ksp, half-velocity coefficient for propionate conversion, were 0.257 mg HPr/mg VSS-hr and 200 mg HPr/l, respectively. The values of kA, maximum acetate utilization rate, and KsA, half-velocity coefficient for acetate conversion, were 0.216 mg HAc/mg VSS-hr and 58 mg HAc/l, respectively. The results of phase III and IV tests indicated there was non-competitive inhibition when the acetate concentration in the reactor exceeded 200 mg/l.