Continuous Addition Of H2O2 Research Articles

Chemo-enzymatic epoxidation of Sapindus mukurossi fatty acids catalyzed with Candida sp. 99–125 lipase in a solvent-free system

The non-edible Sapindus mukurossi oil, containing more than 80% unsaturated fatty acids, has potential applications in plastics manufacturing. In this research, a green and economically attractive chemo-enzymatic production of epoxidized fatty acids was performed in the presence of lipase Candida sp. 99–125 and H2O2 in different systems. The obtained experimental results demonstrated that the solvent-free and n-hexane systems yielded superior results compared to other organic solvent systems. A molecular dynamic simulation further proved the influence of different solvents on the structure of lipase. Maximization of the key parameters including enzyme loading, reaction time, molar ratio of H2O2 to the number of double bonds in the substrate, agitation speed, H2O2 addition frequency, and temperature were performed in a solvent-free system. The oxirane value reached 4.61% in 8h under a gradient temperature profile (first incubated at 30°C for 6h, then increased to 35°C and maintained for another 2h) with continuous addition of H2O2. The total molar amount of H2O2 added was equal to the number of CC bonds in the substrate (expressed in moles).

Effects of hydrogen peroxide feeding strategies on the photochemical degradation of polyvinyl alcohol

ABSTRACTThe performance of batch and fed-batch photoreactors with that of continuous photoreactor for the treatment of aqueous polyvinyl alcohol (PVA) solutions is compared. Hydrogen peroxide feeding strategies, residence time, and [H2O2]/[PVA] mass ratio are examined for their impacts on the molecular weight distribution (MWD) of PVA and the total organic carbon (TOC) removal. The results prove that a continuous addition of H2O2 during the degradation reaction ensures the utilization of the produced radicals to minimize the oxidant consumption and maximize the TOC removal and the PVA degradation in a short irradiation time. Also, the MWD of PVA is found to be bimodal and shifted towards lower molecular weights with small shoulder peak indicating a progressive disappearance of the higher molecular weight fractions that is in accordance with the random chains scission mechanism. Besides, the hydrogen peroxide feeding strategies are found to have a great effect on the reduction in H2O2 residuals in the effluent.

Mathematical modelling of the heterogeneous photo-Fenton oxidation of acetic acid on structured catalysts

This work focused on the development and the validation of a mathematical model for the UV-C photo-Fenton degradation of acetic acid using a LaFeO3 heterogeneous structured catalyst with a monolithic structure. A combined study of the evolved gases and the liquid phase was conducted. The experimental results led to the identification of the main reactions that occur in the system: the complete mineralisation of acetic acid by H2O2 due to the presence of the catalyst and the decomposition of H2O2 to water and O2 in the homogeneous phase. A mathematical model was then developed using Eley–Rideal-type kinetics for the acetic acid consumption and first-order kinetics for the photolysis of hydrogen peroxide. The apparent kinetic constants were estimated, and the accuracy of the model was tested under different experimental conditions to evidence the predictive capability of the model. A very good agreement between the mathematical model calculations and the experimental data obtained in the presence of various H2O2 dosages was achieved. The results demonstrate that the continuous addition of H2O2 during the photo-Fenton reaction ensures the fruitful utilisation of the produced hydroxyl radicals in the acetic acid oxidation reaction to minimise the oxidant consumption and maximise the TOC removal in a shorter irradiation time.

Effect of continuous addition of H2O2 and air injection on ferrioxalate-assisted solar photo-Fenton degradation of Orange II

An experimental study based on ferrioxalate-assisted solar photo-Fenton (SPFox) process shows how non-biodegradable azo dye Orange II (OII) solutions degradation can be enhanced or slowed down by continuous addition of hydrogen peroxide and air injection depending on operation conditions. The decoloration and mineralization of dye solution has been carried out in a solar Compound Parabolic Collector (CPC). An optimization study was done by using Multivariate Experimental Design including the following variables: flow rate of H2O2, air flow rate, pH and initial concentrations of Fe(II) and oxalic acid. The efficiency of photocatalytic degradation was determined from the analysis of color and Total Organic Carbon (TOC). Experimental data were fitted using neural networks (NNs) which allow the simulation of the process for any value of variables in the studied experimental range. The results reveal that the continuous addition of H2O2 improves the photocatalytic efficiency since the scavenger effect of peroxide is minimized. On the other hand, this system permits the use of a ferrous concentration below the discharge legal limit (2ppm) being bubbling of air not necessary in that conditions. In addition, oxalic acid can be used to pH adjustment, reducing the operation costs of Fe removal, chemicals and electric power. Under the optimal conditions, 100% decoloration of dye solution can be reached by using both processes (SPFox with H2O2 addition at the beginning or along the reaction) but with different reaction rates. However, the efficiency of TOC removal was higher in the SPFox process with continuous addition of H2O2 (95% TOC removal in SPFox system with continuous addition of peroxide versus 80% TOC removal in SPFox system when peroxide is added at the beginning of the reaction). Molecular and/or radical reaction pathway was studied by conducting the reaction in the presence and absence of tert-butylalcohol.

Effects of H2O2 under Low- and High-Aeration-Level Conditions on Growth and Catalase Activity in Exiguobacterium oxidotolerans T-2-2T

The effects of H2O2 under low- and high-aeration-level conditions on growth and catalase activity in Exiguobacterium oxidotolerans T-2-2T were investigated. Continuous addition of 5-200 mM H2O2 to the culture medium from the mid-exponential growth phase enhanced the growth of the strain under the low-aeration-level condition, whereas the addition of 5-50 mM H2O2 decreased intracellular specific catalase activity and extracellular total catalases activity. The detection of extracellular catalase by the cells and the decrease in intracellular specific catalase activity and extracellular total catalase activity under the high-aeration-level condition account for the stimulation of growth by the introduced H2O2 and the decrease in catalase activities induced by O(2) from H2O2 in the medium. On the other hand, the addition of H2O2 to the medium prior to the initiation of growth inhibited the growth but increased the specific activity of intracellular catalase in the stationary growth phase. Strain T-2-2T grew when 10 mM H2O2 was added to the medium prior to growth. However, the growth was completely inhibited by the catalase inhibitor 3-amino-1,2,4-triazole (3-AT). The continuous addition of H2O2 at an appropriate concentration from prior to the initiation of growth to the stationary growth phase under the low-aeration-level condition resulted in higher intracellular specific catalase activity and cell growth rate than single H2O2 addition prior to growth.

“Oxidative stress” response in submerged cultures of a recombinant Aspergillus niger (B1‐D)

A recombinant strain of Aspergillus niger (B1-D), engineered to produce the marker protein hen egg white lysozyme, was investigated with regard to its susceptibility to “oxidative stress” in submerged culture in bioreactor systems. The culture response to oxidative stress, produced either by addition of exogenous hydrogen peroxide or by high-dissolved oxygen tensions, was examined in terms of the activities of two key defensive enzymes: catalase (CAT) and superoxide dismutase (SOD). Batch cultures in the bioreactor were generally found to have maximum specific activities of CAT and SOD (Umg · protein−1) in the stationary/early-decline phase. Continuous addition of H2O2 (16 mmole L−1 h−1), starting in the early exponential phase, induced CAT but did not increase SOD significantly. Gassing an early exponential-phase culture with O2 enriched (25 vol%) air resulted in increased activities of both SOD and CAT relative to control processes gassed continuously with air, while gassing the culture with 25 vol% O2 enriched air throughout the experiment, although inducing a higher base level of enzyme activities, did not increase the maximum SOD activity obtained relative to control processes gassed continuously with air. The profile of the specific activity of SOD (U mg CDW−1) appeared to correlate with dissolved oxygen levels in processes where no H2O2 addition occurred. These findings indicate that it is unsound to use the term “oxidative stress” to encompass a stress response produced by addition of a chemical (H2O2) or by elevated dissolved oxygen levels because the response to each might be quite different. © 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 70: 662–669, 2000.

"Oxidative stress" response in submerged cultures of a recombinant Aspergillus niger (B1-D).

A recombinant strain of Aspergillus niger (B1-D), engineered to produce the marker protein hen egg white lysozyme, was investigated with regard to its susceptibility to "oxidative stress" in submerged culture in bioreactor systems. The culture response to oxidative stress, produced either by addition of exogenous hydrogen peroxide or by high-dissolved oxygen tensions, was examined in terms of the activities of two key defensive enzymes: catalase (CAT) and superoxide dismutase (SOD). Batch cultures in the bioreactor were generally found to have maximum specific activities of CAT and SOD (Umg x protein(-1)) in the stationary/early-decline phase. Continuous addition of H2O2 (16 mmole L(-1) h(-1)), starting in the early exponential phase, induced CAT but did not increase SOD significantly. Gassing an early exponential-phase culture with O2 enriched (25 vol%) air resulted in increased activities of both SOD and CAT relative to control processes gassed continuously with air, while gassing the culture with 25 vol% O2 enriched air throughout the experiment, although inducing a higher base level of enzyme activities, did not increase the maximum SOD activity obtained relative to control processes gassed continuously with air. The profile of the specific activity of SOD (U mg CDW(-1)) appeared to correlate with dissolved oxygen levels in processes where no H2O2 addition occurred. These findings indicate that it is unsound to use the term "oxidative stress" to encompass a stress response produced by addition of a chemical (H2O2) or by elevated dissolved oxygen levels because the response to each might be quite different.

EFFECT OF GLUCOSE AND ADENOSINE CYCLIC 3′, 5′-MONOPHOSPHATE ON THE INDUCED SYNTHESIS OF CATALASE IN ESCHERICHIA COLI

The activity of catalase (EC 1.11.1.6) in Escherichia coli was profoundly repressed by growth with such substrates as glucose, mannose, galactose, ribose, glycerol, and pyruvate. The low catalase activity of the cells grown with glucose increased about twice when the cells were incubated with phosphate buffer containing yeast extract for 2hr. This increase of catalase activity was enhanced by continuous addition of H2O2 during the incubation. The increase of catalase activity was completely inhibited by chloramphenicol and Puromycin. The synthesis of catalase induced by H2O2 was repressed by glucose, and the repression was not eliminated by cyclic-AMP.

The catalytic effect of peroxidases on the iodination of tyrosine in the presence of hydrogen peroxide

Summary 1. Myeloperoxidase, horseradish peroxidase, and a thyroid peroxidase preparation (donor: hydrogen-peroxide oxidoreductase, EC 1.11.1.7) were each incubated with [14C]tyrosine (10 μM) and iodide (generally 20 μM) in phosphate buffer (pH 7.4) with continuous addition of H2O2. 2. The catalytic effect of myelo- and horseradish peroxidase on the oxidation of iodide by H2O2 was followed in a spectrophotometer. 3. The results indicated that myelo- and horseradish peroxidase catalyzed the oxidation of iodide, but only myeloperoxidase also catalyzed the formation of the iodo tyrosines 4. Reaction conditions were found by which myeloperoxidase in 30 min catalyzed the formation of 11% monoiodotyrosine and 61% diiodotyrosine 5. The thyroid peroxidase preparation seeemed to be more similar to myeloperoxidase than to horseradish peroxidase 6. The results were discussed with respect to the formation of the iodotyrosines in vivo.