Lipase-catalyzed synthesis of 6-O-glucosyldecanoate from d-glucose and decanoic acid was performed in dimethyl sulfoxide (DMSO), a mixture of DMSO and tert-butanol and tert-butanol alone with a decreasing order of polarity. The highest conversion yield (> 65%) of decanoic acid was obtained in the blended solvent of intermediate polarity mainly because it could dissolve relatively large amounts of both the reactants. The reaction obeyed Michaelis-Menten type of kinetics. The affinity of the enzyme towards the limiting substrate (decanoic acid) was not affected by the polarity of the solvent, but increased significantly with temperature. The esterification reaction was endothermic with activation energy in the range of 60-67 kJ mol⁻¹. Based on the Gibbs energy values, in the solvent blend of DMSO and tert-butanol the position of the equilibrium was shifted more towards the products compared to the position in pure solvents. Monoester of glucose was the main product of the reaction.
A series of bimetallic catalysts containing nickel supported over MgO-ZrO2 were tested for activity in the dry reforming of carbon dioxide. A nickel-cobalt bimetallic catalyst gave the best performance in terms of conversion and coke resistance from a range of Ni-X bimetallic catalysts, X=Ca, K, Ba, La, and Ce. The nitrogen-adsorption and hydrogen-chemisorption studies showed the Ni-Co bimetallic supported catalyst to have good surface area with high metal dispersion. This contributed to the high catalytic activity, in terms of conversion activity and stability of the catalyst, at an equimolar methane/carbon dioxide feed ratio. The kinetics of methane dry reforming are studied in a fixed-bed reactor over an Ni-Co bimetallic catalyst in the temperature range 700-800 °C by varying the partial pressures of CH4 and CO2. The experimental data were analyzed based on the proposed reaction mechanism using the Langmuir-Hinshelwood kinetic model. The activation energies for methane and carbon dioxide consumption were estimated at 52.9 and 48.1 kJ mol(-1), respectively. The lower value of CO2 activation energy compared to the activation energy of CH4 indicated a higher reaction rate of CO2, which owes to the strong basicity of nanocrystalline support, MgO-ZrO2.
Preparation of activated carbon has been attempted using KOH as activating agent by microwave heating from biodiesel industry solid residue, oil palm empty fruit bunch (EFBAC). The significance of chemical impregnation ratio (IR), microwave power and activation time on the properties of activated carbon were investigated. The optimum condition has been identified at the IR of 1.0, microwave power of 600 W and activation time of 7 min. EFBAC was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and nitrogen adsorption isotherm. The surface chemistry was examined by zeta potential measurement, determination of surface acidity/basicity, while the adsorptive property was quantified using methylene blue as dye model compound. The optimum conditions resulted in activated carbon with a monolayer adsorption capacity of 395.30 mg/g and carbon yield of 73.78%, while the BET surface area and total pore volume were corresponding to 1372 m2/g and 0.76 cm3/g, respectively.
Biosorption potential of mustard oil cake (MOC) for Ni(II) from aqueous medium was studied. Spectroscopic studies showed possible involvement of acidic (hydroxyl, carbonyl and carboxyl) groups in biosorption. Optimum biosorption was observed at pH 8. Contact time, reaction temperature, biosorbent dose and adsorbate concentration showed significant influence. Linear and non-linear isotherms comparison suggests applicability of Temkin model at 303 and 313 K and Freundlich model at 323K. Kinetics studies revealed applicability of Pseudo-second-order model. The process was endothermic and spontaneous. Freundlich constant (n) and activation energy (Ea) values confirm physical nature of the process. The breakthrough and exhaustive capacities for 5 mg/L initial Ni(II) concentration were 0.25 and 4.5 mg/g, while for 10 mg/L initial Ni(II) concentration were 4.5 and 9.5 mg/g, respectively. Batch desorption studies showed maximum Ni(II) recovery in acidic medium. Regeneration studies by batch and column process confirmed reutilization of biomass without appreciable loss in biosorption.
Ferulic acid (FA) groups esterified to the arabinan side chains of pectic polysaccharides can be oxidatively cross-linked in vitro by horseradish peroxidase (HRP) catalysis in the presence of hydrogen peroxide (H(2)O(2)) to form ferulic acid dehydrodimers (diFAs). The present work investigated whether the kinetics of HRP catalyzed cross-linking of FA esterified to α-(1,5)-linked arabinans are affected by the length of the arabinan chains carrying the feruloyl substitutions. The kinetics of the HRP-catalyzed cross-linking of four sets of arabinan samples from sugar beet pulp, having different molecular weights and hence different degrees of polymerization, were monitored by the disappearance of FA absorbance at 316 nm. MALDI-TOF/TOF-MS analysis confirmed that the sugar beet arabinans were feruloyl-substituted, and HPLC analysis verified that the amounts of diFAs increased when FA levels decreased as a result of the enzymatic oxidation treatment with HRP and H(2)O(2). At equimolar levels of FA (0.0025-0.05 mM) in the arabinan samples, the initial rates of the HRP-catalyzed cross-linking of the longer chain arabinans were slower than those of the shorter chain arabinans. The lower initial rates may be the result of the slower movement of larger molecules coupled with steric phenomena, making the required initial reaction of two FAs on longer chain arabinans slower than on shorter arabinans.
The removal of Ni(II) from aqueous solution by magnetic nanoparticles prepared and impregnated onto tea waste (Fe(3)O(4)-TW) from agriculture biomass was investigated. Magnetic nanoparticles (Fe(3)O(4)) were prepared by chemical precipitation of a Fe(2+) and Fe(3+) salts from aqueous solution by ammonia solution. These magnetic nanoparticles of the adsorbent Fe(3)O(4) were characterized by surface area (BET), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Fourier Transform-Infrared Spectroscopy (FT-IR). The effects of various parameters, such as contact time, pH, concentration, adsorbent dosage and temperature were studied. The kinetics followed is first order in nature, and the value of rate constant was found to be 1.90×10(-2) min(-1) at 100 mg L(-1) and 303 K. Removal efficiency decreases from 99 to 87% by increasing the concentration of Ni(II) in solution from 50 to 100 mg L(-1). It was found that the adsorption of Ni(II) increases by increasing temperature from 303 to 323 K and the process is endothermic in nature. The adsorption isotherm data were fitted to Langmuir and Freundlich equation, and the Langmuir adsorption capacity, Q°, was found to be (38.3)mgg(-1). The results also revealed that nanoparticle impregnated onto tea waste from agriculture biomass, can be an attractive option for metal removal from industrial effluent.
In this study, calcined Lapindo volcanic mud (LVM) was used as an adsorbent to remove an anionic dye, methyl orange (MO), from an aqueous solution by the batch adsorption technique. Various conditions were evaluated, including initial dye concentration, adsorbent dosage, contact time, solution pH, and temperature. The adsorption kinetics and equilibrium isotherms of the LVM were studied using pseudo-first-order and -second-order kinetic equations, as well as the Freundlich and Langmuir models. The experimental data obtained with LVM fits best to the Langmuir isotherm model and exhibited a maximum adsorption capacity (q(max)) of 333.3 mg g(-1); the data followed the second-order equation. The intraparticle diffusion studies revealed that the adsorption rates were not controlled only by the diffusion step. The thermodynamic parameters, such as the changes in enthalpy, entropy, and Gibbs free energy, showed that the adsorption is endothermic, random and spontaneous at high temperature. The results indicate that LVM adsorbs MO efficiently and could be utilized as a low-cost alternative adsorbent for the removal of anionic dyes in wastewater treatment.
This study investigated the reaction kinetics and degradation mechanism of parabens (methylparaben, ethylparaben, propylparaben and butylparaben) during ozonation. Experiments were performed at pH 2, 6 and 12 to determine the rate constants for the reaction of protonated, undissociated and dissociated paraben with ozone. The rate constants for the reaction of ozone with dissociated parabens (3.3 × 10(9)-4.2 × 10(9)M(-1)s(-1)) were found to be 10(4) times higher than the undissociated parabens (2.5 × 10(5)-4.4 × 10(5)M(-1)s(-1)) and 10(7) times higher than with the protonated parabens (1.02 × 10(2)-1.38 × 10(2)M(-1)s(-1)). The second-order rate constants for the reaction between parabens with hydroxyl radicals were found to vary from 6.8 × 10(9) to 9.2 × 10(9)M(-1)s(-1). Characterization of degradation by-products (DBPs) formed during the ozonation of each selected parabens has been carried out using GCMS after silylation. Twenty DBPs formed during ozonation of selected parabens have been identified. Hydroxylation has been found to be the major reaction for the formation of the identified DBPs. Through the hydroxylation reaction, a variety of hydroxylated parabens was formed.
The present study explores the ability of modified soda lignin (MSL) extracted from oil palm empty fruit bunches (EFB) in removing lead (II) ions from aqueous solutions. The effect of contact time, point zero charge (pH(pzc)) and pH of the solution, initial metal ion concentration and adsorbent dosage on the removal process were investigated. Furthermore, the MSL is characterized by SEM, XRF, FT-IR and surface area analysis. Equilibrium adsorption isotherms and kinetics were investigated. The experimental data were analyzed by the Langmuir, Freundlich and Temkin models of adsorption. The kinetic data obtained at different initial concentrations were analyzed using pseudo-first-order and pseudo-second-order models. The results provide strong evidence to support the hypothesis of adsorption mechanism.
The influence of water activity and water content was investigated with farnesyl laurate synthesis catalyzed by Lipozyme RM IM. Lipozyme RM IM activity depended strongly on initial water activity value. The best results were achieved for a reaction medium with an initial water activity of 0.11 since it gives the best conversion value of 96.80%. The rate constants obtained in the kinetics study using Ping-Pong-Bi-Bi and Ordered-Bi-Bi mechanisms with dead-end complex inhibition of lauric acid were compared. The corresponding parameters were found to obey the Ordered-Bi-Bi mechanism with dead-end complex inhibition of lauric acid. Kinetic parameters were calculated based on this model as follows: V (max) = 5.80 mmol l(-1) min(-1) g enzyme(-1), K (m,A) = 0.70 mmol l(-1) g enzyme(-1), K (m,B) = 115.48 mmol l(-1) g enzyme(-1), K (i) = 11.25 mmol l(-1) g enzyme(-1). The optimum conditions for the esterification of farnesol with lauric acid in a continuous packed bed reactor were found as the following: 18.18 cm packed bed height and 0.9 ml/min substrate flow rate. The optimum molar conversion of lauric acid to farnesyl laurate was 98.07 ± 0.82%. The effect of mass transfer in the packed bed reactor has also been studied using two models for cases of reaction limited and mass transfer limited. A very good agreement between the mass transfer limited model and the experimental data obtained indicating that the esterification in a packed bed reactor was mass transfer limited.
In the effort to find alternative low cost adsorbent for volatile organic vapors has prompted this research in assessing the effectiveness of activated carbon produced from durian shell in removing toluene vapors. Durian shells were impregnated with different concentrations of H3PO4 followed by carbonization at 500 °C for 20 min under nitrogen atmosphere. The prepared durian shell activated carbon (DSAC) was characterized for its physical and chemical properties. The removal efficiency of toluene by DSAC was performed using different toluene concentrations. Results showed that the highest BET surface area of the produced DSAC was 1404 m2/g. Highest removal efficiency of toluene vapors was achieved by using DSAC impregnated with 30% of acid concentration heated at 500 °C for 20 min heating duration. However, there is insignificant difference between removal efficiency of toluene by DSAC and different toluene concentrations. The toluene adsorption by DSAC was better fitted into Freundlich model.
The objective of this research is to investigate the potential of transesterification of crude palm oil (CPO) to biodiesel at 30 degrees C. The mass transfer limitations problem crucial at 30 degrees C due to the viscosity of CPO has been addressed. The process parameters that are closely related to mass transfer effects like enzyme loading, agitation speed and reaction time were optimized. An optimum methanol to oil substrate molar ratio at 6.5:1 was observed and maintained throughout the experiments. The optimum operating condition for the transesterification process was found at 6.67 wt% of enzyme loading and at 150 rpm of agitation speed. The corresponding initial reaction and FAME yield obtained at 6 h were 89.29% FAME yield/hr and 85.01%, respectively. The 85% FAME yield obtained at 30 degrees C operation of CPO transesterification shows that the process is potentially feasible for the biodiesel synthesis.
Dimethyl adipate (DMA) was synthesized by immobilized Candida antarctica lipase B-catalyzed esterification of adipic acid and methanol. To optimize the reaction conditions of ester production, response surface methodology was applied, and the effects of four factors namely, time, temperature, enzyme concentration, and molar ratio of substrates on product synthesis were determined. A statistical model predicted that the maximum conversion yield would be 97.6%, at the optimal conditions of 58.5 degrees C, 54.0 mg enzyme, 358.0 min, and 12:1 molar ratio of methanol to adipic acid. The R(2) (0.9769) shows a high correlation between predicted and experimental values. The kinetics of the reaction was also investigated in this study. The reaction was found to obey the ping-pong bi-bi mechanism with methanol inhibition. The kinetic parameters were determined and used to simulate the experimental results. A good quality of fit was observed between the simulated and experimental initial rates.
Weathered crude oil (WCO) removals in shoreline sediment samples were monitored for 60 days in bioremediation experimentation. Experimental modeling was carried out using statistical design of experiments. At optimum conditions maximum of 83.13, 78.06 and 69.92% WCO removals were observed for 2, 16 and 30 g/kg initial oil concentrations, respectively. Significant variations in the crude oil degradation pattern were observed with respect to oil, nutrient and microorganism contents. Crude oil bioremediation were successfully described by a first-order kinetic model. The study indicated that the rate of hydrocarbon biodegradation increased with decrease of crude oil concentrations.
In this batch study, the adsorption of malathion by using granular activated carbon with different parameters due to the particle size, dosage of carbons, as well as the initial concentration of malathion was investigated. Batch tests were carried out to determine the potential and the effectiveness of granular activated carbon (GAC) in removal of pesticide in agricultural run off. The granular activated carbon; coconut shell and palm shells were used and analyzed as the adsorbent material. The Langmuir and Freundlich adsorption isotherms models were applied to describe the characteristics of adsorption behavior. Equilibrium data fitted well with the Langmuir model and Freundlich model with maximum adsorption capacity of 909.1mg/g. The results indicate that the GAC could be used to effectively adsorb pesticide (malathion) from agricultural runoff.
The objective of this research was to evaluate the treatment ofp-nitrophenol (PNP) as a sole organic carbon source using a sequencing batch reactor (SBR) with the addition of adsorbent. Two types of adsorbents, namely powdered activated carbon (PAC) and pyrolysed rice husk (PRH) were used in this study. Two identical SBRs, each with a working volume of 10 L, were operated with fill, react, settle, draw and idle periods in the ratio of 2:8:1:0.75:0.25 for a cycle time of 12 h. The results showed that, without the addition of adsorbent, increasing the influent PNP concentration to 200 mg/L resulted in the deterioration of chemical oxygen demand (COD) removal efficiency and PNP removal efficiency in the SBRs. Improvement in the performance of the SBR was observed with the addition of PAC. When the dosage of 1.0 g PAC/cycle was applied, COD removal of 95% and almost complete removal of PNP were achieved at the influent PNP concentration of 300 mg/L. The kinetic study showed that the rates of COD and PNP removal can be described by the first-order kinetics. The enhancement of performance in the PAC-supplemented SBR was postulated to be due to the initial adsorption of PNP by the freshly added and the bioregenerated PAC, thus reducing the inhibition on the microorganisms. The PRH was found to be ineffective because of its relatively low adsorption capacity for PNP, compared with that of PAC.
Rubber leaf powder (an agricultural waste) was treated with potassium permanganate followed by sodium carbonate and its performance in the removal of Pb(II) ions from aqueous solution was evaluated. The interactions between Pb(II) ions and functional groups on the adsorbent surface were confirmed by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) coupled with X-ray energy dispersive spectroscopy (EDX). The effects of several important parameters which can affect adsorption capacity such as pH, adsorbent dosage, initial lead concentration and contact time were studied. The optimum pH range for lead adsorption was 4-5. Even at very low adsorbent dosage of 0.02 g, almost 100% of Pb(II) ions (23 mg/L) could be removed. The adsorption capacity was also dependent on lead concentration and contact time, and relatively a short period of time (60-90 min) was required to reach equilibrium. The equilibrium data were analyzed with Langmuir, Freundlich and Dubinin-Radushkevich isotherms. Based on Langmuir model, the maximum adsorption capacity of lead was 95.3 mg/g. Three kinetic models including pseudo first-order, pseudo second-order and Boyd were used to analyze the lead adsorption process, and the results showed that the pseudo second-order fitted well with correlation coefficients greater than 0.99.
Mature landfill leachate is typically non-biodegradable and contains high concentration of refractory organics. The aim of this research was to optimize operating parameters in electro-Fenton process, for the removal of recalcitrant organics from semi-aerobic landfill leachate using response surface methodology (RSM). Effectiveness of important process parameters H(2)O(2)/Fe(2+) molar ratio, current density, pH and reaction time were determined, optimized and modeled successfully. Significant quadratic polynomial models were obtained (R(2)=0.9972 and 0.9984 for COD and color removals, respectively). Numerical optimization based on desirability function were employed; in a 43 min trial 94.07% of COD and 95.83% of color were removed at pH 3 and H(2)O(2)/Fe(2+) molar ratio 1, while current density was 49 mA/cm(2). The results indicate that E-Fenton process was an effective technology for semi-aerobic landfill leachate treatment.
The growths of the African catfish (Clarias gariepinus) and water spinach (Ipomoea aquatica) were evaluated in recirculation aquaponic system (RAS). Fish production performance, plant growth and nutrient removal were measured and their dependence on hydraulic loading rate (HLR) was assessed. Fish production did not differ significantly between hydraulic loading rates. In contrast to the fish production, the water spinach yield was significantly higher in the lower hydraulic loading rate. Fish production, plant growth and percentage nutrient removal were highest at hydraulic loading rate of 1.28 m/day. The ratio of fish to plant production has been calculated to balance nutrient generation from fish with nutrient removal by plants and the optimum ratio was 15-42 gram of fish feed/m(2) of plant growing area. Each unit in RAS was evaluated in terms of oxygen demand. Using specified feeding regime, mass balance equations were applied to quantify the waste discharges from rearing tanks and treatment units. The waste discharged was found to be strongly dependent on hydraulic loading rate.
Tungsten-loaded TiO(2) photocatalyst has been successfully prepared and characterized. TEM analysis showed that the photocatalysts were nanosize with the tungsten species forming layers of coverage on the surface of TiO(2), but not in clustered form. This was confirmed by XRD and FT-Raman analyses where tungsten species were well dispersed at lower loading (<6.5 mol%), but were in crystalline WO(3) at higher loadings (>12 mol%). In addition, loading with tungsten could stabilize the anatase phase from transforming into inactive rutile phase and did not shift the optical absorption to the visible region as shown by DRUV-vis analysis. PZC value of TiO(2) was found at 6.4, but the presence of tungsten at 6.5 mol% WO(3), decreased the PZC value to 3. Tungsten-loaded TiO(2) was superior to unmodified TiO(2) with 2-fold increase in degradation rate of methylene blue, and equally effective for the degradation of different class of dyes such as methyl violet and methyl orange at 1 mol% WO(3) loading.