Continuous lipase‐catalyzed synthesis of hexyl laurate in a packed‐bed reactor: optimization of the reaction conditions in a solvent‐free system

BACKGROUND: Hexyl laurate has been applied widely in cosmetic industries and is synthesized by chemical methods with problems of cost, environmental pollution, and by‐products. In this study, Lipozyme^® IM77 (from Rhizomucor miehei) was used to catalyze the direct‐esterification of hexanol and lauric acid in a solvent‐free system by utilizing a continuous packed‐bed reactor, wherein the aforementioned difficulties could be overcome. Response surface methodology (RSM) and three‐level‐three‐factor Box‐Behnken design were employed to evaluate the effects of synthesis parameters, such as reaction temperature (45–65 °C), mixture flow rate (0.25–0.75 mL min^?1) and concentration of lauric acid (100–300 mmol L^?1) on the production rate (µmol min^?1) of hexyl laurate by direct esterification. RESULTS: The production rate was affected significantly by the mixture flow rate and lauric acid concentration. On the basis of ridge‐max analysis, the optimum synthesis conditions for hexyl laurate were as follows: 81.58 ± 1.76 µmol min^?1 at 55 °C, 0.5 mL min^?1 flow rate and 0.3 mol L^?1 lauric acid. CONCLUSION: The lipase‐catalyzed synthesis of hexyl laurate by Lipozyme^® IM‐77 in a continuous packed‐bed bioreactor and solvent‐free system was successfully developed; optimization of the reaction parameters was obtained by Box–Behnken design and RSM. Copyright © 2008 Society of Chemical Industry     

Optimization of inulinase production by solid‐state fermentation in a packed‐bed bioreactor

BACKGROUND: This work is focused on inulinase production by solid‐sate fermentation (SSF) using sugarcane bagasse, corn steep liquor (CSL), pre‐treated cane molasses, and soybean bran as substrates in a 3‐kg (dry basis) packed‐bed bioreactor. SSF was carried out by the yeast Kluyveromyces marxianus NRRL Y‐7571 and response surface methodology was used to optimize the temperature, air flow rate and initial mass of cells. RESULTS: The optimum inulinase activity (436.7 ± 36.3 U g^?1 dry substrate) was obtained at 24 h at an inlet air temperature of 30 °C, air flow rate 2.2 m³ h^?1 and 22 g of cells for fermentation. Inulinase productivity at these conditions was 18.2 U gds^?1 h^?1. Kinetic evaluation at the optimized conditions showed that the maximum inulinase production was verified at 24 h of fermentation. The carbon dioxide and the metabolic heat generation are directly associated with the consumption of total reducing sugars present in the medium. CONCLUSION: The high productivity achieved in this work shows the technical viability of inulinase production by SSF in a packed‐bed bioreactor. Copyright © 2009 Society of Chemical Industry     

Performance of different immobilized‐cell systems to efficiently produce ethanol from whey: fluidized batch,packed‐bed and fluidized continuous bioreactors

BACKGROUND: The bioconversion of whey into ethanol by immobilized Kluyveromyces marxianus in packed‐bed and fluidized bioreactors is described. Both batch and continuous cultures were analyzed using three different strains of K. marxianus and the effect of the operating mode, temperature, and dilution rates (D) were investigated. RESULTS: All immobilized strains of K. marxianus (CBS 6556, CCT 4086, and CCT 2653) produced similar high yields of ethanol (0.44 ± 0.01 g EtOH g^?1 sugar). Significant variations of conversion efficiencies (66.1 to 83.3%) and ethanol productivities (0.78 to 0.96 g L^?1 h^?1) were observed in the experiments with strain K. marxianus CBS 6556 at different temperatures. High yields of ethanol were obtained in fluidized and packed‐bed bioreactors continuous cultures at different D (0.1 to 0.3 h^?1), with the highest productivity (3.5 g L^?1 h^?1) observed for D = 0.3 h^?1 in the fluidized bioreactor (87% of the maximal theoretical conversion), whereas the highest ethanol concentration in the streaming effluent (28 g L^?1) was obtained for D = 0.1 h^?1. Electronic micrographs of the gel beads showed efficient cell immobilization. CONCLUSION: Batch and continuous cultivations of immobilized K. marxianus in fluidized and packed‐bed bioreactors enable high yields and productivities of ethanol from whey. Copyright © 2012 Society of Chemical Industry     

Nitrification by immobilized cells in a micro‐ecological life support system using packed‐bed bioreactors: an engineering study

The nitrifying component of a micro‐ecological life support system alternative (MELISSA) based on microorganisms and higher plants was studied. The MELISSA system consists of an interconnected loop of bioreactors to allow the recycling of the organic wastes generated in a closed environment. Conversion of ammonia into nitrates in such a system was improved by selection of microorganisms, immobilization techniques, reactor type and operation conditions. An axenic mixed culture of Nitrosomonas europaea and Nitrobacter winogradskyi, immobilized by surface attachment on polystyrene beads, was used for nitrification in packed‐bed reactors at both bench and pilot scale. Hydrodynamics, mass transfer and nitrification capacity of the reactors were analysed. Mixing and mass transfer rate were enhanced by recirculation of the liquid phase and aeration flow‐rate, achieving a liquid flow distribution close to a well‐mixed tank and without oxygen limitation for standard operational conditions of the nitrifying unit. Ammonium conversion ranged from 95 to 100% when the oxygen concentration was maintained above 80% of saturation. The maximum surface removal rates were measured as 1.91 gN‐NH₄⁺ m^?2 day^?1 at pilot scale and 1.77 gN‐NH₄⁺ m^?2 day^?1 at bench scale. Successful scale‐up of a packed‐bed bioreactor has been carried out. Good stability and reproducibility were observed for more than 400 days. Copyright © 2004 Society of Chemical Industry     

Surface modification of non‐woven poly (ethylene terephthalate) fibrous scaffold for improving cell attachment in animal cell culture

BACKGROUND: The development of carriers with biocompatible surfaces are required to meet the needs in animal cell culture. In this work, poly (ethylene terephthalate) (PET) fibrous scaffold surfaces were chemically modified to introduce diethylaminoethyl (DEAE) groups. A packed‐bed bioreactor with DEAE‐conjugated PET fibrous scaffolds was investigated for continuous production of HBsAg by r‐CHO cells. RESULTS: The changes of surface properties were characterized by surface hydrophilicity, Attenuated total reflectance (ATR) analysis, element measurement, and scanning electron microscopy. The results showed that this treatment could improve surface hydrophilicity and roughness. Using an r‐CHO cell line as model cells, the feasibility of the DEAE‐conjugated PET fibrous scaffold in animal cell culture was evaluated by means of cell attachment efficiency measurement, MTT (3‐(4,5)‐dimethylthiathiazo(‐z‐yl)‐3,5‐di‐phenytetrazoliumromide) assay, and scanning electron microscopy observation. Enhancement of cell attachment and proliferation was exhibited in the cell culture on DEAE‐conjugated PET fibrous scaffolds. r‐CHO cells were cultured for continuous HBsAg production in a packed‐bed bioreactor with DEAE‐conjugated PET fibrous scaffolds. A cell density of 1.2 × 10⁷ cells mL^?1 working volume, cell viability of 92.8% and maximum HBsAg concentration of 3.1 mg L^?1 were achieved. CONCLUSION: The packed‐bed bioreactor system with DEAE‐conjugated PET fibrous scaffolds has the potential for industrial animal cell culture application. Copyright © 2008 Society of Chemical Industry     

Synthesis of butyl acrylate in a fixed‐bed adsorptive reactor over Amberlyst 15

The butyl acrylate synthesis from the esterification reaction of acrylic acid with 1‐butanol in a fixed‐bed adsorptive reactor packed with Amberlyst 15 ion exchange resin was evaluated. Adsorption experiments were carried out with nonreactive pairs at two temperatures (323 and 363 K). The experimental results were used to obtain multicomponent adsorption equilibrium isotherms of Langmuir type. Reactive adsorption experiments using different feed molar ratios and flow rates were performed, at 363 K, and used to validate a mathematical model developed to describe the dynamic behavior of the fixed‐bed adsorptive reactor for the butyl acrylate synthesis. Due to the simultaneous reaction and separation steps, it was possible to obtain a butyl acrylate maximum concentration 38% higher than the equilibrium concentration (for an equimolar reactants ratio solution as feed at a flow rate of 0.9 mL min^?1 and 363 K) showing that sorption‐enhanced reaction technologies are very promising for butyl acrylate synthesis. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1263–1274, 2015     

Novel two‐in‐one bioreactor greatly improves lactic acid production from xylose by Lactobacillus pentosus

BACKGROUND: Simultaneous xylose isomerization and fermentation was investigated to improve the lactic acid production from xylose by Lactobacillus pentosus in a novel two‐in‐one bioreactor constructed by packing the immobilized xylose isomerase (65 g) in a fixed bed reactor (diameter 56 mm × 66 mm, packing volume 154 mL) with a permeable wall, which was installed inside a conventional fermenter (2 L) and rotated along the axis together with the mechanical stirrer of the fermenter. RESULTS: Xylose (20 g L^?1) was completely consumed within 24 h in the novel bioreactor, compared with 72 h needed for the control without packed enzyme. The maximum cell density (17.5 g L^?1) in the novel bioreactor was twice that in the control and the lactic acid productivity (0.58 g L^?1 h^?1) was 3.8 times higher. Repeated use of the immobilized enzyme showed that the lactic acid productivity and yield obviously dropped after the first batch fermentation but maintained almost unchanged afterwards. CONCLUSION: Simultaneous xylose isomerization and fermentation significantly improved lactic acid production from xylose by Lactobacillus pentosus. The novel bioreactor made it easier to recycle and reuse the immobilized enzyme. © 2012 Society of Chemical Industry     

Application of chitosan‐entrapped β‐galactosidase in a packed‐bed reactor system

The model enzyme β‐galactosidase was entrapped in chitosan gel beads and tested for hydrolytic activity and its potential for application in a packed‐bed reactor. The chitosan beads had an enzyme entrapment efficiency of 59% and retained 56% of the enzyme activity of the free enzyme. The Michaelis constant (K_m) was 0.0086 and 0.011 μmol/mL for the free and immobilized enzymes, respectively. The maximum velocity of the reaction (V_max) was 285.7 and 55.25 μmol mL^?1 min^?1 for the free and immobilized enzymes, respectively. In pH stability tests, the immobilized enzyme exhibited a greater range of pH stability and shifted to include a more acidic pH optimum, compared to that of the free enzyme. A 2.54 × 16.51‐cm tubular reactor was constructed to hold 300 mL of chitosan‐immobilized enzyme. A full‐factorial test design was implemented to test the effect of substrate flow (20 and 100 mL/min), concentration (0.0015 and 0.003M), and repeated use of the test bed on efficiency of the system. Parameters were analyzed using repeated‐measures analysis of variance. Flow (p < 0.05) and concentration (p < 0.05) significantly affected substrate conversion, as did the interaction progressing from Run 1 to Run 2 on a bed (p < 0.05). Reactor stability tests indicated that the packed‐bed reactor continued to convert substrate for more than 12 h with a minimal reduction in conversion efficiency. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1294–1299, 2004     

Time and cost efficient biodegradation of diesel in a continuous‐upflow packed bed biofilm reactor and effect of surfactant GAELE

BACKGROUND: Biodegradation of diesel hydrocarbons using bioreactors has been proposed as an alternative for diesel contaminated sites remediation. To make this alternative feasible, several factors must be optimized or improved: reducing hydraulic retention times (HRT) and applying design methods to enhance the access of the microorganisms to low soluble and recalcitrant compounds like hydrocarbon fuels. In the present work a time and cost efficient continuous‐flow packed bed bioreactor at low HRT was designed and evaluated. The effect of non‐previously studied anionic surfactant GAELE (glycolic acid ethoxylate lauryl ether) was also investigated. RESULTS: A continuous‐upflow packed bed bioreactor (CPR) was built using an inexpensive support made of volcanic and alluvial stones. The biodegradation experiments conducted with a 12‐month‐old biofilm at a fixed HRT of 0.5 h, recorded removal of up to 97.9% at a diesel concentration of 1120 mg L^?1 with GAELE. A first‐order rate constant of 0.10 h^?1 was calculated. Kinetic analysis using Arvin's model, which introduces mass transfer to the biofilm, showed statistical differences in the kinetic rate parameters (P < 0.001). Moreover, GAELE significantly increased biodegradability at high concentrations, with BOD₅ and COD removals up to 90.8 and 80.7%, respectively. Putative hydrocarbon degrading bacteria responsible for the degradation under nitrate‐reducing conditions were positively identified. CONCLUSIONS: The continuous‐upflow packed bed reactor was capable of high percentage diesel biodegradation at short HRTs. The use of GAELE increased diesel availability and thus enhanced hydrocarbon removal. Therefore, CPR packed with volcanic and alluvial stones combined with GAELE showed potential for the remediation of diesel‐impacted sites. Copyright © 2012 Society of Chemical Industry     

Simultaneous phenol removal and biological reduction of hexavalent chromium in a packed‐bed reactor

BACKGROUND: Phenol and hexavalent chromium are considered industrial pollutants that pose severe threats to human health and the environment. The two pollutants can be found together in aquatic environments originating from mixed discharges of many industrial processes, or from a single industry discharge. The main objective of this work was to study the feasibility of using phenol as an electron donor for Cr(VI) reduction, thus achieving the simultaneous biological removal/reduction of the two pollutants in a packed‐bed reactor. RESULTS: A pilot‐scale packed‐bed reactor was used to estimate phenol removal with simultaneous Cr(VI) reduction through biological mechanisms, using a new mixed bacterial culture originated from Cr(VI)‐reducing and phenol‐degrading bacteria, operated in draw–fill mode with recirculation. Experiments were performed for feed Cr(VI) concentration of about 5.5 mg L^?1, while phenol concentration ranged from 350 to 1500 mg L^?1. The maximum reduction/removal rates achieved were 0.062 g Cr(VI) L^?1 d^?1 and 3.574 g phenol L^?1 d^?1, for a phenol concentration of 500 mg L^?1. CONCLUSION: Phenol removal with simultaneous biological Cr(VI) reduction is feasible in a packed‐bed attached growth bioreactor. Phenol was found to inhibit Cr(VI) reduction, while phenol removal was rather unaffected by Cr(VI) concentration increase. However, the recorded removal rates of phenol and Cr(VI) were found to be much lower than those obtained from previous research, where the two pollutants were examined separately. Copyright © 2008 Society of Chemical Industry     

Production of L‐methionine by immobilized pellets of Aspergillus oryzae in a packed bed reactor

Production of L ‐methionine by immobilized pellets of Aspergillus oryzae in a packed bed reactor was investigated. Based on the determination of relative enzymatic activity in the immobilized pellets, the optimum pH and temperature for the resolution reaction were 8.0 and 60 °C, respectively. The effects of substrate concentration on the resolution reaction were also investigated and the kinetic constants (K_m and V_m) of immobilized pellets were found to be 7.99 mmol dm^?3 and 1.38 mmol dm^?3 h^?1, respectively. The maximum substrate concentration for the resolution reaction without inhibition was 0.2 mol dm^?3. The L ‐methionine conversion rate reached 94% and 78% when substrate concentrations were 0.2 and 0.4 mol dm^?3, respectively, at a flow rate of 7.5 cm³ h^?1 using the small‐scale packed bed reactor developed. The half‐life of the L ‐aminoacylase in immobilized pellets was 70 days in continuous operation. All the results obtained in this paper exhibit a practical potential of using immobilized pellets of Aspergillus oryzae in the production of L ‐methionine. © 2002 Society of Chemical Industry     

Multidimensional modeling of a microfibrous entrapped cobalt catalyst Fischer‐Tropsch reactor bed

Thermal management of highly exothermic Fischer‐Tropsch synthesis (FTS) has been a challenging bottleneck limiting the radial dimension of the packed‐bed (PB) reactor tube to 1.5 in. ID. A computational demonstration of a novel microfibrous entrapped cobalt catalyst (MFECC) in mitigating hot spot formation has been evaluated. Specifically, a two‐dimensional (2‐D) model was developed in COMSOL^®, validated with experimental data and subsequently employed to demonstrate scale‐up of the FTS bed from 0.59 to 4 in. ID. Significant hot spot of 102.39 K in PB was reduced to 9.4 K in MFECC bed under gas phase at 528.15 K and 2 MPa. Improvement in heat transfer within the MFECC bed facilitates higher productivities at low space velocities (≥1000 h^?1) corresponding to high CO conversion (≥90%). Additionally, the MFECC reactor provides an eightfold increase in the reactor ID at hot spots ≤ 30 K with CO% conversions ≥ 90%. This model was developed for a typical FTS cobalt‐based catalyst where CO₂ production is negligible. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1723–1731, 2018     

Aspergillus oryzae Lipase-Catalyzed Synthesis of Dioleoyl; Palmitoyl-Rich Triacylglycerols in Two Reactors

Dioleoyl; palmitoyl‐rich triacylglycerols (OPO‐rich TAG) were synthesized through Aspergillus oryzae lipase (AOL)‐catalyzed acidolysis of palm stearin with commercial oleic acid by a one‐step process in a stirred tank reactor and continuous packed bed reactor to evaluate the feasibility of using immobilized AOL. AOL was found to be valuable for the synthesis of OPO‐rich TAG when compared with commercial lipase from Thermomyces lanuginose (Lipozyme^® TL IM; Novozymes A/S, Bagsvaerd, Denmark). The C52 (triglycerides with a carbon number of 52, stands for OPO, OPL, LPL and their isomers) content of AOL was higher (45.65 %), and the intensity of treatment (IOT: lipase amount × reaction time/TAG amount) of AOL was just 6.25 % of that of Lipozyme^® TL IM under similar reaction conditions in the stirred tank reactor. Response surface methodology were used to optimize the reaction conditions of the AOL‐catalyzed acidolysis is reaction in the packed bed reactor. The optimal point for the set of experimental conditions generated were as follows: residence time 3.0 h; temperature 62.09 °C; substrate molar ratio 7.13 mol/mol. The highest C52 content obtained was 48.60 ± 2.36 %, with 57.46 ± 1.72 % total palmitic acid at the sn‐2 position and 74.21 ± 2.45 % oleic acid at the sn‐1,3 positions. The half‐life of AOL was 24 h in the stirred tank reactor and 140 h in the packed bed reactor. The immobilized AOL achieved similar conversion and selectivity to commercial lipases for the catalyzed synthesis of OPO‐rich TAG and may offer a cheaper alternative.     

Design of different bioreactor configurations: application to ligninolytic enzyme production in semi‐solid‐state cultivation

The production of ligninolytic enzymes by Phanerochaete chrysosporium BKM‐F‐1767 (ATCC 24725) in laboratory‐scale bioreactors was studied. The cultivations were carried out in semi‐solid‐state conditions, employing corncob as carrier, which functioned both as a place of attachment and as a source of nutrients. Several bioreactor configurations were investigated in order to determine the most suitable one for ligninolytic enzyme production: a 1‐dm³‐static‐bed bioreactor, a 1‐dm³‐static‐bed bioreactor with air diffusers into the bed, a 0.5‐dm³‐static‐bed bioreactor with air diffusers into the bed and a tray bioreactor. Although the static‐bed configurations produced maximum individual lignin peroxidase (LiP) activities about 400 U dm⁻³ (1.0‐dm³ bioreactor) and about 700 U dm⁻³ (0.5‐dm³ bioreactor), manganese‐dependent peroxidase (MnP) was not detected throughout the cultures. Nevertheless, the tray configuration led to maximum individual MnP and LiP activities of about 200 U dm⁻³ and 300 U dm⁻³, respectively. Therefore, this configuration is the most adequate of the different bioreactor configurations tested in the present work, since the ligninolytic complex formed by MnP and LiP is more efficient for its application to bio‐processing systems. In addition, the results indicated the influence of the oxygen in ligninolytic enzyme production. © 2001 Society of Chemical Industry     

BTEX removal from contaminated groundwater by a co‐culture of Pseudomonas putida and Pseudomonas fluorescens immobilized in a continuous fibrous‐bed bioreactor

A fibrous‐bed bioreactor with immobilized cells of Pseudomonas putida and Pseudomonas fluorescens was used to treat groundwater contaminated with benzene, toluene, ethylbenzene, and xylenes (collectively know as BTEX). The kinetics of BTEX biodegradation in the fibrous‐bed bioreactor operated under continuous well‐mixed conditions was studied at room temperature. Aeration was not used in the process fed with groundwater samples with an average total BTEX concentration of 2.75 mg dm^?3. All BTEX compounds present in the groundwater feed were concurrently and completely biodegraded even under oxygen‐limited or hypoxic conditions. Nearly 100% removal efficiency was obtained when the retention time was greater than 1 h. BTEX removal efficiency decreased with decreasing the retention time, with p‐ and o‐xylenes showed up first in the treated groundwater, followed by benzene and then other BTEX compounds. Biodegradation rates of BTEX generally increased with increasing BTEX concentration and loading rate. The maximum BTEX biodegradation rate was 5.76 mg h^?1 dm^?3 at the loading rate of 6.54 mg dm^?3 h^?1. The bioreactor had a stable performance, maintaining its ability for efficient BTEX degradation without requiring additional nutrients for more than 1 month. The good performance of the fibrous‐bed bioreactor was attributed to the high cell density (～15 g dm^?3 reactor volume) in the fibrous matrix. © 2002 Society of Chemical Industry     

Valeric acid extraction with tri‐n‐butyl phosphate impregnated in a macroporous resin: II. Studies in fixed bed columns

Extraction and back‐extraction of valeric acid in a fixed bed packed with Amberlite XAD‐4 resin impregnated with tri‐n‐butyl phosphate were experimentally studied at 25 °C. The effects of the feed flow rate, acid concentration in the feed solution and extractant concentration in the impregnated resin on the breakthrough curves, were investigated. The bed saturation capacity was larger under the conditions of higher extractant concentration in the resin phase and higher acid concentration in the feed solution. A dynamic model that considers intraparticle diffusion and external liquid film diffusion as limiting steps in mass transfer rates was successfully applied. The intraparticle effective diffusivities (10^?9 dm² s^?1) were from one to three orders of magnitude lower than the diffusivities in the external liquid film (10^?8–10^?6 dm² s^?1). A fast and complete back‐extraction of valeric acid from the saturated bed was carried out with sodium hydroxide solutions. The operational life of the impregnated resin was also studied. Copyright © 2005 Society of Chemical Industry     

Phenol degradation in a fixed‐bed bioreactor using micro‐cellular polymer‐immobilized Pseudomonas syringae

Highly porous (85% void volume) polymer beads with interconnecting micro‐pores were prepared for the immobilization of Pseudomonas syringae for the degradation of phenol in a fixed‐bed column bioreactor. The internal architecture of this support material (also known as PolyHIPE Polymer) could be controlled through processing before the polymerization stage. The transient and steady state phenol utilization rates were measured as a function of substrate solution flow rate and initial substrate concentration. The spatial concentration of the bacteria on the micro‐porous support particles as well as within them was studied using scanning electron microscopy at various time intervals during the continuous operation of the bioreactor. It was found that although bacterial penetration into the porous support was present after 20 days, bacterial viability however, was compromised after 120 days as a result of the formation of a biofilm on the support particles. The steady state phenol utilization at an initial phenol concentration of 200 mg cm^?3 was 100% provided that the flow rate was less than 7 cm³ min^?1. Substrate inhibition at a constant flow rate of 4.5 cm³ min^?1 was found to begin at 720 mg dm^?3. The critical dilution rate for bacteria washout was high as a result of the highly hydrophobic nature of the support and the reduction of pore interconnect size due to bacterial growth within the pores in the vicinity of the surface of the support. Copyright © 2004 Society of Chemical Industry     

Bio‐oxidation of ferrous ions by Acidithioobacillus ferrooxidans in a monolithic bioreactor

BACKGROUND: The bio‐oxidation of ferrous iron is a potential industrial process in the regeneration of ferric iron and the removal of H₂S in combustible gases. Bio‐oxidation of ferrous iron may be an alternative method of producing ferric sulfate, which is a reagent used for removal of H₂S from biogas, tail gas and in the pulp and paper industry. For practical use of this process, this study evaluated the optimal pH and initial ferric concentration. pH control looks like a key factor as it acts both on growth rate and on solubility of materials in the system. RESULTS: Process variables such as pH and amount of initial ferrous ions on oxidation by A. ferrooxidans and the effects of process variables dilution rate, initial concentrations of ferrous on oxidation of ferrous sulfate in the packed bed bioreactor were investigated. The optimum range of pH for the maximum growth of cells and effective bio‐oxidation of ferrous sulfate varied from 1.4 to 1.8. The maximum bio‐oxidation rate achieved was 0.3 g L^?1 h^?1 in a culture initially containing 19.5 g L^?1 Fe²⁺ in the batch system. A maximum Fe²⁺ oxidation rate of 6.7 g L^?1 h^?1 was achieved at the dilution rate of 2 h^?1, while no obvious precipitate was detected in the bioreactor. All experiments were carried out in shake flasks at 30 °C. CONCLUSION: The monolithic particles investigated in this study were found to be very suitable material for A. ferrooxidans immobilization for ferrous oxidation mainly because of its advantages over other commonly used substrates. In the monolithic bioreactor, the bio‐oxidation rate was 6.7 g L^?1 h^?1 and 7 g L^?1 h^?1 for 3.5 g L^?1 and 6 g L^?1 of initial ferrous concentration, respectively. For higher initial concentrations 16 g L^?1 and 21.3 g L^?1, bio‐oxidation rate were 0.9 g L^?1 h^?1 and 0.55 g L^?1 h^?1, respectively. Copyright © 2008 Society of Chemical Industry     

Continuous biotransformation of pyrogallol to purpurogallin using cross‐linked enzyme crystals of laccase as catalyst in a packed‐bed reactor

Cross‐linked enzyme crystals (CLEC) of laccase were prepared by crystallizing laccase with 75% (NH₄)₂SO₄ and cross‐linking using 1.5% glutaraldehyde. The cross‐linked enzyme crystals were further coated with 1 mmol L^?1 β‐cyclodextrin by lyophilization. The lyophilized enzyme crystals were used as such for the biotransformation of pyrogallol to purpurogallin in a packed‐bed reactor. The maximum conversion (76.28%) was obtained with 3 mmol L^?1 pyrogallol at a residence time of 7.1 s. The maximum productivity (269.03 g L^?1 h^?1) of purpurogallin was obtained with 5 mmol L^?1 pyrogallol at a residence time of 3.5 s. The productivity was found to be 261.14 g L^?1 h^?1 and 251.1 g L^?1 h^?1 when concentrations of 3 mmol L^?1 and 7 mmol L^?1 respectively were used. The reaction rate of purpurogallin synthesis was maximum (2241.94 mg purpurogallin mg^?1 CLEC h^?1) at a residence time of 3.5 s, when 5 mmol L^?1 pyrogallol was used as the substrate. The catalyst to product ratio calculated for the present biotransformation was 1:2241. The CLEC laccase had very high stability in reuse and even after 650 h of continuous use, the enzyme did not lose its activity. Copyright © 2006 Society of Chemical Industry     

Biodegradation kinetics of trans‐4‐methyl‐1‐cyclohexane carboxylic acid in continuously stirred tank and immobilized cell bioreactors

BACKGROUND: Naphthenic acids are carboxylic acid compounds of oil sands wastewaters that contribute to aquatic toxicity. Biodegradation kinetics of an individual naphthenic acid compound in two types of continuous‐flow bioreactors were investigated as a means of improving remediation strategies for these compounds. RESULTS: This study evaluates the kinetics of biodegradation of trans‐4‐methy‐1‐cyclohexane carboxylic acid (trans‐4MCHCA) using two bioreactor systems and a microbial culture developed in previous work. Using a feed concentration of 500 mg L^?1 the biodegradation rate of trans‐4MCHCA in the immobilized cell bioreactor was almost two orders of magnitude higher than that in a continuously stirred tank bioreactor. The maximum reaction rates of 230 mg (L d)^?1 at a residence time of 1.6 d (40 h) and 22 000 mg (L d)^?1 at a residence time of 2.6 h were observed in the continuously stirred tank and immobilized cell bioreactors, respectively. In a second immobilized cell system operating with a feed concentration of 250 mg L^?1, a comparable maximum reaction rate (21 800 mg (L d)^?1) was achieved at a residence time of 1.0 h. CONCLUSION: The use of immobilized cell bioreactors can enhance the biodegradation rate of naphthenic acid compounds by two orders of magnitude. Further, biodegradation greatly reduces the toxicity of the effluent wastewater. Copyright © 2009 Society of Chemical Industry