S. S. Lele

A statistical approach to optimization of fermentative production of poly(γ-glutamic acid) from Bacillus licheniformis NCIM 2324.

This paper reports on the optimization of poly(gamma-glutamic acid) (PGA) production by Bacillus licheniformis NCIM 2324 using a statistical approach. One-factor-at-a-time method was used to investigate the effect of carbon sources, nitrogen sources and pH on PGA production. Plackett-Burman design was adopted to select the most important nutrients influencing the yield of PGA. After identifying effective nutrients, response surface methodology was used to develop a mathematical model to identify the optimum concentrations of the key nutrients for higher PGA production, and confirm its validity experimentally. PGA production increased significantly from 5.27 to 26.12 g/l when the strain was cultivated in the optimal medium developed by using statistical approach, as compared to basal medium.

Fast and very slow reactions: phase transfer catalysis

Abstract The effect of phase transfer catalysts (PTC), such as tricaprylmethyl ammonium chloride (Aliquat-336), cetyl trimethyl ammonium bromide, etc. on the rate of alkaline hydrolysis of different formate and acetate esters was studied. In the case of formate esters extraction is accompanied by fast pseudo-first order reaction in diffusion film; for acetate esters the reaction is insufficiently fast to occur in the diffusion film. The values of the volumetric rate of extraction, R A a, and the specific rate of extraction, R A , with or without PTC, were measured in a fully baffled mechanically agitated contactor and a constant interfacial area stirred cell, respectively. The alkaline hydrolysis reaction was carried out with aqueous solutions of sodium hydroxide or aqueous lime slurry and the effect of speed of agitation and PTC concentration on the rate of hydrolysis was studied. A remarkable increase in the value of R A was realized in the presence of PTC and the enhancement factor for the formate ester hydrolysis reaction ranged from 20 to over 200.

Simultaneous removal of carbon and nitrate in an airlift bioreactor

This paper presents the integrated removal of carbon (measured as chemical oxygen demand i.e. COD) and NO(x)-N by sequentially adapted sludge, studied in an airlift reactor (ALR). Simultaneous removal of COD and nitrate occurs by denitrification (anoxic) and oxidation (aerobic). Aerobic (riser) and anoxic (remaining part) conditions prevail in different parts of the reactor. Studies were carried out in a 42 L ALR operated at low aeration rate to maintain anoxic and aerobic conditions as required for denitrification and COD removal, respectively. The sludge was adapted sequentially to increasing levels of NO(x)-N and COD over a period of 45 days. Nitrate removal efficiency of the sludge increased due to adaptation and degraded 900 ppm NO(3)-N completely in 2h (initially the sludge could not degrade 100 ppm NO(3)-N). The performance of the adapted sludge was tested for the degradation of synthetic waste with COD/N loadings in the range of 4-10. The reduction of COD was significantly faster in the presence of NO(x)-N and was attributed to the availability of oxygen from NO(x)-N and distinct conditions in the reactor. This hypothesis was justified by the material balance of COD.

Use of a batch-stirred reactor to rationally tailor biocatalytic polytransesterification

Despite favorable thermodynamics, high-molecular weight and low-dispersity polyesters are difficult to synthesize biocatalytically in organic solvents. We have reported previously that the elimination of solvent can improve the kinetics and apparent equilibrium significantly (Chaudhary et al., 1997a). We now present the design and use of a batch-stirred enzyme reactor to control the biocatalytic polymerization. Using the reactor, polyester having a molecular weight of 23,400 Da and a polydispersity of 1.69 was synthesized in only 1 h at 60 degrees C. Additional factors like enzyme-deactivation kinetics, enzyme specificity, and initial exothermicity were investigated to develop a better understanding of this complex reaction system.

Modelling of air-lift fluidized bed: Optimization of mass transfer with respect to design and operational parameters

Abstract Biological three-phase reactions are conventionally carried out in bubble columns, stirred contactors or fluidized beds. New bioreactors and fermenters used for production or waste water treatment include ICI deep shaft aerators or internal draft-tube air-lift loop reactors and draft-tube fluidized beds. The fluidized beds have higher productivity than the continuous stirred type and there is no wash out or stratification of biomass. The three-phase fluidized bed has high power requirements and adequate data are not available for design of large-scale equipment. It is proposed to use an external loop air-lift reactor as an air-lift fluidized bed (ALFB), by fluidizing the light particles in the downcomer. The proposed ALFB is expected to have lower shear stress levels and has a high degree of design flexibility. The effect of design and operational parameters were simulated for an air-water system for an ALFB of 100 m3. Recommendations have been made for optimum mass transfer performance and suitable scale up criteria have been developed. The proposed ALFB has been shown to be more promising than the three-phase fluidized bed.

Immobilization of fungal spores on synthetic polymers

Adsorption of fungal spores on a synthetic polymer - High Density Polyethylene was successfully achieved using different pretreatments. Sonication of beads followed by ferric nitrate treatment or use of 0.1% tributyrin gave adsorption upto 46%. Use of dichloromethane as a solvent for sonication is recommended for its better performance in reuse studies (upto 5 times without much decrease in activity). 100 g of immobilized biocatabyst in a 7 L Fluidized Bed Bioreactor was found to perform better than shaker flask at a much lower power input.

Improved adsorption of Aspergillus niger 589 spores on high-density polyethylene for progesterone biotransformation

Aspergillus niger NCIM 589 spores were immobilized on high density polyethylene (HDPE), using polyethyleneimine (PEI) as the surface coating with as high as 50% adsorption compared with 30% reported earlier. The adsorption time was reduced to 2 h from the earlier 24 h, and pretreatment with a solvent was eliminated. The biocatalyst could be used for 11α-hydroxylation of Progesterone to give better conversions than alginate-entrapped or free mycelia.

Underutilization of loop reactors due to desorption

Loop reactors or circulating bubble columns are considered to be promising multiphase contactors to conduct biochemical and chemical reactions due to flexibility in their design, their low power requirement and low fluid shear stresses in these reactors. A generalized model for external loop airlift reactors (EL-ALRs), accounting for axial variations in holdups of the gas and liquid phases and total pressure, is employed, to predict the performance of these reactors when used for slow liquid phase reactions. As the liquid travels upward in the riser, the decrease in the local pressure due to reduction in the static head of liquid reduces the saturation concentration of the solute (coreactant transferred from the gas phase) in the liquid phase. At certain locations in the riser, especially in the top portion of the riser, the liquid phase concentration of the solute may exceed the local saturation level resulting in desorption of the reactive solute. This undesired situation leads to underutilization of the EL-ALR as far as conversion of the absorbed reactant is concerned. The effects of design parameters, such as the height to diameter ratio, area ratio, and sparger location, and operational parameters, such as superficial feed gas velocity, composition of the feed gas, kinetic coefficient, and top pressure, on the performance of the EL-ALR are examined in considerable detail. Existence of optimum values of height-to-diameter ratio, sparger location in the downcomer, area ratio, and top pressure for minimization/obviation of desorption, maximization of net rate, and maximization of net rate per unit power consumption is established. The importance of proper selection of the key design and operating parameters for EL-ALRs for optimal performance of these is demonstrated.

Rheology of Model Dough Formulation

Dough is generally considered a viscoelastic material, and its elasticity is attributed to the hydrated gluten matrix. Since starch is a major constituent of flour (∼70 wt% on dry basis) we may expect it to contribute to dough rheology in a non‐trivial manner. Considering dough to belong to the generic class of soft solid materials, we use the Strain‐Rate Frequency Superposition (SRFS) technique to study rheology of various model dough compositions in which the starch/gluten ratio is systematically varied from 100/0 to 0/100. We find that for compositions containing 0–25% gluten the SRFS superposition principle works well, while for compositions containing greater than 25% gluten the quality of SRFS mastercurves deteriorates gradually. Thus we propose that starch particles contribute substantially to the rheology of dough containing up to 25% gluten.

Modelling of a Bioreactor: Optimization of a Loop Reactor for Biochemical Systems

Loop reactors are considered to be the most versatile bioreactors due to their design flexibility, low power requirements and low shear stresses. A number of biochemical reactions involve handling of gas-liquid-solid three phase systems and are carried out in bubble columns, stirred vessels or three phase fluidized bed reactors (TPR). These contactors are less suitable for biochemical reactions involving shear sensitive microorganisms. Hence a new reactor design is proposed to employ External Loop Air-Lift Reactor (EL-ALR) as an air-lift fluidized bed (ALFB), by downward fluidization of the light particles in the downcomer. Due to unidirectional flow pattern, ALFB is expected to have lower shear stress levels.