Biochemical Engineering Journal (v.27, #2)

IFC (CO2).

BEJ Keywords (II).

Biodegradation of phenolic wastewater in a fixed biofilm reactor by Tzu-Yang Hsien; Yen-Hui Lin (95-103).
A mathematical model was developed to describe the biodegradation of phenolic wastewater in a fixed biofilm process. The model was solved using a combination of orthogonal collocation method and Gear's method. A laboratory-scale column reactor was conducted to verify the model system. The batch kinetic tests were independently conducted to determine biokinetic parameters used in the model simulation while initial thickness of biofilm was assumed so that the model simulated the phenol effluent concentration curve very well. The removal efficiency for phenol was 94%. At a steady-state condition, the phenol concentration obtained from experimental data was slightly higher than that obtained from the model simulation. The approaches presented in this paper could be employed for the design of a fixed biofilm reactor system for the biodegradation of phenolic wastewater in petrochemical and oil refining industries.
Keywords: Biodegradation; Biokinetic parameters; Phenolic wastewater; Fixed biofilm; Mathematical model; Simulation;

A novel strain (designated as QYY) which could grow with bromoamine acid (BAA) as the sole source of carbon, nitrogen and energy was isolated from sludge samples. The strain was identified by 16S rRNA sequencing and physiological-biochemical characteristics. It belonged to proteobacteria alpha subdivision: Sphingomonas xenophaga. For decolorization, the optimal temperature and shaking speed for both growing and resting cells were 30 °C and 150 rpm, respectively. While the most suitable pH was different, 6.5 for growing cells and 8.5 for resting cells. Under the optimal conditions, the removal percent of BAA was over 80–90%. And a conventional substrate-inhibited model-Haldane equation could be applied to describe the decolorization process by resting cells with the concentration range from 10.56 to 114 mg l−1, and the kinetic parameters were as follows: V max  = 2.53 mg l−1  min−1, K s  = 19.90 mg l−1, K si  = 91.91 mg l−1. The products were observed by the UV–vis absorbance spectra and the maximum absorption peak in visible area disappeared completely after a short period of incubation.
Keywords: Biokinetics; Bromoamine acid; DNA; Kinetic parameters; Sphingomonas xenophaga; Wastewater treatment;

Synthesis gas was used to produce ethanol and acetate via fermentation processes. A strict autotrophic bacterium, Clostridium ljungdahlii, was grown on syngas to investigate production of acetate and ethanol. The experiments were conducted with various initial total pressures of syngas at 0.8–1.8 atm with 0.2 intervals. Formation of acetate was almost the same for all initial pressures as well as cell concentrations. Ethanol concentration was promoted by hydrogen and carbon dioxide in the culture media. Maximum acetate production (1.3 g l−1) was obtained at syngas total pressures of 1.4 atm. However, maximum ethanol concentration of 0.6 g l−1 was obtained with the syngas total pressures of 1.6 and 1.8 atm. The cell and product yields were 0.3 g cell g−1 CO and 0.41 g products g−1 CO, respectively. The product ratio of ethanol and acetate was 0.54 g ethanol g−1 acetate at syngas total pressures of 1.6 and 1.8 atm. In this study, a novel prediction was introduced which proposes the death phase of bacteria. Based on predicted model fitted with experimental data, the maximum cell dry weight (x m), inhibition constant (k) and maximum specific growth rate were 1.2 g l−1, 0.003 h−1 and 0.07 h−1, respectively. The kinetic of growth-dependence on CO was represented by Andrew equation to predict inhibition constant in the cultures media. The inhibition constant was obtained at 2 mmol CO l−1.
Keywords: Synthesis gas; Clostridium ljungdahlii; Autotrophic bacterium; Ethanol; Acetate;

Enzymatic reactions in dense gases by Željko Knez; Maja Habulin; Mateja Primožič (120-126).
This article is oriented on application of dense gases as alternative reaction media for enzyme-catalyzed reactions. The main factors influencing enzyme stability (water activity, pressure, temperature, pressurization/depressurization) and the influence of process parameters on the initial reaction rates and productivity are presented.An overview of the research in the field of enzymatic reactions in dense fluids is shown.
Keywords: Enzyme activity; Enzyme biocatalysis; Enzyme bioreactors; Enzyme deactivation; Heterogeneous biocatalysis; Lipase;

Measurement of microalgal photosynthetic activity depending on light intensity and quality by You-Chul Jeon; Chul-Woong Cho; Yeoung-Sang Yun (127-131).
A system that can precisely measure light-dependent microalgal photosynthetic activity was developed and successfully used to obtain the photosynthesis–irradiance responses at different concentrations of algal cells, and intensities of various light sources. The measurement system was designed to finely control both the intensity and spectrum of illuminated light. In order to test reproducibility of the measurement system, Haematococcus pluvialis was used as a model microalgal strain. As a result, the photosynthetic activity, in terms of the oxygen evolution rate, was consistently measured within errors less than 5%. When light sources were changed, the red light was more effectively utilized for algal photosynthesis than green light and even simulated daylight, which is likely to occur because H. pluvialis possesses a special pigment (i.e., Chl a) which enables it to harvest red light region.
Keywords: Algae; Photosynthesis; Biokinetics; Haematococcus pluvialis; Dissolved oxygen; Light;

Adsorption of amoxicillin on chitosan beads: Kinetics, equilibrium and validation of finite bath models by W.S. Adriano; V. Veredas; C.C. Santana; L.R.B. Gonçalves (132-137).
The kinetics and equilibrium of amoxicillin adsorption on chitosan beads have been determined in batch studies. The fit to experimental equilibrium data indicates that the isotherm for this system can be considered of Langmuir type. Two mathematical models proposed in the literature were used to describe the adsorption kinetic. The validation of the models allowed optimizing mass transfer parameters, that describe the phenomena of internal diffusion and external convection on chitosan beads, as well as determining the kinetic rate constant.
Keywords: Adsorption; Amoxicillin; Antibiotic; Bioseparation; Chitosan; Modelling;

A stainless steel mesh packing with 99.0% porosity has been inserted in the riser section of an external loop airlift bioreactor (ELAB). The hydrodynamic characteristics and oxygen mass transfer rates of the ELAB, both with and without packing, were compared. The packing increased the overall volumetric oxygen mass transfer coefficient by an average factor of 2.45 compared to the unpacked column. The packing increased gas holdup, decreased bubble size, and decreased liquid circulation rates in the bioreactor, all of which contributed to the dramatic improvement in the oxygen mass transfer rates.A dynamic, spatial model was used to predict the transient, oxygen concentration distribution in the ELAB with and without a packed bed. This model was compared to simulating the ELAB as a completely stirred reactor and demonstrated improved prediction of the cyclical changes in liquid oxygen concentrations. The oxygen mass transfer coefficient was determined as a best fitting parameter of the model and at higher gas superficial velocities was found to increase to values approaching 0.021 s−1 using the small amount of packing. Finally, simplified correlations were developed to predict the oxygen mass transfer coefficient in the ELAB with and without the packed bed.
Keywords: Hydrodynamics; Gas–liquid mass transfer; Oxygen transfer; Airlift bioreactors; Packed bed bioreactors; Dynamic modeling;

Pseudomonas aeruginosa J4, isolated from wastewater of a petrochemical factory located in southern Taiwan, was used to produce rhamnolipid from a variety of carbon substrates, including hydrophilic substrates, vegetable oils, and mineral oils. The P. aeruginosa J4 strain was able to assimilate the seven carbon substrates examined (namely, glucose, glycerol, olive oil, sunflower oil, grape seed oil, diesel, and kerosene), whereas it grew less efficiently in mineral oils (esp., kerosene). Rhamnolipid production from the J4 strain was affected by temperature and agitation rate, as 30 °C and 200 rpm agitation were favorable for rhamnolipid production. The rhamnolipid concentration (C RL) and production rate ( v RL ) was also influenced by the carbon sources used to grow the J4 strain. Similar v RL (10–12 mg/h/L) and C RL (1400–2100 mg/L) were obtained from using glycerol, glucose, grape seed oil, and sunflower oil as the sole carbon substrate, while using olive oil delivered the best rhamnolipid production. Maximum C RL (3600 mg/L) and v RL (26 mg/h/L) were attained at 10% olive oil. P. aeruginosa J4 also utilized diesel and kerosene for rhamnolipid production but with much lower C RL and v RL values Rhamnolipid was purified (nearly 90% pure) from the culture broth. Mass spectrometry and NMR analysis indicate that the purified product contained two types of commonly found rhamnolipids: l-rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoate (RL1) and l-rhamnosyl l-rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoate (RL2). The rhamnolipid product can reduce the surface tension of water to 31 mN/m with a critical micelle concentration of nearly 50 mg/L. The biosurfactant also achieved a maximum emulsion index of 70 and 78%, for diesel and kerosene, respectively, at a low concentration of about 300 mg/L.
Keywords: Rhamnolipid; Pseudomonas aeruginosa; Biosurfactant; Vegetable oil; Diesel; Kerosene;

A new methodology for the optimal design of batch fermentation plants by Ricardo Simpson; Carolina Astudillo; Fernando Acevedo (155-160).
In the design of batch and fed-batch fermentation plants, the problem of determining the adequate combination of number and size of the fermentors to be used, so to accomplish the desired production schedule must be faced. The problem has infinite solutions, as for any fermentor size, a number of units of that size will do the work, but not all solutions are equal from an economical standpoint. The problem of determining the optimum number of pieces of equipment and the optimum operation schedule has been addressed by several authors in the process engineering field.The optimal combination of size and number of fermentors will be the one that maximizes the net present value. The objective of this work was to develop a methodology for the optimal design of batch fermentation plants based in the maximum net present value criterion and to compare it with the more restricted criterion of minimum investment in production fermentors.Results show that considering only the investment in production fermentors underestimates the optimum number of fermentation units, probably because it only considers the investment in production fermentors and its assumptions of equal preparation and discharge times. On the other hand, the method proposed in this work, although somewhat more complex, gives a more accurate result.
Keywords: Batch fermentation plants; NPV; Production fermentor;

A novel computer approach for in silico molecular modification was here developed and applied to the bacterial enzyme naphthalene 1,2-dioxygenase. A complete set of small deletions was obtained modifying the crystal structure file of the enzyme dimer form, therefore conformational analysis and substrate interaction simulations methods were performed to describe molecule behavior related to different levels of modification. The analysis of interaction zones between all dimers of the examer structure permitted to extend these evaluations to the natural form present on bacterial cells. Four candidates for the biosynthesis of shorter molecules were individuated this way.
Keywords: Protein segments removal effects; Naphthalene 1,2-dioxygenase; Polycyclic aromatic hydrocarbons;

A mathematical model has been developed for predicting the performance and simulation of a packed bed immobilized enzyme reactor performing lactose hydrolysis, which follows Michaelis–Menten kinetics with competitive product (galactose) inhibition. The performance characteristics of a packed bed immobilized enzyme reactor have been analyzed taking into account the simultaneous effects of internal and external mass transfer limitations. The model design equations are then solved by the method of weighted residuals such as Galerkin's method and orthogonal collocation on finite elements.The effects of simultaneous internal and external mass transfer coupled with product inhibition have been studied and their effects were shown to reduce internal effectiveness factor. The effects of product inhibition have been investigated at different operating conditions correlated at different regimes using dimensionless β xo (St, Bi, θ, ϕ). Product inhibition was shown to reduce substrate conversion, and to decrease effectiveness factor when β s  >  β xo; however, it increases internal effectiveness factor when β s  <  β xo. The effectiveness factor is found to be independent of product inhibition at crossover point at which β xo is defined. Effects of St and Bi have been investigated at different kinetic regimes and the results show their effects have a strong dependence on kinetic parameters θ, γ (i.e. K m/K p) and β xo. The dimensionless residence time at crossover point, β xo, has been correlated with kinetic and mass transfer parameters.
Keywords: Biocatalysis; Enzyme bioreactors; Immobilisation; Immobilised enzymes; Product inhibition; Internal mass transfer;

Crude amylases were prepared from Bacillus subtilis ATCC 23350 and Thermomyces lanuginosus ATCC 58160 under solid state fermentation. The effect of various process variables was studied for maximum conversion efficiency of maize starch to glucose using crude amylase preparations. Doses of pre-cooking α-amylase, post-cooking α-amylase, glucoamylase and saccharification temperature were found to produce maximum conversion efficiency and were these selected for optimization. Full factorial composite experimental design and response surface methodology were used in the design of experiments and analysis of results. The optimum values for the tested variables for the maximum conversion efficiency were: pre-cooking α-amylase dose 2.243 U/mg solids, post-cooking α-amylase dose 3.383 U/mg solids, glucoamylase dose 0.073 U/mg solids at a saccharification temperature of 55.1 °C. The maximum conversion efficiency of 96.25% was achieved. This method was efficient; only 28 experiments were necessary to assess these conditions, and model adequacy was very satisfactory, as coefficient of determination was 0.9558.
Keywords: Thermomyces lanuginosus; Bacillus subtilis; α-Amylase; Glucoamylase; Solid state fermentation; Maize starch hydrolysis; Response surface methodology (RSM); Optimization;