Biochemical Engineering Journal (v.7, #3)

Selective separation of amino acids by reactive extraction by D. Cascaval; C. Oniscu; A.-I. Galaction (171-176).
The method of reactive extraction with di-(2-ethylhexyl)phosphoric acid (D2EHPA) for the separation of a range of amino acids is studied. The results obtained on the individual reactive extraction indicated the possibility of the amino acids selective separation as a function of the pH value of aqueous solution and the acidic or basic character of each amino acid. Thus, using multistage extraction, the total separation of the following amino acids groups has been performed: neutral amino acids (l-glycine, l-alanine, l-tryptophan) at pH 5–5.5 (nine extraction stages), basic amino acids (l-lysine, l-arginine) and l-cysteine at pH 4–4.5 (ten extraction stages), l-histidine at pH 3–3.5 (five extraction stages), and acidic amino acids (l-aspartic acid, l-glutamic acid) at pH 2–2.5 (three extraction stages).
Keywords: Amino acids; di-(2-Ethylhexyl)phosphoric acid; Reactive extraction; Selective extraction;

Inhibition kinetics of a commercial mixed culture by ammonium sulfate by Deniz Tanyolaç; Bekir Salih; Abdurrahman Tanyolaç (177-182).
The inhibitory effect of ammonium sulfate on a commercial mixed culture, used in biological waste-water treatment was studied under aerobic batch conditions. Several mathematical models of enzyme and growth kinetics including a death factor were analyzed through nonlinear regression to find the best fit to corresponding data of inhibition. The best fit model was found to be the generalized Monod type with a death factor having the biokinetic parameters; μ max 0.681 h−1, K s 0.224 g dm−3, K i 56240 g dm−3, K 0.055 g dm−3 and k d 0.052 h−1 to represent the experimental data accurately. The low saturation coefficient value along with high maximum specific growth rate and inhibition coefficient denotes the competitive characteristics of commercial mixed cultures in the biological treatment of high ammonium polluted waste waters.
Keywords: Inhibition; Growth kinetics; Ammonium sulfate; Waste-water; Biological treatment;

The ability of dried anaerobic activated sludge to adsorb phenol and chromium(VI) ions, both singly and in combination, was investigated in a batch system. The effects of initial pH and single- and dual-component concentrations on the equilibrium uptakes were investigated. The optimum initial biosorption pH for both chromium(VI) ions and phenol was determined as 1.0. Multi-component biosorption studies were also performed at this initial pH value. It was observed that the equilibrium uptakes of phenol and chromium(VI) ions were changed due to the presence of other component. Adsorption isotherms were developed for both single- and dual-component systems at pH 1.0, and expressed by the mono- and multi-component Langmuir, Freundlich and Redlich–Peterson adsorption models and model parameters were estimated by the non-linear regression. It was seen that the mono-component adsorption equilibrium data fitted very well to the non-competitive Freundlich and Redlich–Peterson models for both the components while the modified Freundlich model adequately predicted the multi-component adsorption equilibrium data at moderate ranges of concentration. The results suggested that the cells of dried anaerobic activated sludge bacteria may find promising applications for simultaneous removal and separation of phenol and chromium(VI) ions from aqueous effluents.
Keywords: Multi-component biosorption; Phenol; Chromium(VI); Dried anaerobic activated sludge; Mono- and multi-component adsorption isotherms;

A surface active layer consisting mainly of phospholipids lines the human conducting airways. Dysfunction of this layer could play a role in the pathogenesis of chronic obstructive airway diseases like asthma and chronic bronchitis. Replacement therapy with exogenous surfactants is being considered in such conditions. The relationship between surfactants and mucus viscosity would be important for such an application. Respiratory mucus is composed of high molecular weight glycoprotein molecules which form temporary cross-links and entanglements to form a gel-like material. The present paper studies the interaction of three therapeutic surfactants — Exosurf, ALEC and Survanta; the main phospholipids of lung surfactant (1,2-dipalmitoyl phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylglycerol (PG)) as well as their binary mixtures (PCPE and PCPG) in a PC:(PE or PG) ratio of 2:3; on the viscosity of mucus gel simulants (MGS — a polymeric gel consisting mainly of gum tragacanth and simulating respiratory mucus). The surfactants were studied with respect to their ability to alter MGS viscosity at shear rates ranging from 0.1498 to 51.2 s−1 in a concentric cylinder viscometer at 37°C. The change in viscosity of the MGS on incubation with surfactant versus shear rate was found be non-Newtonian and to follow a power law model (coefficient of regression R 2≥0.9). The shear rates experienced by a surfactant mixture, while passing through the tracheobronchial tree, were then calculated by modelling the tracheobronchial tree as cylindrical branching tubes. The equation governing the flow of a power law fluid through a cylindrical pipe was used to determine the shear experienced by a surfactant infusion as it passes through various mucus lined branches of the tracheobronchial tree. The surfactants were then compared based on their ability to alter MGS viscosity at shear rates corresponding to that of large, medium and small bronchi, as calculated by the study.
Keywords: Viscosity; Non-Newtonian fluid; Rheology; Biophysical chemistry; Polymer; Phospholipid;

The phenomena of cavitation which is associated with the formation, growth and the collapse of microbubbles, leads to the generation of very high pressures and temperatures locally, which can cause cellular damage. This paper explores the microbicidal effectiveness of cavitation for the disinfection of bore well water for potable use. Experiments performed in this study indicate that hydrodynamic cavitation is an energy efficient and economical technique compared to the other conventional non-chemical water treatment processes and cavitation was found to be a potential physical water disinfection technique for the production of potable water.
Keywords: Cavitation; Hydrodynamic; Disinfection; Potable water;

Experimental and theoretical works were performed for the separation of large polyelectrolyte such as DNA in the column packed with gel particles under influence of an electric field. Since DNA quickly orients through the pores in the field direction, this paper presents how intraparticle convection affects the separation of DNAs in the column. Dimensionless transient mass balance equations were derived considering diffusion and electrophoretic convection. The separation criteria are theoretically studied using two different Peclet numbers in the fluid and solid phases and these criteria were verified using two different DNAs by electrophoretic mobilities measured experimentally, showing how the separation position of DNAs varies in the column according to values of Pe f/Pe g of individual DNA. Governing equations are solved by an operator theory and the characteristic method to yield the column response.
Keywords: Packed column; Convective electrophoretic velocity; DNA; Peclet number;

The kinetics of enzyme treatment of hardwood kraft pulp with commercial xylanase Cartazyme NS-10 was investigated. The enzyme treatment process was found to follow closely the topochemical modified equation of Prout–Tompkins. The influence of the initial enzyme concentration was studied and the applicability of the power kinetic equation was established for the initial rate of the process. An equation of practical use was obtained, which provides the temperature function of the amount of the reducing substances, depending on the enzyme initial concentration. This function made it possible to control the process of prior enzyme treatment of unbleached kraft pulp.
Keywords: Commercial xylanase; Cartazyme NS-10; Kraft pulp; Topochemical mechanism;

Response surface methodology was employed to study the cumulative interactive effect of the macronutrients of the media and to optimize their concentration to enhance the production of maltooligosaccharide-forming amylase from Bacillus circulans GRS 313. A 23 factorial central composite experimental design was used to study the combined effect of the nutritional constituents like soybean meal, yeast extract and wheat bran. The p-value of the coefficient for linear effect of soybean meal concentration was found to be 0.081, suggesting that this was the principal experimental variable having the greatest effect on the production of maltooligosaccharide-forming amylase. The optimal combination of the media constituents for amylase production from the contour plots were: soybean meal=4.84  g/100  ml , yeast extract=1.58  g/100  ml , wheat bran=2.84  g/100  ml . The optimization of the media increased the amylase yield by 1.25 times.
Keywords: Central composite design; Response surface methodology; Maltooligosaccharide-forming amylase; Media constituents; Wheat bran;

An immobilized enzyme reactor system for converting poorly soluble substrate is proposed. In this stirred batch reactor, the solid substrate and immobilized enzyme suspensions are separated by a microporous filter. The advantage of separating the solid substrate from immobilized enzyme is that the fouling and breakage of the immobilized enzyme usually encountered in the stirred tank reactor can be prevented. Pressure swing can be applied to enhance the mass transfer between the two compartments. The hydrolytic reaction converting the poorly soluble substrate p-hydroxyphenylhydantoin (pHPH) into soluble N-carbamoyl-p-d-hydroxyphenylglycine (CpHPG) by immobilized d-hydantoinase is carried out in this reactor. The performance of this pressure-swing reactor is studied by simulation using a simple kinetic model. The pressure-swing operation increases the overall production rate significantly. The pressure swing also makes the reactor perform better for converting the solid substrate at higher concentration.
Keywords: Enzyme bioreactors; Heterogeneous biocatalysis; Modeling; d-hydantoinase; d-amino acid; Pressure swing;

Uptake pathway and continuous removal of nitric oxide from flue gas using microalgae by Hiroyasu Nagase; Ken-ichi Yoshihara; Kaoru Eguchi; Yasunobu Okamoto; Sachi Murasaki; Risako Yamashita; Kazumasa Hirata; Kazuhisa Miyamoto (241-246).
Nitric oxide (NO), a major constituent of NO x in fossil fuel flue gas, can be removed by the microalga, Dunaliella tertiolecta, in a bubble-column-type bioreactor. The uptake pathway of NO was investigated, and it was found that little NO was oxidized in the medium before its uptake by algal cells and that NO mostly permeated directly into the cells by diffusion based on the mass balance of nitrogen and the change in nitrate and nitrite concentration in the medium in batch culture. For further application of this system, it is necessary to remove NO over a long duration, and the stability of NO removal is important. NO removal rate of about 50–60% could be maintained stably for 15 days in continuous culture under the light condition. Because the consumption of nitrate was reduced by the amount of taken NO, NO rather than nitrate is preferentially utilized as a nitrogen source for cell growth. Therefore, this algal system is useful for continuous NO removal and production of algal biomass using NO as a nitrogen source.
Keywords: Microalgae; Dunaliella tertiolecta; Nitric oxide; Bubble columns; Environmental preservation; Waste treatment;