Biochemical Engineering Journal (v.24, #2)

IFC (CO2).

BEJ Keywords (IV).

A systematic procedure for identifying the number of parameters of a model that can be estimated uniquely by nonlinear regression is presented. The objective function to be minimized is in the form of weighted sum of squares of residuals. The assumptions inherent in the choice of weights and the validity of the parameters estimated are verified by statistical tests. The procedure is illustrated by considering the estimation of parameters for Monod kinetics. Simulated data containing known measurement noise are used initially to illustrate the procedure. Finally, parameters are estimated from different sets of experimental data, and the validity and the uniqueness of the parameters are presented.
Keywords: Biokinetics; Dynamic modelling; Microbial growth; Bioreactions;

We have evaluated the mass transfer performance of four commercially available membrane oxygenators in which the blood path is external to and approximately perpendicular to the fiber bundle. Water flowed outside the hollow fibers as an oxygen carrier medium and substitution for blood, and nitrogen gas flowed inside the hollow fibers. The oxygen transfer rates in the membrane oxygenators were measured, and their mass transfer coefficients were obtained. When we analyzed the mass transfer performance using the theory of heat transfer across tube banks, the Sherwood numbers were obviously divided into two regions; one was the data for parallel hollow fibers, and the other was the data for crossed hollow fibers. This indicates that the mass transfer performance of the membrane oxygenator is attributable to the hollow fiber arrangement namely, parallel and crossed hollow fibers, in the same manner as that for heat transfer across tube banks (staggered and in-line bank). New mass transfer correlations have been developed for the membrane oxygenators composed of parallel hollow fibers and crossed hollow fibers. These mass transfer correlations may be used as a guide for the design of a new and efficient membrane oxygenator.
Keywords: Biomedical; Gas–liquid mass transfer; Hollow fibers; Oxygen transfer; Mass transfer correlation; Artificial lung;

In the present work, the use of extended Kalman filter (EKF) to infer the outlet compositions and growth rate of the acetone–butanol–ethanol fermentation process from outlet gas CO2 measurement has been discussed. In order to tune the filter (Q matrix), different methods consist of trial and error; Loan, Mont Carlo simulations and continuous case have been investigated for process noise covariance matrix. The reliability of the developed estimator is discussed with respect to disturbance on CO2 concentration. The performance of the estimator has been evaluated by comparison with other filters such as Wiener and linearized Kalman filter as well as simulation and experimental results. The results show, EKF estimator provides good agreement with the composition values measured off-line while Q is adjusting by Loan method.
Keywords: Kalman filter; Fermentation; State estimation; Acetic acid; Ethanol; Bioreactor;

An unstructured model for the diauxic growth of Penicillium camembertii on glucose and arginine by Abdeltif Amrane; Lydia Adour; Catherine Couriol (125-133).
Penicillium camembertii on glucose and arginine exhibited diauxic behaviour. Glucose was first assimilated and then, after its depletion, arginine was used as a carbon source in addition to a nitrogen source. A simple unstructured model was developed to describe the system. The consumption kinetics of both carbon substrates were described using a modified Verlhust model, without involving the key enzyme responsible for the degradation of the second carbon substrate, arginine. Growth kinetic was deduced from the sequential consumption of both carbon substrates, since biomass on carbon substrate yields were found to be constants. Major products, carbon dioxide and ammonium, resulted from both biosynthesis and viable cell maintenance, and were therefore assumed to be partially linked to growth. An additional term was also added in the production model to account for cessation of production when carbon became limiting, namely after exhaustion of the second carbon source, arginine. For both products, integration of production rate allowed the determination of calculated production kinetics, as well as the respective parts of growth- and non-growth-associated production. This determination showed that ammonium, resulting from arginine deamination, was mainly produced by a growth-associated mechanism; while, at the end of culture, similar contributions of both mechanisms were found for CO2 production.
Keywords: Batch processing; Diauxic growth; Fermentation; Filamentous fungi; Modelling; Penicillium camembertii;

The biological removal of ethyl acetate in air streams was carried out in gas–liquid–solid three-phase flow airlift loop bioreactor, in which biological membrane replaced the activated sludge. The influences of temperature, pH and waste gas influx on the removal efficiency (RE) and the outlet concentration of ethyl acetate were investigated and discussed. The optimum operation conditions were obtained as the temperature of 20–30 °C, pH 6.5–7.5 and waste gas influx of 0.05 m3/h. Under the optimum operation conditions, the average removal efficiency of ethyl acetate is higher than 98%, corresponding to the outlet concentration of ethyl acetate lower than 150 mg/m3. The maximum elimination capacity (EC) of ethyl acetate in gas–liquid–solid three-phase flow airlift loop bioreactor was higher than that in the biofilters reported in the literature.
Keywords: Gas–liquid–solid three-phase flow; Airlift loop bioreactor; Ethyl acetate; VOCs;

The effect of heat stress on freeze-drying and conservation of Lactococcus by M. Ziadi; Y. Touhami; M. Achour; Ph. Thonart; M. Hamdi (141-145).
The production of lactic acid bacteria isolated from Tunisian fermented milk (Lben): Lactococcus lactis subsp. lactis var. diacetylactis (SLT6) was investigated in fed-batch process. The final biomass production was 2.271011  cfu/ml.The effect of heat stress, after fermentation, on the survival rate after freeze-drying and during storage was studied. The survival rate after freeze-drying of SLT6 subject of a thermal treatment was 38.8% whereas it was only 21.9% for unprocessed SLT6.The accelerated shelf life testing (ASLT) method was used to study the effect of heat stress on conservation of Lactococcus. The bacterium was stored at four different temperatures of 4, 15, 25 and 37 °C. Lactococcus cell kinetic behaviour suggested a first order reaction, and the effect of storage temperature was quantified by determination of the half-life period and the activation energy. The beneficial effect of heat stress is clearly associated with a half-life period of 86 days for SLT6T and only 48 days four SLT6NT stored at 4 °C.
Keywords: Lactococcus lactis; Fed-batch culture; Heat stress; Accelerated shelf life testing; Arrhenius curve;

Prediction of protein partition in polymer/salt aqueous two-phase systems using the modified Wilson model by Pedro P. Madeira; Xin Xu; José A. Teixeira; Eugénia A. Macedo (147-155).
The extension of the modified Wilson model to multicomponent mixtures, presented in a previous publication, is applied to predict the partition of the following proteins: bovine serum albumin (BSA), lysozyme, glucosidase and catalase, in the Na2SO4/PEG6000 and K2HPO4/PEG6000 aqueous two-phase systems at 298.15 K. The results obtained with the model are, in general, in fair agreement with the experimental data.In the modelling methodology adopted here, special emphasis on the so-called “charge effects” to the protein partition was given. To our knowledge, no experimental information is available in the literature that allows to estimate the interaction parameters between these macromolecules and the components present in the aqueous two-phase systems (water, salts and polymer). Thus, the deviations observed between calculated and experimental protein partition are mainly due to some assumptions made in the predictive methodology.
Keywords: Protein recovery; Aqueous two-phase systems; Modelling; Excess gibbs energy; Modified Wilson model; Activity coefficients;

The extraction of lactic acid with sulfur dioxide by Yonghui Shi; Maohong Fan; Ming Xu; Robert C. Brown; J. van Leeuwen (157-160).
This paper studies the reaction between SO2 and calcium lactate, which potentially can be used to recover lactic acid from the anaerobic fermentation broth of an SO2 waste stream. The conversion of given amounts of calcium lactate to lactic acid was evaluated under different reaction temperatures and flow rates of SO2. Analyses of concentrations of the produced lactic acid indicated that the reactions between SO2 and calcium lactate were complete under all experimental conditions.
Keywords: Lactic acid; Calcium lactate; Mixing; Separation; Sulfur dioxide; Waste treatment;

Modeling of the simultaneous hydrolysis–ultrafiltration of whey permeate by a thermostable β-galactosidase from Aspergillus niger by Dimitris G. Hatzinikolaou; Efstathios Katsifas; Diomi Mamma; Amalia D. Karagouni; Paul Christakopoulos; Dimitris Kekos (161-172).
A wild type strain of Aspergillus niger, denoted as BTL, produced elevated levels of β-galactosidase when grown in a low cost medium that contained wheat bran as the sole carbon and energy source. The enzyme was collected, concentrated and partially purified from the culture supernatant. Its kinetic and stability properties were thoroughly examined towards its potential use for the hydrolysis of acid whey permeate lactose. The β-galactosidase of A. niger BTL showed increased pH and thermal stability, with activation energy for the first order deactivation constant equal to 180 kJ/mol at pH 3.5. Lactose hydrolysis by the enzyme was described by Michaelis–Menten kinetics with competitive inhibition only from galactose. An integrated process, concerning the simultaneous hydrolysis–ultrafiltration of whey lactose that incorporated the specific kinetic properties of the β-galactosidase was developed and modeled. The model proved very successful in predicting the behavior of a continuous laboratory hydrolysis–ultrafiltration set up, specifically designed for that purpose. The validated model was finally used in a number of computer simulations in order to investigate the effect of the various process parameters on the overall system performance.
Keywords: β-Galactosidase; Whey; Hydrolysis; Ultrafiltration; Process integration; Kinetic parameters; Modeling;

Modeling and control of nitrite accumulation in a nitrifying biofilm reactor by N. Bernet; O. Sanchez; D. Cesbron; J.-P. Steyer; J.-P. Delgenès (173-183).
Biological ammonium oxidation was carried out in an inverse turbulent bed reactor fed with a synthetic mineral wastewater containing a high ammonium concentration (250 or 500 mg N-NH4 +/L). The effects of dissolved oxygen concentration in the reactor, of ammonium concentration in the feeding and of ammonium loading rate on nitrite accumulation was studied in order to optimize ammonium conversion. A model of the biofilm was proposed to describe the experiments and to predict the effects of some operating parameters on nitrite accumulation. The model could also describe oxygen concentration gradients in the biofilm in steady-state conditions. It was shown that the O2/N-NH4 + ratio in the bulk phase is the main parameter controlling nitrite accumulation. This parameter was thus chosen to control the process using on-line dissolved oxygen and ammonium concentration measurements to act on the air flow-rate. Using O2/N-NH4 + ratio set-points of 0.05 and 0.1, it was possible to oxidize up to 80% of the inflow ammonium into nitrite, which is better than results obtained without on-line control. Such a control clearly favors the activity of ammonium-oxidizing bacteria (AOB) over nitrite-oxidizing bacteria (NOB), therefore the selection pressure exerted on the nitrification ecosystem enhance nitrite accumulation in the process.
Keywords: Biofilms; Biokinetics; Control; Modeling; Diffusion-reaction;