Alexandra Cristina Blaga

Distribution of Mixing Efficiency in a Split-Cylinder Gas-Lift Bioreactor with Immobilized Yarrowia Lipolytica Cells Used for Olive Oil Mill Wastewater Treatment

The distribution of mixing in a split-cylinder gas-lift bioreactor has been investigated for suspensions of immobilized Yarrowia lipolytica cells with particles diameter varying between 3 and 4.2 mm. The results indicated important variation of mixing time on the height of riser or downcomer, as well as different behavior of suspensions flows in these two regions. Therefore, for the riser, the mixing efficiency increases from its bottom to the top, allowing the biocatalyst particles with intermediate size (3.6-mm diameter) reaching the most intense circulation of suspension. The analysis of the suspension flow in the downcomer region revealed that the intermediate positions are associated with the highest mixing mainly for the largest immobilized yeast particles (4.2-mm diameter). In both cases, the influence of aeration on turbulence extent is positive only for air superficial velocity up to 1.05–1.35 × 10−3 m/s, the magnitude of this effect being correlated with the biocatalyst size and position on the riser or downcomer. By means of the experimental data, mathematical correlations for mixing time have been proposed for each circulation region, taking into consideration both the operational parameters and the distance from the bioreactor bottom. These equations offer a good concordance with the experiment, the average deviation being of 5.82% for the riser and 6.06% for the downcomer zone.

Effect of bed configuration of immobilized biocatalysts on penicillin G hydrolysis efficiency

The external and internal mass transfer of Penicillin G in the process of its enzymatic hydrolysis to 6-Aminopenicillanic acid under competitive and non-competitive inhibitions have been comparatively analyzed for a bioreactor with mobile bed vs. a stationary basket bioreactor, both with Penicillin amidase immobilized in Eupergit C. The Penicillin G mass transfer and hydrolysis enzymatic rates have been analyzed by means of the ratios’ values between the oxygen mass transfer coefficients, effectiveness factors, external mass flows and Penicillin G concentrations at the biocatalyst particle surface for the considered bioreactors. The results indicated that the bioreactor with mobile bed is more efficient especially for biocatalyst particles with diameter under 1.5 mm. For larger particles the performances of the two bioreactors become similar. Moreover, taking into consideration the external mass flow of Penicillin G and the number of enzymatic hydrolysis cycles, the basket bioreactor is recommended. The mathematical equations proposed are in good concordance with the experimental results, the average deviations varying from ±4.11% for the bioreactor with mobile bed of immobilized Penicillin amidase to ±5.03% for the basket bioreactor.

Diffusional effects on anaerobic biodegradation of pyridine in a stationary basket bioreactor with immobilized Bacillus spp. cells

ABSTRACT The effects of external and internal diffusions of pyridine on its biodegradation rate in a bioreactor with a stationary basket bed of immobilized Bacillus spp. cells have been investigated for various biocatalyst diameters and thicknesses of the basket bed, considering the adapted Haldane kinetic model for substrate inhibition. Due to the very low values of pyridine mass flow inside the biocatalyst particles, the ‘biological inactive region’ appeared mainly near the particles’ centre. This region is extended up to 38.5% from the overall volume of each studied size of the biocatalysts, increasing at higher biocatalyst size and basket bed width. Compared to the system containing free Bacillus spp. cells, the basket configuration of packed bed led to the reduction of biodegradation rate up to 82 times, similar to the mobile bed or column packed bed. The cumulated analysis of the influences of the studied factors allowed concluding that the optimum diameter of biocatalysts is 3 mm.

ENGINEERING ASPECTS OF PENICILLIN G TRANSFER AND CONVERSION TO 6-AMINOPENICILLANIC ACID IN A BIOREACTOR WITH A MOBILE BED OF IMMOBILIZED PENICILLIN AMIDASE

This article presents studies on the external and internal mass transfers of penicillin G for 6-aminopenicillanic acid enzymatic production using a bioreactor with a stirred bed of immobilized penicillin amidase. By means of the substrate mass balance for a single particle of biocatalyst and considering the kinetic model adapted for competitive and noncompetitive inhibitions, specific mathematical models were developed for describing the profiles of penicillin G concentration in the outer and inner regions of biocatalyst and for estimating its mass flows in the liquid boundary layer surrounding the particle and inside the particle. The values of the mass flows are significantly influenced by the internal diffusion velocity and rate of the enzymatic conversion of substrate. These cumulated influences led to the appearance of an enzymatic inactive region near the particle center, its magnitude varying from 0 to 9.2% of the overall volume of particles.