https://hal.archives-ouvertes.fr/hal-01394969/document

Measuring techniques in gas–liquid and gas–liquid–solid reactors

Application of airlift gas-liquid-solid reactors in biotechnology

The culture of coccolithophorid algae is an attractive option for sequestration or recycling of CO2 as they can fix carbon by photosynthesis as well as in calcium carbonate scales known as coccoliths. They also produce high amounts of lipids which have a potential application as a renewable fuel. 

Five species of coccolithophorids (Pleurochrysis carterae, CCMP647, Pleurochrysis sp. CCMP1211, Gephyrocapsa oceanica CS-335/2, Emiliania huxleyi CCMP371, and Emiliania huxleyi CS-369) were screened for their ability to grow at high temperature. All species grew up to 28oC except E. huxleyi CS-369. However, Pleurochrysis sp. CCMP 1211 which was found to clump and can therefore not be recommended for large-scale cultivation. The salinity tolerance of these species was also examined. 

Growth of P. carterae, G. oceanica, and E. huxleyi in laboratory scale closed photobioreactors (plate, carboy, airlift, and tubular photobioreactors) showed the plate photobioreactor to be the best closed cultivation system. The highest productivities were achieved by P. carterae in the plate photobioreactor and were 0.54 g.L-1.d-1, 0.12 g.L-1.d-1, 0.06 g.L-1.d-1 for total dry weight, lipid and CaCO3 respectively. The growth of P. carterae and E. huxleyi was also examined in an outdoor raceway pond. The E. huxleyi culture was easily contaminated resulting in the loss of the culture in less than three weeks, but P. carterae grew well over a period of 13 months. The overall total dry weight productivity of P. carterae was 0.19 g.L-1.d-1 with lipid and CaCO3 contents of up to 33% and 10% of dry weight respectively. There was little protozoan and bacterial contamination. Medium pH increased to pH 11 during the day and was found to be a reliable variable for maintaining the health of the culture. A maximum pH achieved during the day of less than pH 8.5 indicated the imminent collapse of the culture. Heavy rain and low temperature were the main reasons for culture loss in mid winter, whereas high temperature during summer favoured P. carterae growth. A comparison of the growth of P. carterae and Dunaliella salina MUR8 in the raceway ponds showed no significant differences between these two species with regard to areal total dry weight productivity and lipid content. 

The effects of several limiting factors were also examined. A reduction in medium pH resulting from CO2 addition inhibited the growth of E. huxleyi in the plate photobioreactor, whereas P. carterae growth and productivities increased in the pH range of pH 7.7 to 8.0 in the plate photobioreactor and pH 9.1 to 9.6 in the outdoor raceway pond. The best operational pond depth for outdoor raceway culture of P. carterae was between 16 cm and 21 cm. Early morning temperatures, especially during the winter, highly affected the growth of P. carterae in the raceway pond, whereas artificially increasing the medium temperature improved the health of the culture but resulted in little increase in productivity. Photosynthesis of P. carterae was found to be highly inhibited by high oxygen concentration in the medium irrespective of temperature or irradiance. 

An economic model of P. carterae in a 63 ha raceway plant resulted in a cost for the biomass of between 7.35 Aus$.Kg-1 and 14.17 Aus$.Kg-1 depending on the harvesting method used.

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The culture of coccolithophorid algae for carbon dioxide bioremediation

Protein enrichment of potato processing waste through yeast fermentation

Effects of antifoam and scale-up on operation of bioreactors were experimentally investigated using two external loop airlift reactors. The volumes of the small and large reactors were 55 and 700 l, respectively. The addition of minute quantities of silicone-based antifoam lead to reduction in both hydrodynamic and mass transfer characteristics of all reactors. New simple empirical correlations were found for the reactors design parameters: gas hold-up, liquid circulation velocity and volumetric mass transfer coefficient. No discernible relation of antifoam concentration with scale-up of airlift reactors was found for all the design parameters.

Effects of antifoam and scale-up on operation of bioreactors

Bakers' yeast cultivation on by-products and wastes of potato and wheat starch production on a laboratory and pilot-plant scale

Investigations were carried out in a 9 m high, 4 m(3) volume, pilot plant airlift tower loop bioreactor with a draft tube. The reactor was characterized by measuring residence time distributions of the gas phase using pseudostochastic tracer signals and a mass spectrometer and by evaluating the mixing in the liquid phase with single-pulse tracer inputs. The local gas holdup and the bubble size (piercing length) were measured with two-channel electrical conductivity probes. The mean residence times and the intensities of the axial mixing in the riser and downcomer and the circulation times of the phases as well as the fraction of the recirculated gas phase were evaluated. The gas holdup in the riser is nearly uniform along the reactor. In the downcomer, it diminishes from top to bottom. The liquid phase dispersion coefficients, D(L), are smaller than those measured in the corresponding bubble columns. In the pilot plant with tap water the following relationship was found: D(Lr) = cw(SG) (n); with c = 203.4; n = 0.5;D(Lr)(cm(2) s(-1);) and W(SG)(cm s(-1)) where D(Lr) is the longitudinal dispersion coefficient in the riser and W(SG) is the superficial gas velocity. The gas phase dispersion coefficients in the riser of the pilot plant, D(Gr), are also enlarged with increasing superficial gas velocity, W(SG), however, no simple relationship exists. Parameter D(Gr) is the highest in the presence of antifoam agents, intermediate in tap water, and the smallest in ethanol solution.

Characterization of a pilot plant airlift tower loop bioreactor. I, Evaluation of the phase properties with model media

The local properties of the dispersed gas phase (gasholdup, bubble diamater, and bubble velocity) were measured and evaluated at different positions in the riser and downcomer of a pilot plant reactor and, for comparison, in a laboratory reactor. These were described in Parts I and II of this series of articles during yeast cultivation and with model media. In the riser of the pilot plant reactor, the local gas holdup and bubble velocities varied only slightly in axial direction. The gas holdup increased considerably, while the bubble velocity increased only slightly with aeration rate. The bubble size diminished with increasing distance from the aerator in the riser, since the primary bubble size was larger than the equilibrium bubble size. In the downcomer, the mean bubble size was smaller than in the riser. The mean bubble size varied only slightly, the bubble velocity was accelerated, and the gas holdup decreased from top to bottom in the downcomer. In pilot plant at constant aeration rate, the properties of the dispersed phase were nearly constant during the batch cultivation, i.e., they depended only slightly on the cell concentration. In the laboratory reactor, the mean bubble sizes were much larger than in the pilot plant reactor. In the laboratory reactor, the bubble velocities in the riser and downcomer increased, and the mean gas holdup and bubble diameter in the downcomer remained constant as the aeration rate was increased.

Characterization of a pilot plant airlift tower loop reactor: III. Evaluation of local properties of the dispersed gas phase during yeast cultivation and in model media

Saccharomyces cerevisiae was cultivated in a 4-m 3 pilot plant airlift tower loop reactor with a draft tube in batch and continuous operations and for comparison in a laboratory airlift tower loop reactor of 0.08 m 3 volume. The reactors were characterized during and after the cultivation by measuring the distributions of the residence times of the gas phase with pseudostochastic tracer signals and mass spectrometer and by evaluating the mixing in the liquid phase with a pulse-shaped volatile tracer signal and mass spectrometer as a detector. The mean residence times and the intensities of the axial mixing in the riser and downcomer, the circulation times of the gas phase, and the fraction of the recirculated gas phase were evaluated and compared.

M. Seekamp

Papers

Bakers' yeast cultivation on by-products and wastes of potato and wheat starch production on a laboratory and pilot-plant scale

Characterization of a pilot plant airlift tower loop bioreactor. I, Evaluation of the phase properties with model media

Characterization of a pilot plant airlift tower loop reactor: III. Evaluation of local properties of the dispersed gas phase during yeast cultivation and in model media

Characterization of a pilot plant airlift tower loop bioreactor: II. Evaluation of global mixing properties of the gas phase during yeast cultivation.