Hydrodynamic and mass transfer characteristics of three-phase gaslift bioreactor systems

Advances in airlift reactors: modified design and optimization of operation conditions

Airlift reactor (ALR) is a promising multiphase reactor for industrial applications. Abundant reports about modifications of the conventional ALR and optimization of their operation conditions for the purpose of performance enhancement have been accumulated in literatures, demanding a review paper to summarize the reactor design modifications and operation condition optimization of the ALR. In this review, the published research findings and results have been summarized. The basic concepts including the ALRs’ conventional design, classification, principles of operation, and characteristic parameters have been analyzed and systematically organized. The updated advances in the ALR design modifications have been reported. In particular, the concepts of the “groveled ALR” solving the scaling up problem in wastewater treatment, large-scale application, and the ALR with the cross-shaped geometry modifier stabilizing and strengthening the reactor were considered. Also, new operation modes and optimal conditions for enhancing the performance of the ALR have also been summed up. Except for conventional gas-driven methods, new driven methods for the ALR, such as mixture emission of the gas and the liquid and gas-inducing impeller, have been introduced. Optimization of operation conditions for the ALR includes varying position of the gas spargers, utilizing elevated pressure reactor, and exploring the impact of operation parameters, such as superficial gas velocity, static liquid level, and fluid properties. Comparisons between conventional ALRs and the modified systems are carried out paying attention to analogies, similarities, and differences. Most of the documented research results are obtained for various reactor designs at a laboratory scale; studies at pilot and full scale are still insufficient, which indicates that universal scale up design rules permitting the ALR design with a high confidence are required.

Macromixing hydrodynamic study in draft-tube airlift reactors using electrical resistance tomography

The present study summarizes results of mixing characteristics in a draft tube airlift bioreactor using ERT. This technique offers the possibility for noninvasive and nonintrusive visualization of flow fields in the bioreactor and has rarely been utilized previously to analyze operating parameters and mixing characteristics in this type of bioreactors. Several operating parameters and geometric characteristics were examined. In general, results showed that the increase in superficial gas velocity corresponds to an increase in energy applied and thus, to a decrease in mixing time. This generally corresponded to an increase in liquid circulation velocity and shear rate values. Bottom clearances and draft tube diameters affected flow resistance and frictional losses. The influence of sparger configurations on mixing time and liquid circulation velocity was significant due to their effect on gas distribution. However, the effect of sparger configuration on shear rate was not significant, with 20% reduction in shear rates using the cross-shaped sparger. Fluid viscosity showed a marked influence on both mixing times and circulation velocity especially in the coalescing media of sugar and xanthan gum (XG) solutions. Results from this work will help to develop a clear pattern for operation and mixing that can help to improve several industrial processes, especially the ones related to emerging fields of technology such as the biotechnology industry.

Haematococcus pluvialis cultivation in split-cylinder internal-loop airlift photobioreactor under aeration conditions avoiding cell damage

The effects of superficial gas velocity in the riser (U(Gr)) and gas entrance velocity (v) on the growth of Haematococcus pluvialis cultivated in a split-cylinder internal-loop airlift photobioreactor were investigated. Cell growth decreased when U(Gr) and v were increased above 12 mm s(-1) and 22.8 m s(-1), respectively. The maximum cell density of H. pluvialis was 110 x 10(4) vegetative cells ml(-1) and the chlorophyll-a titer was 7 mg l(-1). The cell damage in the photobioreactor was greater when v was increased by an increase in U(Gr) rather than by a decrease in sparger internal diameter. The overall volumetric mass transfer coefficient (k(L)a) of the photobioreactor was measured at the same U(Gr) (6-24 mm s(-1)) and v (12-80 m s(-1)). The k(L)a values reached in the airlift photobioreactor were between 10 h(-1) and 32 h(-1).