Three-phase Airlift Bioreactor Research Articles

Removal of gaseous tetrahydrofuran via a three-phase airlift bioreactor loaded with immobilized cells of GFP-tagged Pseudomonas oleovorans GDT4

Tetrahydrofuran (THF) is a common highly toxic cyclic aliphatic ether that frequently exists in waste gases. Removal of gaseous THF is a serious issue with important environmental ramifications. A novel three-phase airlift bioreactor (TPAB) loaded with immobilized cells was developed for efficient THF removal from gas streams. An effective THF-degrading transformant, Pseudomonas oleovorans GDT4, which contains the pTn-Mod-OTc-gfp plasmid and was tagged with a green fluorescent protein (GFP), was constructed. Continuous treatment of THF-containing waste gases was succeeded by the GFP-labelled cells immobilized with calcium alginate and activated carbon fiber in the TPAB for 60 days with >90% removal efficiency. The number of fluorescent cells in the beads reached 1.7 × 1011 cells·g−1 of bead on day 10, accounting for 83.3% of the total number of cells. The amount further increased to 3.0 × 1011 cells·g−1 of bead on day 40. However, it decreased to 2.5 × 1011 cells·g−1 of bead with a substantial increase in biomass in the liquid because of cell leakage and hydraulic shock. PCR-DGGE revealed that P. oleovorans was the dominant microorganism throughout the entire operation. The maximum elimination capacity was affected by empty bed residence time (EBRT). The capacity was only 25.9 g m−3·h−1 at EBRT of 80 s, whereas it reached 37.8 g m−3·h−1 at EBRT of 140 s. This work provides an alternative method for full-scale removal of gaseous THF and presents a useful tool for determining the biomass of a specific degrader in immobilized beads.

Simultaneous Diesel and Oxygen Transfer Rate on the Production of an Oil-degrading Consortium in an Airlift Bioreactor: High-dispersed Phase Concentration

Abstract The aim of this study was to simultaneously evaluate diesel transfer rate (DTR) and oxygen transfer rate (OTR) on the production of an oil-degrading consortium in a three-phase airlift bioreactor (ALB) working at high hydrocarbon phase concentration with the purpose of determine whether the oxygen transfer rate is increased or diminished by an increase in the oil-phase concentration. Increase in hydrocarbon concentration allows an increase in DTR and a consequently higher DTR/OTR ratio thus avoiding hydrocarbon mass transfer limitations. This study demonstrates evidence that at high diesel concentrations, the main carbon fate is the production of biosurfactants.

Simultaneous hexadecane and oxygen transfer rate on the production of an oil-degrading consortium in a three-phase airlift bioreactor

The hexadecane (HXD) transfer rate (HTR) and the oxygen transfer rate (OTR) were simultaneously evaluated as a single engineering criterion to enhance the production of an oil-degrading bacterial consortium. In order to accomplish the task, a 10-L three-phase airlift bioreactor (ALB) was used. Oxygen transfer volumetric coefficient (kLaO2) values of 25–49h−1 were found for several superficial gas velocities (Ug 0.15–2.7cms−1). HXD transfer volumetric coefficient (kLaHXD) values of 0.005–0.041h−1 were obtained for the same range of Ug values. OTR and HTR were calculated as the product of kLaO2 or kLaHXD and the respective concentration gradient. HXD transfer parameters were evaluated by using an early reported novel technique. During 14 days culture, using constant Ug values, the ratio of HTR to OTR (HTR/OTR) never reached the stoichiometric ratio (0.25±0.05g HXD (gO2)−1). However, the productivity at the higher assayed constant Ug (2.7cms−1) was as good as 1.02±0.03g SS (Ld)−1. We propose a variable Ug strategy that consumes 33% less energy than a higher constant Ug strategy to achieve the same yield and productivity. In this study, the oil-degrading consortium, able to remediate contaminated soils and water, productivity was successfully enhanced with simultaneous HXD and oxygen transfer considerations.

Dynamic Technique to Determine Hexadecane Transfer Rate from Organic Phase to Aqueous Phase in a Three-Phase Bioreactor

Determination of mass transfer of non-water soluble substrates, as hexadecane (HXD), is an important constraint in three-phase airlift bioreactor. A new simple dynamic technique able to measure the hexadecane transfer rate (HTR) in a three-phase airlift bioreactor (ALB) was studied in this work. The image analyses technique allowed measuring the resulting specific mass transfer area (aHXD). Gas chromatography was used to measure time-dependent transferred HXD and therefore the HXD transfer coefficient (kLHXD). Finally, HTR was calculated by using the equation HTR = kLaHXD•(CHXD* - CHXD) where CHXD* and CHXD are the saturation HXD-aqueous interphase and HXD aqueous phase concentration, respectively. As case study, we successfully applied to the measurement of HTR during a typical ALB microbial consortium culture; values from 0.010 to 0.042 mg HXD (L h)-1 were found. This technique could be used to compare similar simultaneously occurring parameters to assess mass transfer constraints in three-phase systems.

Dynamic Technique to Determine Hexadecane Transfer Rate from Organic Phase to Aqueous Phase in a Three-Phase Bioreactor

Determination of mass transfer of non-water soluble substrates, as hexadecane (HXD), is an important constraint in three-phase airlift bioreactor. A new simple dynamic technique able to measure the hexadecane transfer rate (HTR) in a three-phase airlift bioreactor (ALB) was studied in this work. The image analyses technique allowed measuring the resulting specific mass transfer area (aHXD). Gas chromatography was used to measure time-dependent transferred HXD and therefore the HXD transfer coefficient (kLHXD). Finally, HTR was calculated by using the equation HTR = kLaHXD•(CHXD* - CHXD) where CHXD* and CHXD are the saturation HXD-aqueous interphase and HXD aqueous phase concentration, respectively. As case study, we successfully applied to the measurement of HTR during a typical ALB microbial consortium culture; values from 0.010 to 0.042 mg HXD (L h)-1 were found. This technique could be used to compare similar simultaneously occurring parameters to assess mass transfer constraints in three-phase systems.

Treatment of Acetone Waste Gases Using Slurry-Phase Airlift Embedded with Polyacrylamide-Entrapped Cell Beads

Acetone is the most common chemical used in the Hsinchu Science Park in Taiwan. The three-phase airlift biore-actor was designed to absorb acetone into the 39 L of medium solution and then degraded by 2-L polyacryl-amide (PAA)-entrapped Thiosphaera pantotropha cell beads. The airlift medium was successfully regenerated and circulated for more than 5 months. The elimination capacity of 350-part per million (ppm) acetone at 10 L ∙ min−1 was 258.4 g · m−3hr−1 (160.4 g-C · m−3hr−1) with 100% removal efficiency in Stage II, higher than previously reported biofiltration results. The maximum chemical oxygen demand:nitrogen ratio of 100:2.9 is achieved, and a balanced nutrient state was indicated by the change in redox potential. The pH of the system was maintained at neutral because of the strong buffer agent added to the medium (final buffer intensity, β=1.18 ×10-2 M). The PAA-entrapped cell beads could also provide a good barrier for high salinity gradient environment and the inoculum source to maintain steady operation of the system.

Investigation of biofilm growth and attrition in a three‐phase airlift bioreactor using 35SO42− as a radiolabelled tracer

AbstractThe growth and biomass loss pattern for immobilized cells growing on diatomaceous earth particles in a three‐phase airlift bioreactor (TPALB) is studied using 35S as a radiolabelled tracer. A monoculture of Beneckea natriegens was grown immobilized on support particles in a 3 L TPALB. Sterile conditions were maintained during the experiments, and n‐propanol was used as the sole carbon source. After the system reached steady state, the unlabelled sulfate (SO42−) in the feed tank was substituted by a radioactive grade (35SO42−), and the assimilation of 35S in the immobilized and in the suspended cells was monitored. The results indicated that the growth rate of immobilized biomass was not uniform throughout the biofilm. More specifically, it was concluded that cells growing closer to the external biofilm layer exhibit a higher growth rate, and that biomass loss from the biofilm was through attrition at the outer biofilm surface rather than by sloughing off of whole sections of biofilm. Copyright © 2006 Society of Chemical Industry

Hydrodynamic considerations on optimal design of a three‐phase airlift bioreactor with high solids loading

AbstractThe hydrodynamic study of a three‐phase airlift (TPAL) bioreactor with an enlarged gas–liquid dual separator was carried out. Different lengths and diameters of the draft tube were tested to show how the design of the separator zone affects the hydrodynamic performance of the TPAL reactor. Ca‐alginate beads with entrapped yeast biomass at different loadings (0, 7, 14 and 21% v/v) were used in order to mimic the solid phase of conventional high cell density systems, such as those with cells immobilized on carriers or flocculating cells. Important information on multiphase flow and distribution of gas and solid phases in the internal‐loop airlift reactor (ALR) with high solids loading was obtained, which can be used for suggesting optimal hydrodynamic conditions in a TPAL bioreactor with high solids loading. It is finally suggested that the ALR with a dual separator and a downcomer to riser cross‐sectional area ratio (AD/AR) ranging from 1.2 to 2.0 can be successfully applied to batch/continuous high cell density systems, where the uniform distribution of solid phase, its efficient separation of particles from the liquid phase, and an improved residence time of air bubbles inside the reactor are desirable. Copyright © 2003 Society of Chemical Industry

Continuous Primary Beer Fermentation with Brewing Yeast Immobilized on Spent Grains

This work demonstrated the technological feasibility of the three-phase airlift bioreactor (ALR) with brewing yeast immobilized on spent grains (a brewing by-product) for continuous beer production. The optimum fermentation performance of the one stage immobilized cell bioreactor was achieved at residence times between 18–25 h (dilution rate 0.04–0.055 h−1) and was characterized by an apparent degree of attenuation in the range of 70–80%. The productivity of the system in terms of ethanol concentration in green beer (ca. 4.2%) was satisfactory. Although the diacetyl concentration in the young beer was high (0.32 mg L−1 at D = 0.04 h−1) it is speculated that the level could be reduced by cell growth control, aeration and temperature optimisation. The immobilized yeast fermentation in the ALR was shown to be robust in recovery after process upsets.

Steady state behaviour of three phase air lift bioreactors - an integrated model and experimental verification

Beneckea natriegens growing both in suspension and immobilised on diatomaceous earth (silica) support particles, in a 3 dm three phase air lift bioreactor (TPALB), was employed to demonstrate the relationship between substrate loading rate and immobilised biomass loading at steady state. Sterile conditions were maintained during the experiments, while the hydraulic conditions and the inlet flowrate remained constant. The experiment ran for 12 days, whilst the inlet substrate (n-propanol) concentration was varied both upwards and downwards between 250 and 750 mg dm−3. The bulk liquid substrate concentration and the immobilised biomass loading were found to vary between 6–120 mg dm−3 and 71–159 mg(dry biomass) g−1 (silica), respectively. The experimental results demonstrated that there is a positive relationship between substrate loading and immobilised biomass loading. A mathematical model is proposed to calculate biofilm thickness and bulk liquid substrate concentration (for steady state) using the inlet flowrate and the inlet substrate concentration as input parameters. The model was able to predict both biofilm thickness and immobilised biomass loading for the lower substrate loading rates applied. © 1999 Society of Chemical Industry

Hydrodynamic studies in an airlift reactor with an enlarged degassing zone

The hydrodynamic behaviour of a 60 l three-phase airlift bioreactor, of the concentric draught tube type, with an enlarged degassing zone has been studied. Ca-alginate beads were used as the solid phase. Airflow rate (from 1.9 to 90.2 l/min), solids loading (0% to 40% (v/v)) and solids density (1016 and 1038 kg/m3) were manipulated and their influence on solids and gas holdup, circulation and mixing times and in the interstitial liquid velocity was determined. Riser and downcomer solids holdup was found to decrease with the increase of airflow rate and to increase with solids loading and density. On the contrary, gas holdup in the riser and in the downcomer increased with airflow rate and decreased with solids loading and density. By increasing airflow rate, a decrease in circulation time was observed while the effects of solids loading and density were negligible. Mixing time decreased with airflow rate, increased with solids density, in the studied range, and presented a maximum for solids loading of approximately 20% (v/v).

Comparative Scale-Up and Cost Estimation of a Biological Trickling Filter and a Three-Phase Airlift Bioreactor for the Removal of Methylene Chloride from Polluted Air

Laboratory scale biological trickling filters and three-phase airlift bioreactors have been studied for the elimination of methylene chloride (or dichloromethane) vapors from waste air, and the results used herein for the design of small industrial-scale reactors. The conditions chosen for scale-up were an air flow rate of 100 m3 h-1, a methylene chloride inlet concentration of 2 g m-3, and a target removal of 99.5%. The scale-up procedure, design, and cost analysis are discussed. The full-scale biotrickling filter appears to be the most cost-effective reactor, with global costs of about $62 per 1,000 m3 treated. Treatment in the airlift reactor was estimated to be twice as expensive and catalytic oxidation 5 times as expensive. Biological waste air treatment offers economical alternatives to conventional techniques for waste air treatment.

Specific ATP and specific oxygen uptake rate in immobilized cell aggregates: Experimental results and theoretical analysis using a structured model of immobilized cell growth

In this work the quality and activity of immobilized Beneckea natriegens have been measured using Specific ATP (SATP) [mg (ATP) g(-1) (dry biomass)] and Specific Oxygen Uptake Rate (SOUR) [mg O(2) g(-1) (dry biomass) h(-1)]. The cells were grown in a 3 L Three Phase Air Lift Bioreactor (TPALB) and were immobilized on diatomaceous earth (silica) support particles; sterile conditions were employed during the experiment, with n-propanol as the sole carbon source. Two sets of experiments were performed, one with varying dilution rate and the other with varying inlet substrate concentration. The average SATP and SOUR of the immobilized biomass was 3-4 times lower than the values obtained for suspended Beneckea natriegens growing at its maximum growth rate. The suspended biomass present in the TPALB was generated primarily through attrition from the outer layer of the biofilm, and maintained higher levels of SATP and SOUR than the immobilized biomass. This result indicates that the immobilized biomass quality/activity is higher at the external layer of the biofilm. A structured model in which biomass is divided into two compartments, active and inert, was used to describe the experimental results. This model predicts the biomass quality/activity and substrate concentration distributions in the biofilm. These distributions were integrated to give overall values of SATP and SOUR for the immobilized biomass which compared favorably with experimental data. The primary implication of the results is that the location of immobilized biomass in the biofilm affects its biocatalytic activity, and should be taken into account when modeling immobilized biomass bioreactors. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 660-673, 1997.

Hydrodynamic performance of a three-phase airlift bioreactor with an enlarged degassing zone

The hydrodynamics of biotechnological processes is complex. So far, few studies were made with bioreactors of the airlift type with an enlarged degassing zone.In this work, the influence of solids loading, solids specific gravity and draught tube dimensions on mixing and circulation times and critical air flow rate for an internal loop airlift bioreactor with an enlarged sedimentation/degassing zone is studied.The results indicate that the critical air flow rate as well as the mixing time increase with an increase in solids loading in the bioreactor. Circulation time presents a maximum for a solids load between 5 and 10% (v/v). It is also shown that small variations in solids specific gravity, for values close to that of the liquid, have a significant influence on the critical air flow rate and on the mixing time.An optimal (minimal) value for the circulation time and for the critical air flow rate was obtained for a riser to down comer diameter ratio of 0.46. The minimum mixing time was obtained for a riser to down comer height ratio of 0.80.

Hydrodynamic performance of a three-phase airlift bioreactor with an enlarged degassing zone

Hydrodynamic performance of a three-phase airlift bioreactor with an enlarged degassing zone

Use of ATP to characterize biomass viability in freely suspended and immobilized cell bioreactors

This work describes investigations into the viability of cells growing on 3,4-dichloroaniline (34DCA). Two bioreactors are employed for microbial growth, a continuous stirred tank (CST) bioreactor with a 2-L working volume, and a three-phase air lift (TPAL) bioreactor with a 3-L working volume. Experiments have been performed at several dilution rates between 0.027 and 0.115 h(-1) in the CST bioreactor and between 0.111 and 0.500 h(-1) in the TPAL bioreactor. The specific ATP concentration was calculated at each dilution rate in the suspended biomass in both bioreactors as well as in the immobilized biomass in the TPAL bioreactor. The ATP was extracted from the cells using boiling tris-EDTA buffer (pH 7.75), and the quantity determined using a firefly (bioluminescence) technique. The cultures were inspected under an electron microscope to monitor compositional changes. Results from the CST bioreactor showed that the biomass-specific ATP concentration increases from 0.44 to 1.86 mg ATP g(-1) dry weight (dw) as dilution rate increases from 0.027 to 0.115 h(-1). At this upper dilution rate the cells were washed out. The specific ATP concentration reached a limiting average value of 1.73 mg ATP g(-1) dw, which is assumed to be the quantity of ATP in 100% viable biomass. In the TPAL bioreactor, the ATP level increased with dilution rate in both the immobilized and suspended biomass. The specific ATP concentration in the immobilized biomass increased from approximately 0.051 mg ATP g(-1) dw at dilution rates between 0.111 and 0.200 h(-1) to approximately 0.119 mg ATP g(-1) dw at dilution rates between 0.300 and 0.500 h(-1). This indicates that the immobilized biomass contained a viable cell fraction of around 5%. Based on these results, kinetic data for freely suspended cells should not be applied to the modeling of immobilized cell systems on the assumption that immobilized biomass is 100% viable.