Mass Transfer and Bioremediation of Naphthalene and Methyl Naphthalenes in Baffled and Bead Mill Bioreactors

Mass transfer and bioremediation of naphthalene, 2‐methylnaphthalene and 1,5‐dimethylnaphthalene have been studied in a rotating bioreactor modified with the addition of baffles and beads. Mass transfer rates of these low solubility organic particles dissolving in water (based on the working volume of the bioreactor) were highest in the bioreactor that combined beads and baffles, with the overall mass transfer coefficient (K_La) reaching up to 25 h^?1. Based on its capacity to hold the largest volume of polluted media, the simple baffled bioreactor was considered to be the optimum roller bioreactor design. Using Pseudomonas putida, the bioremediation rate of naphthalene reached 61 mg/l‐h in this vessel and using mixed substrates, the bioremediation rate of 2‐methylnaphthalene reached 30 mg/l‐h. The dissolution rates for hydrophobic particles into the culture media during the bioremediation process were up to four times higher compared to mass transfer rates into abiotic controls, which was likely due to the production of biosurfactants by P. putida.     

Bio‐oxidation of ferrous ions by Acidithioobacillus ferrooxidans in a monolithic bioreactor

BACKGROUND: The bio‐oxidation of ferrous iron is a potential industrial process in the regeneration of ferric iron and the removal of H₂S in combustible gases. Bio‐oxidation of ferrous iron may be an alternative method of producing ferric sulfate, which is a reagent used for removal of H₂S from biogas, tail gas and in the pulp and paper industry. For practical use of this process, this study evaluated the optimal pH and initial ferric concentration. pH control looks like a key factor as it acts both on growth rate and on solubility of materials in the system. RESULTS: Process variables such as pH and amount of initial ferrous ions on oxidation by A. ferrooxidans and the effects of process variables dilution rate, initial concentrations of ferrous on oxidation of ferrous sulfate in the packed bed bioreactor were investigated. The optimum range of pH for the maximum growth of cells and effective bio‐oxidation of ferrous sulfate varied from 1.4 to 1.8. The maximum bio‐oxidation rate achieved was 0.3 g L^?1 h^?1 in a culture initially containing 19.5 g L^?1 Fe²⁺ in the batch system. A maximum Fe²⁺ oxidation rate of 6.7 g L^?1 h^?1 was achieved at the dilution rate of 2 h^?1, while no obvious precipitate was detected in the bioreactor. All experiments were carried out in shake flasks at 30 °C. CONCLUSION: The monolithic particles investigated in this study were found to be very suitable material for A. ferrooxidans immobilization for ferrous oxidation mainly because of its advantages over other commonly used substrates. In the monolithic bioreactor, the bio‐oxidation rate was 6.7 g L^?1 h^?1 and 7 g L^?1 h^?1 for 3.5 g L^?1 and 6 g L^?1 of initial ferrous concentration, respectively. For higher initial concentrations 16 g L^?1 and 21.3 g L^?1, bio‐oxidation rate were 0.9 g L^?1 h^?1 and 0.55 g L^?1 h^?1, respectively. Copyright © 2008 Society of Chemical Industry     

Profiles of xylose reductase,xylitol dehydrogenase and xylitol production under different oxygen transfer volumetric coefficient values

BACKGROUND: Xylitol is a sugar alcohol (polyalcohol) with many interesting properties for pharmaceutical and food products. It is currently produced by a chemical process, which has some disadvantages such as high energy requirement. Therefore microbiological production of xylitol has been studied as an alternative, but its viability is dependent on optimisation of the fermentation variables. Among these, aeration is fundamental, because xylitol is produced only under adequate oxygen availability. In most experiments with xylitol‐producing yeasts, low oxygen transfer volumetric coefficient (K_La) values are used to maintain microaerobic conditions. However, in the present study the use of relatively high K_La values resulted in high xylitol production. The effect of aeration was also evaluated via the profiles of xylose reductase (XR) and xylitol dehydrogenase (XD) activities during the experiments. RESULTS: The highest XR specific activity (1.45 ± 0.21 U mg_protein^?1) was achieved during the experiment with the lowest K_La value (12 h^?1), while the highest XD specific activity (0.19 ± 0.03 U mg_protein^?1) was observed with a K_La value of 25 h^?1. Xylitol production was enhanced when K_La was increased from 12 to 50 h^?1, which resulted in the best condition observed, corresponding to a xylitol volumetric productivity of 1.50 ± 0.08 g_xylitol L^?1 h^?1 and an efficiency of 71 ± 6.0%. CONCLUSION: The results showed that the enzyme activities during xylitol bioproduction depend greatly on the initial K_La value (oxygen availability). This finding supplies important information for further studies in molecular biology and genetic engineering aimed at improving xylitol bioproduction. Copyright © 2008 Society of Chemical Industry     

D‐arabitol production from lactose by Kluyveromyces lactis at different aerobic conditions

BACKGROUND: The pentitol D‐arabitol has been produced from D‐glucose utilizing osmophilic yeast strains, however, there are remarkably few reports available on the production of D‐arabitol from lactose. Previous studies in the laboratory have shown that the osmophilic yeast Kluyveromyces lactis NBRC 1903 can convert lactose to extracellular D‐arabitol without extracellular accumulation of D‐glucose or D‐galactose. The present study was undertaken to determine the participation of aeration on the D‐arabitol synthesis in K. lactis NBRC 1903. RESULTS: The highest D‐arabitol concentration of 91.7 mmol L^?1 was achieved after 120 h cultivation in medium containing 555 mmol L^?1 of lactose with initial volumetric liquid‐phase mass transfer coefficient of oxygen (k_La)₀ of 85.5 h^?1. The fractional yield of D‐arabitol was affected by not only aeration but also growth phase. The highest fractional yield of D‐arabitol in terms of lactose consumption was 0.255 that was obtained at stationary phase with (k_La)₀ of 85.5 h^?1. CONCLUSION: It was found that oxygen supply is a key factor in the production of D‐arabitol. Patterns of metabolism were classified according to the level of oxygen supply and the growth phase. Copyright © 2010 Society of Chemical Industry     

Effect of surfactants and biomass on the gas/liquid mass transfer in an aqueous‐silicone oil two‐phase partitioning bioreactor using Rhodococcus erythropolis T902.1 to remove VOCs from gaseous effluents

BACKGROUND: The two‐phase partitioning bioreactor (TPPB) has become a new strategy for waste gas treatment. However, the impact of biomass and surfactants on gas/liquid (G/L) mass transfer needs to be better evaluated because the effects on the mass transfer coefficient K_L and the interfacial area a, respectively, remains misunderstood. RESULTS: This study showed that, first, the surfactant extract produced by Rhodococcus erythropolis reduced the surface hydrophobicity of the biomass. Secondly, an optimal concentration appeared to exist for both components, respectively 0.5 g L^?1 and 0.7 g L^?1 for biomass (B) and surfactant extract (SE) when the global mass transfer coefficient (K_La) of oxygen was measured in a silicone oil/water TPPB. However, the combination of B and SE was found to induce a negative synergism. In particular, SE improved the interfacial area a by increasing the bubble diameter, while B reduced it as soon as a concentration of 1 g L^?1 was exceeded. In contrast, the SE acted negatively on the K_L, while B improved it overall. CONCLUSION: Better consideration is needed of the effect of biotic components in order to understand the phenomenon of G/L mass transfer in a TPPB. The behaviour of biomass growth and surfactants may strongly influence the mathematical models proposed in the literature. Copyright © 2009 Society of Chemical Industry     

Mass transfer in external-loop airlift bioreactors using static mixers

The influence of static mixers on the overall gas-liquid volumetric mass transfer coefficient (K_La_L) was examined in an external-loop type airlift bioreactor (approximately 15 L volume, 1.8 m static liquid height, A_r/A_d = 0.444). The study was conducted with aqueous salt solution (0.15 kmol ? m^?3 NaCl) and with pseudoplastic solutions of carboxymethyl cellulose (0.2 ? 0.6 wt./vol. % (g/100 mL) CMC). Over a broad range of power law parameters K (10^?3 ? 10 Pa ? sⁿ) and n (0.5 ? 1.0), the presence of static mixers in the riser was found to enhance the K_La_L relative to mixer-free mode of operation. The extent of increase in K_La_L depended on the fluid “thickness”, K: the higher the K, the greater the K_La_L intensification due to static mixers. For otherwise identical conditions, the presence of static mixers improved K_La_L by 30-500%, depending on the fluid. The boost in K_La_L was associated with increased gas holdup and gas-liquid interfacial area, which arose due to bubble breakup accomplished by the static mixing elements. Potential advantages of static mixers in upgrading the performance of oxygen-limited fermentations were pointed out.     

Intensification of the biocatalytic oxidation of phenol with the use of activators of interface oxygen transfer

The transport of oxygen from the gas to the aqueous phase determines the rate of the biocatalytic oxidation of phenol. In this work, activators of the interphase transfer of O₂ are used to intensify the process, thus raising considerably the rate of gas entering the reaction space without additional power consumption, in contrast to the widely used methods of mixing and bubbling. We present the results from studies of the effect a number of substances on the value of K _L a at various mixing speeds of 100 to 1200 rpm. The solid-liquid phase and its activators are compared in terms of effectiveness. The maximum K _L a increase under different hydrodynamic conditions was achieved for activated carbon (3.7 times), aerosol (1.5 times), n-dodecane (3.1 times). These results are explained by a shuttle mechanism of O₂ phase transfer. It is shown that when K _L a is increased from 2.8 to 18.5 h^T-1, the biocatalytic oxidation of phenol is accelerated by a factor of 2.4. Using activated carbon as an activator of O₂ phase transfer allows us to increase the rate of the biocatalytic oxidation of phenol by ∼20%.     

Gas transfer in an external loop bioreactor with built-in ultrafiltration

The SGI Ultrafermenter is an external loop bioreactor with circulation through an ultrafiltration module allowing removal of medium and soluble products during fermentation. The contents are continually circulated during operation and the vessel is also equipped with a stirring turbine. The interaction of these two mixing agents on gas transfer was investigated. Both mechanisms produced similar increments in K_La over their working ranges, with values from approximately 0–700 h^?1 at 200 dm³ h^?1 airflow. The effects of these two mechanisms on K_La were approximately additive at low values but the combined mixing produced a maximum K_La value also in the region of 700 h^?1. The power-draw of mixing using the two agents was calculated and stirring was found to be 10–20 times more efficient than circulation.     

Hydrodynamic behaviour and oxygen transfer rate in a pilot plant fermenter. I. Influence of viscosity

The effects of varying impeller speed, aeration rate and viscosity on mixing time, power consumption and oxygen transfer rate were studied in the pilot plant fermenter. The rheological behaviour of erythromycin fermentation broth was simulated by colloidal starch solutions at apparent viscosities of 0.02–0.20 Pa/s. The volumetric oxygen transfer rate coefficient was determined by the sulphite and static method. The experimental results showed that at low viscosities, up to of 0.02 Pa/s, the suitable range of impeller speed is 250–300 min^?1 at aeration rate 0.6–0.8 VVM from the point of view of power input (2.6–2.8 kW/m³) and sufficient coefficient K_La (160–200 h^?1). At viscosities higher than 0.02 Pa/s (with pseudoplastical character) the suitable range of impeller speed is 300–350 min^?1 at the same aeration rate. Then the power input for mixing is 3.0–3.5 kW/m³ and the coefficient K_La ～ 50 h^?1.     

Improved mass transfer and biodegradation rates of naphthalene particles using a novel bead mill bioreactor

One of the main challenges in the treatment of polycyclic aromatic hydrocarbons (PAHs) in controlled bioreactors is the hydrophobicity and low solubility of these compounds in the aqueous phase, resulting in appreciable mass transfer limitations within the bioreactor. To address this challenge, we have developed a modified roller bioreactor (Bead Mill Bioreactor) in which inert particles are used to improve mass transfer from the solid phase to the aqueous phase. Experimental results with naphthalene as a model PAH and Pseudomonas putida as a candidate bacterium indicate that both the mass transfer rate from the solid phase to liquid phase and the biodegradation rate in the Bead Mill Bioreactor (BMB) were significantly higher than those in a conventional roller bioreactor (20‐fold and 5.5‐fold, respectively). The enhancement of mass transfer was dependent on the type, size and volumetric loading of the inert particles, as well as concentration of particulate naphthalene. The highest mass transfer coefficient (k_La = 2.1 h^?1) was achieved with 3 mm glass beads at a volumetric loading of 50% (particle volume/working volume) with 10 000 mg dm^?3 particulate naphthalene. The maximum biodegradation rate of naphthalene attained in the bead mill bioreactor (59.2 mg dm^?3 h^?1 based on the working volume and 118.4 mg dm^?3 h^?1 based on the liquid volume) surpasses most other rates published in the literature and is equivalent to values reported for more complex bioreaction systems. The bead mill bioreactor developed in the present work not only enjoys a simple design but shows excellent performance for treatment of PAHs suspended in an aqueous phase. This fundamental information will be of significant value for future studies involving soil‐bound PAHs. Copyright © 2005 Society of Chemical Industry     

Optimized Process and Bioreactor Characterization

The mass transfer coefficient (k_L)and the value of the interfacial area (a) is used to characterize bioreactor systems for their oxygen transfer capability. The k_La value and the mixing time are amongst the most important performance indicators for bioreactors. Their calculation and modeling is extremely complex in highly aerated systems. This paper describes a new methodology for measuring the k_La value to accurately determine the coefficient. The valuable insights obtained allow for improved bioreactor characterization, thus, making it easier to meet regulatory requirements. Furthermore, examples outlining the benefits in the practical application of the new methodology are presented.     

Oxygen transfer and uptake in Streptomyces coelicolor A3(2) culture in a batch bioreactor

This paper provides quantitative information on oxygen transfer as well as the kinetic and metabolic parameters related to oxygen uptake in Streptomyces coelicolor A3(2) cultured in a 20 dm³ computer controlled bioreactor using both defined and complex media. It is evident from the literature that production of antibiotics is strongly affected by the dissolved oxygen concentration. Many processes of antibiotic fermentations have been developed to the point at which the microbial oxygen demand exceeds the oxygen transfer capability of the existing fermentation facilities. As a consequence, the oxygen transfer rate has become the rate limiting factor in such processes. It is necessary to know the oxygen kinetic and metabolic parameters of an aerobic fermentation for a successful scale-up and operational control of the process. In the literature, information concerning the oxygen uptake kinetics of the Streptomyces cultures is scarce despite their industrial importance. This paper, therefore, provides useful quantitative information on oxygen transfer and uptake rates in S. coelicolor cultures. In the defined medium, the total oxygen uptake rates were in the range of 5–6 mmol O₂ dm⁻³ h⁻¹ throughout the active growth phase, the maximum specific oxygen uptake rate was 7·44 mmol O₂ g cell⁻¹ h⁻¹, the specific oxygen maintenance demand was 1·88 mmol O₂ g cell⁻¹ h⁻¹, and the k_La values were in the range of 40–100 h⁻¹. In the complex medium, however, the k_La values varied in the range of 18–70 h⁻¹. © 1998 Society of Chemical Industry     

Wood Pulp as Model Fluid to Mimic the Oxygen Mass Transfer in Aspergillus Niger Fermentation

To characterize the oxygen mass transfer in a fermentation system and to study the efficiency of mixing devices, model fluids are often used so that experimental conditions can be better controlled. In this study, wood pulp suspensions were used in an attempt to mimic the rheological properties of fermentation broths of Aspergillus niger. Two different types of bioreactor were used: a reciprocating plate bioreactor and a stirred (Rushton) bioreactor. The oxygen mass transfer coefficient (K_La) was measured for various mixing intensities, airflow rates and wood pulp concentrations, and a correlation of K_La as a function of the power input per unit volume and the superficial gas velocity was derived for each bioreactor and each pulp concentration. K_La was found to increase with agitation and air flow rate, and was adversely affected by an increase in pulp concentration in the case of the reciprocating plate bioreactor.     

Batch production of L(+) lactic acid from whey by Lactobacillus casei (NRRL B‐441)

The effects of temperature, pH, and medium composition on lactic acid production by Lactobacillus casei were investigated. The highest lactic acid productivity values were obtained at 37 °C and pH 5.5. The productivity was 1.87 g dm^?3 h^?1 at 37 °C in shake flasks. In the fermenter, a productivity of 3.97 g dm^?3 h^?1 was obtained at pH 5.5. The most appropriate yeast extract concentration was 5.0 g dm^?3. Whey yielded a higher productivity value than the analytical lactose and glucose. Initial whey lactose concentration did not affect lactic acid productivity. MnSO₄ ·H₂O was necessary for lactic acid production by L casei from whey. Product yields were approximately 0.93 g lactic acid g lactose^?1. Copyright © 2004 Society of Chemical Industry     

The effects of emulsified polydimethylsiloxane FG‐10 on the oxygen transfer coefficient (kLa) and lipase production by Staphylococcus warneri EX17

BACKGROUND: In this study the effects of the addition of emulsified polydimethylsiloxane (PMDS) FG‐10 on the oxygen transfer coefficient (k_La) of submerged cultures of Staphylococcus warneri EX17 and its lipase production is described. FG‐10 is an emulsified silicone capable of dissolving 50 times more oxygen than water. The combined effects of FG‐10 concentration and different conditions of agitation were optimized in bioreactors using statistical design tools, and the cultures were run using raw glycerol from biodiesel synthesis as the sole carbon source. RESULTS: The optimal conditions found to improve lipase production were FG‐10 concentration of 11.2% (v/v) and speed agitation of 527 rpm, respectively, producing around 861 U L^?1 of lipolytic activity, a maximal cell concentration of 8.4 g L^?1, and a k_La of 99 h^?1, values that are approximately 3 times higher than cultures without FG‐10. CONCLUSIONS: This is the first report in the literature on the use of this class of chemicals as oxygen carriers in microbial cultures and its effect on k_La and lipase production, demonstrating the potential use of FG‐10 in microbial cultures. Copyright © 2012 Society of Chemical Industry     

Mass transfer and deodorization efficiency in a countercurrent spray tower for low superficial gas velocities

The aim of this study was to characterize mass transfer and deodorization efficiency in a countercurrent spray tower for low superficial gas velocities. The influence of operating parameters (U_G = 0.005 to 0.025 m s^?1, U_L = 6.1 × 10^?5 to 2.4 × 10^?4 m s^?1) on the liquid retention (ε_L), the drop diameter (d_g), the interfacial area (a) and the overall liquid and gas phase mass transfer coefficients (K_La, K_Ga) were estimated. The spray efficiency of some malodorous compounds was also estimated. A negative influence of the superficial gas velocity was demonstrated, during the spraying of water or chemical neutralizing scrubbing solutions. There was also an increase with the liquid flow rate. Abatements obtained were very good with respect to ammonia (>90%), and acceptable for the other compounds.     

Mass Transfer of Ozone Using a Microporous Diffuser Reactor System

An ozone reactor was constructed using a tubular gas diffuser made of microporous stainless steel to significantly reduce gas bubble size and increase overall mass transfer area. Overall mass transfer coefficient, K_La [s ^?1], was correlated with gas (G) and liquid (L) flow rates using K_La = AL^αG^β , with A = 3.96 × 10 ⁸ [s^?1], α = 1.53, and β = 0.40, with L and G in [m ³s^?1]. The reactor is essentially plug flow at high G or L. This system achieves one of the highest ozone mass transfer rates observed in the literature.     

Yeast fermentation in a cocurrent downflow contacting reactor (CDCR)

The growth kinetics and mass transfer characteristics of Saccharomyces cerevisiae in a cocurrent downflow contacting reactor (CDCR) were studied for various glucose concentrations at constant air and liquid flow rates. Increasing glucose concentration increased the biomass concentration thus resulting in an increase in the volumetric oxygen uptake rate. The volumetric mass transfer coefficient, k_La, however, decreased with increasing glucose concentration. It was observed that the growth of S cerevisiae in the CDCR would fit the classical Monod kinetics and the maximum specific growth rate was determined to be 0.545 h⁻¹. © 2000 Society of Chemical Industry     

Continuous production of biosurfactant with foam fractionation

A glucose‐limited chemostat was used to determine the growth parameters of BBK006 for continuous production of the biosurfactant surfactin. The continuous cultivation exhibited low maintenance metabolism (m = 0.39 mmol_glucose g_bacteria^?1 h^?1) and high molar growth yield ( g_bacteria mol_glucose^?1). It was found that the surfactin production rate in continuous culture was not only a function of dilution rate but also varied with the initial concentration of glucose in the feed. A high steady state concentration of surfactin (18 mg L^?1) was maintained in the culture at a dilution rate of 0.2 h^?1 when glucose concentration in the feed was 0.25 g L^?1. This is the first demonstration of continuous surfactin production and recovery using glucose as a carbon source. The production of surfactin is known to be related to the age of the microorganisms and a simple mathematical model has been constructed to show how the age‐related production can be quantified. Copyright © 2006 Society of Chemical Industry     

Biodegradation of phenol-polluted air using an external loop airlift bioreactor

Biological air treatment methods are an alternative to conventional treatment methods such as activated carbon adsorption and chemical scrubbing. An external loop airlift bioreactor has been utilized to treat phenol-contaminated air using Pseudomonas putida. Saturated air was found to be cleansed of phenol below the detectable limit because of the high mass transfer rate of the pollutant from the air and the high growth rate of Pseudomonas putida. The bioreactor was found to degrade over 99% of the inlet phenol at rates from 21·5 to 194 mg h^?1 at concentrations between 650 and 850 mg m^?3 of air. A model of the system is developed based on an initial transient period followed by a pseudo-steady state period. The simulations compared well with the experimental data.