Performance of different immobilized‐cell systems to efficiently produce ethanol from whey: fluidized batch,packed‐bed and fluidized continuous bioreactors

BACKGROUND: The bioconversion of whey into ethanol by immobilized Kluyveromyces marxianus in packed‐bed and fluidized bioreactors is described. Both batch and continuous cultures were analyzed using three different strains of K. marxianus and the effect of the operating mode, temperature, and dilution rates (D) were investigated. RESULTS: All immobilized strains of K. marxianus (CBS 6556, CCT 4086, and CCT 2653) produced similar high yields of ethanol (0.44 ± 0.01 g EtOH g^?1 sugar). Significant variations of conversion efficiencies (66.1 to 83.3%) and ethanol productivities (0.78 to 0.96 g L^?1 h^?1) were observed in the experiments with strain K. marxianus CBS 6556 at different temperatures. High yields of ethanol were obtained in fluidized and packed‐bed bioreactors continuous cultures at different D (0.1 to 0.3 h^?1), with the highest productivity (3.5 g L^?1 h^?1) observed for D = 0.3 h^?1 in the fluidized bioreactor (87% of the maximal theoretical conversion), whereas the highest ethanol concentration in the streaming effluent (28 g L^?1) was obtained for D = 0.1 h^?1. Electronic micrographs of the gel beads showed efficient cell immobilization. CONCLUSION: Batch and continuous cultivations of immobilized K. marxianus in fluidized and packed‐bed bioreactors enable high yields and productivities of ethanol from whey. Copyright © 2012 Society of Chemical Industry     

Fermentation of cheese whey powder solution to ethanol in a packed‐column bioreactor: effects of feed sugar concentration

BACKGROUND: Cheese whey powder (CWP) is a concentrated source of lactose and other essential nutrients for ethanol fermentation. CWP solution containing different concentrations of total sugar was fermented to ethanol in an up‐flow packed‐column bioreactor (PCBR) at a constant hydraulic residence time (HRT) of 50 h. Total sugar concentration in the feed was varied between 50 and 200 g L^?1 and a pure culture of Kluyveromyces marxianus was used for ethanol fermentation of lactose. Variations of ethanol and sugar concentrations with the height of the column and with the feed sugar concentration were determined. RESULTS: Ethanol concentration increased and total sugar decreased with the column height for all feed sugar contents. The highest effluent ethanol concentration (22.5 g L^?1) and ethanol formation rate were obtained with feed sugar content of 100 g L^?1. Percentage sugar utilization decreased with increasing feed sugar content above 100 g L^?1 yielding lower ethanol contents in the effluent. The highest ethanol yield coefficient (0.52 gE g^?1S) was obtained with a feed sugar content of 50 g L^?1. Biomass concentration also decreased with column height, yielding low ethanol formation in the upper section of the column. CONCLUSION: The packed column bioreactor was found to be effective for ethanol fermentation from CWP solution. The optimum feed sugar content maximizing the effluent ethanol and the specific rate of ethanol formation was found to be 100 g L^?1. High sugar content above 100 g L^?1 resulted in low ethanol productivities due to high maintenance requirements. Copyright © 2008 Society of Chemical Industry     

Studies on the structural features of sodium alginate entrapped Kluyveromyces marxianus NCYC179 cells used for alcohol production from whey permeate

Alginate-entrapped living Kluyveromyces marxianus NCYC179 cells were successfully used in alcohol production from whey permeate. Using 10% whey lactose as substrate, an alcohol production efficiency of 81.5–84.9% and 84.0–88.2% with cell viability maintenance between 82.8–84.3% and 81.0–84.3% of the immobilised cells during the monitoring periods, in batch (six repeat runs) and continuous (23 days of experimenting time) systems, respectively. The immobilised samples remained stable during the course of fermentation with no leakage of K. marxianus cells into the surrounding medium in the case of the batch system. However, slight leakage after 10 days of continuous run in the continuous process was recorded. The scanning electron microscopic studies of the beads containing entrapped yeast cells and sections or crushed samples of the beads carried out at the start and termination of fermentation in both the processes (batch and continuous) revealed that the immobilisation procedure does not influence any morphological change in the entrapped cells during the prolonged periods of fermentation. Moreover, the gel matrix structure was also found to be unaffected by the fermentation conditions employed during the course of present studies.     

Acid and enzymatic saccharification of agricultural mixed polymers for alcohol production

The paper reports the evaluation of potentials of acid (HCl and H₂SO₄) and enzymatically (cellulase) saccharified corncob, groundnut shell, sugarcane bagasse and wheat straw biopolymers for ethanol production. Of the three yeast isolates tested, Saccharomyces cerevisiae var. ellipsoideus was found to be most efficient, closely followed by Kluyveromyces marxianus NCYC 179 in its ability to ferment enzymatically hydrolysed mash of all the substrates tested to ethanol. However, S. cerevisiae NCYC 240 and acid hydrolysed agricultural polymers were found to be a poor organism and poor substrates, respectively, for ethanol fermentation. The order of ethanol production on substrate basis was corncob > wheat straw > sugarcane bagasse > groundnut shell biomass biopolymer. An incubation period of 24 h was found optimum for the optimal production of ethanol by S. cerevisiae var. ellipsoideus in both acid and enzymatically hydrolysed agricultural residues.     

Optimization of inulinase production by solid‐state fermentation in a packed‐bed bioreactor

BACKGROUND: This work is focused on inulinase production by solid‐sate fermentation (SSF) using sugarcane bagasse, corn steep liquor (CSL), pre‐treated cane molasses, and soybean bran as substrates in a 3‐kg (dry basis) packed‐bed bioreactor. SSF was carried out by the yeast Kluyveromyces marxianus NRRL Y‐7571 and response surface methodology was used to optimize the temperature, air flow rate and initial mass of cells. RESULTS: The optimum inulinase activity (436.7 ± 36.3 U g^?1 dry substrate) was obtained at 24 h at an inlet air temperature of 30 °C, air flow rate 2.2 m³ h^?1 and 22 g of cells for fermentation. Inulinase productivity at these conditions was 18.2 U gds^?1 h^?1. Kinetic evaluation at the optimized conditions showed that the maximum inulinase production was verified at 24 h of fermentation. The carbon dioxide and the metabolic heat generation are directly associated with the consumption of total reducing sugars present in the medium. CONCLUSION: The high productivity achieved in this work shows the technical viability of inulinase production by SSF in a packed‐bed bioreactor. Copyright © 2009 Society of Chemical Industry     

Continuous ethanol production from carob pod extract by immobilized Saccharomyces cerevisiae in a packed-bed reactor

The continuous production of ethanol from carob pod extract by immobilized Saccharomyces cerevisiae in a packed-bed reactor has been investigated. At a substrate concentration of 150 g dm^?3, maximum ethanol productivity of 16 g dm^?3 h^?1 was obtained at D = 0·4 h^?1 with 62·3% of theoretical yield and 83·6% sugars′ utilization. At a dilution rate of 0·1 h^?1, optimal ethanol productivity was achieved in the pH range 3·5–5·5, temperature range 30–35·C and initial sugar concentration of 200 g dm^?3. Maximum ethanol productivity of 24·5 g dm^?3 h^?1 was obtained at D = 0·5 h^?1 with 58·8% of theoretical yield and 85% sugars′ utilization when non-sterilized carob pod extract containing 200 g dm^?3 total sugars was used as feed material. The bioreactor system was operated at a constant dilution rate of 0·5 h^?1 for 30 days without loss of the original immobilized yeast activity. In this case, the average ethanol productivity, ethanol yield (% of theoretical) and sugars′ utilization were 25 g dm^?3 h^?1, 58·8% and 85·5%, respectively.     

Production,purification and immobilisation of inulinase from Kluyveromyces fragilis

Kluyveromyces fragilis (NCIM 3217), Kluyveromyces marxianus (NCIM 3231), Hansenula polymorpha (NCIM 3377), Pichia fermentan (NCIM 3408), Pichia polymorpha (NCIM 3419) and Debaryomyces castellii (NCIM 3446) were grown on an inulin-based growth medium. Only K. fragilis produced extracellular inulinase with a maximum after 36 h of growth at 25–27°C. Sucrose and fructose were weak inducers of inulinase as compared to inulin whereas with glucose the inulinase level was minimal. An aqueous extract of chicory roots containing 1% fructan was a better carbon source than inulin and peptone was the best nitrogen source for the production of inulinase. The maximum yield of inulinase was about 7 units cm^?3 of medium. The invertase to inulinase ratio of 10 in the culture filtrate was reduced to 1·6 on purifying inulinase by ethanol precipitation followed by chromatography on Sephadex G-200, DEAE-cellulose and CM-cellulose columns. Using this purification procedure, inulinase was purified 26-fold. With inulin as substrate, the shape of the velocity curve was nearer to a sigmoidal pattern whereas with sucrose the curve was hyperbolic. The molecular weight of inulinase was determined as 250 ± 10 kDa. The crude and purified inulinase preparations did not release sucrose or oligosaccharides from inulin, indicating that the enzyme has primarily exo-inulinase activity. Using the metal-link chelation method, 40% of inulinase was immobilised on cellulose. Maximum activity of crude, purified and immobilised inulinase preparations was observed at 55°C. The half-life of immobilised inulinase at 25°C was 5 days.     

Kinetic modelling of lactic acid production from whey by Lactobacillus casei (NRRL B‐441)

The biomass growth, lactic acid production and lactose utilisation kinetics of lactic acid production from whey by Lactobacillus casei was studied. Batch fermentation experiments were performed at controlled pH and temperature with six different initial whey lactose concentrations (9‐77 g dm^?3) in a 3 dm³ working volume bioreactor. Biomass growth was well described by the logistic equation with a product inhibition term. In addition, biomass and product inhibition effects were defined with corresponding power terms, which enabled adjustment of the model for low‐ and high‐substrate conditions. The Luedeking‐Piret equation defined the product formation kinetics. Substrate consumption was explained by production rate and maintenance requirements. A maximum productivity of 2.5 g dm^?3 h^?1 was attained with an initial lactose concentration of 35.5 g dm^?3. Copyright © 2006 Society of Chemical Industry     

Kinetic study on ethanol production using Saccharomyces cerevisiae ITV‐01 yeast isolated from sugar cane molasses

BACKGROUND: Bio‐ethanol production from renewable sources, such as sugar cane, makes it a biofuel that is both renewable and environmentally friendly. One of the strategies to reduce production costs and to make ethanol fuel economically competitive with fossil fuels could be the use of wild yeast with osmotolerance, ethanol resistance and low nutritional requirements. The aim of this work was to investigate the kinetics of ethanol fermentation using Saccharomyces cerevisiae ITV‐01 yeast strain in a batch system at different glucose and ethanol concentrations, pH values and temperature in order to determine the optimum fermentation conditions. RESULTS: This strain showed osmotolerance (its specific growth rate (µ_max) remained unchanged at glucose concentrations between 100 and 200 g L^?1) as well as ethanol resistance (it was able to grow at 10% v/v ethanol). Activation energy (Ea) and Q₁₀ values calculated at temperatures between 27 and 39 °C, pH 3.5, was 15.6 kcal mol^?1 (with a pre‐exponential factor of 3.8 × 10¹² h^?1 (R² = 0.94)) and 3.93 respectively, indicating that this system is biologically limited. CONCLUSIONS: The optimal conditions for ethanol production were pH 3.5, 30 °C and initial glucose concentration 150 g L^?1. In this case, a maximum ethanol concentration of 58.4 g L^?1, ethanol productivity of 1.8 g L^?1 h^?1 and ethanol yield of 0.41 g g^?1 were obtained. Copyright © 2010 Society of Chemical Industry     

Continuous ethanol fermentation using immobilized yeast in a fluidized bed reactor

Continuous ethanol fermentation of glucose using fluidized bed technology was studied. Saccharomyces cerevisiae were immobilized and retained on porous microcarriers. Over two-thirds of the total reactor yeast cell mass was immobilized. Ethanol productivity was examined as dilution rate was varied, keeping all other experimental parameters constant. Ethanol yield remained high at an average of 0.36 g ethanol g^?1 glucose (71% of theoretical yield) as the dilution rate was increased stepwise from 0.04 h^?1 to 0.14 h^?1. At a dilution rate of 0.15 h^?1, the ethanol yield steeply declined to 0.22 g ethanol g^?1 glucose (44% of theoretical yield). The low maximum percentage of theoretical yield is primarily due to an extended mean cell residence time, and possibly due to the inhibitory effect of a high dissolved carbon dioxide concentration, enhanced by the probable intermittent levels of low pH in the reactor. Constant ethanol production was possible at a high glucose loading rate of 840 g dm^?3 day^?1 (attained at a dilution rate of 0.14 h^?1). Although the highest average ethanol concentration (97.14 g dm^?3) occurred at the initial dilution rate of 0.04 h^?1, the peak average ethanol production rate (2.87 g (g yeast)^?1 day^?1) was reached at a greater dilution rate of 0.11 ^h-1. Thus, the optimal dilution rate was determined to be between 0.11 h^?1 and 0.14 h^?1. Ethanol inhibition on yeast cells was absent in the reactor at average bulk-liquid ethanol concentrations as high as 97.14 g dm^?3. In addition, zero-order kinetics on ethanol production and glucose utilization was evident.     

Performance evaluation of a water/silicone oil two‐phase partitioning bioreactor using Rhodococcus erythropolis T902.1 to remove volatile organic compounds from gaseous effluents

BACKGROUND: In the framework of biological processes used for waste gas treatment, the impact of the inoculum size on the start‐up performance needs to be better evaluated. Moreover, only a few studies have investigated the behaviour of elimination capacity and biomass viability in a two‐phase partitioning bioreactor (TPPB) used for waste gas treatment. Lastly, the impact of ethanol as a co‐substrate remains misunderstood. RESULTS: Firstly, no benefit of inoculation with a high cellular density (>1.5 g L^?1) was observed in terms of start‐up performance. Secondly, the TPPB was monitored for 38 days to characterise its behaviour under several operational conditions. The removal efficiency remained above 63% for an inlet concentration of 7 g isopropylbenzene (IPB) m^?3 and at some time points reached 92% during an intermittent loading phase (10 h day^?1), corresponding to a mean elimination capacity of 4 × 10^?3 g L^?1 min^?1 (240 g m^?3 h^?1) for a mean IPB inlet load of 6.19 × 10^?3 g L^?1 min^?1 (390 g m^?3 h^?1). Under continuous IPB loading, the performance of the TPPB declined, but the period of biomass acclimatisation to this operational condition was shorter than 5 days. The biomass grew to approximately 10 g L^?1 but the cellular viability changed greatly during the experiment, suggesting an endorespiration phenomenon in the bioreactor. It was also shown that simultaneous degradation of IPB and ethanol occurred, suggesting that ethanol improves the biodegradation process without causing oxygen depletion. CONCLUSION: A water/silicone oil TPPB with ethanol as co‐substrate allowed the removal of a high inlet load of IPB during an experiment lasting 38 days. Copyright © 2008 Society of Chemical Industry     

Removal of dimethyl sulfide in a thermophilic membrane bioreactor

BACKGROUND: Several sources such as the paper and pulp industry and waste treatment plants emit waste gases containing volatile organic sulfur compounds at elevated temperature. Since cooling the hot gases increases the operational cost of biological reactors, application of thermophilic microorganisms could be a cost‐effective solution. The objectives of this study were to investigate the possibility of removal of dimethyl sulfide from waste gases under thermophilic conditions (52 °C) in a membrane bioreactor and to examine the long‐term stability of the reactor at elevated temperature. The effects of operating conditions such as gas residence time, nutrient supply, temperature decrease and short‐term shutdown on elimination capacity were investigated. RESULTS: A maximum elimination capacity of 54 g m^?3 h^?1 (0.108 g m^?2 h^?1) was obtained at a mass loading rate of 64 g m^?3 h^?1 (0.128 g m^?2 h^?1) with a removal efficiency of 84% at a gas residence time of 24 s. The long‐term operation of the thermophilic membrane bioreactor was followed for 9 months. Although the removal efficiency decreased to 50% after 3 months of continuous operation, it recovered (>96%) after the excess biomass was removed by applying high‐velocity liquid recirculation. CONCLUSION: This study demonstrated that the dimethyl sulfide removal is possible in a thermophilic membrane bioreactor with an elimination capacity of 54 g m^?3 h^?1 (0.108 g m^?2 h^?1) at a gas residence time of 24 s. 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     

Oxidation of ethanol vapors in a spiral bioreactor

A fixed film spiral bioreactor containing immobilized activated sludge microorganisms has been used to degrade ethanol vapors. The effect of air flow rate, and ethanol feed concentration on elimination capacity has been investigated. Air flow rate is varied in the range from 2?34 to 40?0 dm³ min^?1. Ethanol feed concentration is varied in the range from 600 to 7000 ppmv. In the concentration range studied, the elimination capacity increased proportionately with an increase in feed concentration. However, the elimination capacity decreased significantly at flow rates greater than 20 dm³ min^?1 owing to insulfficient residence time. The maximum elimination capacity observed was 185 g ethanol h^?1 m^?3 of reactor volume. Critical ethanol loading, defined as the maximum loading to achieve greater than 99% elimination at various residence times have been determined. These data are extremely useful in designing bioreactor for large scale applications.     

Conversion efficiency of glucose/xylose mixtures for ethanol production using Saccharomyces cerevisiae ITV01 and Pichia stipitis NRRL Y‐7124

BACKGROUND: Efficient conversion of glucose/xylose mixtures from lignocellulose is necessary for commercially viable ethanol production. Oxygen and carbon sources are of paramount importance for ethanol yield. The aim of this work was to evaluate different glucose/xylose mixtures for ethanol production using S. cerevisiae ITV‐01 (wild type yeast) and P. stipitis NRRL Y‐7124 and the effect of supplying oxygen in separate and co‐culture processes. RESULTS: The complete conversion of a glucose/xylose mixture (75/30 g L^?1) was obtained using P. stipitis NRRL Y‐7124 under aerobic conditions (0.6 vvm), the highest yield production being Y_p/s = 0.46 g g^?1, volumetric ethanol productivity Q_pmax = 0.24 g L^?1 h^?1 and maximum ethanol concentration P_max = 34.5 g L^?1. In the co‐culture process and under aerobic conditions, incomplete conversion of glucose/xylose mixture was observed (20.4% residual xylose), with a maximum ethanol production of 30.3 g L^?1, ethanol yield of 0.4 g g^?1 and Q_pmax = 1.26 g L^?1 h^?1. CONCLUSIONS: The oxygen present in the glucose/xylose mixture promotes complete sugar consumption by P. stipitis NRRL Y‐7124 resulting in ethanol production. However, in co‐culture with S. cerevisiae ITV‐01 under aerobic conditions, incomplete fermentation occurs that could be caused by oxygen limitation and ethanol inhibition by P. stipitis NRRL Y‐7124; nevertheless the volumetric ethanol productivity increases fivefold compared with separate culture. Copyright © 2011 Society of Chemical Industry     

Effect of temperature on fermentation kinetics of waste sulphite liquor by Saccharomyces cerevisiae

The optimum operating temperatures for the maximum production of ethanol and the maximum utilization of substrate in batch fermentations of a waste sulphite liquor (WSL) as well as a synthetic medium using Saccharomyces cerevisiae were determined. The fastest consumption of substrate resulting in the shortest fermentation times of 13 h and 45 h was achieved at 35°C and 30°C for the synthetic medium and the WSL, respectively. The concentrations of ethanol in the two media were also maximum under these conditions: 11.6g dm^?3 and 9.4 g dm^?3 for the synthetic medium and the WSL, respectively. The productivities of biomass and ethanol increased with the increase of temperature and reached maximum values of 0.89 g dm^?3 h^?1 and 0.21 g dm^?3 h^?1 in the synthetic medium and the WSL, respectively. The inhibiting agents in the waste sulphite liquor affected the metabolic rates of microbial activities and prolonged the overall fermentation time while decreasing the productivities of biomass and ethanol. From analysis of the fermentation kinetics a mathematical model based on the Monod model was developed to describe the cellular growth and ethanol production. The model included inhibition terms for ethanol and the inhibiting agents in the waste liquor. The temperature dependence of the model parameters followed the Arrhenius law for temperatures between 15°C and 35°C. The activation energies (E) and the frequency constants (A) of these parameters were also determined.     

Novel two‐in‐one bioreactor greatly improves lactic acid production from xylose by Lactobacillus pentosus

BACKGROUND: Simultaneous xylose isomerization and fermentation was investigated to improve the lactic acid production from xylose by Lactobacillus pentosus in a novel two‐in‐one bioreactor constructed by packing the immobilized xylose isomerase (65 g) in a fixed bed reactor (diameter 56 mm × 66 mm, packing volume 154 mL) with a permeable wall, which was installed inside a conventional fermenter (2 L) and rotated along the axis together with the mechanical stirrer of the fermenter. RESULTS: Xylose (20 g L^?1) was completely consumed within 24 h in the novel bioreactor, compared with 72 h needed for the control without packed enzyme. The maximum cell density (17.5 g L^?1) in the novel bioreactor was twice that in the control and the lactic acid productivity (0.58 g L^?1 h^?1) was 3.8 times higher. Repeated use of the immobilized enzyme showed that the lactic acid productivity and yield obviously dropped after the first batch fermentation but maintained almost unchanged afterwards. CONCLUSION: Simultaneous xylose isomerization and fermentation significantly improved lactic acid production from xylose by Lactobacillus pentosus. The novel bioreactor made it easier to recycle and reuse the immobilized enzyme. © 2012 Society of Chemical Industry     

The fermentation of mixtures of D‐glucose and D‐xylose by Candida shehatae,Pichia stipitis or Pachysolen tannophilus to produce ethanol

The fermentation of mixtures of D ‐glucose and D ‐xylose by three non‐traditional yeasts: Candida shehatae (ATCC 34887), Pachysolen tannophilus (ATCC 32691) and Pichia stipitis (ATCC 58376) have been studied to determine the optimal strain and initial culture conditions for the efficient production of ethanol. The comparison was made on the basis of maximum specific growth rate (µ_m), biomass productivity, the specific rates of total substrate consumption (q_s) and ethanol production (q_E) and the overall yields of ethanol and xylitol. All the experiments were performed in stirred‐tank batch reactors at a temperature of 30 °C. The initial pH of the culture medium was 4.5. The highest values of µ_m (above 0.5 h^?1) were obtained with P stipitis in cultures containing high concentrations of D ‐xylose. All three yeasts consumed the two monosaccharides in sequence, beginning with D ‐glucose. The values of q_s diminished during the course of each experiment with all of the yeasts. The highest values of the specific rates of total substrate consumption and ethanol production were obtained with C shehatae (for t = 10 h, q_s and q_E were above 5 g g^?1 h^?1 and 2 g g^?1 h^?1, respectively), although the highest overall ethanol yields were fairly similar with all three yeasts, at around 0.4 g g^?1. © 2002 Society of Chemical Industry     

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     

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