Batch and Continuous Production of Lactic Acid from Beet Molasses by Lactobacillus delbrueckii IFO 3202

Process variables were optimized for the production of lactic acid from pretreated beet molasses by Lactobacillus delbrueckii IFO 3202 for batch and continuous fermentations. In the batch fermentation, maximum yields (95·4% conversion, 77·1% effective) and maximum lactic acid volumetric productivity (4·83 g dm⁻³ h⁻¹) was achieved at 45°C, pH 6·0, 78·2 g dm⁻³ sugar concentration with 10 g dm⁻³ yeast extract. Various cheaper nitrogen sources were replaced with yeast extract on equal nitrogen bases in batch fermentation. Of all the nitrogen sources tested, yeast extract yielded the highest and malt sprouts yielded the second highest level of lactic acid. In the continuous fermentation, maximum lactic acid (4·15%) was obtained at a dilution rate of 0·1 h⁻¹. Maximum volumetric lactic acid productivity (11·20 g dm⁻³ h⁻¹) occurred at D = 0·5 h⁻¹ dilution rate. © 1997 SCI.     

Technological and kinetic aspects of sublethal acid toxicity in microbial gum production

Chemostat culture of Xanthomonas campestris were obtained at a dilution rate of 0·05 h⁻¹ and the normal feed then supplemented with 0·58 and 1·74 mmol dm⁻³ isobutyric acid (IBA). Data revealed that the organism responded to sublethal acid stress by overproducing xanthan. The acid additions led to transient zones in the continuous cultivation profiles. By adding feed containing 1·74 mmol dm⁻³ IBA, volumetric growth rate immediately decreased from 0·059 to 0·026 g dm⁻³ h⁻¹ whereas the specific xanthan formation rate increased from 0·23 g g⁻¹ biomass h⁻¹ to a maximum 0·65 g g⁻¹ biomass h⁻¹ (with 1·0 mmol dm⁻³ IBA addition), before decreasing as the concentration of acid attained that of the feed. By monitoring the outlet CO₂ in parallel with biomass and polysaccharide levels in the IBA fermentation a 10% diversion of the total carbon flux from biomass synthesis to xanthan biosynthesis was detected. A consistent pattern of variation in activity was detected in enzymes of intermediary metabolism, suggesting an action at the regulatory level. Enhanced activities of carbon catabolism and xanthan anabolic reactions (phosphomannose isomerase) were observed in the presence of the acid. Batch experiments carried out in the pres-ence of IBA gave results which correlated with the undissociated acid form con-centration. An undissociated acid fraction of 6·5×10⁻³ mmol dm⁻³ was calculated in a set of flasks under the same conditions and a statistically vali-dated 12% increase in xanthan production was found. The maximum activation was determined to be below 1·1×10⁻² mmol dm⁻³ when a 58% specific xanthan production rate increase occurred in parallel with a 35% decrease in biomass concentration.     

Estimating growth kinetics of Penicillium chrysogenum through the use of respirometry

The applicability of respirometry to characterize fungal growth kinetics was studied using Penicillium chrysogenum as the model microorganism. Oxygen uptake data were used in conjunction with a nonlinear parameter estimation technique to determine the kinetic parameters associated with microbial growth. The theoretical model that used the Contois equation for microbial growth was able to accurately describe experimental oxygen uptake data. Penicillium chrysogenum was characterized by average values of 0·195 h⁻¹ and 4·13 for the maximum specific growth rate, μ_max, and the Contois saturation coefficient, K_c, respectively. The average true growth yield was 0·405 mg mg⁻¹. As only oxygen uptake information is required for biokinetic parameter estimation, respirometry is a very convenient tool for studying microbial growth as high quality experimental data can be obtained with relatively little experimental effort. © 1998 SCI     

Continuous process for yeast biomass production from sugar beet stillage by a novel strain of Candida rugosa and protein profile of the yeast

Thermotolerant yeast Candida rugosa isolated from East Africa was used for the continuous production of yeast protein from sugar beet stillages at 40°C. At a dilution rate of 0·15 h⁻¹, biomass productivity was at a maximum (0·85 dm⁻³ h⁻¹) and the Chemical Oxygen Demand reduction rate of the stillage was 30·4%. This yeast contained 45·1% crude protein, 36·5% actual protein and 5·6% RNA. The yeast protein had adequate essential amino acids, except for sulphur-containing types.     

A trickling fibrous-bed bioreactor for biofiltration of benzene in air

A novel trickling fibrous-bed bioreactor was developed for biofiltration to remove pollutants present in contaminated air. Air containing benzene as the sole carbon source was effectively treated with a coculture of Pseudomonas putida and Pseudomonas fluorescens immobilized in the trickling biofilter, which was wetted with a liquid medium containing only inorganic mineral salts. When the inlet benzene concentration (C_gi) was 0·37 g m⁻³, the benzene removal efficiency in the biofilter was greater than 90% at an empty bed retention time (EBRT) of 8 min or a superficial air flow rate of 1·8 m³ m⁻² h⁻¹. In general, the removal efficiency decreased but the elimination capacity of the biofilter increased with increasing the inlet benzene concentration and the air (feed) flow rate. It was also found that the removal efficiency decreased but the elimination capacity increased with an increase in the loading capacity, which is equal to the inlet concentration divided by EBRT. The maximum elimination capacity achieved in this study was ∽11·5 g m⁻³ h⁻¹ when the inlet benzene concentration was 1·7 g m⁻³ and the superficial air flow rate was 3·62 m³ m⁻² h⁻¹. A simple mathematical model based on the first-order reaction kinetics was developed to simulate the biofiltration performance. The apparent first order parameter K_l in this model was found to be linearly related to the inlet benzene concentration (K_l=4·64−1·38 C_gi). The model can be used to predict the benzene removal efficiency and elimination capacity of the biofilter for benzene loading capacity up to ∽30 g m⁻³ h⁻¹. Using this model, the maximum elimination capacity for the biofilter was estimated to be 12·3 g m⁻³ h⁻¹, and the critical loading capacity was found to be 14 g m⁻³ h⁻¹. The biofilter had a fast response to process condition changes and was stable for long-term operation; no degeneration or clogging of the biofilter was encountered during the 3-month period studied. The biofilter also had a relatively low pressure drop of 750 Pa m⁻¹ at a high superficial air flow rate of 7·21 m³ m⁻² h⁻¹, indicating a good potential for further scale up for industrial applications. © 1998 Society of Chemical Industry     

Mathematical modelling of the alcoholic fermentation of glucose by Zymomonas mobilis mobilis

The kinetics of alcoholic fermentation of a strain of Zymomonas mobilis, isolated from sugarcane juice, has been studied with the objective of determining the constansts of a non-structured mathematical model that represents the fermentation process. Assays in batch and in continuous culture have been carried out with different initial concentrations of glucose. The final concentrations of glucose, ethanol and biomass were determined. The following kinetic parameters were obtained: μ_max, 0·5 h^?1; K_s, 4·64 g dm^?3; P_max, 106 g dm^?3; Y_x/s, 0·0265 g g^?1; m, 1·4 g g^?1 h^?1; α, 17·38 g g^?1; β, 0·69 g g^?1 h^?1.     

Removal of Hydrogen Sulphide by Immobilized Thiobacillus sp. strain CH11 in a Biofilter

An autotropic Thiobacillus sp. CH11 was isolated from piggery wastewater containing hydrogen sulphide. The removal characteristics of hydrogen sulphide by Thiobacillus sp. CH11 were examined in the continuous system. The hydrogen sulphide removal capacity was elevated by the BDST (Bed Depth Service Time) method (physical adsorption) and an immobilized cell biofilter (biological conversion). The optimum pH to remove hydrogen sulphide ranged from 6 to 8. The average specific uptake rate of hydrogen sulphide was as 1·02×10⁻¹³ mol-S cell⁻¹ h⁻¹ in continuous systems. The maximum removal rate and saturation constant for hydrogen sulphide were calculated to be V_m = 30·1 mmol-S day⁻¹ (kg-dry bead)⁻¹ and K_s = 1·28 μmol dm⁻³, respectively. A criterion to design a scale-up biofilter was also studied. The maximum inlet loading in the linear region (95% removal) was 47 mmol-S day⁻¹ (kg-dry bead)⁻¹. Additionally, the biofilter exhibited high efficiency (>98·5%) in the removal of hydrogen sulphide at both low (<0·026 mg dm⁻³) and high (0·078 mg dm⁻³) concentrations. The results suggested that the Thiobacillus sp. CH11 immobilized with Ca-alginate is a potential method for the removal of hydrogen sulphide. © 1997 SCI.     

Carbon Dioxide Fixation by Algal Cultivation Using Wastewater Nutrients

Chlorella vulgaris was cultivated in wastewater discharged from a steel-making plant with the aim of developing an economically feasible system to remove ammonia from wastewater and CO₂ from flue gas simultaneously. Since no phosphorus compounds existed in wastewater, external phosphate (15·3–46·0 g m⁻³) was added to the wastewater. After adaptation to 5% (v/v) CO₂, the growth of C. vulgaris was significantly improved at a typical concentration of CO₂ in flue gas of 15% (v/v). Growth of C. vulgaris in raw wastewater was better than that in wastewater buffered with HEPES at 15% (v/v) CO₂. CO₂ fixation and ammonia removal rates were estimated as 26·0 g CO₂ m⁻³ h⁻¹ and 0·92 g NH₃ m⁻³ h⁻¹, respectively, when the alga was cultivated in wastewater supplemented with 46·0 g PO₄³ m⁻³ without pH control at 15% (v/v) CO₂. © 1997 SCI.     

Intraparticle diffusivity of Cd ions in a new biosorbent material

Cadmium equilibrium sorption isotherms were determined for formaldehyde crosslinked Sargassum fluitans, establishing that an effective regeneration of the new biosorbent material is possible by an acid wash. Batch desorption kinetics were investigated at pH values of 1·0 and 2·0. By incorporating the linear and non-linear Langmuir equilibrium isotherm relationships into the rate equations, a mathematical model was proposed for modeling the metal desorption process. The model was solved numerically and a MATLAB computer program was used to curve-fit the experimental data. The model successfully predicted the Cd²⁺ elution concentration profile in a batch reactor. The average values of the intraparticle diffusivity of Cd²⁺ in the algal biosorbent calculated from the model were 3·40 × 10⁻⁶ and 1·65 × 10⁻⁶ cm² s⁻¹, 0·473 and 0·229 times the molecular diffusivity of Cd²⁺ in water, at pH values of 1·0 and 2·0, respectively. These values agreed well with theoretical predictions.     

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.     

Morpholine Biodegradation in a Bioreactor

The degradation of morpholine, often reported as a recalcitrant compound, by a mixed culture consisting of nine bacteria and two yeasts in a bioreactor is described. The fermentation process was first carried out in discontinuous culture using different initial morpholine concentrations. The time variation of biomass and morpholine concentrations were used to determine the parameters characterizing the specific growth rate which is based on Monod's model modified to take into account the inhibition due to the substrate. In discontinuous cultures, the biomass concentration reached a maximum of 4·5 g dm^-3 with an initial morpholine concentration of 7 g dm^-3. When switching to continuous culture, the biomass reached 8·8 g dm^-3 with a dilution rate varying from 0·024 h^-1 to 0·052 h^-1 while reducing morpholine concentration to zero within 300 h. A numerical simulation was set up by integrating with time the mass balance equations for morpholine and biomass in the presence of a constant cell death rate. The results of the simulation were in close agreement with the observed data. The model was then extended to a membrane bioreactor. Experiments were first run with partial recycling (bleeding rate of 0·011 h^-1). The biomass concentration reached 27 g dm^-3 after 200 h while the morpholine concentration stabilized itself at 0·2 g dm^-3. With total recycling, the biomass reached 32 g dm^-3, when it became limited by the oxygen transfer of the apparatus. Here again the model was in good agreement with the observations except when the dilution rate was changed suddenly. This study indicates that data obtained in discontinuous batch mode can serve to predict the biomass and morpholine concentration variation in continuous mode in a membrane reactor and to determine the correct parameters for steady state operation.     

One-step preparation of asymmetric ceramic membranes based on sea urchin-like mullite whisker skeletons and their oil-water separation properties

In this work, novel sandwich-type asymmetric ceramic microfiltration membranes with a sea urchin-like mullite whisker skeleton were prepared one step. Their structural properties and oil-water separation performance were investigated. The results show that after sintering at 1400 °C, the prepared membrane possesses good hydrophilic, underwater oleophobic, and anti-fouling properties. During the continuous separation of a 300 mg/L oil-in-water emulsion, a maximum stable flux of 267 L·m⁻²·h⁻¹ was achieved without membrane cleaning. After chemical cleaning and simple physical cleaning, the membranes recovered to a steady flux of 397 L·m⁻²·h⁻¹ and 305 L·m⁻²·h⁻¹, respectively, and maintained a 95% oil rejection. The good underwater oleophobicity and selective permeability brought about by the flat-lying whiskers on the top surface, coupled with the efficient water channels between the sea urchin-like structures inside the membrane, are considered to be the main reasons for its improved separation characteristics over conventional low-cost ceramic membranes.     

Energetics of Pseudomonas cepacia G4 growth in a chemostat with phenol limitation

Analysis of the growth of Pseudomonas cepacia G4 on phenol in continuous culture has been carried out. The data were checked for consistency using both available electron and carbon balances. Coupled with the covariate adjustment estimation technique, the best estimates for true biomass energetic yield, η_max and maintenance, m_e, were obtained when the carbon dioxide measurements were excluded. However, upon making corrections to the gas measurements, the best estimates were the maximum likelihood estimates (MLE) based on the complete data. The method therefore allows discrimination to be made between data. Also, similar estimates were obtained using Pirt's model based on the Monod approach and a modified form based on substrate uptake rate being the limiting factor. For the aerobic growth of P. cepacia G4 on phenol, η_max = 0·417 and m_e = 0·0513 h^?1 were obtained when the CO₂ data were excluded. When corrections were made to the gas measurements to take into account the dissolved CO₂ and the effect of operating temperature, η_max = 0·432 and m_e = 0·0684 h^?1 were obtained. From the 95% confidence intervals, a maximum of about 38–47·5% of the energy contained in phenol is incorporated into the biomass while the balance (52·5–62%) is evolved as heat with only a little energy needed for the maintenance of the organism.     

Production of optically pure L-alanine by immobilized Pseudomonas sp. BA2 cells

The conditions for immobilizing the new L -aminoacylase-producing bacterial strain, Pseudomonas sp. BA2, by entrapment in κ-carrageenan gel, were investigated. The optimal gel concentration and cell load were determined. The addition of CoCl₂ and N-acetyl-L -alanine to the immobilizing matrix enhanced L -aminoacylase activity. The enzymatic properties of immobilized Pseudomonas sp. BA2 were investigated. Enzyme activity in immobilized cells was optimal at a pH of 6·5 using 0·15 mol dm⁻³ Tris–maleate buffer at 45°C. The presence of 0·7 mmol dm⁻³ CoCl₂ in the enzymatic reaction mixture improved L -aminoacylase activity. The immobilized cell preparation was used for the production of L -alanine from N-acetyl-DL -alanine in a batch reactor. Conversions of 100% were obtained using substrate concentrations ranging from 20 to 200 mmol dm⁻³. The reactor production was 0·74 mol h⁻¹ g cell⁻¹ dm⁻³ which is noticeably higher than that previously reported in the literature. © 1998 Society of Chemical Industry     

Improved Ethanol Production by Saccharomyces cerevisiae with EDTA,Ferrocyanide and Zeolite X Addition to Sugar Beet Molasses

The influence of ethylenediaminetetra acetic acid (EDTA), potassium ferrocyanide and zeolite X on ethanol production from sugar beet molasses by Saccharomyces cerevisiae was studied. For all of the three substances used, the effect was more pronounced when added to the fermentation medium rather than to the growth medium; 1·9 mmol dm⁻³ potassium ferrocyanide caused an increase in the final ethanol concentration of about 16·4% and 47·5% with respect to control culture on addition to growth and fermentation media respectively. The greatest stimulation in product yield was obtained with zeolite X introduced during the fermentation stage; 8·0 g dm⁻³ zeolite X increased ethanol concentration by 53·3%. © 1997 SCI.     

Biological degradation of EDTA: Reaction kinetics and technical approach

The microbial mineralization of EDTA in waste water by a mixed culture was studied with suspended and immobilized cells. Efficient degradation of EDTA could be achieved, though the chelator is stated not to be biodegradable. A complete set of kinetic parameters was determined that enables the modelling of EDTA degradation and, related to this, bacterial growth, ammonium release, maintenance requirement as well as oxygen uptake. In order to obtain important technical scale-up parameters, the microorganisms were immobilized on different carrier particles and employed in continuously operated three-phase airlift-loop reactors. The reactors could be operated at a dilution rate up to D=1·2 h⁻¹ (D≪μ_max) that, at an EDTA concentration of 450 mg dm⁻³, led to EDTA degradation rates up to 12·8 kg m⁻³ day⁻¹. The extent of EDTA deg-radation remained constant at 95–99% with increasing values of D. Achieved kinetic parameters of the biofilm systems were compared with those which were obtained from experiments with suspended cells. © 1998 Society of Chemical Industry     

Steady-state behaviour of an aerobic mixed culture growing on phenol in a continuous stirred reactor

The kinetic behaviour of an aerobic mixed culture was studied in a well-stirred reactor at various dilution rates with phenol as the sole carbon source and limiting factor. In the range of dilution rates investigated (up to 0.51 h⁻¹), biomass washout from the reactor was not observed. Analysis of steady-state data using the inhibitory kinetic parameters obtained in a previous batch growth study gave a very poor prediction of the reactor's performance. Since microbial growth occurred on the reactor walls, the experimental data were analysed using two steady-state equations (one with Monod, the other with Haldane growth kinetics) together with the Topiwala-Hamer model to describe the wall attachment. The mathematical model using Monod kinetics gave a good fit to the experimental data and the values of the kinetic parameters obtained using this model were as follows: maximum specific growth rate, 0.340 h⁻¹; saturation constant, 1.61 mg l⁻¹; wall growth constant, 2.84 mg l⁻¹. Furthermore, the yield and maintenance coefficients were calculated to be 0.47 mg mg⁻¹ and 0.007 mg mg⁻¹ h⁻¹ respectively.     

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     

Adsorption of Phenols onto Granular Activated Carbon in a Liquid–Solid Fluidized Bed

The adsorption of phenol, p-chlorophenol and p-nitrophenol onto granular activated carbon (GAC) in a liquid–solid fluidized-bed adsorber has been studied. The effects of particle sizes of activated carbon (0·937, 1·524 mm), liquid flow rate (1·2, 2·0, 4·0 dm³ min⁻¹), initial phenol concentrations (1·12×10⁻⁴, 5·88×10⁻⁴ mol dm⁻³) and activated carbon mass (75, 150, 300 g) were investigated. The isotherm data were analysed by using the well-known isotherm equations to realize the adsorption characteristics of granular activated carbon. The model, which takes into account the external mass transfer with film-surface diffusion, surface adsorption equilibrium and internal mass transfer, was employed to fit the experimental data of the breakthrough curve. The model agreed with the experimental results very well when the Langmuir isotherm was employed and can be used for design and parametric studies. © 1997 SCI.     

Photosynthetic production of Dunaliella biomass from natural salt water and carbon dioxide

A Dunaliella strain has been isolated and grown in a medium containing saline lake water. Using 40% saline water and mixture of CO₂-air (4% CO₂) the algae grew with a specific growth rate of 0.073 h⁻¹. The maximum cell concentration was 5.6 × 10⁷ cells cm⁻³ which corresponded to 3.63 g dm⁻³ of dry biomass. Using 80% saline water, a glycerol concentration of 1.47 g glycerol g⁻¹ of, protein was obtained which amounted to 44.3% of Dunaliella dry weight. Fermentor CO₂ from a continuous yeast culture was also used as carbon source for photosynthetic growth. At 2.5% CO₂ in the exit gas a decrease of the specific growth rate was observed but the final concentration attained was comparable to that obtained with CO₂-air mixtures.