Influence Of Dilution Rate Research Articles

Utilization of Anabaena sp. in CO2 removal processes

This paper focuses on modelling the growth rate and exopolysaccharides production of Anabaena sp. ATCC 33047, to be used in carbon dioxide removal and biofuels production. For this, the influence of dilution rate, irradiance and aeration rate on the biomass and exopolysaccharides productivity, as well as on the CO(2) fixation rate, have been studied. The productivity of the cultures was maximum at the highest irradiance and dilution rate assayed, resulting to 0.5 g(bio) l(-1) day(-1) and 0.2 g(eps) l(-1) day(-1), and the CO(2) fixation rate measured was 1.0 gCO(2) l(-1) day(-1). The results showed that although Anabaena sp. was partially photo-inhibited at irradiances higher than 1,300 μE m(-2) s(-1), its growth rate increases hyperbolically with the average irradiance inside the culture, and so does the specific exopolysaccharides production rate. The latter, on the other hand, decreases under high external irradiances, indicating that the exopolysaccharides metabolism hindered by photo-damage. Mathematical models that consider these phenomena have been proposed. Regarding aeration, the yield of the cultures decreased at rates over 0.5 v/v/min or when shear rates were higher than 60 s(-1), demonstrating the existence of thus existence of stress damage by aeration. The behaviour of the cultures has been verified outdoors in a pilot-scale airlift tubular photobioreactor. From this study it is concluded that Anabaena sp. is highly recommended to transform CO(2) into valuable products as has been proved capable of metabolizing carbon dioxide at rates of 1.2 gCO(2) l(-1) day(-1) outdoors. The adequacy of the proposed equations is demonstrated, resulting to a useful tool in the design and operation of photobioreactors using this strain.

Evaluation of the composition of continuously-cultivated Arthrospira ( Spirulina) platensis using ammonium chloride as nitrogen source

This work is focused on the influence of dilution rate (0.08 ≤ D ≤ 0.32 d −1) on the continuous cultivation and biomass composition of Arthrospira ( Spirulina) platensis using three different concentrations of ammonium chloride ( c No = 1.0, 5.0 and 10 mol m −3) as nitrogen source. At c No = 1.0 and 5.0 mol m −3 the biomass protein content was an increasing function of D, whereas, when using c No = 10 mol m −3, the highest protein content (72.5%) was obtained at D = 0.12 d −1. An overall evaluation of the process showed that biomass protein content increased with the rate of nitrogen supply ( D c No) up to 72.5% at D c No = 1.20 mol m −3 d −1. Biomass lipid content was an increasing function of D only when the nitrogen source was the limiting factor for the growth ( D c No ≤ 0.32 mol m −3 d −1), which occurred solely with c No = 1.0 mol m −3. Under such conditions, A. platensis reduced its nitrogen reserve in the form of proteins, while maintaining almost unvaried its lipid content. The latter was affected only when the concentration of nitrogen was extremely low ( c No = 1.0 mol m −3). The most abundant fatty acids were the palmitic (45.8 ± 5.20%) and the γ-linolenic (20.1 ± 2.00%) ones. No significant alteration in the profiles either of saturated or unsaturated fatty acids was observed with c No ≤ 5.0 mol m −3, prevailing those with 16 and 18 carbons.

Production of astaxanthin by Haematococcus pluvialis: Taking the one‐step system outdoors

The feasibility of a one-step method for the continuous production of astaxanthin by the microalga Haematococcus pluvialis has been verified outdoors. To this end, influence of dilution rate, nitrate concentration in the feed medium, and irradiance on the performance of continuous cultures of H. pluvialis was firstly analyzed indoors in bubble column reactors under daylight cycles, and then outdoors, using a tubular photobioreactor. At the laboratory scale, the behavior of the cultures agreed with that previously recorded in continuous illumination experiences, and attested that the major factors determining biomass and astaxanthin productivity were average irradiance and specific nitrate supply. The rate of astaxanthin accumulation was proportional to the average irradiance inside the culture, provided that a nitrate limiting situation had been established. The accumulation of astaxanthin under daylight cycles was maximal for a specific nitrate input of 0.5 mmol/g day. The recorded performance has been modeled on the basis of previously developed equations, and the validity of the model checked under outdoor conditions. Productivity values for biomass and astaxanthin of 0.7 g/L day and 8.0 mg/L day respectively, were obtained in a pilot scale tubular photobioreactor operating under continuous conditions outdoors. The magnitude of the experimental values, which matched those simulated from the obtained model, demonstrate that astaxanthin can be efficiently produced outdoors in continuous mode through a precise dosage of the specific nitrate input, taking also into consideration the average irradiance inside the culture.

Continuous treatment process of mercury removal from aqueous solution by growing recombinant E. coli cells and modeling study

A continuous treatment process was developed to investigate the capability of genetically engineered E. coli to simultaneously accumulate mercuric ions and reproduce itself in a continuous stirred tank reactor (CSTR) system. The influence of dilution rate and initial Hg 2+ concentration on continuous process was evaluated. Results indicated that the recombinant E. coli could effectively accumulate Hg 2+ from aqueous solution with Hg 2+ removal ratio up to about 90%, and propagate its cells at the same time in the continuous treatment system under suitable operational conditions. A kinetic model based on mass balance of Hg 2+ was proposed to simulate the continuous process. The modeling results were in good agreement with the experimental data.

Cultivation of Spirulina platensis by continuous process using ammonium chloride as nitrogen source

Abstract This work is focused on the influence of dilution rate (0.08⩽D⩽0.32 d−1) on the kinetics of continuous cultivation of Spirulina platensis at two different concentrations of ammonium chloride (N0=1.0 and 10 mM) as nitrogen source. Cell productivity increased in both series of runs up to D≅0.12–0.16 d−1, and then decreased. While at N0=1.0 mM biomass washing was certainly the cause of progressive cell concentration decrease, a combination of this phenomenon with the toxic effect of excess ammonia was responsible, at N0=10 mM and D⩾0.20 d−1, for quick stop of cell growth just beyond the achievement of maximum cell productivity (92.4 mg l−1 d−1). Similar profile was observed for protein productivity, that achieved a maximum value of 67.0 mg l−1 d−1, because of the very high protein content (72.5%) of biomass produced under these conditions. The yield of nitrogen-to-biomass was much higher at the lower N0, because of the low protein content, and reached a maximum value of 9.7 g g−1 at D=0.08–0.12 d−1. The yield of nitrogen-to-protein showed less marked difference, being most of the nitrogen present in the cell as proteins or free amino-acids.

Biological phenol removal using immobilized cells in a pulsed plate bioreactor: Effect of dilution rate and influent phenol concentration

The continuous aerobic biodegradation of phenol in synthetic wastewater was carried out using Nocardia hydrocarbonoxydans immobilized over glass beads packed between the plates in a pulsed plate bioreactor at a frequency of pulsation of 0.5 s −1 and amplitude of 4.7 cm. The influence of dilution rate and influent phenol concentration on start up and steady state performance of the bioreactor was studied. The time taken to reach steady state has increased with increase in dilution rate and influent phenol concentration. It was found that, as the dilution rate is increased, the percentage degradation has decreased. Steady state percentage degradation was also reduced with increased influent phenol concentration. Almost 100% degradation of 300 and 500 ppm influent phenol could be achieved at a dilution rate of 0.4094 h −1 and more than 99% degradation could be achieved with higher dilution rates. At a higher dilution rate of 1.0235 h −1 and at concentrations of 800 and 900 ppm the percentage degradation has reduced to around 94% and 93%, respectively. The attached biomass dry weight, biofilm thickness and biofilm density at steady state were influenced by influent phenol concentration and dilution rate.

Effect of aeration and dilution rate on nisin Z production during continuous fermentation with free and immobilized Lactococcus lactis UL719 in supplemented whey permeate

The influence of dilution rate (D) and aeration on soluble and cell-bound nisin Z production was investigated during continuous free (FC) and immobilized cell (IC) cultures with Lactococcus lactis subsp. lactis biovar diacetylactis UL719 in supplemented whey permeate. Maximum total bacteriocin titres during non-aerated continuous FC and IC cultures were obtained for low D, with 1490 and 1090 IU mL−1 for 0.15 h−1 or 0.25 and 0.5 h−1, respectively. For both systems, aeration increased nisin total production with maximum titres of 2560 and 2430 IU mL−1 for low D, respectively, as well as specific production. Volumetric productivity was the highest for an intermediate D of 0.4 h−1 during FC cultures (460 IU mL−1 h−1 for both aerated and non-aerated cultures), while it increased continuously with D during IC cultures, reaching high values of 1090 and 1760 IU mL−1 h−1 at 2.0 h−1 without and with aeration, respectively. In comparison with previous data for FC batch cultures, data from this study may indicate that during continuous fermentations at steady state, some steps in nisin biosynthesis are limiting. In these conditions, nisin production by immobilized cells is reduced.

Influence of dilution rate on enzyme synthesis in Aspergillus niger in continuous culture.

Summary: Aspergillus niger was grown in continuous culture under steady-state conditions in citrate-limiting or glucose-limiting medium. The specific activities of hexokinase, phosphofructokinase, pyruvate kinase, fructose diphosphatase, 6-phosphogluconate dehydrogenase and, to a limited extent, citrate synthase under citrate limitation remained at a relatively constant steady-state level irrespective of the dilution rate (0.01 to 0.5 h-1). Increase in dilution rate led to an increase in the specific activities of aconitase, NAD(P) isocitrate dehydrogenase, malate dehydrogenase, and glucose-6-phosphate dehydrogenase in both citrate and glucose limiting culture, and to an increase in citrate synthase, hexokinase, phosphofructokinase, pyruvate kinase, and 6-phosphogluconate dehydrogenase only in glucose limitation. A decrease in specific activity with increasing dilution rate occurred with isocitrate lyase in both citrate and glucose limitation and for fructose diphosphatase only in glucose limitation. The specific activity of malate synthetase showed a peak activity in the middle range of dilution rates.

Influence of dilution rate and cell immobilization on plasmid stability during continuous cultures of recombinant strains of Lactococcus lactis subsp. lactis

The influence of dilution rate and cell immobilization on plasmid stability in recombinant strains of Lactococcus lactis subsp. lactis was investigated during continuous cultures. The studied strains, L. lactis IL2682 and IL2683, contained plasmids pIL9 (Lac +), pIL205 (Cm R) and plasmids pIL252 (low copy number) and pIL253 (high copy number), respectively, that conferred resistance to erythromycin. Plasmid pIL205 was remarkably stable. Dilution rate did not affect the rate of loss of plasmids pIL252 and pIL253 significantly. Nevertheless, the loss of plasmid pIL253 was apparent after a further 21 generations when the dilution rate was decreased from 0.70 h −1 to 0.55 h −1. Cell immobilization in beads of κ-carrageenan/locust bean gum improved plasmid stability by factors of 4.5 for pIL253 and 6.5 for pIL252. Thus, 10% of cells containing plasmids pIL252 or pIL253 were still present after 370 or 540 generations, respectively, compared with 50 or 210 generations in free cell cultures.

Influence of dilution rate and dissolved oxygen concentration on continuous keto acid production by Gluconobacter oxydans subsp. melanogenum

The influence of dilution rate and dissolved oxygen concentration on continuous production of 2,5-diketogluconic acid (2,5-DKGA) by Gluconobacter oxydans subsp. melanogenum is described. Under suitable dissolved oxygen conditions, the glucose oxidation rate is independent of variations in dilution rates over a wide range ( D < 0.33 h −1). The higher dilution rate, however, leads to a partial oxidation of the substrate and therefore accumulation of more gluconic acid. Contrary to this, a longer residence time (lower dilution rate) was more suitable for better ketogenic activity, thereby facilitating accumulation of 2,5-DKGA in higher yields. A high dissolved oxygen concentration is further shown to positively influence the overall oxidation process through an organized induction of membrane-bound NAD(P) +-independent dehydrogenases.

High‐concentration cultivation of Lactococcus cremoris in a cell‐recycle reactor

High-cell concentration cultivation of Lactococcus cremoris, a homofermentative lactic acid producer, in a cell-recycle fermentor is described. Cross-flow filtration allowing continuous removal of the inhibitory metabolite, the influence of dilution rate on growth was investigated in total or partial cell-recycle cultures. The dependence of growth characteristics on operating conditions was identified and quantified using lactose as the carbon source. Growth kinetics could be described by both lactate removal efficiency and nutrient availability. Based on physiological observations, biomass and lactic acid productivities were predicted in partial cell-recycle cultures.

Influence of dilution rate and induction of cloned gene expression in continuous fermentations of recombinant yeast

The effects of growth rate on cloned gene product synthesis in recombinant Saccharomyces cerevisiae have been studied in continuous culture. The plasmid employed contains a yeast GAL10-CYC1 hybrid promoter directing expression of the E. coli lacZ gene. beta-Galactosidase production was therefore controlled by the yeast galactose regulatory circuit, and the induction process and its effects were studied at the various dilution rates. At all dilution rates plasmid stability decreased with induction of lacZ gene expression. In some instances, two induced "steady states" were observed, the first 10-15 residence times after induction and the second after 40-50 residence times. The second induced steady state was characterized by greater biomass concentration and lower beta-galactosidase specific activity relative to the first induced "steady-state." beta-Galactosidase specific activity and biomass concentration increased as dilution rate was reduced, and despite lower flow rate and plasmid stability, overall productivity (activity/L/hr) was substantially higher at low dilution rate. Important factors influencing all of the trends were the glucose and galactose (inducer) concentrations in the vessel and inducer metabolism.

Continuous culture of the marine microalga Tetraselmis sp. — productivity analysis

An outdoor experimental system for continuous culture of the marine microalga Tetraselmis sp. is described. The influence of dilution rate, initial biomass concentration and the intensity of solar radiation on the amount of biomass obtained was examined. The average rate of production of cells, G m, is a parabolic function of the dilution rate and reached a maximum value at D = 0.09 h −1. The intensity of light, I o, influences productivity up to approximately 100 W/m 2, above which saturation was observed. The experimental results G m- I o were adjusted to an exponential model for light-restricted growth. The average rate of production of cells, versus the initial biomass concentration, C o, reached a maximum value. G m decreased as C o increased to high cell density values due to light limitation and when C o decreased to low cell density values due to decreased efficiency in the use of incident solar radiation.

Influence of dilution rate on the acidogenic phase products distribution during two‐phase lactose anaerobiosis

Acidogenic fermentation of lactose was carried out in a continuous stirred reactor with a mixed anaerobic culture. From the variation of the reactor products with pH and dilution rate two possible carbon flow schemes were proposed for the reaction. In both schemes the carbon flow from pyruvate to butyrate and lactate was assumed to occur in parallel. A change in gas composition and in product concentrations at dilution rates between 0.1 and 0.15 h(-1) for pH levels between 4.5 and 6.0 was ascribed to a shift in microbial population. To clarify the mechanism radiotracer tests were made using [U-(14)C]-butyrate, [2-(14)C]-propionate and [U-(14)C]-lactate to determine the path of carbon flow during acidogenesis of lactose using a mixed culture. At a dilution rate between 0.1 and 0.15 h(-1) and pH from 4.5 to 6.0 a rise in the lactate concentration in the product was shown to be due to a microbial population shift which disabled the conversion of lactate to other intermediary metabolites. It was also found that the flow of carbon from pyruvate to butyrate and lactate occurred by parallel pathways. Also, in the presence of hydrogen reducing methanogens, lactate was almost completely converted to acetate and not propionate. Butyrate was found to be converted to acetate at a slow rate as long as hydrogen reducing methanogens were present. The role played by propionibacteria in this lactose acidogenic eocosystem was minor. From the carbon flow model it can be concluded that lactate is the most suitable marker for optimizing an acidogenic reactor in a two-phase biomethanation process.

The influence of dilution rate, temperature, and influent substrate concentration on the efficiency of steady-state biomass production in continuous microbial culture.

The efficiency of steady-state biomass production was defined as the ratio of the biomass produced at steady state to the biomass that would be produced if influent substrate were completely and permanently incorporated. The scope of analysis was confined to microbial growth processes described by a Monod reaction mechanism. A thermo-kinetic analysis of this mechanism with coefficient values estimated from experimental data showed: (table; see text) (1) As the dilution rate was increased, the efficiency passed through a single peak. Raising the temperature did not markedly change the peak efficiency, but did broaden and shift the peak toward higher dilution rates. In contrast, elevating the influent substrate concentration significantly improved the peak efficiency while still broadening and shifting the peak toward higher dilution rates. (2) As the temperature was raised, the efficiency also showed a single peak. Increasing the dilution rate did not significantly alter the peak value or breadth, but did shift the peak to higher temperatures. In contrast, elevating the influent substrate concentration substantially improved the peak efficiency and caused the peak to shift toward lower temperatures without broadening. (3) As the influent substrate concentration was elevated, the peak efficiency improved and asymptotically approached unity. These results suggested that relatively high influent substrate concentrations, low temperatures, and moderate dilution rates would be needed to optimize the efficiency of steady-state biomass production by Monod processes with coefficient values similar to those used in this paper.

Kinetics of biphasic growth of yeast in continuous and fed‐batch cultures

AbstractThe influence of dilution rate on the production of biomass, ethanol, and invertase in an aerobic culture of Saccharomyces carlsbergensis was studied in a glucose‐limited chemostat culture. A kinetic model was developed to analyze the biphasic growth of yeast on both the glucose remaining and the ethanol produced in the culture. The model assumes a double effect where glucose regulates the flux of glucose catabolism (respiration and aerobic fermentation) and the ethanol utilization in yeast cells. The model could successfully demonstrate the experimental results of a chemostat culture featuring the monotonic decrease of biomass concentration with an increase of dilution rate higher than 0.2 hr−1 as well as the maximum ethanol concentration at a particular dilution rate around 0.5 hr−1. Some supplementary data were collected from an ethanol‐limited aerobic chemostat culture and a glucose‐limited anaerobic chemostat culture to use in the model calculation. Some parametric constants of cell growth, ethanol production, and invertase formation were determined in batch cultures under aerobic and anaerobic states as summarized in a table in comparison with the chemostat data. Using the constants, a prediction of the optimal control of a glucose fed‐batch yeast culture was conducted in connection with an experiment for harvesting a high yield of yeast cells with high invertase activity.

Influence of dilution rate on NAD(P) and NAD(P)H concentrations and ratios in a Pseudomonas sp. grown in continuous culture.

A freshwater Pseudomonas sp. was grown in continuous culture under steady-state conditions in L-lactate-, succinate-, glucose- or ammonium-limited media. Under carbon limitation, the NAD(H) (i.e. NAD + NADH) concentration of the organisms increased exponentially from approximately 2 to 7 mumol/g dry wt as the culture dilution rate (D) was decreased from 0.5 to 0.02 h-1. Organisms grown at a given D in any of the carbon-limited media possessed very similar levels of NAD(H). Therefore, under these conditions, cellular NAD(H) was only a function of the culture O and was independent of the nature of the culture carbon source. D had no influence on the NAD(H) content of cells grown under ammonium limitation. In contrast, cellular NADH concentration was not influenced by D in carbon- or ammonium-limited media. In L-lactate-limited medium, bacteria possessed 0.14 mumol NADH/g dry wt; very similar levels were found in organisms grown in the other media. The results are consistent with those of Wimpenny & Firth (1972) that bacteria rigidly maintain a constant NADH level rather than a constant constant NADH: NAD ratio. NADP(H) (i.e. NADP + NADPH) and NADPH levels were also not influenced by changes in the culture carbon source or in D; in L-lactate-limited medium these concentrations were 0.97 and 0.53 mumol/g cell dry wt, respectively. The NADPH:NADP(H) ratio was much higher than the NADH:NAD(H) ratio, averaging 55% in carbon-limited cells.

Influence of Dilution Rate on Enzymes of Intermediary Metabolism in Two Freshwater Bacteria Grown in Continuous Culture

Two freshwater bacteria, a Pseudomonas sp. and a Spirillum sp., were grown in continuous culture under steady-state conditions in L-lactate-, succinate-, ammonium- or phosphate-limited media. In Pseudomonas sp., NAD-independent and NAD-dependent L-lactate dehydrogenases, aconitase, isocitrate dehydrogenase and glucose 6-phosphate dehydrogenase activities increased up to 10-fold as the dilution rate (D) was decreased from 0.5 to 0.02 h-1, regardless of whether the growth-limiting nutrient was carbon, ammonium or phosphate. In contrast, 2-oxoglutarate dehydrogenase and succinate dehydrogenase activities were not influenced by D, and NADH oxidase activity increased with D. Spirillum sp. gave different results in some respects, but it also exhibited an increase in the activity of several enzymes at low D values. Such increases may emanate from release of catabolite repression, and catabolite repressors for the five enzymes in Pseudomonas sp. showing such increases are probably compounds of carbon, nitrogen and phosphorus. It is likely that increased enzyme syntheses in low D cultures represent the normal physiological state for bacteria in aquatic environments where growth occurs slowly under nutrient limitations. Such increases probably permit a more effective utilization of nutrients present at sub-saturating concentrations.