Dissolved Carbon Dioxide Concentration Research Articles

Comparative performance of CO2 measuring methods: Marine aquaculture recirculation system application

Many methods are available for the measurement of dissolved carbon dioxide in an aqueous environment. Standard titration is the typical field method for measuring dissolved CO2 in aquaculture systems. However, titrimetric determination of dissolved CO2 in marine water aquaculture systems is unsuitable because of the high dissolved solids, silicates, and other dissolved minerals that interfere with the determination. Other methods used to measure dissolved carbon dioxide in an aquaculture water included use of a wetted CO2 probe analyzer, standard nomographic methods, and calculation by direct measurements of the water's pH, temperature, and alkalinity. The determination of dissolved CO2 in saltwater based on partial pressure measurements and non-dispersive infra-red (NDIR) techniques with a CO2 gas analyzer are widely employed for oceanic surveys of surface ocean CO2 flux and are similar to the techniques employed with the head space unit (HSU) in this study. Dissolved carbon dioxide (DC) determination with the HSU using a infra-red gas analyzer (IRGA) was compared with titrimetric, nomographic, calculated, and probe measurements of CO2 in freshwater and in saltwater with a salinity ranging from 5.0 to 30ppt, and a CO2 range from 8 to 50mg/L. Differences in CO2 measurements between duplicate HSUs (0.1–0.2mg/L) were not statistically significant different. The coefficient of variation for the HSU readings averaged 1.85% which was better than the CO2 probe (4.09%) and that for the titrimetric method (5.84%). In all low, medium and high salinity level trials HSU precision was good, averaging 3.39%. Differences existed between comparison testing of the CO2 probe and HSU measurements with the CO2 probe readings, on average, providing DC estimates that were higher than HSU estimates. Differences between HSU and titration based estimates of DC increased with salinity and reached a maximum at 32.2ppt. These differences were statistically significant (P<0.05) at all salinity levels greater than 0.3ppt. Results indicated reliable replicated results from the head space unit with varying salinity and dissolved carbon dioxide concentrations.

English

English

Shallow ocean overturning and the heat and carbon content of the Glacial Tropical Ocean

Mechanisms affecting the heat and carbon content of the Glacial Tropical Ocean (21,000 years BP) remain controversial. Exchange with the deep ocean via vertical mixing and the overturning circulation is one aspect that is clearly relevant to greenhouse gas concentrations and future climate change. We examined evidence of the possible role of the shallow overturning contribution on the Glacial Tropical Ocean temperature and carbonate ion concentration. Compared to the present, we find that the Glacial tropical upper ocean (0–1000 m) had enhanced vertical gradients in temperature and carbonate ion concentration, reduced turbulent diffusivity (vertical mixing rate) (by 20% or more), and weakened Ekman pumping in middle-latitudes, all consistent with reduced shallow overturning. The weakened property exchanges between the tropical upper ocean and the ocean below (cold with high total dissolved carbon-dioxide concentration) provide a unified explanation for both the unexpectedly-small sea surface cooling and the lower carbon-dioxide content in the Glacial tropical upper ocean and the atmosphere.

Metabolic and transcriptional response of recombinant Escherichia coli to elevated dissolved carbon dioxide concentrations

The effect of dissolved carbon dioxide (dCO(2)) concentration on the stoichiometric and kinetic constants and by-product accumulation was determined for Escherichia coli cells producing recombinant green fluorescent protein (GFP). Constant dCO(2), in the range of 20-300 mbar, was maintained during batch cultures by manipulating the inlet gas composition. As dCO(2) increased, specific growth rate (micro) decreased, and acetate accumulation and the time for onset of GFP production increased. Maximum biomass yield on glucose and GFP concentration were affected for dCO(2) above 70 and 150 mbar, respectively. Expression analysis of 16 representative genes showed that E. coli can respond at the transcriptional level upon exposure to increasing dCO(2), and revealed possible mechanisms responsible for the detrimental effects of high dCO(2). Genes studied included those involved in decarboxylation reactions (aceF, icdA, lpdA, sucA, sucB), genes from pathways of production and consumption of acetate (ackA, poxB, acs, aceA, fadR), genes from gluconeogenic and anaplerotic metabolism (pckA, ppc), genes from the acid resistance (AR) systems (adiA, gadA, gadC), and the heterologous gene (gfp). The transcription levels of tricarboxylic acid (TCA) cycle genes (icdA, sucA, sucB) and glyoxylate shunt (aceA) decreased as dCO(2) increased, whereas fadR (that codes for a negative regulator of the glyoxylate operon) and poxB (that codes for PoxB which is involved in acetate production from pyruvate) were up-regulated as dCO(2) increased up to 150 mbar. Furthermore, transcription levels of genes from the AR systems increased as dCO(2) increased up to 150 mbar, indicating that elevated dCO(2) triggers an acid stress response in E. coli cells. Altogether, such results suggest that the increased acetate accumulation and reduction in mu, biomass yield and maximum GFP concentration under high dCO(2) resulted from a lower carbon flux to TCA cycle, the concomitant accumulation of acetyl-CoA or pyruvate, and the acidification of the cytoplasm.

Effect of elevated dissolved carbon dioxide concentrations on growth of Corynebacterium glutamicum on d-glucose and l-lactate

The effect of increased dissolved carbon dioxide concentrations on growth of Corynebacterium glutamicum was studied with continuous turbidostatic cultures. The carbon sources were either l-lactate or d-glucose. To increase the dissolved carbon dioxide concentration the carbon dioxide partial pressure of the inlet gas stream pCO2,IN was increased stepwise from 0.0003 bar (air) up to 0.79 bar, while the oxygen partial pressure of the inlet gas stream was kept constant at 0.21 bar. For each resulting carbon dioxide partial pressure pCO2 the maximum specific growth rate mu(max) was determined from the feed rate resulting from the turbidostatic control. On d-glucose and pCO2 up to 0.26 bar, mu(max) was mostly constant around 0.58 h(-1). Higher pCO2 led to a slight decrease of mu(max). On l-lactate mu(max) increased gradually with increasing carbon dioxide partial pressures from 0.37 h(-1) under aeration with air to a maximum value of 0.47 h(-1) at a pCO2 of 0.26 bar. At very high pCO2 (0.81 bar) mu(max) decreased down to 0.35 h(-1) independent of the carbon source.

Spectrophotometric Determination of Ammonia in Estuarine Waters by Hybrid Reagent‐Injection Gas‐Diffusion Flow Analysis

A flow‐injection gas‐diffusion technique is described for the online determination of ammonia in estuarine waters covering a salinity range of S=0 to 36. The flow analysis system, which is a hybrid of reagent injection and conventional sample‐injection flow systems, avoids the need for a rotary injection valve. Whereas gas‐diffusion techniques have been widely applied in conventional sample‐injection flow analysis, reagent‐injection flow analysis involving gas diffusion has been little used because it is susceptible to interference from dissolved gaseous species such as carbon dioxide coexisting with ammonia in the sample. This source of interference has been overcome by online adjustment of sample to pH 8.4 prior to the injection of the base that initiates gas diffusion of ammonia. The pore sizes of hydrophobic membranes used in gas diffusion were characterized by a bubble‐point test prior to use in the flow analysis system. These showed wide variation in pore size, and grading and careful selection was necessary in order to obtain reliable gas diffusion measurements of ammonia. The proposed flow‐injection system can be operated in a continuous flow mode, at a sample throughput of 135 measurements hr−1 with a typical limit of detection (LOD) of 9 µg N L−1, or in stopped‐flow mode at 60 measurements hr−1 with a LOD of 3 µg N L−1. The technique was validated using water samples containing a wide range of dissolved carbon dioxide concentrations, salinity, and pH. Excellent agreement (r=0.999) was observed between results obtained using the reagent‐injection system and an approved reference method. The authors were invited to contribute this paper to a special issue of the journal entitled “Spectroscopy and Automation”. This special issue was organized by Miguel de la Guardia, Professor of Analytical Chemistry at Valencia University, Spain.

Neutralization of the Acidified Seawater Effluent from the Flue Gas Desulfurization Process: Experimental Investigation, Dynamic Modeling, and Simulation

The neutralization of the seawater effluent in a wet flue gas desulfurization (FGD) process was investigated. Before discharge, the acidified seawater effluent from a absorber is neutralized, using the natural alkalinity in seawater, and aeration is performed to enhance the neutralization due to the stripping of carbon dioxide dissolved in the effluent. Experimental investigation, dynamic modeling, and simulation have been performed to elucidate the neutralization of the seawater effluent in a FGD process. We have measured changes in solution pH and the dissolved carbon dioxide concentration and carbon dioxide concentration in the outlet gas, relative to the time of aeration. Increases in the aeration rate, salinity, dissolved SO2 concentration, and temperature increased the neutralization rate. We have developed a rate-based model to simulate the neutralization process of the acidified seawater effluent. In the modeling, nonideal mixing in the gas phase is described using a tanks-in-series model while the liquid is assumed to be completely mixed. The model, which is based on reaction kinetics and equilibrium in the liquid phase and gas−liquid mass transfer, combined with the nonideal mixing in the gas phase, consists of five ordinary differential equations. In simulating the neutralization of the acidified seawater effluent, the effects of its temperature and salinity on the neutralization rate were taken into account. The proposed model, which included no adjustable parameters, could describe the present experimental results for the dynamic changes of solution pH, dissolved CO2 concentration, and CO2 concentration in the gas phase successfully.

Measurement of Overall Volumetric Mass Transfer Coefficients for Carbon Dioxide in a Well-Mixed Reactor Using a pH Probe

Carbon dioxide can serve as a source of carbon for photosynthetic cell cultures, but it must reside in the aqueous phase prior to uptake. Carbon dioxide is a gas at room temperature and pressure, and its solubility in water is very low. It resides in the aqueous phase as four different species, carbon dioxide, CO2; carbonic acid, H2CO3; bicarbonate ion, HCO3-; and carbonate ion, CO3=, whose equilibrium concentrations are pH dependent. With these factors taken into account, a model has been developed to allow the pH profile of an aqueous phase, undergoing a sudden application of bubbles containing carbon dioxide, to be used as a measure of the transient dissolved carbon dioxide concentration in a reactor. Experimentally measured carbon dioxide profiles were used to calculate the overall volumetric mass transfer coefficients for carbon dioxide into a well-mixed reactor as a function of temperature, stirring speed, and aeration rate. Finally, an empirical correlation is provided to predict the overall volume...

Development of a novel approach for secondary modelling in predictive microbiology: incorporation of microbiological knowledge in black box polynomial modelling

This research deals with the development of a novel secondary modelling procedure within the framework of predictive microbiology. The procedure consists of three steps: (i) careful formulation of the available microbiological information, both from literature and from the experimental case study at hand, (ii) translation of these requirements in mathematical terms under the form of partial derivatives throughout the complete interpolation region of the experimental design, and (iii) determination of parameter values with suitable optimisation techniques for a flexible black box modelling approach, e.g., a polynomial model or an artificial neural network model. As a vehicle for this procedure, the description of the maximum specific growth rate of Lactobacillus sakei in modified BHI-broth as influenced by suboptimal temperature, water activity, sodium lactate and dissolved carbon dioxide concentration is under study. The procedure results in a constrained polynomial model with excellent descriptive and interpolating features in comparison with an extended Ratkowsky-type model and classical polynomial model, by combining specific properties of both model types. The developed procedure is illustrated on the description of the lag phase as well. It is stressed how the confrontation with experimental data is very important to appreciate the descriptive and interpolating capacities of new or existing models, which is nowadays not always carefully performed. Alternatively, the first two steps of the novel procedure can be used as a tool to demonstrate clearly (possible) interpolative shortcomings of an existing model with straightforward spreadsheet calculations.

Colloid Stability and the Influence of Dissolved Gas

The colloidal stability of synthetic silica spheres with clean, methylated, and dehydroxylated surfaces was studied at different concentrations of dissolved gas and KC1 electrolyte at a fixed pH of 4.2. A classic stability ratio/electrolyte concentration analysis shows that hydrophobic, methylated particles undergo faster rates of aggregation with increasing concentrations of dissolved carbon dioxide. Similar data for hydrophilic particles and dehydroxylated particles show no change as a function of dissolved carbon dioxide concentration. Zeta-potential data behave similarly, showing a strong influence of dissolved gas only for methylated particles. The results are interpreted in terms of DLVO theory, with the surface-to-surface interaction dominated by the presence of very small, protruding bubbles.

Phosphoruscalcium carbonate saturation relationships in a lowland chalk river impacted by sewage inputs and phosphorus remediation: an assessment of phosphorus self-cleansing mechanisms in natural waters

The relationship between calcium carbonate saturation and phosphorus concentrations for seven sites on the upper reaches of the River Kennet are examined. The findings are related to issues of groundwater supplies and the introduction of phosphorus treatment of effluent from the Marlborough sewage treatment works (STW) at part of the way along the study reach. Being supplied from a Cretaceous Chalk aquifer, the Kennet is mainly of a calcium-bicarbonate type and has a relatively constant composition of many major water quality determinands. Typically, the waters average a pH of approximately eight (range approx. 7.5–8.5) during the day with the lowest values occurring at the upstream site. Dissolved carbon dioxide varies from approximately 5 to 35 times atmospheric pressure during the late morning with the highest values occurring at the upstream site. However, in-stream biological activity gives rise to marked diurnal fluctuations in pH and dissolved carbon dioxide concentrations and during the summer months, by mid to late afternoon, pH is at its maximum and dissolved carbon dioxide is at its lowest: this is shown by continuous measurements at one of the river sites. Alkalinity and calcium concentrations remain relatively constant at approximately 4700 μEq/l (range 3500–6000 μEq/l) and 120 mg/l (range 85–150 mg/l), respectively, and the waters are oversaturated with respect to calcium carbonate (calcite) typically by a factor of six (range 2–25). Along the reach, soluble reactive phosphate (SRP) increases from the first to the second site with the introduction of sewage supplies from the Marlborough STW, and then declines further downstream as sewage dilution and uptake by the river bed/aquatic plants increases. The differences in concentration decrease after phosphorus removal from Marlborough STW. Despite this change, there is no clear indication of any calcite solubility control except perhaps at times of extreme baseflow during the growing season when within-stream photosynthesis is maximal and within-stream residence times are longer. A comparison of river and groundwater data shows that the groundwaters have similar alkalinities and calcium concentrations. However, the groundwaters have (a) higher carbon dioxide saturations (a factor of 2–5 times the value for the river), (b) lower pHs (0.5–1.5 units), (c) lower SRP concentrations (a quarter or less of the river values) and (d) waters near calcite saturation (unlike the surface waters which are oversaturated). The findings indicate a river system dominated by the input carbon dioxide laden groundwaters in approximate equilibrium with calcite attenuated by within-channel biological and physical processes. Within the river: (a) the waters degas carbon dioxide increasing the pH, producing oversaturated conditions; and (b) oscillating pH-dissolved carbon dioxide levels occur between day and night due to changing balances between photosynthesis and respiration. It seems that lowering the phosphorus levels have not resulted in calcite precipitation within the water column and that no significant within-stream self-cleansing mechanisms are occurring that might be predicted from theory: other components in the water such as dissolved organic carbon may inhibit calcite nucleation. However, the low SRP levels in the groundwater coupled with calcite saturation, may well indicate that phosphorous concentrations within the groundwater are regulated by such processes: the number of calcite nucleating sites are orders of magnitude higher and the calcite inhibitors may be less prevalent.

Top Pressure and Temperature Control the Fusel Alcohol/Ester Ratio through Yeast Growth in Beer Fermentation

Temperature and top pressure are key factors for maintaining a consistent quality of lager beer. Their influence on yeast growth, CO2 production, final concentrations of fusel alcohol and ester and production kinetics was analysed under industrial conditions. Fermentations of 12°P lager wort were performed at 10°C or 16°C temperature and 1.05 bars or 1.8 bars top pressure, corresponding to dissolved carbon dioxide concentrations of 1.98 g/litre to 3.65 g/litre. Analysis of variance was performed to test the significance of temperature and dissolved C2. Results show that temperature increases fermentation rate and the production ratio and final concentration of fusel alcohol, independently of the top pressure applied. Conversely, dissolved carbon dioxide controls the production rate and final concentration of ester by limiting yeast growth. Relationships between initial or maximum ester production rates and maximal growth rates were shown. Considering the metabolic pathways occurring during anaerobic growth of yeast, a limited production of acetyl CoA was expected in cultures with high concentrations of dissolved carbon dioxide. Also, final ester concentration and biomass produced are linearly correlated. Furthermore, whatever the ester considered, its synthesis is not influenced by corresponding fusel alcohol availability. It was demonstrated that fermentations performed with a reasoned combination of temperature and top pressure can result in a beer of distinctive aroma without resorting to modification of the initial wort or yeast strain.

The water quality of the River Wear, north-east England

A 1-year detailed study of water quality in the River Wear in combination with longer (decadal) term Environment Agency data (Harmonised Monitoring Scheme) show the influences of historic lead–zinc and coal mining and sewage inputs. The water quality for many determinands, such as sodium, chloride, boron, nitrate, and soluble reactive phosphorus, varies seasonally due to changing flow conditions. For most dissolved determinands, concentrations decrease with increasing flow in response to dilution of point and diffuse sources by rainfall. However, concentrations increase with increasing flow for dissolved organic carbon, aluminium, lead, iron, yttrium, and the lanthanides and actinides. This increase probably reflects two processes. Firstly, trace element-enriched runoff occurs from the acidic moorland areas of the catchment when it wets up. Secondly, at high flows, increased production of transition metals bearing microparticulate material occurs; these pass through conventional filters used to separate dissolved from particulate materials. For the particulate components, iron, manganese, aluminium, and some trace transition metals are present above the analytical detection limits and concentrations increase with increasing flow in response to increasing suspended sediment levels. However, particulate metal concentrations are relatively low for the Wear compared to the other eastern UK rivers, even though historic lead–zinc mining activity in the upper portions of the Wear catchment has led to extensive spoil contamination of the land. This feature probably reflects the lack of a significant flood plain area, where trace contaminants can accumulate within the sediments. The importance of inputs of pumped water from former coalmines is highlighted; increased manganese and dissolved carbon dioxide concentrations and reduced pH result. Examination of the Harmonised Monitoring Scheme data indicate no clear long-term changes in water quality for all but one determinand, although analysis is hampered by changes in sampling frequency for all determinands and changes in detection limits for certain trace metals. The only clear long-term change is a reduction in the micro-organic insecticide, aldrin. Nonetheless, the long-term data, when plotted as a function of month, follow the same pattern as the LOIS data. For aldrin, the higher values during the early period of record occurred in the latter half of each year, presumably as a consequence of seasonal application and enhanced leaching during the autumn.

Indirect methods for characterization of carbon dioxide levels in fermentation broth

Various factors which influence dissolved carbon dioxide levels were indirectly evaluated in pilot scale and laboratory studies. For pilot scale studies, off-gas carbon dioxide (percentage in exit air) was measured using a mass spectrometer and then its potential impact on dissolved carbon dioxide concentrations qualitatively examined. Greater volumetric air flowrates reduced off-gas carbon dioxide levels more effectively at lower airflow ranges and thus lowered expected dissolved carbon dioxide levels through gas stripping. Lower broth pH values decreased off-gas carbon dioxide levels but increased expected dissolved carbon dioxide levels due to the pH-dependence of the gas/liquid carbon dioxide equilibrium. While back-pressure increases had an insignificant effect on off-gas carbon dioxide levels, they directly affected expected dissolved carbon dioxide levels according to Henry's law. Laboratory studies, conducted using both uninoculated and inoculated fermentation media, quantified the response of the media to pH changes with bicarbonate addition, specifically its buffering capacity. This effect then was related qualitatively to expected dissolved carbon dioxide levels. Higher dissolved carbon dioxide levels, as demonstrated by reduced pH changes with bicarbonate addition, thus would be expected for salt solutions of increased ionic strength and higher protein content media. In addition, pH changes with greater bicarbonate additions declined for fermentation samples taken over the course of a one week cultivation, most likely due to the higher protein content associated with biomass growth. The presence of weak acids/bases initially in the media or formed as metabolic by products, as well as the concentration of buffering ions such as phosphate, also were believed to be important contributing elements to the buffering capacity of the solution.

Development of a lipase fermentation process that uses a recombinant Pseudomonas alcaligenes strain.

Pseudomonas alcaligenes M-1 secretes an alkaline lipase, which has excellent characteristics for the removal of fatty stains under modern washing conditions. A fed-batch fermentation process based on the secretion of the alkaline lipase from P. alcaligenes was developed. Due to the inability of P. alcaligenes to grow on glucose, citric acid and soybean oil were applied as substrates in the batch phase and feed phase, respectively. The gene encoding the high-alkaline lipase from P. alcaligenes was isolated and characterized. Amplification of lipase gene copies in P. alcaligenes with the aid of low- and high-copy-number plasmids resulted in an increase of lipase expression that was apparently colinear with the gene copy number. It was found that overexpression of the lipase helper gene, lipB, produced a stimulating effect in strains with high copy numbers (> 20) of the lipase structural gene, lipA. In strains with lipA on a low-copy-number vector, the lipB gene did not show any effect, suggesting that LipB is required in a low ratio to LipA only. During scaling up of the fermentation process to 100 m3, severe losses in lipase productivity were observed. Simulations have identified an increased level of dissolved carbon dioxide as the most probable cause for the scale-up losses. A large-scale fermentation protocol with a reduced dissolved carbon dioxide concentration resulted in a substantial elimination of the scale-up loss.

Climatically linked carbon isotope variation during the past 430,000 years in Southern Ocean sediments

We use the isotopic composition of carbon from organic matter enclosed within diatom frustules as a proxy for paleoproductivity and paleo‐dissolved carbon dioxide concentrations in ocean surface waters. A Southern Ocean record from south of the Antarctic Polar Front and spanning 430,000 years of carbon isotopic variation in diatomaceous organic matter is presented for the first time. The most refractory diatomaceous organic matter fraction was extracted and analyzed to avoid problems associated with diagenesis. The results clearly indicate cyclic changes in organic carbon isotopic ratios, with 13C depleted values associated with all of the last five glacial periods, reflecting changes in surface water properties and primary productivity. Changes in dissolved carbon dioxide concentrations are the most probable cause of these cycles, but the possible effect of seawater pH changes cannot be excluded.

Preliminary study of the chemistry of pore water extracted from tuff by one-dimensional compression : Peters, C A; Yang, I C; Higgins, J D; Burger, P A Proc 7th International Symposium on Water-Rock Interaction, Park City, 13–18 July 1992V1, P741–745. Publ Rotterdam: A A Balkema, 1992

A specially designed and fabricated one-dimensional compression cell is being used to extract water from nonwelded and densely welded tuffs having degrees of saturation greater than 16 and 37 percent respectively. Chemical analyses of pore water obtained at increasing pressures are used to evaluate possible changes in chemistry caused by compression. The extracted pore water varies form a calcium chloride type to a sodium bicarbonate type. The mean concentration of dissolved ions generally decreases during compression. The relative abundance of the major cations varies little with increasing pressure. Possible causes of the pore-water-chemistry changes include: (1) dilution of pore water by low ionic strength adsorbed water from zeolites and clays; (2) dissolution reactions caused by the increase in dissolved carbon dioxide concentrations that may result from pressurization; (3) membrane filtration by zeolites and clays; and (4) ion exchange with the zeolites and clays.

Acceleration of cell growth and ester formation by ultrasonic wave irradiation

The effects of ultrasonic wave irradiation on cell growth and the formation of ethanol and other volatile components in the fermentation process were investigated. The fermentation periods were reduced to 50–64% in wine, beer, and sake made from saccharified rice solution when weak ultrasonic waves were irradiated at 30 mW/cm 2; the total intensity was 590 mW. YEPD medium fermented by a combination of optimal thermal trajectory control and continuous ultrasonic irradiation yielded a concentration of isoamylacetate about 2.5 times greater than the maximum concentration under isothermal conditions (20°C). Irradiation had virtually no effect when the dissolved carbon dioxide concentration (DCO 2) was maintained at a level lower than the experimental value of Bunsen's CO 2 absorption coefficient. Therefore, it is suggested that irradiation accelerates the formation of ethanol and other components mainly by decreasing DCO 2.

Dissolved carbon dioxide measurement and its correlation with operating parameters in fermentation processes.

A silicone tubing probe was used to measure dissolved carbon dioxide in two industrial fermentation processes. The two processes differed markedly in their broth viscosities: one had high viscosity (2000-3000 cP) and the other had low viscosity (< 100 cP). The goal was to study changes in dissolved carbon dioxide concentration in fermentation broth when operating parameters, such as total pressure, air flow rate and, agitation rate, were modified. It was shown that in high-viscosity fermentation broths the dissolved carbon dioxide concentration can reach as high as 190% of that calculated by assuming an equilibrium between the air coming out of the fermentor and the fermentation broth. For low-viscosity broth, the highest dissolved carbon dioxide concentration was found to be about 133% of the equilibrium value. On the basis of the material balance over the entire fermentor, the ratio of actual dissolved carbon dioxide partial pressure and carbon dioxide partial pressure in air leaving the fermentor was correlated to the operating parameters of pressure, air flow, and carbon dioxide transfer coefficient. Since carbon dioxide transfer coefficients are not readily available, we recommend a method of using oxygen transfer coefficients to develop a correlation that can be used on-line to predict changes in dissolved carbon dioxide concentration when operating parameters are changed or when process improvements and scale-up are undertaken.

Continuous ethanol fermentation using immobilized yeast in a fluidized bed reactor

AbstractContinuous 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.