Comparative study on enhanced pectinase and alkali-oxygen degummings of sisal fibers

This paper reports an improved traditional fiber degumming method, where sisal fibers were treated by alkali oxygen and pectinase, respectively, after the solute alkali pretreatment. To explore the influence of various factors on its degumming, efficiency of degumming through single factor and orthogonal experiments was aasessed. The results showed that pectinase/alkali-oxygen method after the first alkali treatment had a good effect on the degumming of sisal fiber, and most of the non-cellulose components such as hemicellulose, lignin and pectin had been removed. After pectinase treatment, the cellulose content and crystallinity were 71.87% and 66.29%, respectively. After alkaline oxygen treatment, the cellulose content was 77.16%, and the crystallinity was 69.09%. In terms of degumming rate, alkali oxygen treatment worked better than pectinase treatment, the degumming rate of pectinase method was about 10%, while that of alkali-oxygen method was more than 20%. In other hand, the pectinase method was much milder and had less damage to fibers. It would provide some references for the future application and development of sisal fiber.

     

Influence of a new axial impeller on K L a and xylanase production by Penicillium canescens 10-10c

The effects of a new axial impeller (HTPG4) on oxygen volumetric transfer coefficient, K _L a, and xylanase production by Penicillium canescens 10-10c were studied and compared for dual-impeller systems, one with one DT4 impeller below and one HTPG4 above (DT4-HTPG4) and one with two DT4 (DT4-DT4) impellers, in a 5-L bioreactor. The volumetric coefficient of oxygen transfer was measured in culture medium using a gassing-out method at different gassing rates and agitation speeds. We observed that the DT4-HTPG4 combination provided better K _L a performance than the DT4-DT4 combination. The two combinations were also tested for their influence on xylanase production by a filamentous microorganism; P. canescens 10-10c. These experiments demonstrated that the DT4-HTPG4 combination impeller enhanced enzyme production up to 23% compared with the DT4-DT4 combination at an aeration rate of 1 vvm and an agitation speed of 600 rpm. The main cause for this difference is thought to be a higher shear stress generated by the DT4-DT4 combination, which damages the mycelium of P. canescens and decreases xylanase production.     

Cellulose fiber biodegradation in natural waters: river water,brackish water,and seawater

Cellulose, the main component of plant cell walls, is degradable in nature. However, to the best of our knowledge, this is the first report that compares the biodegradability of cellulose fibers with different structures in natural waters. River water, brackish water, and seawater were collected from the Kamo River and Osaka Bay, Japan. Biodegradation of cellulose fibers with different structures and crystallinities, ramie, mercerized ramie, and regenerated cellulose fibers in the collected natural water was investigated in the dark at 20 °C for 30 days. The primary and aerobic ultimate biodegradability were evaluated by weight loss and biochemical oxygen demand (BOD) tests, respectively. In the weight-loss test, cellulose fibers were found to be degraded by more than 50% in any natural water within 30 days. However, in the BOD test, biodegradation was diminished, with values of 40%, 20–30%, and 2–10% in river water, brackish water, and seawater, respectively. These results indicate that cellulose fibers are easily degraded into fine fragments, but it is difficult to cause their ultimate decomposition into water and carbon dioxide. Existence of such a tendency in the degree of biodegradation among the cellulose fibers remains unclear. The molecular weight of cellulose fibers in natural water was also measured during their degradation. The degradation behavior in river water and seawater was observed to be different from that in brackish water. The results thus obtained indicate that the microorganisms and enzymes that degrade cellulose fibers differ depending on the natural water, which influences the degree and mechanism of biodegradation.

     

Diffusive transport across unconfined hollow fiber membranes

The mass transfer characteristics of gas permeable, hollow fiber membranes in a liquid jet mixed reactor are studied. A membrane module, operated in the sealed-end mode, was pressurized with oxygen at the base of the fibers and centered within a submerged jet discharge. Unlike conventional membrane module designs, this configuration did not have the hollow fibers enclosed within a tubular shell. The membranes were unconfined and free to move within the generated flow field. This design is especially well suited for use in waters containing high solid concentrations. The membranes have a greater degree of freedom for movement and are therefore less likely to become fouled due to solids being lodged within the fiber bundle. Mass transfer rates were measured over a practical range of physical and process parameters. A mass transfer correlation for the unconfined configuration is presented and the transfer performance of this configuration is compared with conventional membrane contactor designs.     

Bioreactor design considerations in the production of high-quality microbial exopolysaccharide

An examination into the effect of bioreactor design on the production of β,1,3-glucan exopolysaccharide (“curdlan”) by selected patent cultures ofAlcaligenes faecalis andAgrobacterium radiobacter revealed that low shear mixing achieved through the replacement of the radial-flow flat-blade impellers that are commonly supplied in “standard” commercial bioreactors, by low shear (high-pumping) axialflow impellers, leads to an increase in thequality of the exopolymer recovered during the stationary-phase of batch fermentations. Whereas “Rushton turbine” impellers were effective in providing high rates of oxygen transfer necessary for high cell density fermentations, the high shear-to-flow ratio characteristic of this design produced a product of inferior quality, but with characteristics very similar to that of the commercially available “curdlan standard.” Curdlan is water insoluble, and consequently, the fermentation broth is of a relative low viscosity compared to other soluble microbial polysaccharides. Whereas curdlan does not constrain mass transfer from gas to liquid, it nevertheless offers a resistance to oxygen transfer from the liquid to the cell by virtue of the layer of insoluble exopolymer surrounding the cell mass, thereby necessitating an unexpectedly high dissolved oxygen concentration for maximal productivity. The requirement for high volumetric oxygen transfer can be met by low shear designs with axial-flow impellers, providing gas dispersion is assisted by the use of sparging devices consisting of microporous materials.

     

Enhancement of oxygen transfer by pressure pulsation in aqueous glycerol fermentation

Aeration plays an important role in the production of glycerol by fermentation with yeast. Effective aeration depends on a number of factors, such as amount of air, fineness of air dispersion, rate of agitation, and time of gasliquid contact. This investigation dealt with the effect of periodic variation in gas pressure on oxygen transfer measured by sulfite oxidation and glycerol fermentation in stirred tanks. The oxygen transfer rate measured with the sulfite oxidation method was improved by 20–30% under the condition of pressure pulsation (PP) at 30°C. The yield and productivity of glycerol were increased by about 26 and 6.8%, respectively, in 48 h by employing a glucose concentration of 250 g/L with PP at 30°C.     

Influence of operating conditions and vessel size on oxygen transfer during cellulase production

The production of low-cost cellulase enzyme is a key step in the development of an enzymatic-based process for conversion of lignocellulosic biomass to ethanol. Although abundant information is available on cellulase production, little of this work has examined oxygen transfer. We investigated oxygen transfer during the growth of Trichoderma reesei, a cellulase-producing microorganism, on soluble and insoluble substrates in vessel sizes from 7 to 9000 L. Oxygen uptake rates and volumetric mass transfer coefficients (k _La) were determined using mass spectroscopy to measure off gas composition. Experimentally measured k _La values were found to compare favorably with a k _La correlation available in the literature for a non-Newtonian fermentation broth during the period of heavy cell growth.     

Fumaric acid production in airlift loop reactor with porous sparger

Airlift loop reactors with porous spargers were investigated and used in the process of fumaric acid production byRhizopus oryzae ATCC 20344. In order to enhance oxygen mass transfer, which is very important for organic acid production, two kinds of porous spargers (stainless steel membrane tube and porcelain tube) were examined. Gas holdup, liquid circulation velocity, mixing time, bubble size, and bubble rise velocities were measured in a 50 L rectangular airlift loop reactor with different ratios of the cross-sectional area of the riser and downcomer. The local volumetric mass transfer coefficient (K_La) was also measured in the gas sparger zone. The results indicated that high K_La and excellent hydrodynamics can be obtained in the airlift loop reactor with a porous sparger. A 10 L laboratory airlift loop reactor was employed for the fumaric acid fermentation. Results showed that the turbulence of two-phase flow in the airlift loop reactor not only produced favorable conditions for mass transfer, but was also useful for forming and suspending small, well-distributed mycelial pellets (1ç2 mm). A production rate of up to 0.814 g/L/h and efficiency yield of 50.1% (w/w) was obtained in the airlift loop reactor. The performance was compared with the typical stirred tank fermentor fermentation results.

     

A novel electrode architecture for passive direct methanol fuel cells

The supply of cathode reactants in a passive direct methanol fuel cell (DMFC) relies on naturally breathing oxygen from ambient air. The successful operation of this type of passive fuel cell requires the overall mass transfer resistance of oxygen through the layered fuel cell structure to be minimized such that the voltage loss due to the oxygen concentration polarization can be reduced. In this work, we propose a new membrane electrode assembly (MEA), in which the conventional cathode gas diffusion layer (GDL) is eliminated while utilizing a porous metal structure for transporting oxygen and collecting current. We show theoretically that the new MEA enables a higher mass transfer rate of oxygen and thus better performance. The measured polarization and constant-current discharging behavior showed that the passive DMFC with the new MEA yielded better and much more stable performance than did the cell having the conventional MEA. The EIS spectrum analysis further demonstrated that the improved performance with the new MEA was attributed to the enhanced transport of oxygen as a result of the reduced mass transfer resistance in the fuel cell system.     

Determination of the mass transfer coefficients in direct immersion solid‐phase microextraction

Diffusion of the analytes across the diffusion boundary layers and subsequently through the fiber coatings determines the extraction kinetics of solid‐phase microextraction in aqueous matrices. Besides, the matrix effects can distort the behaviors of the analytes transferring across the diffusion boundary layers. However, these processes were always studied via certain simplification, which often left the mass transfer through the fiber coatings unconsidered and the matrix effects partially investigated. Herein, a comprehensive study on the mass transfer processes in direct immersion solid‐phase microextraction was presented. Under different agitation speeds, it was determined that the mass transfer coefficients across the diffusion boundary layers were three to six orders larger than those through the fiber coatings. However, the mass transfer across the diffusion boundary layers was generally the major rate‐limiting step. In addition, the shuttle effect and the barrier effect, which were responsible for accelerating and retarding the extraction kinetics, respectively, were found to be the dominant matrix effect alternately under different agitation speeds. This study comprehensively illustrated the major rate‐limiting step and the dominant matrix effects through recording the mass transfer coefficients.     

Improvement of oxygen transfer coefficient duringPenicillium canescens culture

To improve xylanase productivity fromPenicillium canescens 10–10c culture, an optimization of oxygen supply is required. Because the strain is sensitive to shear forces, leading to lower xylanase productivity as to morphological alteration, vigorous mixing is not desired. The influence of turbine design, agitation speed, and air flow rate on K₁a (global mass transfer coefficient, h^-1) and enzyme production is discussed. K₁a values increased with agitation speed and air flow rate, whatever the impeller, in our assay conditions. Agitation had more influence on K₁a values than air flow, when a disk-mounted blade’s impeller (DT) is used; an opposite result was obtained with a hub-mounted pitched blade’s impeller (PBT). Xylanase production appeared as a function of specific power (W/m³), and an optimum was found in 20 and 100 L STRs fitted with DT impellers. On the other hand, the use of a hub-mounted pitched blade impeller (PBT8), instead of a disk-mounted blade impeller (DT4), reduced the lag time of hemicellulase production and increased xylanase productivity 1.3-fold.

     

Plastic pellets sorptive extraction: Low-cost,rapid and efficient extraction of polycyclic aromatic hydrocarbons from environmental waters

For the first time, plastic pellets, a low-cost and easy to reach industrial raw material, are reported as an efficient sorbent material for the laboratory extraction of polycyclic aromatic hydrocarbons (PAHs) from environmental waters. The proposed methodology, termed plastic pellets sorptive extraction (P2SE), consisted of a two-step procedure whereby target analytes were initially adsorbed onto the surface of three low-density polyethylene (LDPE) pellets and then desorbed using microliters of an organic solvent. Interphase mass transfer was greatly accelerated by means of vortex agitation. Organic extracts were analyzed by means of liquid chromatography-fluorescence detection. Different experimental parameters were controlled and the optimum conditions found were: three LDPE pellets (∼80 mg) added to 20 mL aqueous sample (20% w:v NaCl) followed by vortex agitation at 3000 rpm; for desorption, the three LDPE pellets were immersed in 100 μL of acetonitrile and the mixture was shaken at 3000 rpm for 5 min using the vortex agitator. The calculated calibration curves gave high levels of linearity yielding coefficients of determination (r²) greater than 0.9913. The precision of the proposed method was found to be good and the limits of the detection were calculated in the low ng L⁻¹ level. Matrix effects were determined by applying the proposed method to spiked river water, treated municipal wastewater and seawater samples. To compensate for the low recoveries of the more hydrophobic PAHs in spiked effluent wastewater and seawater samples the standard addition methodology was applied. The proposed method was applied to the determination of target pollutants in real seawater samples using the standard addition method. Overall, the performance of the proposed P2SE method suggests that the use of inexpensive and easy to reach sorbent materials for extracting analytes in the laboratory merits more intensive investigation.     

Solid suspension and gas dispersion in gas-solid-liquid agitated systems

The aim of the research work was to investigate the effect of superficial gas velocity and solids concentration on the critical agitator speed, gas hold-up and averaged residence time of gas bubbles in an agitated gas-solid-liquid system. Experimental studies were conducted in a vessel of the inner diameter of 0.634 m. Different high-speed impellers: Rushton and Smith turbines, A 315 and HE 3 impellers, were used for agitation. The measurements were conducted in systems with different physical parameters of the continuous phase. Liquid phases were: distilled water (coalescing system) or aqueous solutions of NaCl (non-coalescing systems). The experiments were carried out at five different values of solids concentration and gas flow rate. Experimental analysis of the conditions of gas bubbles dispersion and particles suspension in the vessel with a flat bottom and four standard baffles showed that both gas and solid phases strongly affected the critical agitation speed necessary to produce a three-phase system. On the basis of experimental studies, the critical agitator speed for all agitators working in the gas-solid-liquid systems was found. An increase of superficial gas velocity caused a significant increase of the gas hold-up in both coalescing and non-coalescing three-phase systems. The type of the impeller strongly affected the parameters considered in this work. Low values of the critical impeller speed together with the relatively short average gas bubbles residence time tR in three phase systems were characteristic for the A 315 impeller. Radial flow Rushton and Smith turbines are high-energy consuming impellers but they enable to maintain longer gas bubbles residence time and to obtain higher values of the gas hold-up in the three-phase systems. Empirical correlations were proposed for the critical agitator speed, mean specific energy dissipated and the gas hold-up prediction. Its parameters were fitted using experimental data.     

Retrofit of CD-6 (smith) impeller in fermentation vessels

We extended prior studies on the influence of impeller type on fermentation performance to include a novel low-power-number, high-efficiency radial flow impeller, the CD-6, possessing six curved blades on a disk turbine. Dual impeller combinations of CD-6/CD-6, CD-6/Maxflo T, and CD-6/HE-3 were compared with Rushton/Rushton and Maxflo T/Maxflo T base cases. Qualitative comparisons of unaerated and aerated power draw in both water and glycerol were conducted. These suggested minimal power drops with aeration for dual CD-6 impellers and hybrids containing the CD-6 impeller design. We also examined fermentation performance for Streptomyces and Glarea secondary metabolite fermentations. A qualitative comparison of the data suggested that dual CD-6 impellers and hybrids containing the CD-6 impeller design resulted in reasonable power draws, improved mass transfer rates with airflow increases, and acceptable peak titers. These arrangements may warrant further study under a wider range of production conditions.     

Enhancement of oxygen gas–liquid mass transfer with colloidal gas aphron dispersions

In this work, an attempt was made to enhance gas–liquid mass transfer of oxygen with the aid of colloidal gas aphron (CGA) dispersion. The gas–liquid volume mass transfer coefficients (k_La) of oxygen in CGA dispersions were measured and related to stirring velocity, type and concentration of surfactants, and temperature. Four surfactants, sodium dodecyl sulfate (SDS), hexadecyltrimethyl ammonium chloride (HTAC), nonylphenol ethoxylate (NP-10), and potassium mono lauryl phosphate (MAPK), were examined in forming CGAs and thereby affecting the mass transfer of oxygen in the dispersions. It was found that effects of surfactants on the oxygen gas–liquid mass transfer were type-dependent. As concentrations rose, the k_La of oxygen increased evidently for SDS and an enhancement of k_La by a factor of three was observed at the concentration of 2.75 g/L. However the k_La decreased for MAPK. Nonylphenol ethoxylate was found to have little effect on k_La and HTAC showed mixed behavior. In SDS dispersion, it was found that the mass transfer reached a maximum value at a stirring velocity of 8000 r/min, but further benefit was not observed afterwards. With the increase of temperature, the mass transfer of oxygen was intensified but no much benefit was observed above 308 K.     

Interfacial adsorption of microorganisms and its effect on oxygen absorption by fermentation broths

Steady-state mass transfer experiments were done to determine whether certain strains of bacteria in homogeneous suspension will accumulate at the gas:liquid interface and thereby significantly increase the oxygen transfer rate to the suspension. In particular, with suspensions ofB. licheniformis, the measured transfer rates are as much as three times the rate expected for a uniform suspension. In contrast, suspensions ofM. luteus show no increase in oxygen flux above expected values. The fact thatB. licheniformis is motile, whereasM. luteus is not suggests that cell motility may play an important role in the accumulation process.

     

An improved model for mass transfer during the formation of polymeric membranes by the immersion-precipitation process

An analysis is presented, which describes the isothermal ternary diffusion process encountered in the formation of a cellulose acetate polymeric membrane by a direct immersion-precipitation of polymeric solutions in a nonsolvent bath. A material coordinate was employed to derive the mass transfer equations for the membrane solution and the convective mass transfer in the coagulation bath was taken into account by solving the hydrodynamic boundary layer equations. Diffusion coefficients were measured and used to deduce ternary phenomenological coefficients. The computed results are found to agree with the experimental precipitation time and membrane morphologies observed in scanning electron photomicrographs. © 1994 John Wiley & Sons, Inc.     

Experimental analysis of the hydrodynamics of a three-phase system in a vessel with two impellers

Results of experimental analysis concerning gas hold-up and average residence time of gas bubbles in a three-phase gas-solid-liquid system produced in a baffled, double-impeller vessel are presented. Measurements were carried out in a vessel with the internal diameter of 0.288 m. Two different double-impeller configurations were used for agitation: Rushton turbine (lower) — A 315 (upper) and Rushton turbine (lower) — HE 3 (upper). Upper impellers differed in the fluid pumping mode. Coalescing and non-coalescing systems were tested. Liquid phases were distilled water (coalescing system) and aqueous solutions of NaCl (non-coalescing systems). The ability of gas bubbles to coalesce in the liquid was described using parameter Y. Dispersed phases were air and particles of sea sand. The experiments were conducted at seven different gas flow rates and two particle loadings. Effects of the ability of gas bubbles to coalesce (liquid phase properties), operating parameters (superficial gas velocity, impeller speed, solids loadings), and of the type of the impeller configuration on the investigated parameters were determined. The results were approximated mathematically. For both impeller configurations tested, significantly higher gas hold-up values were obtained in the non-coalescing gas-solid-liquid systems compared to the coalescing one. Out of the tested impeller systems, the RT-A 315 configuration proved to have better performance ensuring good gas dispersion in the liquid in the three-phase systems.     

Cellulose membrane modified with polypyrrole as an extraction device for the determination of emerging contaminants in river water with gas chromatography–mass spectrometry

In this study, a simple, efficient, and reusable device based on cellulose membranes modified with polypyrrole was developed to extract 14 emerging contaminants from aqueous matrices. For chemical polymerization, a low‐cost cellulose membrane was immersed in 0.1 mol/L pyrrole and 0.5 mol/L ammonium persulfate for 40 min in an ice/water bath. The cellulose membranes modified with polypyrrole were accommodated in a polycarbonate holder suitable for solid‐phase extraction disks. Solid‐phase extraction parameters that affect extraction efficiency, such as sample volume, pH, flow rate, and desorption were optimized. Subsequently, determination of target compounds was performed by gas chromatography with mass spectrometry. The linear range for analytes ranged from 0.05 to 500 μg/L, with coefficients of determination above 0.990. The limits of quantification varied between 0.05 and 10 μg/L, with relative standard deviations lower than 17%. The performance of the proposed cellulose membranes modified with polypyrrole device for real samples was evaluated after extraction of emerging contaminants from a river water sample from the city of Curitiba, Brazil. Bisphenol A (6.39 μg/L), caffeine (17.83 μg/L), and paracetamol (19.28 μg/L) were found in these samples.     

膜吸收-再生循环技术捕集CO_2操作性能及其参数优化研究

采用N-甲基二乙醇胺(MDEA)+哌嗪(PZ)复合溶液作为捕集CO2吸收剂,研究了膜吸收-再生循环装置的操作性能,考察了气液流量、吸收剂浓度和再生电压等因素对捕集率和传质通量的影响,采用正交实验方法,优化操作条件,确定最佳操作方案。结果表明,气体流量对捕集率的影响明显大于液体流量的影响;气体流量增大对传质通量影响不明显;吸收剂浓度的增大使传质通量迅速增大,但大于一定值时通量不再增大;正交实验得出最佳操作条件为液体流量110 mL/min、气体流量0.65 L/min、吸收剂总浓度2.5 mol/L和再生电压210 V,捕集率大于95%,传质通量维持在5.86×10-4mol/(m2.s)。