Growth and pigment production of Synechocystis sp. PCC 6803 under shear stress

Cyanobacteria, such as Synechocystis, have recently become attractive hosts for sustainable production of biofuels and bio-fixation of CO₂ due to their genetic tractability and relatively fast growth. Cultivation of cyanobacteria requires shear stress, which is generated by mixing and air bubbling. In the present work, the impact of shear stress caused by stirring and air bubbling on the growth and pigment production of Synechocystis sp. PCC 6803 is investigated. For this purpose, agitated and airlift bubble column photobioreactors were used. The results showed that the growth and yield production were improved by mixing the culture system. However, there is a limit to this improvement: In the case of air bubbling, increasing shear stress (by rising air bubbling flow rate) to more than 185 mPa did not show any significant growth enhancement, while increasing the shear stress from 40 to 185 mPa improved the yield production up to 85%. At the optimal stirring rate, the yield production in the stirred photobioreactors increased by about 60% as compared to that of unstirred culture. The measurements of chlorophyll_a and carotenoid showed a strong correlation between biomass production and total pigment content. The highest level of cellular pigment (pigment per cell) was detected at the early stages of culture growth when cells were preparing for the rapid exponential growth phase.     

Genome‐scale modeling of Synechocystis sp. PCC 6803 and prediction of pathway insertion

BACKGROUND: Cyanobacterium Synechocystis sp. PCC 6803 has been used widely as a model system for the study of photosynthetic organisms and higher plants. The aim of this work was to integrate the genomic information, biochemistry and physiological information available for Synechocystis sp. PCC 6803 to reconstruct a metabolic network for system biology investigations. RESULTS: A genome‐scale Synechocystis sp. PCC 6803 metabolic network, including 633 genes, 704 metabolites and 831 metabolic reactions, was reconstructed for the study of optimal Synechocystis growth, network capacity and functions. Heterotrophic, photoautotrophic and mixotrophic growth conditions were simulated. The Synechocystis model was used for in silico predictions for the insertion of ethanol fermentation pathway, which is a novel approach for bioenergy and biofuels production developed in the authors' laboratory. Simulations of Synechocystis cell growth and ethanol production were compared with actual metabolic measurements which showed a satisfactory agreement. CONCLUSION: The Synechocystis metabolic network developed in this study is the first genome‐scale mathematical model for photosynthetic organisms. The model may be used not only in global understanding of cellular metabolism and photosynthesis, but also in designing metabolic engineering strategies for desirable bio‐products. Copyright © 2008 Society of Chemical Industry     

螺旋迭错式空间全曲面生物填料流场模拟分析

引言 填料是生物膜法装置的核心组成部分,除了提供生物膜生长的环境,还能过滤水中悬浮物.本课题组于2009年开发出了一种具有螺旋迭错式空间全曲面结构的生物填料(专利号:200920256153.7.以下简称空间全曲面填料).其结构如图1所示,由波纹状的三维全曲面结构PVC薄片构成,具有近似圆锥状的孔隙,使水流紊乱,产生许多旋涡.旋涡使浮游物依密度分离,滞留在填料内部的不同位置,其中含有细菌、真菌、藻类、原生动物和后生动物等微生物,这些微生物与填料表面结合并大量繁殖,从而形成生物膜(挂膜).大颗粒悬浮物易于被波纹状的孔隙拦截,孔隙率高(根据填料大小在82%～92.4%之间),过滤阻力小,可高效、顺畅地进行过滤.     

Rheological behavior of molten epoxide prepolymers

Flow properties of four molten epoxide prepolymers of number average molecular weight 900(I), 1,500(II), 2,100(III) and 4,000(IV), were measured at temperatures ranging from 361 to 463K, and shear rates from 500 to 10,000 s^?1. Apparent shear viscosities showed that all prepolymers used have Newtonian behavior up to shear rates of 2,000 s^?1. Shear thinning occurs at higher shear rates. Flow activation energies at constant shear rates in the range of 500 to 7,000 s^?1 vary for prepolymer III from 5 to 24 kcal/mol, and for prepolymer IV from 9 to 25 kcal/mol. Flow indices in the same shear rate range vary for prepolymer III from 1.0 to 0.7 and for prepolymer IV from 1.0 to 0.3.     

Identification of Specific Variations in a Non-Motile Strain of Cyanobacterium Synechocystis sp. PCC 6803 Originated from ATCC 27184 by Whole Genome Resequencing

Cyanobacterium Synechocystis sp. PCC 6803 is a widely used model organism in basic research and biofuel biotechnology application. Here, we report the genomic sequence of chromosome and seven plasmids of a glucose-tolerant, non-motile strain originated from ATCC 27184, GT-G, in use at Guangzhou. Through high-throughput genome re-sequencing and verification by Sanger sequencing, eight novel variants were identified in its chromosome and plasmids. The eight novel variants, especially the five non-silent mutations might have interesting effects on the phenotype of GT-G strains, for example the truncated Sll1895 and Slr0322 protein. These resequencing data provide background information for further research and application based on the GT-G strain and also provide evidence to study the evolution and divergence of Synechocystis 6803 globally.     

Characterization of particles packing in alumina green tape

Aqueous alumina slurry was prepared with a commercial powder of elongated particles, which has the aspect ratio ranging from 1 to 3.5 with the mean of 1.6, to examine the effect of forming conditions on the particle alignment in green tapes. The slurry appeared pseudoplastic with a yield stress, but showed no thixotropic behavior. Its flow curve fitted very well to the Herschel–Bulkley model approximation, which suggested shear-thinning constant of 0.54. Polarized microscopy with the liquid immersion technique was applied to examine the particle orientation through the direction along the tape thickness. In the absence of coquette flow, randomly oriented particles were noted in the tape. At the top surface, particles were aligned with their long-axes (a-axis) along the casting direction. The variation in the degree of orientation was 6.8 ± 1.2. In the area near the Mylar carrier, a-axis of particle made an angle to the carrier surface with the degree of orientation about 5.8 ± 1.0. As the combination of pressure flow and coquette flow, tape cast with casting velocity of 2.5 and 91.5 cm/min, which respectively resulted in shear rate of 1.38 and 50.8 s^?1, were observed. The orientation was significant near the top surface and was higher than that above the carrier surface. The a-axis of particles above the carrier surface was inclined to the surface at low shear rate (1.38 s^?1), but was nearly parallel at high shear rate (50.8 s^?1). Nevertheless, the orientation varies with the location in the tape prepared at the shear rate of 50.8 s^?1.     

Influence of bubbles characteristics on the skin friction and velocity gradient on solid sphere

A detailed study of the effects of individual bubbles at high gas flow‐rate has shown, that the dominant influence on skin friction over a solid sphere is the bubble volume in compared to bubble frequency. Nevertheless the bubble frequency is very important in case of low gas flow‐rate. Referring to bubbles produced by a gas distributor, statistical and spectral analyses were performed to study the influence of bubbling on exposure time and magnitude of fluctuations. Referring to a calibrated bubble train, the existence of critical frequency is demonstrated. A bubble with larger volume and a mobile, oscillatory surface generates larger velocity gradient. In the case of gas distribution, histograms of the velocity gradient for a 2 mm glass sphere creating bubble coalescence reveal the maximum exceeds 48 000 s^?1 in the front zone and 2000 s^?1 in the rear zone (θ = 180°). For 5 mm plastic spheres creating bubble break‐up, the maximum of the velocity gradient is only 8100 s^?1 for the front part of the sphere and 2000 s^?1 in the rear zone.     

Rheological properties of new polymer compositions for sand consolidation and water shutoff in oil wells

The rheological properties of some newly developed polymer compositions have been investigated with and without crosslinking. These polymer compositions were developed as a water shutoff and sand consolidation treatment agents for producing oil and gas wells. The effects of several variables on the rheology of the compositions were evaluated over a wide range of temperatures (25–110°C), shear rates (0–500 s^?1), brine percentages (0–15%), crosslinker types and concentrations (0–3%), and polymer concentrations (6–50%). It was found that increasing the shear rate from 0 s^?1 to 100 s^?1 caused shear thinning and reduction of the viscosity of the dilute solutions (6–13%) from 25 cP to ～ 3 cP at 80°C. In contrast, for the concentrated solutions (20–50%), the viscosity dropped slightly in the shear rate range 0–10 s^?1, and subsequently decreased more slowly up to shear rates of 500 s^?1. The viscosities of all polymer solutions dropped by a factor of 2 as the brine concentration increased from 0% to 15%. Finally, aging time coupled with shear rates and higher percentages of crosslinkers accelerate the buildup of viscosity and gelation time of the polymer compositions. For concentrated solutions, shear rates ranging within 0–200 s^?1 accelerated gelation time from 9.75 h to 2–3 h, when they were sheared at 80°C. The polymeric solutions exhibited Newtonian, shear‐thinning (pseudo‐plastic), and shear‐thickening (dilatant) behavior, depending on the concentration, shear rate, and other constituents. In most cases, the rheological behavior could be described by the power law. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Drying Characteristics of Barley Grain Dried in a Spouted-Bed and Combined IR-Convection Dryers

A study was performed to determine the drying characteristics and quality of barley grain dried in a laboratory scale spouted-bed dryer at 30, 35, 40, and 45°C and an inlet air velocity of 23 m/s^?1, and in an IR-convection dryer under an infrared radiation intensity of 0.048, 0.061, 0.073, and 0.107 W cm^?2 at an air velocity of 0.5 m/s^?1. The results show that the first, relatively short, phase of a sharp decrease in the drying rate was followed by the phase of a slow decrease. The time of barley drying depended on temperature of inlet air in a spouted-bed dryer and on radiation intensities in an IR-convection dryer. Barley drying at 45°C in a spouted-bed dryer was accompanied by the lowest total energy consumption. The average specific energy consumption was lower and the average efficiency of drying was higher for drying in a spouted-bed dryer. The effective diffusivities were in the range 2.20–4.52 × 10^?11 m² s^?1 and 3.04–4.79 × 10^?11 m²/s^?1 for barley dried in a spouted-bed and in an IR-convection dryer, respectively. There were no significant differences in kernel germination energy and capacity between the two drying methods tested.     

Effects of riser height and total solids inventory on the gas-solids in an ultra-tall CFB riser

More and more CFB boilers with large capacity and ultra-tall furnaces are used for power generation. Understanding the fluid dynamics in the ultra-tall furnace is important. However, existing studies on fluid dynamics in the CFB furnace are limited to the risers with rather short height. An experimental study was conducted with a cold CFB test rig of 240 mm in I.D. and 38 m and 54 m in height respectively. The influences of total solid inventory I_v, and fluidizing gas velocity U_g on the axial voidage profile along the riser and solid circulation rate G_s were investigated. Experimental results showed that when U_g exceeded the transport velocity, an S-shaped voidage profile characterized by fast fluidization was established in the riser. In such circumstance, the voidage at top dilute section kept constant and G_s reached saturation carrying capacity (G_s = G_s^?) and inappreciably change with riser height and I_v. Moreover, G_s^? increased from 40 kg to 50 kg when the riser height increased from 38 m to 54 m. The results indicated that even for the 600 MWe supercritical CFB boiler with a 54 m tall furnace, only a modest increase of I_v and power of forced draft fans is needed to obtain high enough G_s to meet the requirements of heating surfaces arrangement in furnace and the circulation loop. The necessary conditions to form the S-shaped profile of voidage in the riser were also discussed.     

Optimization of growth operational conditions for CO2 biofixation by native Synechocystis sp.

BACKGROUND: A fundamental step in assessing the viability of a CO₂ biofixation system based on microalgae is to identify the maximum CO₂ biofixation yield that can be achieved for this microorganism when it is cultivated under optimum operational growth conditions. Response surface methodology was applied to determine optimum culture conditions for CO₂ biofixation by a recently isolated freshwater cyanobacterium Synechocystis sp. The strain was cultivated in a 1 L bubble column photobioreactor, in semicontinuous mode. RESULTS: Statistical analysis showed that temperature (from 22 to 39 °C), pH (from 7.2 to 8.8) and light intensity (from 928 to 2272 µE m^?2 s^?1), in addition to some of their interactions, had a significant effect on CO₂ biofixation. An optimum CO₂ biofixation rate of 2.07 gCO₂ L^?1culture day^?1 was found within the experimental region, at an average light intensity 686 µE m^?2 s^?1, pH 7.2 and temperature 35.3 °C. CONCLUSIONS: Based on these results, it is concluded that Synechocystis sp. presents a good tolerance to both high temperature and light intensity, characteristics which facilitate its application in outdoor CO₂ biofixation systems. Copyright © 2011 Society of Chemical Industry     

Molecular orientation of polydimethylsiloxane induced by elongational and shearing strains

A study examining the molecular orientation of poly(dimethylsiloxane) for different combinations of elongational and shear strains is presented. Three different cases were studied: (1) pure elongational strain; (2) increasing shear and decreasing elongational strains; (3) increasing shear and increasing elongational strains. The experiments were performed in a converging flow cell (at room temperature), where elongational and shearing strain rates achieved values of 370 s^?1 and 640 s^?1 respectively. Values of the Hermans orientation function were obtained from measurements of birefringence and polarization angles while strain rates were estimated from laser Doppler anemometry velocity measurements. Prospects for predicting molecular orientation from the stress-optical laws and rheological flow models are outlined and commented on.     

Industrial aluminas and hexahydrated aluminum chloride chlorinations by phosgene in LiClKCl eutectic melt at 470°C

The variations of pO^2? during the chlorination by phosgene of industrial aluminas and hexahydrated aluminium chloride were observed by means of an yttria-stabilized zirconia electrode. The curves obtained showed that chlorinations carried out in a continuous flow reactor, take place rapidly (30 min with a phosgene rate of flow of 157 cm³ min^?1 and a simple bubbler). Transformation of oxychloride to tetrachloroaluminate is the slow step; its specific rate constant k_s and its order α have been determined (k_s = 0.19 mol^?1 kgs^?1; α = 2). The latter value is interpreted by postulating the involvement of the complex Al₂OCl^?₅. The catalytic effect of the presence of aluminum chloride on the chlorination of the alumina has also been illustrated.     

Shear Thinning Behavior of Calcium Silicate‐Based Mold Fluxes at 1623 K

There have been consistent efforts on understanding rheological behavior of molten mold flux, used in continuous casting of steels. It is prevalent view that molten mold flux shows non‐Newtonian behavior, meaning that the viscosity varies with shear rate history. Hence, the present study attempts to evaluate shear thinning, which is one of the characteristic non‐Newtonian behaviors, by measuring its viscosity with a rotating type viscometer at 1623 K. Furthermore, Raman spectroscopy analysis is used to appreciate the structure of molten mold flux and shear thinning. Mold fluxes tested reveal definite shear thinning characteristic of decreasing viscosity with increasing shear rate. The degree of shear thinning has been well quantified by Oswald‐De Waele power law model. Lastly, the degree of polymerization, obtained from Raman spectroscopic data has proportional relationship with degree of shear thinning in the range of 1–5 s^?1 shear rate. Also, it has a downward parabolic relationship with degree of shear thinning at entire shear rate ranges up to 100 s^?1. This study also verifies possibility to use shear thinning behavior on actual continuous casting process.     

Low Pressure Microfilter Design Aspects and Filtration Performance

Abstract

A microfilter should retain micron-sized material yet provide minimal resistance to liquid flow. A slotted pore surface microfilter was oscillated while filtering yeast cells under constant rate. At shear rates over 7760 s^?1, a pore blocking model fitted the data. The operating pressure was very low (<1000 Pa), but particle retention was limited by the 4 micron pore slot width. A sintered glass micro-bead coating improved yeast rejection: 95% at 1.7 microns at a shear rate of 5000 s^?1, with a 1.2 kPa transmembrane pressure. Two models were validated to assist with the design of future micro-bead coatings constructed from spherical particles.     

Polarographic and voltammetric measurements of disproportionation of uranium(V) in sulphate and other complexing media on mercury electrodes

The rate of disproportionation of uranium(V) was studied at a hme using single sweep and cyclic voltammetry in sulphate solutions at an almost constant ionic strength (I = 1.2-1.0 mol1^?1) as a function of pH and concentration of uranium(VI). The rate constant of disproportionation of uranium(V) in 0.4 M Na₂SO₄ recalculated for the activity of hydrogen ion equal unity is k₀ = 6.3 × 10⁵ mol^?21²s^?1. Also standard rate constants k_s were determined.In preliminary dc polarography experiments in other complexing media as citrate, tartarate and oxalate a higher increase of the limiting current than in sulphate was found for the same pH values pointing to the assumption that in these media the disproportionation reaction of uranium(V) might proceed still faster than in sulphate solutions.     

Experimental observations of the effect of pressure and buoyancy on cellulose co-current smoldering

An experimental study has been performed to determine the potential effect of buoyancy on the rate of propagation of a co-current smolder reaction through a porous solid fuel, and the range of flow velocities where buoyancy effects are significant. In the co-current smolder reaction, the fuel and oxidizer enter the reaction zone from the same direction. In the present experiments this is accomplished by initiating the reaction at the top of the fuel bed, α-cellulose packed at a void fraction 0.85, so that the smolder wave propagates downward opposing an upward forced flow of air. Since in a stratified density field, buoyancy is proportional to the product of gravity and density difference, buoyancy can be controlled by varying either the gravity vector or the gas density. In this study the latter method is followed, varying gas density through the ambient pressure at which the experiments are performed. The smolder velocity is measured for air flow rates varying from 0.2 to 6 gm^?2s^?1 at constant ambient pressures of 0.6, 0.8 and 1 atm. The results show that for flow rates larger than 1 gm^?2s^?1 the smolder velocity increases linearly with the air flow rate but is independent of pressure. The reaction peak temperature is weakly dependent on flow rate and independent of pressure. For the present experimental conditions the effect of buoyancy is only observed at very low air flow rates. The mechanisms by which it affects the smolder process appears to be by altering the transport of air to the reaction zone from upstream and downstream of the reaction.     

Particle Deposition in Museums: Comparison of Modeling and Measurement Results

Deposition of airborne particles may lead to soiling and /or chemical damage of objects kept indoors, including works of art in museums. Measurements recently were made of the deposition velocity of fine particles (diameter range: 0.05–2.1 μm) onto surfaces in five Southern California museums. In this paper, theoretical predictions of particle deposition velocities onto vertical surfaces are developed for comparison against the experimental results. Deposition velocities are calculated from data on surface-air temperature difference and near-wall air velocity using idealized representations of the air flow field near the wall. For the five sites studied, the wall-air temperature differences were generally in the range of a few tenths to a few degrees Kelvin. Average air velocities measured at 1 cm from the wall were in the range 0.08–0.19 m s^?1. Based on a combination of modeling predictions and measurement results, the best estimate values of deposition velocity for the wall studied at each site are obtained. These values are in the range (1.3–20) × 10^?6 m s^?1 for particles with 0.05–μm diameter and (0.1–3.3) × 10^?6 for particles with 1-μm diameter. The range of 15–30 in deposition velocity for a given particle size is due primarily to differences among sites in the near-wall air flow regime, with the low and high values associated with forced laminar flow and homogeneous turbulence in the core of the room, respectively.     

Stress growth and relaxation of a molten polyethylene in a modified weissenberg rheogoniometer

A Weissenberg rheogoniometer was modified^1-3 to improve sample temperature uniformity and constancy (to within ±0.5°C) and to give a quicker response to normal thrust changes (estimated gap change ≤0.1 μm/kg thrust; gap angle = 8.046°; gap radius = 1.2 cm; servomechanism replaced by an open-loop cantilever spring of 10 kg/μm stiffness). Low-density polyethylenes (IUPAC samples A and C, melt index at 190°C = 1.6) at 150°C were used in step-function shear rate experiments. Inspection of marked sectors in the samples showed substantial uniformity of shear at values of ? = 0.1, 2, and 5 sec^?1; for ? = 10 sec^?1 and S ≤ 2 shear units (S = ?t), the shear was highly nonuniform at and near the free boundary. Using selected premolded samples A, scatter in seven replicate tests at ? = 1.0 sec^?1 did not exceed ±6% for N₁(t) and ±5% for σ(t) (N₁ = primary normal stress difference; σ = shear stress; t = time of deformation from the initiation of experiment at zero time). N₁(t) and σ(t) data agreed with Meissner's¹; for ? = 0.1, 2.0, 5.0, and 10.0 sec^?1, torque maxima occurred at S = 6 shear units, and thrust maxima occurred in the range of 10 to 20 shear units. σ(t) and N₁(t) data do not satisfy the van Es and Christensen⁴ test for rubber-like liquids with strain rate invariants included in the memory function. On cessation of shear (after a shear strain S at constant shear rate ?), initial values of ?dσ(t)/dt and ?dN₁(t)/dt were found to depend strongly on S, in some cases passing through maxima as S was increased. After shearing at ? = 0.1 sec^?1 for 500 sec, such that stresses became constant, stress relaxation data satisfied Yamamoto's⁵ equation of dN₁(t)/dt = ?2?σ(t).