Design and performance of an α-type tubular photobioreactor for mass cultivation of microalgae

Ab α-shape tubular photobioreactor was designed and constructed based on knowledge of algal growth physiology using sunlight. The algal culture is lifted 5 m by air to a receiver tank. From the receiver tank, the culture flows down parallel polyvinyl-chloride tubes of 25 m length and 2.5 cm internal diameter, placed at an angle of 25 ° with the horizontal to reach another set of air riser tubes. Again the culture is lifted 5 m to another receiver tank, then flows down parallel tubes connected to the base of the first set of riser tubes. Thus, the bioreactor system looks like the symbol α. As there is no change in the direction of the liquid flow, high liquid flow rate and Reynolds Number can be achieved at relatively low air flow rate in the riser tubes. Due to the high area-volume ratio of the bioreactor, and equable photosynthetically available radiance and culture temperature, biomass density of exceeding 10 g dry weight L^-1 and daily output rate of 72 g dry weight m^-2 land d^-1 were achieved.     

Bubble characteristics and mass transfer in an airlift reactor with multiple net draft tubes

A pilot scale airlift reactor with multiple net draft tubes was developed. The reactor, 29?cm in diameter and 300?cm height, had four modules of double net draft tubes. Bubble size, bubble number, gas holdup, and volumetric mass transfer coefficient were measured under different superficial air velocities. The air velocity had little effect on bubble size but had significant influence on bubble number. A bubble column was also investigated for comparison. The airlift reactor had a higher gas holdup and volumetric mass transfer coefficient than those in the bubble column. The draft tubes in the airlift reactor substantially improved the reactor performance.     

Transport processes during sterilization of vertical and 5 degree horizontal dead-legs

Experimental temperature profiles and biological kill data from dead-ended tubes of various diameters and lengths commonly used in biotechnology applications were compared to those predicted by a finite element model for steam-in-place (SIP) sterilization at 122°C. Diameter was shown experimentally and numerically to have a significant effect with larger diameter tubes exhibiting greater buoyant driven convective flow and more rapid sterilization. The overall Grashof number was shown to be the significant parameter relating magnitude of convective flow to tube diameter and varied as the diameter cubed. Analysis of air/steam mixture flow patterns showed air displacement from 0.4 cm diameter tubes to be due primarily to molecular diffusion, whereas 1.0 and 1.7 cm tubes showed a two-stage convective flow pattern. There exists a critical diameter of 0.4 cm below which SIP sterilization due to buoyancy driven flow does not occur and steam bleeders should be used.     

Influence of cultivation conditions on mechanical and morphological properties of bacterial cellulose tubes

Bacterial cellulose (BC) was deposited in tubular form by fermenting Acetobacter xylinum on top of silicone tubes as an oxygenated support and by blowing different concentrations of oxygen, that is, 21% (air), 35%, 50%, and 100%. Mechanical properties such as burst pressure and tensile properties were evaluated for all tubes. The burst pressure of the tubes increased with an increase in oxygen ratio and reached a top value of 880 mmHg at 100% oxygen. The Young's modulus was approximately 5 MPa for all tubes, irrespective of the oxygen ratio. The elongation to break decreased from 30% to 10-20% when the oxygen ratio was increased. The morphology of the tubes was characterized by Scanning Electron Microscopy (SEM). All tubes had an even inner side and a more porous outer side. The cross section indicated that the tubes are composed of layers and that the amount of layers and the yield of cellulose increased with an increase in oxygen ratio. We propose that an internal vessel wall with high density is required for the tube to sustain a certain pressure. An increase in wall thickness by an increase in oxygen ratio might explain the increasing burst pressure with increasing oxygen ratio. The fermentation method used renders it possible to produce branched tubes, tubes with unlimited length and inner diameters. Endothelial cells (ECs) were grown onto the lumen of the tubes. The cells formed a confluent layer after 7 days. The tubes potential as a vascular graft is currently under investigation in a large animal model at the Centre of Vascular Engineering, Sahlgrenska University     

Zona fracture damage and its avoidance during the cryopreservation of mammalian embryos

Although fracture damage to the zonae pellucidae and blastomeres is frequently observed after the cryopreservation of mammalian embryos, little is known of the mechanism by which this occurs. The incidence of damage to zonae was measured when bovine ova with normal zonae were frozen in straws or glass test tubes by standard embryo cryopreservation procedures that yield high rates of survival. Ova were examined for zona damage after warming by procedures that ought to produce little or no thermal stress (slow warming in 20 degrees C air) or high levels of stress (rapid warming in liquid baths). Ova frozen in straws exhibited no zona damage after slow warming at 150 degrees C/min in air (n = 206). However, the incidence of zona damage increased when the straws were warmed rapidly in 20 degrees C (n = 157) or 36 degrees C (n = 159) water (17 and 24%, respectively). Ova in straws warmed rapidly in nonaqueous liquids (ethylene glycol, or silicone oil) exhibited lower rates of zona damage (2 to 5%). Ova frozen in glass tubes exhibited a much higher incidence of zona damage than those frozen in straws, regardless of the warming conditions. Thus, 30% of 114 ova exhibited damage when tubes were warmed slowly at 25 degrees C/min in air, while 54% of 98 ova showed zona damage when tubes were warmed rapidly at 500 degrees C/min in 36 degrees C water. These results are consistent with the view that zona damage is associated with thermally-induced fracturing of the suspension during rapid changes of temperature.     

The Joensuu dasotrons: A new facility for studying shoot,root, and soil processes

A new, controlled, environment facility for growing trees was built at Joensuu, Finland, between 1996 and 1998. It consists of four large rooms called dasotrons, with four large root pots in each. Each room is a separate unit, with independent control of air and soil temperature, air humidity and light. The environmental variables can be controlled to simulate conditions ranging from tropical to boreal. The controller set-points can be programmed locally or through a central control system running on a PC. The floor area and height of the rooms allows us to grow small trees (up to 3.7 m height) for several growing seasons. In each dasotron, there are four cylindrical pots with a removable upper section. There are access holes in the walls of the pots for the installation of sensors and minirhizotron tubes. Each pot has a drain, with valves, at the bottom to enable the removal of excess water or the collection of percolate samples. The operation of the facility was tested during one simulated annual growing cycle. During this test period, the dasotrons worked reliably and no systematic differences were found in the environmental conditions or in the growth of Norway spruce seedlings between the dasotrons. This new facility will enable diverse physiological and ecophysiological studies to be carried out on the responses of trees to their below- and above-ground environment.     

A water activity control system for enzymatic reactions in organic media

A water activity control system for enzymatic synthesis in organic media, for litre-scale reactors has been constructed. Water activity, a(w), is a key factor when using enzymes in non-conventional media and the optimum value varies for different enzymes. The control system consists of a water activity sensor in the headspace of a jacketed glass reactor (equipped with narrow steel tubes to introduce air), gas-washing bottles containing blue silica gel (a(w)=0) and water (a(w)=1), a PC to monitor water activity and a programmable logic controller (PLC) to control the water activity. The system was evaluated by adjusting water activity in the medium, with a deviation from the set point of less than +/-0.05. Synthesis of cetyl palmitate, under controlled water activity and catalysed by two different lipase preparations, namely, Novozym 435 (immobilised Candida antarctica lipase B) and immobilised Candida rugosa lipase, were also performed. Novozym 435 catalyses reactions very well at extremely low water activity while C. rugosa lipase shows low activity for a(w)<0.5.     

Combined Screw-Cap and Rubber-Stopper Closure for Hungate Tubes (Pre-reduced Anaerobically Sterilized Roll Tubes and Liquid Media)

A double-closured method introduced for Hungate tubes eliminates clamps or special racks to hold the rubber stoppers in place while the tubes are being processed. The system prevents stoppers from being dislodged by gas-producing anaerobes and keeps the stoppers sterile so that the closed system of transfer can be conveniently utilized. Open and closed systems for handling a gas-producing anaerobe were compared. Ten tubes containing Clostridium perfringens were opened; the organism was detected in the air by use of an impingement collector. The gloved hand of the operator also revealed the test organism. A similar trial with culture material removed by the closed system (syringe transfer) resulted in no detectable contamination of the environment.     

Sterilization of various diameter dead-ended tubes

Effect of tube diameter on steam-in-place sterilization of dead-ended tubes was studied by examining temperature profiles and rates of kill of Bacillus stearothermophilus spores. Time required for sterilization was determined for 9.4-cm-long tubes with various inside diameters from 0.4 to 1.7 cm. Sterilization time increased with decreasing tube diameter. Experimentally measured kill kinetics in 1.7-cm tubes were in agreement with those predicted if measured temperatures represented saturated steam. A 12-log spore reduction was achieved in 1.7-cm diameter vertical and horizontal tubes in less than 63 minutes. For smaller diameter tubes, entrapped air remained after 2 hours and rates of kill were very dependent on position within the tube, tube diameter, and tube orientation with respect to the gravitational vector. Times to achieve a 1-log drop in spore population in the smaller tubes were as much as 10 times greater than those expected if measured temperatures represented saturated steam. Sterilization was not achieved throughout the 0.4-cm tubes. Recommendations are made for including steam bleeders or using prevaccum cycles for these smaller diameter tubes. (c) 1993 John Wiley & Sons, Inc.     

Mixing time and oxygen transfer characteristics of double draft tube airlift fermentor

Despite the increasing importance of airlift fermentors, very little published information is available on how the geometric configurations of the draft tubes and the air-sparging system affect the mixing and oxygen transfer characteristics of the fermentor. A 14-L air-lift fermentor was designed and build with a fixed liquid height to diameter ratio of 1.5 utilizing four equally spaced air jets at the bottom. Two jet orifice sizes were used, 1.27 and 3.81 mm i.d., and for each jet size the following four geometric configurations were used: Single inner concentric draft tube, single outer concentric draft tube, two concentric draft tubes, and no draft tubes where the fermentor was operated as a shallow bubble column. It was found that the presence of draft tubes stabilized liquid circulation patterns and gave systemically higher mixing times than those obtained in the absence of draft tubes. In addition, the double draft tube geometry resulted in higher mixing times than the single draft tubes. For the power unit volume range 20 to about 250 W/m³ the larger 3.81-mm orifices gave systemically higher k_L a values than the smaller 1.27-mm i.d. orifices. At 200 W/m³ the use of a single outer draft tube with the 3.81-mm orifices resulted in 94% increase in k_L a values over that obtained with no draft tubes. However, the effect of draft tube geometry on k_L a values when the 1.27-mm orifices were used was not significant. The air bubble formation characteristics at the jet orifices were found to be different, which reflected the differences observed in mass transfer and mixing characteristics. The power economy for oxygen transfer was found to be depend strongly on the orifice size and less on the geometric configuration of draft tubes.     

Life history traits and dispersal shape neutral genetic diversity in metapopulations

Journal of Mathematical Biology - In insect respiration, oxygen from the air diffuses through a branching system of air-filled tubes to the cells of the body and carbon dioxide produced in cellular...     

DIALYSIS WITH STIRRING

Substances to be purified by dialysis are placed in collodion bags together with a toy "marble" or a bubble of air. The bags are stoppered and placed in glass tubes of a rocking machine. Distilled water of the desired temperature is circulated through the tubes (around the bags) at a rate of about 8 cc. per minute per bag while the machine is in motion. The rolling of the marbles or bubbles causes stirring which makes it possible to remove the salts from a protein solution in 24 to 48 hours.     

聚四氟乙烯塑料管研磨法对测定C4植物碳同位素比值的影响

聚四氟乙烯(PTFE)塑料管研磨法是测定植物碳同位素比率(δ¹³C)值常用的前处理方法。该方法处理样品高效快捷,但对植物δ¹³C可能存在污染。本研究利用人工气候室开展双因素交互试验,包括空气相对湿度(50%和80%)和空气δ¹³C(¹³C富集和贫化的空气)两个因素,对比了PTFE塑料管研磨法和不锈钢管研磨法处理C4植物糙隐子草δ¹³C的结果。结果表明: 在相同湿度条件下,不同空气δ¹³C处理的植物¹³C分馏值(Δ¹³C,矫正了光合作用底物的δ¹³C差异)原本可以视为重复,但由于PTFE塑料颗粒的混入,相同湿度不同¹³C丰度空气培养下植物叶片Δ¹³C平均差值为4.8‰。该污染效应导致单个叶片δ¹³C测定的误差高达8‰。考虑到C4植物的Δ¹³C较低(通常为1‰~8‰),这种污染效应已经超出了可以接受的误差范围。通过建立类似Keeling曲线的二元混合模型对误差进行了有效消除,并准确估算了植物样品和污染物的δ¹³C。说明广泛采用的PTFE管研磨方法对研究C4植物Δ¹³C并不适用,将导致较大的误差。对精度要求较高的研究内容建议使用不锈钢瓶进行研磨。     

The study of neural network-based controller for controlling dissolved oxygen concentration in a sequencing batch reactor

The design and development of the neural network (NN)-based controller performance for the activated sludge process in sequencing batch reactor (SBR) is presented in this paper. Here we give a comparative study of various neural network (NN)-based controllers such as the direct inverse control, internal model control (IMC) and hybrid NN control strategies to maintain the dissolved oxygen (DO) level of an activated sludge system by manipulating the air flow rate. The NN inverse model-based controller with the model-based scheme represents the controller, which relies solely upon the simple NN inverse model. In the IMC, both the forward and inverse models are used directly as elements within the feedback loop. The hybrid NN control consists of a basic NN controller in parallel with a proportional integral (PI) controller. Various simulation tests involving multiple set-point changes, disturbances rejection and noise effects were performed to review the performances of these various controllers. From the results it can be seen that hybrid controller gives the best results in tracking set-point changes under disturbances and noise effects.     

Factors influencing the in vitro growth of Mycobacterium leprae: effect of oxygen.

In our efforts to evaluate factors responsible for in vitro growth of Mycobacterium leprae in DH medium and also to improve the system, effects of oxygen tension on in vitro growth of M. leprae were determined. This was achieved by varying the ratio between DH medium and free air space above the medium in the culture tubes. Growth-competent M. phlei (ATCC 11758) could tolerate all the oxygen it can get in the medium. On the other hand, M. leprae seemed to be of microaerophilic nature. In vivo-grown M. leprae cells were more sensitive than their counterparts that were adapted to in vitro environment. In vivo-grown cells grew better when 70% of the space in culture tube was occupied by DH medium. These in vitro-adapted cells gave optimum growth in subcultures when the air spaces in the culture tubes were 40-50%. The role of oxygen tensions in the development of lesions in leprosy patients and armadillos has been discussed.     

A system for measuring leaf gas exchange based on regulating vapour pressure difference

A system for measurement of leaf gas exchange while regulating leaf to air vapour pressure difference has been developed; it comprises an assimilation chamber, leaf temperature controller, mass flow controller, dew point controller and personal computer. A relative humidity sensor and air and leaf temperature sensors, which are all used for regulating the vapour pressure difference, are mounted into the chamber. During the experiments, the computer continuously monitored the photosynthetic parameters and measurement conditions, so that accurate and intenstive measurements could be made.When measuring the light-response curve of CO₂ assimilation for single leaves, in order to regulate the vapour pressure difference, the leaf temperature and relative humidity in the chamber were separately and simultaneously controlled by changing the air temperature around the leaf and varying the air flow rate through the chamber, respectively. When the vapour pressure difference was regulated, net CO₂ assimilation, transpiration and leaf conductance for leaves of rice plant increased at high quantum flux density as compared with those values obtained when it was not regulated.When measuring the temperature-response curve of CO₂ assimilation, the regulation of vapour pressure difference was manipulated by the feed-forward control of the dew point temperature in the inlet air stream. As the vapour pressure difference was regulated at 12 mbar, the maximum rate of and the optimum temperature for CO₂ assimilation in rice leaves increased 5 molCO₂ m^–2 s^–1 and 5°C, respectively, as compared with those values obtained when the vapour pressure difference took its own course. This was reasoned to be due to the increase in leaf conductance and the decrease in transpiration rate. In addition, these results confirmed that stomatal conductance essentially increases with increasing leaf temperature under constant vapour pressure difference conditions, in other words, when the influence of the vapour pressure difference is removed.This system may be used successfully to measure inter- and intra-specific differences and characteristics of leaf gas exchange in plants with a high degree of accuracy.Abbreviations A CO₂ assimilation rate - A_max Maximum rate of CO₂ assimilation - A_opt Optimum teperature for CO₂ assimilation - CTWB Controlled-temperature water bath - DPC Dew point controller - E Transpiration rate; gl, leaf conductance - HCC Humidity control circuit - IRGA Infrared gas analyzer - LT Leaf temperature - LTC Leaf temperature controller - MFC Mass flow controller - QFD Quantum flux density - RH Relative humidity - RHC Relative humidity controller - VPD Vapour pressure difference - CO₂ Difference of CO₂ concentration between inlet and outlet air     

TipChip: a modular,MEMS‐based platform for experimentation and phenotyping of tip‐growing cells

Large‐scale phenotyping of tip‐growing cells such as pollen tubes has hitherto been limited to very crude parameters such as germination percentage and velocity of growth. To enable efficient and high‐throughput execution of more sophisticated assays, an experimental platform, the TipChip, was developed based on microfluidic and microelectromechanical systems (MEMS) technology. The device allows positioning of pollen grains or fungal spores at the entrances of serially arranged microchannels equipped with microscopic experimental set‐ups. The tip‐growing cells (pollen tubes, filamentous yeast or fungal hyphae) may be exposed to chemical gradients, microstructural features, integrated biosensors or directional triggers within the modular microchannels. The device is compatible with Nomarski optics and fluorescence microscopy. Using this platform, we were able to answer several outstanding questions on pollen tube growth. We established that, unlike root hairs and fungal hyphae, pollen tubes do not have a directional memory. Furthermore, pollen tubes were found to be able to elongate in air, raising the question of how and where water is taken up by the cell. The platform opens new avenues for more efficient experimentation and large‐scale phenotyping of tip‐growing cells under precisely controlled, reproducible conditions.     

Carbon dioxide induces endotrophic germ tube formation in Candida albicans

Candida albicans formed germ tubes when exposed to air containing 5 to 15% carbon dioxide (CO2). The CO2-mediated germ tube formation occurred optimally at 37 degrees C in a pH range of 5.5 to 6.5. No germ tubes were produced at 25 degrees C, even when the optimal concentration of CO2 (10%) was present in the environment. The requirement of CO2 for germ tube formation could be partially substituted by sodium bicarbonate but not by N2. Carbon dioxide was required to be present throughout the entire course of germ tube emergence suggesting that its role is not limited to an initial triggering of morphogenic change. We suggest that carbon dioxide may be a common effector responsible for the germ tube promoting activity of certain chemical inducers for C. albicans.     

Effects of air ions on germination ofHelminthosporium teres

Effects of host — pathogen interactions with respect to relatively high concentrations of artificially produced air ions were studied in the laboratory. Continuous and long exposures ofHelminthosporium teres in the culture medium and under controlled conditions to positive air ions, produced a time — delay of about 6 hours on spore germination. Negative ions produced no such effect. Temporary structural abnormalities of the germ tubes were observed for two to three hours when exposed to either positive or negative air ions. Sprayed inoculum of spores on actual leaf surfaces of barley plants, exposed to positive ions, suppressed germination for a considerably longer time than those observed in the culture medium.     

A parallel bubble column system for the cultivation of phototrophic microorganisms

An incubator with up to 16 parallel bubble columns was equipped with artificial light sources assuring a light supply with a homogenous light spectrum directly above the bioreactors. Cylindrical light reflecting tubes were positioned around every single bubble column to avoid light scattering effects and to redirect the light from the top onto the cylindrical outer glass surface of each bubble column. The light reflecting tubes were equipped with light intensity filters to control the total light intensity for every single photo-bioreactor. Parallel cultivations of the unicellular obligate phototrophic cyanobacterium, Synechococcus PCC7942, were studied under different constant light intensities ranging from 20 to 102 microE m(-2)s(-1) at a constant humidified air flow rate supplemented with CO(2).