Degradation of waste gas containing toluene in an airlift bioreactor

Suspension microorganisms in an internal-loop airlift bioreactor were utilized to treat waste gas containing toluene. The working volume of the reactor was 35 L, and the biomass concentration was 3 kg/m3. The gas pollutant flowed into the reactor from the bottom; it then transferred from the gas phase to the liquid phase and was degraded by the microorganisms suspended in the liquid phase. The microorganisms were able to degrade 50-90% of the inlet toluene when its concentration was from 0.5 to 10 g/m3, and the superficial gas velocity ranged from 0.15 to 1.23 cm/s. A comprehensive mathematical model was also developed to describe the overall degradation process of toluene in the internal-loop airlift bioreactor. The overall degradation process included gas flow, gas-liquid mass transfer, flow and dispersion of the liquid phase, and microbial kinetics. The hydrodynamic properties including the gas and liquid superficial velocities, the gas holdup, the volumetric mass transfer coefficients of toluene and oxygen, and the microbial kinetics were obtained for this model. The substrate inhibition theory was used to simulate the microorganism growth kinetics, and its kinetic constants were obtained experimentally. The penetration theory was used to predict the volumetric mass transfer coefficient. And the drift-flux theory was used to predict the hydrodynamic properties in each section (riser, gas-liquid separator, downcomer, and bottom) of the airlift bioreactor. The concentration distributions of toluene and oxygen in the airlift bioreactor and the removal efficiency of toluene predicted by the mathematical model agreed well with the experimental data.     

Development of rectangular airlift bubble column installed with support material for enhancement of nitrogen removal

To enhance nitrogen removal during wastewater treatment using activated sludge, a rectangular airlift bubble column installed with support material is proposed. The flow characteristics and nitrogen removal performance were examined and compared with those of a column without support material. In the two columns, the riser was aerobic and the lower part of downcomer was anaerobic. The effects of operational conditions on the liquid circulation flow rate and liquid-phase volumetric mass transfer coefficient were examined. Using these flow characteristics, the distribution of dissolved oxygen (DO) concentration in the column was calculated. From the DO distribution, the anaerobic volume fraction in the column was estimated. The optimal anaerobic volume fraction for nitrogen removal was found to be approximately 50%. The column installed with support material showed higher nitrogen removal than the column without it.     

Kojic acid production in an airlift bioreactor using partially hydrolyzed raw corn starch

In a culture of Aspergillus oryzae MK-107-39 in a 3-l airlift bioreactor, kojic acid was not produced when glucose/wheat germ medium (GM1) was used. However, when a jar fermentor was used, the kojic acid yield was high. A suitable medium for culture in an airlift bioreactor consisting of partially hydrolyzed corn starch and a small amount of corn steep liquor (CSL) (SM1) was selected. In the cultivation in the airlift bioreactor using SM1, nearly 40 g/l of kojic acid was produced, which was the same as the amount produced in the jar fermentor containing GM1. The optimum aeration rate for the airlift bioreactor was 2.0 vvm (0.66 cm/s of superficial linear velocity (Vs)). The cost of SM1 using the airlift bioreactor was reduced to 40% that of GM1 using the jar fermentor. Furthermore, the energy cost of kojic acid production using SM1 in the airlift bioreactor was less than one-fourth of that for the jar fermentor using GM1.     

Effect of soybean oil on oxygen transfer in the production of tetracycline with an airlift bioreactor

Corn starch and soybean oil are suitable carbon sources for the production of tetracycline by Streptomyces aureofacience CG-1. However, it could not produce more than 6 g/l of tetracycline even if initial corn starch concentration was increased to more than 100 g/l. It was confirmed by shaking flask experiments that the k_La in a mixture of 2% soybean oil in water was four folds compared with that without soybean oil. With the addition of soybean oil to the starch medium in a shaking flask, tetracycline production was significantly improved. By scaling-up to a 5.5-l airlift bioreactor from 500-ml Erlenmeyer flask, more than 10 g/l of tetracycline was produced with the addition of 60 g/l of soybean oil to the medium containing 100 g/l of corn starch. The dissolved oxygen level in the airlift bioreactor containing soybean oil was higher than that without soybean oil. This suggests that soybean oil is not only a suitable carbon source but is also a surface-active agent which may accelerate the oxygen transfer. This may lead to the possibility of the enhanced production of tetracycline at a low cost in airlift bioreactor.     

Biosynthesis of high molecular weight hyaluronic acid by Streptococcus zooepidemicus using oxygen vector and optimum impeller tip speed

The potential use of n-dodecane and n-hexadecane as oxygen vectors for enhancing hyaluronic acid (HA) biosynthesis by Streptococcus zooepidemicus ATCC 39920 was investigated using a 2-L stirred-tank bioreactor equipped with helical ribbon or Rushton turbine impellers. The volumetric fraction of the oxygen vector influenced the gas-liquid volumetric oxygen transfer coefficient (K(L)a) positively. Batch HA fermentation with 1% (v/v) n-dodecane or 0.5% (v/v) n-hexadecane addition was carried out at different impeller tip speeds. Even though cell growth was lower in the fermentation with oxygen vector addition, the HA productivity and molecular weight were higher when compared to the fermentation without oxygen vector at low impeller tip speed. The highest HA concentration (4.25 gHA/l) and molecular weight (1.54 × 10(7) Da) were obtained when 0.5% (v/v) n-hexadecane and 0.785 m/s impeller tip speed of helical ribbon were used.     

喷射自吸式生化反应器气液传质的研究

<正> 一、前言 从宏观分析,生化反应器是非均质的包含物理传质过程的催化反应器,其催化剂为有生命活性的微生物菌体或酶。从微观概念出发,每一个微生物活细胞本身就是一个微型反应器。维持反应系统的气(氧)-液(水和营养基质、代谢产物)-固(微生物菌体)三相良好的混合与分散,尤其是较高的溶氧传质速率,是需氧生化反应器设计和放大的关键。在生化工程领域,通常以体积溶氧系数K_La和溶氧比能耗(P_W/V_L)/OTR表征气液传质效能。 我们在上文已介绍了喷射自吸式反应器的喷射吸气特性,并推导出吸气速率的数学表达式;本研究对喷射自吸式反应器的另一个重要特性——气液传质性能及其与反应器喷射     

Effect of mixing time on taxoid production using suspension cultures of Taxus chinensis in a centrifugal impeller bioreactor

The effects of fluid mixing on the cell growth and secondary metabolite production of plant cells were investigated in a low-shear centrifugal impeller bioreactor (CIB) system. Suspension cultures of Taxus chinensis cells producing taxuyunnanine C (Tc), a physiologically active secondary metabolite, were used as a model system for this investigation. The mixing time (t(m)) and volumetric oxygen transfer coefficient (k(L)a) in the bioreactor were characterized at various cell densities and operating conditions. A constant t(m) of 5 s or 10 s was maintained during cultivation by adjusting the impeller agitation speed with no detrimental effect on the cultured cells. A higher cell density, Tc content and total Tc production were obtained under the shorter mixing time of 5 s. The favorable effect of more rapid mixing on Tc production was also confirmed when the Tc accumulation was significantly increased through culture elicitation using 100 microM methyl jasmonate (MJA). The lower Tc production at the longer t(m) of 10 s was mainly attributed to oxygen transfer limitation in the dead zones and larger cell aggregates resulting from poor mixing.     

双液相发酵系统中氧传递机理的研究

以一种液态烷烃为油相，将其引入青霉素发酵过程以提高氧的传递。通过摇瓶和罐发酵对该双液相系统的发酵过程进行了研究，实验结果表明，油相分数为２％时，发酵体系中的传氧能力得到了最大程度的提高并最终导致了青霉素产量的提高。通过对体积传氧系数及油相与水相物理化学性质的研究，对油相引入后，发酵能力提高的现象作了初步的解释，并提出了双液相系统中氧从气泡传递到微生物细胞的宏规模型。     

Scale-up of L-lactic acid production by mutant strain Rhizopus sp. MK-96-1196 from 0.003 m3 to 5 m3 in airlift bioreactors

In order to study the feasibility of commercial-scale L-lactic acid production by Rhizopus sp. MK-96-1196 using large scale airlift bioreactors (ALBs), a scale-up study from 0.003 m3 to 5 m3 ALB was carried out using oxygen transfer rate (OTR) as the scale-up criterion. Enhanced L-lactic acid production was achieved at OTRs higher than 0.28 (g-O2/l/h) irrespective of the scale of the bioreactor in question: in the range of 0.003 m3 to 5 m3, more than 90 g/lL-lactic acid was produced with a yield of approximately 80%, based on the initial glucose concentration. In future research, we plan to design an ALB greater than 3000 m3 (working volume: 2000 m3) for further studies on the production of L-lactic acid in large quantities.     

Optimization and scale-up of L-lactic acid fermentation by mutant strain Rhizopus sp. MK-96-1196 in airlift bioreactors

We determined the optimum culture conditions such as inoculum size, initial starch concentration, pH during the fermentation and aeration rate for L-lactic acid production by Rhizopus sp. MK-96-1196 in a 3-l airlift bioreactor. More than 90 g/l of L-lactic acid was produced from only partially enzymatically hydrolyzed corn starch with a production rate of 2.6 g/l/h and a product yield of 87% based on the starch consumed under the optimum conditions in the 3-l airlift bioreactor. Scale-up from the 3-l to a 100-l airlift bioreactor for L-lactic acid fermentation was carried out using V(s)(cm/s) as a scale-up criterion. The production rates and yields of L-lactic acid in both bioreactors appeared to be fairly well correlated with k(L)a (1/h).     

P-RC APMP制浆废水沸腾传热系数的研究

研究了P-RC APMP制浆废水的沸腾传热系数,实验在强制循环蒸发器上进行,考察了热通量、流体流速、流体浓度对P-RC APMP制浆废水沸腾传热系数的影响。结果表明,在一定的热通量下,随着流体流速的增加,P-RC APMP制浆废水沸腾传热系数增加;浓度不同,流速对传热系数的影响不同,浓度越大,流速对传热系数的影响越大。     

Designing hypolimnetic aeration and oxygenation systems--a review

When properly designed, hypolimnetic aeration and oxygenation systems can replenish dissolved oxygen in water bodies while preserving stratification. The three primary devices are the airlift aerator, Speece Cone, and bubble-plume diffuser. In each device, gas bubbles in contact with water facilitate interfacial transfer of oxygen, nitrogen, and other soluble gases. However, early design procedures for airlift aerators were empirical, while most bubble-plume models did not account for stratification or gas transfer. Using fundamental principles, a discrete-bubble model was first developed to predict plume dynamics and gas transfer for a circular bubble-plume diffuser. The discrete-bubble approach has subsequently been validated using oxygen transfer tests in a large vertical tank and applied successfully at full-scale to an airlift aerator as well as to both circular and linear bubble-plume diffusers. The performance of each of the four completely different full-scale systems (on a scale of 10 m or more) was predicted based on the behavior of individual bubbles (on a scale of about 1 mm). The combined results suggest thatthe models can be used with some confidence to predict system performance based on applied air or oxygen flow rate, initial bubble size, and, in the case of bubble plume diffusers, near-field boundary conditions. The discrete-bubble approach has also been extended to the Speece Cone, but the model has not yet been validated due to a lack of suitable data. The unified suite of models, all based on simple discrete-bubble dynamics, represents the current state-of-the-art for designing systems to add oxygen to stratified lakes and reservoirs.     

环流筛板塔式生化反应器研究

本文针对内环流反应器在通气发酵过程中应用时存在的一些问题,设计了一种在导流筒上面设多段环流筛板的新型塔式生化反应器,内径D=200mm,总高H=2500mm;并对其流动特性、气含率和传质系数进行了研究,[用压差法测定了全塔及导流筒内的气含率εc,用Na_2SO_3—空气氧化法测定了传氧系数k(?)、气液相界比表面积a(524-1224m-1)及容积传质系数k_La(1171-3278h~(-1)],得出了这种反应器中气含率εc_1,相界面比表面积a和传氧系数k(?)的关联式: 此外,还得出了这种反应器的最佳板间距(H_1=2h_1)和最佳操作气速(Uc=6.2cm/s),推导出筛板环流筒长度的计算式:供放大设计时参考。     

500米~3生物反应器K_(La)的测定技术

在500米~3活性污泥生物反应器中,用动态测量法测定氧的体积传递系数(K_L a),本文提供了一种简便方法。这种方法对有机废水处理有实用意义。     

Production of L-lactic acid from corncob

The optimum temperature, initial pH, amount of added enzyme and substrate (corncob) for the hydrolysis of corncob by Acremonium cellulase were 35 degrees C, 4.5, 10 u/g-corncob and 100 g/l, respectively. Under the optimum conditions, more than 55 g/l of reducing sugars were hydrolyzed from 100 g/l of corncob to 34 g/l of glucose and 12 g/l of xylose based on dried corncob. More than 25 g/l of L-lactic acid was produced from this enzymatic hydrolyzate and less than 5 g/l of xylose remained in the 3-l airlift bioreactor. The production of L-lactic acid by simultaneous saccharification and fermentation (SSF) was also carried out in the 3-l airlift bioreactor using Acremonium thermophilus (cellulose-producer) and Rhizopus sp. MK-96-1196 (lactic acid-producer). More than 24 g/l of L-lactic acid was produced from 100 g/l of untreated raw corncob.     

High gravity primary continuous beer fermentation using flocculent yeast biomass

The current work assessed a new immobilized cell reactor system throughout a long‐term (54 days) continuous primary fermentation of lager‐type wort of high specific gravity. The experiment was performed in a 4 L airlift bioreactor and immobilization of biomass was attained solely by flocculation. Despite the constant liquid agitation and washout of biomass, up to 53 g dry wt/L of yeast remained immobilized in the system. Two types of beer were produced without interrupting the reactor, based on two types of wort: a Pilsener type with high specific gravity of 15.6 ± 0.3°P; and a dark lager wort with specific gravity of 14.4 ± 0.03°P. Even during the inlet of high gravity wort, the desired attenuation was achieved without the need for either recirculation or an auxiliary second stage bioreactor. The specific saccharide consumption rate was kept around 7.9 ± 0.4 g/L/h and ethanol productivity oscillated at 3.36 ± 0.2 g/L/h for nearly a month. During this period the volumetric productivity of the current bioreactor reached 1.6 L beer/L/day. The green beers produced from the Pilsener and dark lager worts met the standards of regular finished primary beer fermentation. The productivity of diacetyl through the entire experiment could be correlated to the free amino nitrogen consumption rate. Copyright © 2014 The Institute of Brewing & Distilling     

Effect of oxygen in a thin-film rotating disk photocatalytic reactor

A novel experimental procedure was developed to measure oxygen mass transfer during the oxygenation of water in a thin film of a rotating disk photocatalytic reactor (RDPR). The increase in dissolved oxygen (DO) of initially deaerated water was monitored with time in the reactor vessel at different disk angular velocities after exposure of the reactor to the atmosphere. Oxygenation was predominantly achieved by oxygen mass transport through the thin liquid film carried by the disk and to a much lesser extent by direct oxygenation of the water in the reactor vessel via a surface renewal mechanism. A mathematical model was developed to simulate the phenomenon considering both cases of presence and absence of oxygen mass transport limitations. In the latter case, the model considered that the amount of liquid carried by the disk was saturated with oxygen when returning to the reactor vessel. On the basis of the model and the experimental data, it was proven that mass-transfer limitations existed until the water in the reactor vessel became saturated with oxygen. Results obtained from the model were validated by an alternative analysis using dimensionless groups characteristic to the system. The study revealed that the mass-transfer coefficient increased linearly with disk angular velocity and thus disk Reynolds number. The results showed that oxygen mass-transfer limitations decreased with increasing disk angular velocity, mainly due to an increase in the overall mass-transfer coefficient. In the presence of UV radiation, the influence of oxygen on the photocatalytic oxidation of 4-chlorobenzoic acid was investigated in the RDPR operated in batch and continuous mode. The photocatalytic reactions occurred in a thin film of liquid carried by the disk in the presence of UV radiation and ST-B01 composite spherical ceramic (SiO2/Al2O3) balls coated with anatase TiO2 catalyst. It was found that the initial degradation rate followed Langmuir kinetics with respect to oxygen concentration in the gas phase. When the oxygen concentration in the gas phase surpassed that in air, the degradation rates did not improve significantly, suggesting that operation with air instead of oxygen is most probably a more realistic practical choice. Measurements of DO during the presence and absence of UV radiation suggested that the photocatalytic reactions were mainly oxygen concentration-limited rather than oxygen mass-transfer-limited.     

不同剪切速率下储仓内小麦剪胀特性的三轴试验研究

利用改进的三轴试验仪,开展了麦堆三轴剪切试验,研究了剪切速率对剪切应力应变及体变应变的影响,获得了剪切速率对麦堆内摩擦角、剪胀角的影响规律。研究结果表明：不同剪切速率、不同围压下麦堆剪切应力应变及应变体变曲线类似。随着轴向应变增加剪切应力逐渐增加,达到剪切强度峰值后呈现一定的软化现象;随着轴向应变增加,体变应变曲线表明麦堆的剪切发生由减缩到剪胀的变化过程。剪切速率影响麦堆峰值剪切强度及体变应变曲线均有影响,剪切速率越大,内摩擦角越小,剪胀角越小。本文获得的不同剪切速率下麦堆内摩擦变化范围为23.2°-24.7°,剪胀角为5.6°-14.8°。根据试验结果,麦堆合理的三轴剪切速率为0.2 mm/min-0.5 mm/min。     

Biosynthesis of 1-Octen-3-ol and 10-Oxo-trans -8-decenoic Acid Using a Crude Homogenate of Agaricus bisporus: Reaction Scale Up

ABSTRACT: The enzymatic reaction that produces 1 -octen-3-ol and 10-oxo-trans-8-decenoic acid was successfully scaled up from a 1 -L to a 10-L bioreactor using a crude mushroom homogenate of Agaricus bisporus . For this non-Newtonian reaction broth, the agitation rate was considered the most important controlling factor for the scale up. An agitation rate of 600 rpm, for an aeration rate of 0.44 m³/m³/h, was found to be the minimum to maintain the yield constant for the 1-L reactor. Subsequently, the agitation rate for the 10-L reactor was determined using 2 different approaches: a constant power per volume of liquid and a constant volumetric mass transfer coefficient (k_La). The constant power per volume of liquid approach predicted an agitation rate of 364 rpm that resulted in being too low to maintain the same yield obtained with the 1-Lreactor. Measurement of the kLa for the 10-Lreactor, at 364 rpm and an aeration of 0.44 m³/m³/h, produced a value of 11.7/h, thus confirming that the reaction in the larger reactor was oxygen-deprived. Therefore, the use of constant volumetric mass transfer coefficient (kLa) strategy was used instead. k_La was experimentally determined at different agitation rates for the 10-L reactor. It was found that 750 rpm produced a k_La of 40.2/h. Confirmatory reactions were run in both reactors with the same batch of mushrooms, and the results were equivalent, thus indicating that was a good criterion for scaling up this process.     

Effect of bottom clearance on performance of airlift bioreactor in high-density culture of Panax notoginseng cells

A fed-batch cultivation of Panax notoginseng cells in a concentric-tube airlift reactor was performed to study the effects of bottom clearance on cell growth and the production of ginseng saponin and polysaccharide. At a bottom clearance of 4.0 cm, the highest cell density of 29.1+/-1.6 g/l by dry weight was obtained, and the accumulation of saponin and polysaccharide also reached a maximum, i.e., 2.39+/-0.43 and 2.73+/-0.40 g/l, respectively. Cell growth and metabolite production were limited at a small (2.5 cm) or large (5.0 cm) bottom clearance. By analyzing the time constants of mixing, mass transfer and oxygen consumption, bulk gas-liquid oxygen transfer was found to be responsible for the growth limitation at a small bottom clearance (2.5 cm). The decrease in cell density at a large bottom clearance (5.0 cm) was related to cell sedimentation at the reactor bottom. This work is beneficial for the scale-up and efficient operation of the airlift reactor in cell cultures.