Removal of toluene from air streams using a gas–liquid–solid three‐phase airlift loop bioreactor containing immobilized cells

Toluene, a kind of volatile organic compound (VOC), is widely used as a solvent (paints and coatings, gums, resins, rubber) as well as a reagent (medicines, dyes, perfumes) and is one of the components of gasoline. Over the more recent decades, many studies have led to the development of biological methods to treat toluene. This paper presents the results of a study on the treatment of airborne toluene using a laboratory‐scale gas–liquid–solid three‐phase airlift loop bioreactor containing immobilized cells. Based on the optimum operating conditions such as the temperature of 28–30 °C, pH of 7.0–7.2, and an empty bed residence time (EBRT) of 39.6 s, a continuous bioprocess showed that this immobilized airlift loop bioreactor had a steady‐state performance within 15 days, the outlet concentrations of toluene were lower than the national emission standard in China (GB 16297‐1996), and the chemical oxygen demand and NH₄⁺‐N of the effluent also satisfied the primary discharge standard in China (GB 8978‐1996). In addition, this immobilized airlift loop bioreactor had a good ability to tolerate shock loads, while the maximum elimination capacity of toluene was 168 g m^?3 h^?1 which was higher than those not only in biofilters and biotrickling filters but also in the airlift bioreactor with free microorganisms. Copyright © 2005 Society of Chemical Industry     

Preparation of sorbitol from D‐glucose hydrogenation in gas–liquid–solid three‐phase flow airlift loop reactor

A new process for D ‐glucose hydrogenation in 50 wt% aqueous solution, into sorbitol in a 1.5 m³ gas–liquid–solid three‐phase flow airlift loop reactor (ALR) over Raney Nickel catalysts has been developed. Five main factors affecting the reaction time and molar yield to sorbitol, including reaction temperature (T_R), reaction pressure (P_R), pH, hydrogen gas flowrate (Q_g) and content of active hydrogen, were investigated and optimized. The average reaction time and molar yield were 70 min and 98.6% under the optimum operating conditions, respectively. The efficiencies of preparation of sorbitol between the gas–liquid–solid three‐phase flow ALR and stirred tank reactor (STR) under the same operating conditions were compared. Copyright © 2004 Society of Chemical Industry     

Phenolic wastewater treatment in a three‐phase fluidised bed bioreactor containing low density particles

The treatment of phenolic wastewater was investigated in a gas–liquid–solid fluidised bed bioreactor containing polypropylene particles of density 910 kg m^?3. Measurements of chemical oxygen demand (COD) versus residence time (t) were performed for various ratios of settled bed volume to bioreactor volume (V_b/V_R) and air velocities (u) to determine the values of (V_b/V_R) and u for which the largest reduction in COD occurred. Optimal operation, corresponding to the largest COD removal, was attained when the bioreactor was controlled at the ratio (V_b/V_R) = 0.55 and an air velocity u = 0.036 m s^?1. Under these conditions, the value of COD was practically at steady state for times greater than 50 h. At this steady state, only about 50% COD removal was achieved in the treatment of a ‘raw’ wastewater (no mineral salts added), whereas in the operation with wastewater enriched in nutrient salts approximately 90% COD removal was attained. The following amount of mineral salts (mg dm^?3): (NH₄)₂SO₄—500; KH₂PO₄—200; MgCl₂—30; NaCl—30; CaCl₂—20; and FeCl₃—7, when added to wastewater before treatment, was sufficient for biomass growth. The application of low density particles (used as biomass support) in a bioreactor allowed the control of biomass loading in the apparatus. In the cultures conducted after change in (V_b/V_R) at a set u, the steady state mass of cells grown on the particles was achieved after approximately 6 days of operation. With change in u at a set (V_b/V_R), the new steady state biomass loading occurred after culturing for about 2 days. Phenolic wastewater was successfully treated in a bioreactor. In the operation conducted in a bioreactor optimally controlled at (V_b/V_R) = 0.55, u = 0.036 m s^?1 and t = 50 h, conversions greater than 99% were achieved for all phenolic constituents of the wastewater. Conversions of about 90% were attained for other hydrocarbons. Copyright © 2005 Society of Chemical Industry     

Hydrodynamic considerations on optimal design of a three‐phase airlift bioreactor with high solids loading

The hydrodynamic study of a three‐phase airlift (TPAL) bioreactor with an enlarged gas–liquid dual separator was carried out. Different lengths and diameters of the draft tube were tested to show how the design of the separator zone affects the hydrodynamic performance of the TPAL reactor. Ca‐alginate beads with entrapped yeast biomass at different loadings (0, 7, 14 and 21% v/v) were used in order to mimic the solid phase of conventional high cell density systems, such as those with cells immobilized on carriers or flocculating cells. Important information on multiphase flow and distribution of gas and solid phases in the internal‐loop airlift reactor (ALR) with high solids loading was obtained, which can be used for suggesting optimal hydrodynamic conditions in a TPAL bioreactor with high solids loading. It is finally suggested that the ALR with a dual separator and a downcomer to riser cross‐sectional area ratio (A_D/A_R) ranging from 1.2 to 2.0 can be successfully applied to batch/continuous high cell density systems, where the uniform distribution of solid phase, its efficient separation of particles from the liquid phase, and an improved residence time of air bubbles inside the reactor are desirable. Copyright © 2003 Society of Chemical Industry     

Three‐phase airlift internal loop reactor: correlations for predicting the main fluid dynamic parameters

Three‐phase airlift loop reactors have many industrial applications. Examples include applications in the chemical, metallurgical, biochemical and minerals‐processing industries; fluid dynamics in such systems is a critical factor affecting efficiency. The experimental work was carried out at a pilot‐plant scale in a tank with a cylindrical shape and conical bottom (height 1.25 m; diameter 0.42 m), water and air were used as liquid and gas phases, and for different solid phases, different loads of glass spheres (diameters: 0.25 and 1 mm; density 2.6 g cm^?3), and polystyrene cylinders (diameter and length 3 mm; density 1.0 g cm^?3) were introduced. Air was injected through the bottom of the tank by means of 12 nozzles (diameter 1 mm each). An internal draft tube riser was tested on different configurations as its diameter was varied (44, 82, 125 and 240 mm) as was its height (1050 and 630 mm). Corresponding liquid velocities in the adjacent annular downcomer were determined by a thermal tracer technique, solid holdups were determined by conductivity methods, riser overall gas holdups were deduced from the liquid level, and riser gas holdup from manometer readings. Several adjusted correlations were considered in a method to predict the main fluid dynamic parameters (solids and gas holdups, and superficial liquid velocities). Copyright © 2005 Society of Chemical Industry     

Clustering behaviour in gas–liquid–solid circulating fluidized beds with low solid holdups of resin particles

The flow in a gas–liquid–solid circulating fluidized bed is self‐organised and manifests itself with clustering of particles and bubbles. The clustering behaviour in the fluidized bed at low solid holdups of resin particles was experimentally investigated with a high‐speed image measurement and treatment technique of complementary metal oxide semiconductor to enhance the fundamental understanding on such a flow. Several new physical quantities were suggested to characterise such ordered flow structures. The main findings are as follows. The clusters of solid particles largely exist as doublets and triplets, the mixed groups of particles and bubbles mostly exist as one bubble carrying two to four particles. Increasing superficial liquid velocity, particle diameter or density weakens the aggregation degrees of both particle and mixed clusters in the riser and downer, except that the increase of superficial liquid velocity enhances the mixed clustering behaviour in the riser. The climbing of the auxiliary liquid velocity or liquid phase viscosity intensifies the aggregation behaviour, except that the increase of liquid phase viscosity reduces the mixed clustering degree in the riser. The influences of superficial gas velocity and surface tension of liquid phase on the clustering behaviour seem to be a little complex and the trends are not simply increasing or decreasing. The life cycle of solid particle clusters in the GLS riser is not sensitive to the operation conditions, being around 0.07 s. The mixed clusters' life cycle is more sensitive to the conditions and physical properties of phases, changing from 0.02 to 0.07 s.     

A novel three‐phase airlift reactor without circulation of solids

A novel configuration of a three‐phase internal loop airlift reactor is proposed. The draft is divided in two sections: (top) gas–liquid contact section; (bottom) liquid–solid contact section. Solids particles are fluidized in the bottom section by liquid circulation. The main advantage compared with classic airlift or three‐phase fluidized bed is the reduced stress on particles as interference with bubbles is prevented. Experiments with silica sand (325 µm diameter) were carried out to characterise the hydrodynamics of the airlift. The influence of superficial gas velocity, overall solids hold‐up and sparger height were assessed. A theoretical analysis was proposed to derive simple design criteria.     

固体颗粒对三相气升式环流反应器流动特性的影响

将液相视为连续相,气相和固相视为分散相,同时考虑各相之间的相互作用,结合气液固三相流体的动力学理论,建立气液固三相环流反应器三流体湍流流动的Eulerian模型.采用计算模拟软件Fluent对三相环流反应器的流动状况进行模拟,考察表观气速、固含率、颗粒大小对反应器的气含率以及液体流动速度的影响.模拟结果较好地解释了气升式环流反应器内的三相流体行为,模型与实验结果较好地吻合,表明了模型的可行性.     

Sensor‐based flow pattern detection—gas–liquid–liquid upflow through a vertical pipe

Flow distribution during gas–liquid–liquid upflow through a vertical pipe is investigated. The optical probe technique has been adopted for an objective identification of flow patterns. The probability density function (PDF) analysis of the probe signals has been used to identify the range of existence of the different patterns. Dispersed and slug flow have been identified from the nature of the PDF, which is bimodal for slug flow and unimodal for dispersed flow. The water continuous, oil continuous, and emulsion type flow distributions are distinguished on the basis of the PDF moments. The method is particularly useful at high flow rates where visualization techniques fail. Based on this, a flow pattern detection algorithm has been presented. Two different representations of flow pattern maps have been suggested for gas–liquid–liquid three phase flow. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3362–3375, 2014     

环流反应器生化处理皂化废水研究

以17L的环流反应器为曝气设备,研究了皂化废水的生物降解过程。环流反应器可高效处理皂化废水,水力停留时间仅6h,皂化废水的生物降解过程满足一级宏观动力学,最佳活性污泥质量浓度范围为5～9g/L;活性污泥系统连续运行稳定,出水化学需氧量稳定在100mg/L左右。扫描电镜显示驯化污泥相较接种污泥有较大变化,微生物的活性提高,种类更为丰富。     

Hydrodynamic modeling on the external liquid–solid wetting efficiency in a trickling flow reactor

A three‐region model was proposed, which considers the bed cross section being composed of a stagnant liquid region, a liquid film region, and a rivulet flow region. To estimate the fractions of the three regions, the fraction of film flow was evaluated first, by transforming the complex trickling flow texture into pure liquid film flow. Through the measurements of liquid holdup and pressure drop for the film flow, a relationship between relative permeability and gas saturation was established, and from which the fraction of film flow region was obtained. It shows packing size is most important to the faction of rivulet flow. The external wetting efficiency of the packing was correlated as the sum of two‐third power of the liquid film fraction and the rivulet flow fraction, besides, a correlation based on Reynolds and Galileo numbers of the two phases in the form of was proposed. © 2012 American Institute of Chemical Engineers AIChE J, 59: 283–294, 2013     

Gas holdup for high gas velocities in a gas–liquid cocurrent upward‐flow system

Gas holdup has been measured in an 83‐mm diameter, 2.2‐m high column at high gas superficial velocities — 0.22 to 2.7 m/s — and at liquid (water) superficial velocities of 0 to 0.47 m/s, by means of a differential pressure transducer. The equation of Hills (1976) based on the slip velocity gives good predictions of the gas holdup for 0.1 ≤ E_g ≤ 0.4. However, the holdups predicted by this approach are considerably higher than the experimental values at gas velocities high enough that E_g > 0.4. Other equations from the literature are also shown to be inadequate. The new data and earlier data at high gas velocities are therefore correlated with a new dimensional equation for U_l ≤ 0.23 m/s.     

A CFD study of gas–solid jet in a CFB riser flow

Three‐dimensional high‐resolution numerical simulations of a gas–solid jet in a high‐density riser flow were conducted. The impact of gas–solid injection on the riser flow hydrodynamics was investigated with respect to voidage, tracer mass fractions, and solids velocity distribution. The behaviors of a gas–solid jet in the riser crossflow were studied through the unsteady numerical simulations. Substantial separation of the jetting gas and solids in the riser crossflow was observed. Mixing of the injected gas and solids with the riser flow was investigated and backmixing of gas and solids was evaluated. In the current numerical study, both the overall hydrodynamics of riser flow and the characteristics of gas–solid jet were reasonably predicted compared with the experimental measurements made at NETL. Published 2011 American Institute of Chemical Engineers AIChE J, 2012     

膜生物反应器工艺处理炼油废水中试研究

采用中空纤维膜生物反应器(MBR)工艺处理炼油废水,了解膜生物反应器在炼油废水处理中的性能.研究结果表明,采用膜生物反应器工艺可有效地处理炼油废水,COD、氨氮和油去除率分别为91.5%、96.7%、84.7%,MBR出水COD为64 mg/L,氨氮为1.85 mg/L,油含量<3.0 mg/L,出水水质达到国家一级排放标准.     

Gas–liquid interfacial area in the oxygen absorption to oil‐in‐water emulsions in an airlift reactor

The present work includes an exhaustive study about gas–liquid interfacial area between gas phase and liquid heterogeneous medium generated in an airlift bioreactor. The system studied is composed by water, methyl ricinoleate (MR), and Tween‐80, since it is the base of the medium used for the production of γ‐decalactone, a peach‐like aroma compound of industrial interest that can be produced biotechnologically through the biotransformation of ricinoleic acid, by the yeast Yarrowia lipolytica. Experimental results allow describing the hydrodynamic behaviour of the gas phase into the biphasic medium.     

Identification of the flow structures and regime transition in gas–solid fluidized beds through moment analysis

Using statistic parameters of solids holdup signals, a moment consistency data processing method (MCDPM) was proposed. Experiments were carried out using FCC particles of 76 μm under different operating conditions, and MCDPM was used to successfully obtain solids holdups of the dense and dilute phases and the phase fractions over five fluidization regimes, bubbling (BFB), turbulent (TFB), circulating turbulent (CTFB), high‐density circulating (HDCFB), and circulating (CFB) fluidized bed systems. In BFB, TFB, and CTFB regimes, only dense phase fraction decreased with increasing air velocity, while the transition from HDCFB to CFB experienced appreciable change in the solids holdup of the dense phase. From the low‐velocity to the high‐velocity regimes, both the solids holdup and the fraction of the dense phase experienced a drastic decrease, suggesting that this transition corresponded to a profound change in flow structure and further suggesting that CTFB is in reality still a TFB. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1479–1490, 2013     

Equilibrium and non‐equilibrium gas–liquid two phase flow in long and short pipelines following a rupture

The two‐phase flow following the blowdown of pipeline carrying flashing liquid is numerically investigated by using thermodynamic equilibrium and non‐equilibrium models. Model equations are solved numerically by the finite volume method. The values of fluxes at cell boundaries are obtained by AUSM+‐up. To obtain proper values for the coefficients of dissipation, both single phase liquid and two phase shock tube problems are investigated. The transient release from the pressurized pipeline is studied for two cases of long and short pipes. Comparison of the predictions against experimental data reveals non‐equilibrium model performs a little better than equilibrium model in the prediction of temporal variations of pressure and void fraction of the long pipe. However, equilibrium model totally overestimates pressure and void fraction of the short pipe. The relative error of equilibrium model in the prediction of pressure variation with time exceeds 50% and it is 20% for non‐equilibrium model. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3214–3223, 2017     

Critical gas velocity in a three‐phase internal loop airlift reactor with low‐density particles

In the present investigation the effects of the addition of organic additives (propanol, benzoic acid, iso‐amyl alcohol and carboxymethyl cellulose) on the critical gas velocity, (U_sg)_c, in an internal airlift loop reactor with low‐density particles (Nylon‐6 and polystyrene) were reported. Whereas the (U_sg)_c was reduced by adding the above additives, it increased with solids loading and density of the particles. The draft tube‐to‐reactor diameter ratio (D_E/D) in the range of 0.5–0.6 gave minimum (U_sg)_c values. The proposed dimensionless correlation predicted the experimental data well. Copyright © 2004 Society of Chemical Industry