Continuous bioremediation of phenol‐polluted air in an external loop airlift bioreactor with a packed bed

An external loop airlift bioreactor with a small amount (99% porosity) of stainless steel mesh packing inserted in the riser section was used for bioremediation of a phenol‐polluted air stream. The packing enhanced volatile organic chemical and oxygen mass transfer rates and provided a large surface area for cell immobilization. Using a pure strain of Pseudomonas putida, fed‐batch and continuous runs at three different dilution rates were completed with phenol in the polluted air as the only source of growth substrate. 100% phenol removal was achieved at phenol loading rates up to 33 120 mg h^?1 m^?3 using only one‐third of the column, superior to any previously reported biodegradation rates of phenol‐polluted air with 100% efficiency. A mathematical model has been developed and is shown to accurately predict the transient and steady‐state data. Copyright © 2006 Society of Chemical Industry     

Hydrodynamic characteristics of a spinning sparger,external loop airlift bioreactor

In this work, the traditional external loop, airlift bioreactor has been fitted with a spinning sparger. Baffles were located beyond the sparger circumference to prevent vortex motion throughout the bioreactor. The flat plate, spinning sparger had six orifices and was located below the downcomer connection to prevent the generation of a high shear environment inside the bulk medium as would be found in a stirred tank bioreactor. The spinning motion of the sparger produces smaller diameter bubbles with higher gas hold-ups and interfacial areas inside the bioreactor. Data and empirical correlations are presented for these features as well as liquid circulation velocity and mixing characteristics as functions of the spinning rate, superficial gas velocity and type of medium.     

Biodegradation of phenol-polluted air using an external loop airlift bioreactor

Biological air treatment methods are an alternative to conventional treatment methods such as activated carbon adsorption and chemical scrubbing. An external loop airlift bioreactor has been utilized to treat phenol-contaminated air using Pseudomonas putida. Saturated air was found to be cleansed of phenol below the detectable limit because of the high mass transfer rate of the pollutant from the air and the high growth rate of Pseudomonas putida. The bioreactor was found to degrade over 99% of the inlet phenol at rates from 21·5 to 194 mg h^?1 at concentrations between 650 and 850 mg m^?3 of air. A model of the system is developed based on an initial transient period followed by a pseudo-steady state period. The simulations compared well with the experimental data.     

包埋固定化技术去除水体中氨氮的研究进展

在氮污染日益严重化的今天,脱氮已成为当今水处理中亟待解决的问题。传统生物脱氮技术中存在许多问题,固定化微生物技术能够弥补传统方法中的不足之处,实现高效脱氮。固定化技术中的包埋法是应用最广泛的一种方法。主要介绍了包埋载体的选择情况以及包埋法固定化脱氮技术在国内外的研究进展情况,并针对将该技术实用化提出了现阶段需要解决的问题。     

Bioremediation of toluene‐contaminated air using an external loop airlift bioreactor

An external loop airlift bioreactor (ELAB) has been used to capture and degrade toluene from a contaminated air stream. Using a spinning sparger, the toluene could be transferred from small, uniform bubbles into the aqueous culture media with an overall mass transfer coefficient as high as 1.1 h^?1. Due to the very volatile nature of toluene, Pseudomonas putida (ATCC 23973) was cultured and maintained on benzyl alcohol, the first intermediate compound in the metabolic degradation pathway for toluene. Consequently, before successful continuous operation of the ELAB with toluene‐contaminated air, Pseudomonas putida was acclimatized to toluene by using 30 min intermittent sparging of contaminated air into the bioreactor. Continuous sparging of toluene‐contaminated air could then be successfully carried out with 100% capture and biodegradation efficiency at a contaminated air concentration of 15 mg dm^?3 and a loading rate of 35 mg dm^?3 h^?1. Higher concentrations and loading rates were only partially degraded. Although this capture matches only the low rates reported earlier using biofilters to remediate toluene, the ELAB operates using submerged culture and requires no packing which can plug during biofilter operation. In this study, Pseudomonas putida grew on toluene at a maximum specific growth rate of only 0.05 h^?1. © 2003 Society of Chemical Industry     

Effects of surface active agents on hydrodynamics and mass transfer characteristics in a split-cylinder airlift bioreactor with packed bed

The effects of three types of surface active agents (containing SDS, HCTBr and Tween 40) with various concentrations (0–5 ppm) on the hydrodynamic and oxygen mass transfer characteristics in a split-cylinder airlift bioreactor with and without packing were investigated. It was observed that in the surfactant solutions, surface tension of the liquid decreased and smaller bubbles were produced in comparison with pure water. So, surfactants presence strongly enhanced mixing time and gas hold-up although oxygen mass transfer coefficient and the liquid circulation velocity reduced. Furthermore, the packing installation enhanced the overall gas–liquid volumetric mass transfer coefficient by increasing flow turbulency and Reynolds number compared to an unpacked column. The packing increased gas hold-up and decreased bubbles size and liquid circulation velocity.     

Hydrodynamics of a novel multi-stage external loop airlift reactor

In the present investigation a novel multi-stage external loop airlift reactor with hydro-dynamically induced continuous bubble generation, breakup and regeneration has been proposed. The system has been designed to operate with relatively large sized bubbles, so that interfacial circulation can be induced in the liquid-bubble interfaces and faster transfer of components can take place by turbulent diffusion through the interface of the bubbles and also due to the physical rupture and reformation of the bubbles. The system was also designed to operate in three stages operating in series so that in each stage completely deaerated liquid could be brought in contact with freshly generated bubbles. Detailed studies on the gas holdup and liquid circulation velocity have been carried out with respect to various values of superficial gas as well as liquid velocities. The gas holdup of the proposed multi-stage system is 45% higher than the single stage system, which results in better mass transfer characteristics. Empirical correlations describing the performance of the proposed reactor have been presented in this paper.     

气升式振荡环流反应器的数值模拟和结构优化

气升式振荡环流反应器（ARLR）作为一种新型的气升式环流反应器,能够有效地提高反应器的气含率和传质系数,并已得到生物发酵实验的验证。本文通过CFD的手段研究了反应器内的流动和传质状况,并利用CFD模拟和响应面分析相结合的方法,优化了反应器的结构参数,如高径比（H/D）、升液区降液区面积之比、导流筒高度等。经过实验测量,优化后的气升式振荡环流反应器与传统的气升式环流反应器相比,气含率提高了32%以上,传质系数提高了11%以上。结果表明,气升式振荡环流反应器作为生化反应器有着非常广阔的应用空间。     

三相环流反应器流体力学行为

气升式三相环流反应器综合了鼓泡塔和机械搅拌釜的优良性能,具有结构简单、无机械传动部件、易密封、造价低、容易实现工业放大等优点,在石油、化工、电化学和生物化工等领域得到了广泛应用．随着能源形势的日趋紧张,环流反应器在液相法合成甲醇、浆态床一步法合成二甲醚、煤液化等过程中的应用得到许多研究人员的重视,并取得了重要的研究进展．由于目前对其内部流动行为尚缺乏系统的认识,进行工业设计和操作过程中仍显理论指导不足     

Study of pressure fluctuations in an internal loop airlift bioreactor

The origin and coupling of pressure fluctuations in an internal loop airlift bioreactor are investigated. The pressure fluctuations in the reactor are divided into two categories: global pressure fluctuations and local pressure fluctuations. It is found that the coupling between global pressure fluctuations and local pressure fluctuations mainly focuses in the frequency region between 10 and 30 Hz. Local pressure fluctuations in the reactor are strongly affected by pressure waves originating from the air‐supply system, while pressure fluctuations caused by the bubble eruption at the liquid surface have less influence on local pressure fluctuations. Based on the coherence analysis, the pressure signal at a certain position in the reactor is decomposed into three different parts: coherent part, joint incoherent part and exclusive incoherent part. The energy ratios of these different parts are helpful to study the interaction among pressure fluctuations from different sources. Three flow regimes were identified from the evolution of the energy ratio of the joint incoherent part. © 2011 Canadian Society for Chemical Engineering     

Effects of free ammonia and dissolved oxygen on nitrification and nitrite accumulation in a biofilm airlift reactor

The purpose of this research is to find out the effects of free ammonia concentration and dissolved oxygen on nitrification and nitrite accumulation in a biofilm airlift reactor. Free ammonia seriously inhibited the activity of nitrite oxidizers at the concentration higher than 0.1 mg NH₃-N/L and it was very effective for nitrite accumulation. Dissolved oxygen limitation in the biofilm also caused nitrite accumulation. Long term inhibition decreased the growth rate for nitrite oxidizers, and ammonia oxidizers were the dominant nitrifiers in the wastewater nitrification. Selective accumulation of ammonia oxidizers in the biofilm could be another reason for nitrite accumulation. Free ammonia inhibited nitrite oxidizers immediately, and adaptation to free ammonia was not observed. Therefore, the optimum control of free ammonia and dissolved oxygen concentration is critical for nitrite accumulation and the strategy can be used for selective accumulation of ammonia oxidizers in a bioreactor system.     

Biodegradation of natural and synthetic estrogens in moving bed bioreactor

Estrogen hormones as a group of endocrine disruptive compounds(EDC) can interfere with endocrine system in humans and animals. The goal of this study was to investigate the elimination rate of Estrone(El), 17β-estradiol(E2) and 17α-ethinyl estradiol(EE2) in Moving Bed Bioreactor(MBBR). These analytes extracted by Dispersive Liquid-Liquid Microextraction(DLLME) technique, followed by derivatization, and detected by GC/MS. Estrogen removal efficiency in MBBR improved at high solid retention times(SRTs), which notion is owing to development of nitrification. Estrogen specific removal rate was between 0.22-1.45 μg·(g VSS)~(-1)·d~(-1) for natural and synthetic hormones. The adsorption rate was 0.9%-3.2%, 0-1.3%, and 0.7%-5.7% for El, E2, and EE2, respectively. In addition, the biodegradation rates were more than 95% for these compounds. These results illustrated that in MBBR,the biodegradation and the adsorption to biomass are considered as two significant routes for elimination of estrogenic compounds. As a whole, the deterioration rate of estrogens enhanced by MBBR compared to other biological wastewater treatment processes such as conventional activated sludge.     

Liquid circulation hydrodynamics in an external loop airlift reactor

The radial profiles of axial liquid velocity and gas hold‐ups are investigated in the riser of a pilot plant scale external loop airlift reactor (ELAR) using a modified Pavlov tube and differential pressure technique. The experimental investigation reveals that there exist two different kinds of liquid circulation structures in an ELAR, which has rarely been reported in the literature, namely internal liquid circulation, which exists only in the riser and external liquid circulation, which circulates through the downcomer. A power–law relationship is used to correlate the gas hold‐up and superficial gas velocity, which gives good agreement with experimental data. Experiments for axial liquid velocity profiles are analysed in analogy to a model described for a conventional bubble column. The results predicted by the model are in excellent agreement with the experimental data obtained under various operating conditions. © 2011 Canadian Society for Chemical Engineering     

气升式外环流反应器的体积传质系数

以Higbie的渗透理论和Kolmogoroff的湍流理论为基础,提出了计算液体旋涡在气液相界面暴露时间的方法,并建立了预测体积传质系数的模型方程。在不同管径比下的外环流反应器中,对空气 水体系测定了操作气速对体积传质系数、循环液速和气含率的影响。将体积传质系数与表观气速和下降管与上升管的面积比按幂函数进行关联,其预测值和试验值符合较好。     

Macro-mixing in a draft-tube airlift bioreactor

Airlift reactors are pneumatically agitated reactors that have been widely used in industries, particularly in bioprocesses. Extensive studies about the flow dynamics in airlift column reactors exist; however, most of these studies have focused on global hydrodynamic parameters using conventional techniques. The local flow characteristics, such as the macro-mixing and the turbulence intensity, are crucial for reliable design and scale-up, and they remain unclear. This work focuses on studying the macro-mixing in a draft-tube airlift bioreactor utilizing an advanced flow dynamic measurement technique, computer automated radioactive particle tracking (CARPT). True residence time distribution analyses for the overall column as well as individual regions, i.e., the riser, the downcomer, the top, and the bottom regions, are conducted for the first time based on CARPT measured particle trajectories. The effects of the superficial gas velocity and the top/bottom clearances on the macro-mixing are also discussed. The results suggest that although the flow structures in the overall draft-tube column reactor, as well as in the riser and in the downcomer, are close to plug flows, bypassing and stagnancy exist in the top and the bottom regions.     

外循环气升式膜反应器中的体积传质系数

传质系数是决定气升式反应器传质特性的主要参数之一,文中介绍了一种新型的将陶瓷膜曝气系统与外环流反应器耦合的外环流膜反应器,考察了不同曝气气量,曝气压力,曝气方式以及曝气位置条件下反应器中体积传质系数的变化情况。结果表明,曝气气量,曝气压力,曝气孔孔径都能影响体积传质系数,孔径的影响尤为显著,采用膜微孔曝气,体积传质系数相比曝气头曝气提高近2倍。将膜管曝气和曝气头曝气耦合起来,可在获得良好气液循环的条件下有较大的气液接触面,从而优化气液传质。     

Process intensification with a hybrid system: A tubular packed bed bioreactor with immobilized activated sludge culture coupled with membrane filtration

Performance of a hybrid system consisting of a tubular bioreactor and a membrane filter was studied for removing carbohydrate and protein. Microporous polyurethane (sponge) was used as the packing medium for immobilization activated sludge culture. The bioreactor was operated in series with a cross flow ultrafiltration system to study the effect of influent flow rate and chemical oxygen demand (COD) concentration on the overall system performance. The removal efficiency in the bioreactor decreased linearly with increase in loading. The decline of removal efficiency at higher loadings was more significant for protein than carbohydrate. Coupling the bioreactor with a membrane separation process increased the overall removal rates and provided a consistent effluent quality. The flux through ultrafiltration membrane did not change significantly even when the bioreactor effluent had high levels of protein. Morphological examination of the packing medium both visually and by SEM showed significant accumulation of organisms on the surface which indicates that biofilm thickness was controlled by diffusion limitations. Advantages of the hybrid system include small footprint, economical packing medium, and space savings by coupling the bioreactor with a membrane filtration process.     

Nitrification and sludge characteristics in a submerged membrane bioreactor on synthetic inorganic wastewater

A submerged membrane bioreactor (SMBR) treating ammonia-bearing synthetic inorganic wastewater withoutsludge purge was studied in respect to nitrification and microbial parameters over a period of 210 days. The reactor was operated at a hydraulic retention time (HRT) of 24 h, and the NH_4-N volumetric loading rate increased from 0.18 to 1.30 kg NH₄⁺-N m⁻³d⁻¹ by increasing influent NH₄⁺-N from 180 mg/l⁻¹ to 1300 mg/l⁻¹. With the exception of a short period after the failure of pH control, the NH₄⁺-N⁺ removal rate, was constantly above 99%. Due to the influent characteristics and the interception of the membrane module, the mixed liquor suspended solids (MLSS) varied from 3000 to 5000 mg/l⁻¹ and the nitrifying bacteria were dominant in the SMBR. The numbers of ammonia oxidizers and nitrite oxidizers in the mixed liquor increased from 0.9×10⁸ ml⁻¹ and 1.0×10⁸ ml to 1.6×10⁸ ml⁻¹ and 9×10⁸ ml⁻¹ respectively, and the specific nitrification rate from 0.27 to 0.56 g NH₄⁺-N g⁻¹ SS⁻¹ d⁻¹. An increasing occurrence of extracellular polymeric substances (EPS) around microbial clusters with operation time was clearly observed on scanning electron micrographs (SEM). The pressure difference of the membrane module was not over 0.01 mPa over the whole operation period. Present results show that SMBR can be operated efficiently and stably as a high-rate nitrifying technology.     

Microbial community structure in an intermittently aerated submerged membrane bioreactor treating domestic wastewater

The microbial community structure in an intermittently aerated submerged membrane bioreactor treating domestic wastewater was investigated using the respiratory quinone profiling method. The operating cycle consisted of feeding the domestic wastewater into a 90-min oxic condition and a 60-min anoxic condition. A slight difference was observed in the microbial community structure of the suspended microorganisms in anoxic and oxic conditions. The dominant quinone type of anoxic and oxic conditions was ubiquinone (UQ)-8 followed by UQ-10 and menaquinone (MK)-6. The quinone profiles of the suspended microorganisms in the intermittently aerated SMBR with anoxic and oxic cycling showed that Nitrosomonas species, Alcaligenes species, and Thiobacillus, the dominant quinone of there are UQ-8 actively contributed to the biological nitrification/denitrification. The microbial diversities of suspended microorganisms in the anoxic and oxic conditions calculated on the molar fraction basis of all quinone compositions were 8.79-10.38 and 10.03-11.82, respectively.     

Gas transfer in an external loop bioreactor with built-in ultrafiltration

The SGI Ultrafermenter is an external loop bioreactor with circulation through an ultrafiltration module allowing removal of medium and soluble products during fermentation. The contents are continually circulated during operation and the vessel is also equipped with a stirring turbine. The interaction of these two mixing agents on gas transfer was investigated. Both mechanisms produced similar increments in K_La over their working ranges, with values from approximately 0–700 h^?1 at 200 dm³ h^?1 airflow. The effects of these two mechanisms on K_La were approximately additive at low values but the combined mixing produced a maximum K_La value also in the region of 700 h^?1. The power-draw of mixing using the two agents was calculated and stirring was found to be 10–20 times more efficient than circulation.