膜生物反应器中的生物学特征

由于在膜生物反应器内膜的截留作用 ,使膜生物反应器内的一些生物学特征与传统的活性污泥过程有所不同。本文系统地阐述了膜生物反应器内的微生物群落、活性污泥及微生物产物的生理生化特征。     

膜生物反应器的研究进展

膜生物反应器是近年来发展的废水处理新技术,具有活性污泥浓度高、污泥龄长、占地面积小、投资省的特点。利用膜生物反应器进行污水处理不仅可以大大节约水资源,还可以大大节约能源,节省设备和运行费用,已成为二十一世纪研究热点。膜生物反应器是通过高效膜分离技术与活性污泥相结合,增大污泥中的特效菌来加快生化反应速率,提高废水处理效果。目前处理对象已从生活污水扩展到高浓度的有机废水和难降解的工业废水。本文综述了膜生物反应器在废水中的应用研究情况,并分析比较了各种膜材质的特点、适用范围以及膜的污染因素和清洗方法,展望了膜生物反应器的应用前景及进一步研究方向。     

固定化细胞膜反应器生产6－APA的研究

将青霉素酰化酶基因工程菌大肠杆菌A56(pPA22)通过交联截留固定化在由中空纤维膜或平板膜构成的膜反应器内,提高了单位体积反应器的酶活,实现了高浓度青霉素的裂解。采用反冲模式操作的中空纤维膜反应器裂解7．8％医用青霉素钠盐50批,产品6－APA的平均重量收率达到90．1％,纯度达98．6％,50批反应操作后,膜反应器内剩余酶活力仍在80％以上。     

厌氧膜生物反应器及其应用研究实例

厌氧膜生物反应器(anaerobic membrane bioreactor,AnMBR)是一种耦合了厌氧发酵和膜工艺的新型废水生物处理技术。其优点包括出水水质优良、有机负荷高、污泥产率低以及生物甲烷回收等。归纳了厌氧发酵的原理,常见厌氧膜生物反应器的结构和种类,以及厌氧膜生物反应器的发展历程及其应用。详细介绍了笔者的最新研究成果:厌氧膜生物反应器在高浓度厨余垃圾处理中的应用,及其在城市污水处理中的研究进展。最后总结了该工艺的应用及发展现状,指出其在高浓度有机废水处理中拥有广阔的应用前景。     

氧对膜生物反应器短程硝化的影响

为了研究膜生物反应器的短程硝化性能以及氧对短程硝化的影响,通过对比耗氧率和供氧率,提出了膜生物反应器短程硝化的控制优化建议。在膜生物反应器硝化过程中,DO小于1 mg/L开始出现亚硝氮积累;DO降到0.5 mg/L,出水氨氮浓度与亚硝氮浓度之比接近1∶1;DO调控在0.5-1 mg/L范围内,有利于前置硝化反应器与后续厌氧氨氧化反应器衔接。膜生物反应器中污泥浓度可达20 g/L,耗氧能力可达19.86 mg O2/(L·s),但最大供氧能力仅为0.369 mg O2/(L·s),供氧成为反应器运行的制约瓶颈,"低DO高流量"曝气是继续提高短程硝化效能的控制策略。     

EMBR技术处理工业园区综合废水试验研究

国内工业园区排放的综合废水中会产生复合污染且污染物具有多样性,致使目前常用的废水处理工艺难以达到国家废水处理的标准。本研究在膜生物反应器的基础上构建了电场-膜生物反应器,研究了电流密度和冲击负荷对COD_(cr)、氨氮和TN的影响。发现了电流密度对电场-膜生物反应器去除COD_(cr)效率没影响,而对TN去除率有很大的影响,冲击负荷对氨氮的去除效率没有影响。经过63 d连续运行,中试试验结果显示:电场-膜生物反应器的耦合对解决工业园区综合废水处理的难题有明显的效果,出水水质基本达到《城镇污水处理厂污染物排放标准》(GB18918-2002)的一级B标准。     

膜技术在生物技术中应用

合成膜和其相关过程是一种新颖分离技术,由于它可以在维持原生物体系环境下实现分离,以及膜反应器可以使生物转化和产品分离结合起来等特点,近年已被广泛应用生物技术的产品分离和开发高效反应器中,展现了广阔的应用前景。     

MBR运行初期对基因工程菌的截留特性研究

在膜-生物反应器(MBR)中实施基因工程菌生物强化时, 运行初期基因工程菌流失是生态风险评价的重要内容。在一体式微滤膜-生物反应器中, 考察了运行初期不同运行条件对基因工程菌流失密度和截留效率的影响, 并对截留特性进行了探讨。结果表明, 膜-生物反应器运行初期, 不同运行条件对基因工程菌的截留效率影响不同：污泥浓度增加, 截留效率提高; 提高膜通量和曝气量, 截留效率降低。基因工程菌接种密度为1.0×1010 CFU/mL时, 不同运行条件下的流失密度为1.0×102 CFU/mL~2.5×102 CFU/mL, 最大截留效率大于8 lg。膜-生物反应器运行初期, 膜组件截留、污泥吸附以及对悬浮细胞迁移阻碍是影响截留效率的主要因素, 一定条件下其截留效率贡献率分别为82.3%、14.9%和2.8%。膜-生物反应器稳定运行过程中形成凝胶层, 可以提高截留效率。一定条件下, 膜组件、污泥和凝胶层对基因工程菌的截留贡献率分别为75.3%、10.7%和14.0%。     

MBR运行初期对基因工程菌的截留特性研究

在膜-生物反应器(MBR)中实施基因工程菌生物强化时,运行初期基因工程菌流失是生态风险评价的重要内容.在一体式微滤膜-生物反应器中,考察了运行初期不同运行条件对基因工程菌流失密度和截留效率的影响,并对截留特性进行了探讨.结果表明,膜-生物反应器运行初期,不同运行条件对基因工程菌的截留效率影响不同:污泥浓度增加,截留效率提高;提高膜通量和曝气量,截留效率降低.基因工程菌接种密度为1.0×1010CFU/mL时,不同运行条件下的流失密度为1.0×102 CFU/mL～2.5×102 CFU/mL,最大截留效率大于8 lg.膜-生物反应器运行初期,膜组件截留、污泥吸附以及对悬浮细胞迁移阻碍是影响截留效率的主要因素,一定条件下其截留效率贡献率分别为82.3%、14.9%和2.8%.膜-生物反应器稳定运行过程中形成凝胶层,可以提高截留效率.一定条件下,膜组件、污泥和凝胶层对基因工程菌的截留贡献率分别为75.3%、10.7%和14.0%.     

膜片状填料固定化酵母薯干酒精发酵生物反应器的研究

针对以薯干为原料固定化酵母带渣酒精发酵的特点,研制了一种新型的容积为1m~3的膜片状填充床生物反应器,并历时半年多考察了该反应器的操作稳定性,得出较佳的发酵周期和醪液循环量等.实验结果表明:膜片状填充床固定化酵母生物反应器的酒精发酵速率远大于传统式发酵罐;其淀粉利用率可达91～92%,乙醇生产能力可达9.5kg EtOH/m~3·h.     

Membrane bioreactors: Engineering aspects

Membrane bioreactors have in-situ separation capability lacking in other types of immobilized cell reactors. This makes them very useful for certain systems. Enzyme reactions utilizing cofactors and hydrolysis of macromolecules are advantageous in membrane reactors. Anaerobic cell culture may be efficiently carried out in membrane cell recycle systems, while aerobic cultures work well in dual hollow fiber reactors. Animal and plant cells have much a better chance of success in membrane reactors because of the protective environment of the reactor and the small oxygen uptake rate of these cells.     

Optimal design of a number of membrane reactors in series using Michaelis-Menten one-substrate reversible kinetics

Summary Exact analytical expressions are derived for the optimal design (minimum overall reaction volume) of N perfectly mixed membrane reactors in series carrying out an enzyme catalysed Michaelis-Menten, one-substrate/one-product reversible reaction. The equations enable the direct calculation of the smallest total reactor volume needed for a given overall conversion degree. Results show that when substrate rejection is present, membrane reactors perform better compared with continuous stirred tank reactors.     

Reactor design for minimizing product inhibition during enzymatic lignocellulose hydrolysis: II. Quantification of inhibition and suitability of membrane reactors

Product inhibition of cellulolytic enzymes affects the efficiency of the biocatalytic conversion of lignocellulosic biomass to ethanol and other valuable products. New strategies that focus on reactor designs encompassing product removal, notably glucose removal, during enzymatic cellulose conversion are required for alleviation of glucose product inhibition. Supported by numerous calculations this review assesses the quantitative aspects of glucose product inhibition on enzyme-catalyzed cellulose degradation rates. The significance of glucose product inhibition on dimensioning of different ideal reactor types, i.e. batch, continuous stirred, and plug-flow, is illustrated quantitatively by modeling different extents of cellulose conversion at different reaction conditions. The main operational challenges of membrane reactors for lignocellulose conversion are highlighted. Key membrane reactor features, including system set-up, dilution rate, glucose output profile, and the problem of cellobiose are examined to illustrate the quantitative significance of the glucose product inhibition and the total glucose concentration on the cellulolytic conversion rate. Comprehensive overviews of the available literature data for glucose removal by membranes and for cellulose enzyme stability in membrane reactors are given. The treatise clearly shows that membrane reactors allowing continuous, complete, glucose removal during enzymatic cellulose hydrolysis, can provide for both higher cellulose hydrolysis rates and higher enzyme usage efficiency (kg_product/kg_enzyme). Current membrane reactor designs are however not feasible for large scale operations. The report emphasizes that the industrial realization of cellulosic ethanol requires more focus on the operational feasibility within the different hydrolysis reactor designs, notably for membrane reactors, to achieve efficient enzyme-catalyzed cellulose degradation.     

Comparison and Analysis of Membrane Fouling between Flocculent Sludge Membrane Bioreactor and Granular Sludge Membrane Bioreactor

The goal of this study is to investigate the effect of inoculating granules on reducing membrane fouling. In order to evaluate the differences in performance between flocculent sludge and aerobic granular sludge in membrane reactors (MBRs), two reactors were run in parallel and various parameters related to membrane fouling were measured. The results indicated that specific resistance to the fouling layer was five times greater than that of mixed liquor sludge in the granular MBR. The floc sludge more easily formed a compact layer on the membrane surface, and increased membrane resistance. Specifically, the floc sludge had a higher moisture content, extracellular polymeric substances concentration, and negative surface charge. In contrast, aerobic granules could improve structural integrity and strength, which contributed to the preferable permeate performance. Therefore, inoculating aerobic granules in a MBR presents an effective method of reducing the membrane fouling associated with floc sludge the perspective of from the morphological characteristics of microbial aggregates.     

A comparative study of gel entrapped and membrane attached microbial reactors for biodegrading phenol

A comparative study between two reactors, one using microorganisms entrapped in calcium alginate gel, and the other using microorganisms attached on the surface of a membrane (polymeric microporous sheeting, MPS^TM) to biodegrade phenol is performed. Results indicate that the alginate bead bioreactor is efficient at higher phenol concentrations while the membrane bioreactor shows better performance at lower phenol concentrations. This unique response is primarily attributed to the different techniques by which the microorganisms are immobilized in the two reactors.In batch mode, below a starting concentration of 100 ppm phenol, biodegradation rates in the membrane bioreactor are (7.58 to 12.02 mg phenol/h · g dry biomass) atleast 10 times the rates in alginate bead bioreactor (0.74 to 1.32 mg phenol/h · g dry biomass). Biodegradation rates for the two reactors match at a starting concentration of 250 ppm phenol. Above 500 ppm phenol, the rates in the alginate bead bioreactor are (7.3 to 8.1 mg phenol/h · g dry biomass) on an average 5.5 times the corresponding rates in the membrane bioreactor (2.18 to 1.03 mg phenol/h · g dry biomass).In continuous feed mode the steady state degradation rates in the membrane bioreactor are one to two orders of magnitude higher than the alginate bead bioreactor below 150 ppm inlet phenol concentration. At an inlet concentration around 250 ppm phenol the rates are comparable. Above 500 ppm of phenol the rates in the alginate bioreactor are an order of magnitude high than the membrane bioreactor.Due to substrate inhibition, and its inability to sustain a high biomass concentration, the membrane bioreactor shows poor efficiencies at phenol concentrations above 250 ppm. At low phenol concentrations the apparent reaction rates in the alginate bead bioreactor decrease due to the diffusional resistance of the gel matrix, while biodegradation rates in the membrane bioreactor remain high due to essentially no external diffusional resistance.Results indicate that a combined reactor system can be more effective for bioremediation than either separate or attached microbial reactors.     

Viscosity decrease of pectin and fruit juices catalyzed by pectin lyase from Penicillium italicum in batch and continuous-flow membrane reactors

Summary The extracellular pectin lyase (PNL, E.C. 4.2.2.10) from Penicillium italicum was utilized in batch and confined in a continuous-flow ultrafiltration membrane reactor. The enzyme catalyzed the decrease in viscosity of pectin solutions at pH 6.0 as well as of different fruit juices at their respective pH. PNL decreased the viscosity of pectin solutions in the membrane (60% after 30 min) more than in the batch (46% after 70 min) reactors, but similar viscosity reduction of fruit juices was achieved in both reactors. The enzyme decreased the viscosity of grape, peach and melon juices to different extents, but failed to do so with apple or pear juices. It can be concluded that the utilization of PNL in a membrane reactor appears of interest for the clarification of fruit juices.     

Enzymatic membrane reactors for biodegradation of recalcitrant compounds. Application to dye decolourisation

Membrane bioreactors are being increasingly used in enzymatic catalysed transformations. However, the application of enzymatic-based treatment systems in the environmental field is rather unusual. The aim of this paper is to overview the application of enzymatic membrane reactors to wastewater treatment, more specifically to dye decolourisation. Firstly, the basic aspects such as different configurations of enzymatic reactors, advantages and disadvantages associated to their utilisation are revised as well as the application of this technology to wastewater treatment. Secondly, dye decolourisation by white-rot fungi and their oxidative enzymes are discussed, presenting an overall view from for in vivo and in vitro systems. Finally, dye decolourisation by manganese peroxidase in an enzymatic membrane reactor in continuous operation is presented.     

Current and future trends for biofilm reactors for fermentation processes

Biofilms in the environment can both cause detrimental and beneficial effects. However, their use in bioreactors provides many advantages including lesser tendencies to develop membrane fouling and lower required capital costs, their higher biomass density and operation stability, contribution to resistance of microorganisms, etc. Biofilm formation occurs naturally by the attachment of microbial cells to the support without use of any chemicals agent in biofilm reactors. Biofilm reactors have been studied and commercially used for waste water treatment and bench and pilot-scale production of value-added products in the past decades. It is important to understand the fundamentals of biofilm formation, physical and chemical properties of a biofilm matrix to run the biofilm reactor at optimum conditions. This review includes the principles of biofilm formation; properties of a biofilm matrix and their roles in the biofilm formation; factors that improve the biofilm formation, such as support materials; advantages and disadvantages of biofilm reactors; and industrial applications of biofilm reactors.     

Community shifts in a seeded 3-chlorobenzoate degrading membrane biofilm reactor: indications for involvement of in situ horizontal transfer of the clc-element from inoculum to contaminant bacteria

Pseudomonas putida BN210, carrying the self- transferable clc-element encoding degradation of 3-chlorobenzoate on the chromosome, was used as inoculum in different membrane biofilm reactors treating 3-chlorobenzoate-contaminated model wastewater. Analysis of the bacterial population in the effluent and in the biofilm showed the loss of BN210 beyond detection from the reactors and the appearance of several novel 3-chlorobenzoate mineralizing bacteria mainly belonging to the beta-proteobacteria. In contrast, in non-inoculated reactors, no 3-chlorobenzoate degradation was observed and no 3-chlorobenzoate degraders could be recovered. Southern blots hybridization of genomic DNA using clc-element-specific probes and FIGE analysis indicated the presence of the complete clc-element in one or more copies in the isolates. Moreover, the isolates could transfer the clc genes to Ralstonia metallidurans recipients. Two representative reactor isolates, Ralstonia sp. strains KP3 and KP9 demonstrated a higher growth rate on 3-chlorobenzoate than strain BN210 in batch cultures. When BN210, KP3 and KP9 were simultaneously inoculated in a membrane reactor supplied with 3-chlorobenzoate, strain KP3 outcompeted the two other strains and remained the major 3-chlorobenzoate degrading population in the reactor. Our data suggest that in situ horizontal transfer of the clc-element from the inoculum to contaminant bacteria in the reactors was involved in the establishment of novel 3-chlorobenzoate degrading populations that were more competitive under the defined reactor conditions than the inoculum strain.     

Membrane electrochemical reactors (MER) for NADH regeneration in HLADH-catalysed synthesis: comparison of effectiveness

Two membrane electrochemical reactors (MER) were designed and applied to HLADH-catalysed reduction of cyclohexanone to cyclohexanol. The regeneration of the cofactor NADH was ensured electrochemically, using either methyl viologen or a rhodium complex as electrochemical mediator. A semi-permeable membrane (dialysis or ultra-filtration) was integrated in the filter-press electrochemical reactor to confine the enzyme(s) as close as possible to the electrode surface. When methyl viologen was used, the transformation ratio of cyclohexanone varied from 0 to 65% depending on the internal arrangement of the reactor. Matching the reactor configuration to the reaction system was essential in this case. With the rhodium complex, the ultra-filtration MER was tested in continuous and recycling configurations. The best conditions led to 100% transformation of 0.1 L volume of 0.1 M cyclohexanone after 70 h with the recycling mode. Finally, the performances of the reactors are discussed with respect to different evaluations of the production yields.