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关键词： Microbubbles   Sintered porous metal membrane impeller   Microbubbles stirred tank bioreactor   Mass transfer  

摘要： Stirred tank bioreactors are one of the most widely used bio-fermentation systems at both the laboratory and factory scale for the production of high value bioproducts. However, conventional systems suffer from irreconcilable contradictions to ensure adequate volumetric oxygen mass transfer rates (k(L)a) the necessary operating conditions to increase the energy consumption and the shear conditions. Adaptation of systems that incorporate microbubbles (MBs) generated by microporous sparger are advantageous for high viscosity and low shear stress bio-fermentation systems due to their superior k(L)a's, high gas-liquid interfacial area to volume ratios, high gas holdup, and slow coalescence rates. Herein, we describe the development of a novel microbubble-based stirred tank bioreactor (MSTBR) using a sintered porous metal plate impeller as gas sparger that produces MBs in both Newtonian and non-Newtonian fluids. The MSTBR showed increased k(L)a and improved the gas holdup by forming an abundance of MBs, while avoiding the high shear stress and reducing the mixing energy consumption that are typically caused by utilization of Rushton turbine impellers. To validate the robustness of the MSTBR, arachidonic acid (ARA)-rich oil was produced from the shear-sensitive, high oxygen consuming filamentous fungus Mortierella alpine. The total ARA content produced using the MSTBR system was found to be 2.82 times that of the control bioreactor. Taken together, our data indicates that the new MSTBR bio-fermentation system can be broadly utilized in applications requiring elevated oxygen levels, shear-sensitive microorganisms, and high viscosity medium during the bio-fermentation process. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Mass transfer rate   Stoichiometry   Hexadecane   Oxygen   Airlift bioreactor   Oil-degrading consortium  

摘要： The production of oil-degrading bacteria in multiphase airlift reactors (ALBs) could be limited by the mass transport of both the gaseous and oil phases. In our study, the mass transfer rates of hexadecane and oxygen (HTR/OTR) were evaluated during the production of oil-degrading bacteria in a 3-L airlift reactor. To improve the HTR/OTR ratios during kinetics, a high initial concentration of hexadecane (77 g L (1)) and constant superficial gas velocity (U-G) in the range of 1.5-3.5 cm s (1) were used. Under these conditions, all initial HTR/OTR were close to the stoichiometric consumption ratio (SCR, similar to 0.28), which in turn decreased at the end of the culture until 0.173 +/- 0.013, 0.108 +/- 0.006 and 0.123 +/- 0.006 (g HXD) (g O-2) (1) for U-G of 1.5, 2.5, 3.5 cm s (1), respectively. The evaluation of the Damkohler numbers suggested an enhancement of HXD mass transport that allowed for obtaining a maximum suspended solids (SS) production of 4.9-6.0 g SS (L h) (1). Since the operation of the ALB at high superficial gas velocities may lead to high power inputs, the variable UG technique was used for energy saving, finding similar maximum SS production (6.09 g SS (L h) (1)) to that obtained at a constant U-G of 2.5 cm s (1) and an energy saving of 33.4%. The improvement in the HTR/OTR ratio during ALB performance allowed us to enhance the production of an oil-degrading microbial consortium. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Fermentation   X-ray absorption near edge spectroscopy   Iron   Phosphates   Sludges  

摘要： A new phosphorus (P) removal and recovery process that integrates an FeCl3-dosing, membrane bioreactor (MBR), and side-stream cofermentation was developed for wastewater treatment. The Fe and P species and their transformation mechanisms via aerobic and anaerobic conditions were investigated with X-ray absorption near edge structure (XANES) spectroscopy. In the new treatment system, 98.4% of the total P in domestic wastewater was removed and retained in activated sludge in the MBR. During the subsequent acidogenic cofermentation with food waste, P in the MBR sludge was released and eventually recovered as vivianite, achieving an overall P recovery efficiency of 61.9% from wastewater. The main pathways for P removal and recovery with iron dosing and acidogenic fermentation were determined by XANES analysis. The results showed that Fe enhanced P removal with the MBR was mainly achieved by precipitation as ferric phosphate (24.2%) and adsorption onto hydrous iron oxides (60.3%). During anaerobic fermentation, transition from Fe(III)-P to Fe(II)-P complex occurred in the sludge, leading to Fe(II) dissolution and P release. The pH decrease and microbial Fe reduction were crucial conditions for effective P extraction from the MBR sludge. The efficiency of P recovery increased with an increase in the fermentation time and organic load and a decrease of pH in the solution.

关键词： Membrane bioreactor   surface and pores   constant flux   polypropylene hollow fiber membrane   UV grafting   hydrophilic  

摘要： To investigate the effect of hydrophobic and hydrophilic polypropylene hollow fiber membranes (PPHFMs) applied in membrane bioreactors (MBR), the fouling behaviors of membrane surfaces and pores have been tested. The structural and morphological features on the membrane surface were characterized using attenuated total reflection-Fourier transform infrared spectroscopy, field emission scanning electron microscopy, atomic force microscope, energy dispersive X-ray spectroscopy and laser granularity distribution analysis. The results showed that significantly more polysaccharide, protein and inorganic ingredients were accumulated in the original membrane compared to the hydrophilic membrane. Furthermore, it was found that the pore size influenced the particle distribution and accumulation, such that smaller pore size membranes tended to contain fewer pollutants and a narrow size distribution. Under a constant flux of 11.5 L/m(2) h, the transmembrane pressure (TMP) varied narrowly between 38 and 53 KPa. Alongside this, a relatively hydrophilic membrane (PP-g-AA) showed the characteristics of lower TMP in comparison to hydrophobic membranes (PP). Indeed, the flux recovery was 30% higher than those of the original PPHFM. This investigation broadens our understanding of membrane modifying and fouling behavior in integrated MBRs.

关键词： Microbial fuel cell   Slaughterhouse wastewater   Nitrogen recovery   Biotreatment   Electricity generation  

摘要： A novel integrated system consisted of microbial fuel cell, aerobic bioreactor, and anoxic bioreactor (MFC-AB-ANB) was designed and constructed to investigate its potential for the treatment of slaughterhouses wastewater associated with power generation and nitrogen recovery. A biocathodic tubular type MFC was used in this study and was inoculated with freshly collected activated sludge. The MFC-AB-ANB system was continuously operated for 163 days. The results revealed that maximum efficiencies of COD removal, ammonium oxidation, nitrate reduction, nitrogen recovery, Columbic efficiency, and power generation were 99%, 99.3%, 100%, 100%, 13.37% and 162.55 mW/m(2), respectively. A mathematical model was developed based on Nernst-Monod model coupled with nitrification-denitrification model to predicate and describe the removal of COD, ammonium, and nitrate during continuous operation of the system. Significant agreement between the predicted and experimental results was observed for the removal of COD, ammonium, nitrate, and power generation with determination coefficients of 0.9750, 0.95675, 0.95499, and 0.89897, respectively.

关键词： Aerobic sludge   Floc size   Shear rate   Couette-taylor bioreactor  

摘要： Biological floc size is an important reactor microenvironment parameter that is often not experimentally controlled due to a lack of suitable methods. Here, we introduce the Couette-Taylor bioreactor (CTB) as an improved tool for controlling biological floc size, specifically as compared with bubble -column sequencing batch reactors (SBRs). A CTB consists of two concentric walls, either of which may be rotated to induce fluid motion. The induced flow produces hydrodynamic shear which is more uniform than that produced through aeration in SBRs. Because hydrodynamic shear is a major parameter controlling floc size, we hypothesized the ability to better control shear rates within a CTB would enable better -controlled floc sizes. To test this hypothesis, we measured the particle size distributions of activated sludge flocs from CTBs with either inner (iCTB) or outer (oCTB) rotating walls as well as SBRs with varying height to diameter ratios (0.5,1.1, and 9.4). The rotation speed of the CTBs and aeration rate of the SBRs were varied to produce predicted mean shear rates from 25 to 250 s(-1). Further, the shear rate distributions for each experiment were estimated using computational fluid dynamics (CFD). In all SBR experiments, the floc distributions did not significantly vary with shear rate or geometry, likely because shear rates (estimated by CFD) differed much less than originally predicted by theory. In the CTB experiments, the mean particle size decreased proportionally with increased hydrodynamic shear, and iCTBs produced particle size distributions with smaller coefficients of variation than oCTBs (0.3 vs. 0.5-0.7, respectively). (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Backwash   Membrane bioreactors   Physical cleaning   Fouling mitigation   Relaxation   Sludge rheology  

摘要： Fouling is one of the most pressing limitations during operation of membrane bioreactors, as it increases operating costs and is the cause of short membrane lifespans. Conducting effective physical cleanings is thus essential for keeping membrane operation above viable performance limits. The nature of organic foulants present in the sludge and the membrane properties are among the most influential factors determining fouling development and thus, efficiency of fouling mitigation approaches. The role of other factors like sludge viscosity on fouling is still unclear, given that contradictory effects have been reported in the literature. In the present study we use a new research approach by which the complex interplay between fouling type, levels of permeate flux, membrane material and feed properties is analyzed, and the influence of these factors on critical flux and membrane permeability is evaluated. A variety of systems including activated sludge and model solutions with distinct rheological behavior has been investigated for two membranes differing in pore size distribution. We present a novel method for assessing the efficiency of fouling removal by backwash and compare it with the efficiency achieved by means of relaxation. Results obtained have proven that backwash delays development of critical fouling as compared with relaxation and reduces fouling irreversibility regardless of fluid rheology. It was shown that backwash is especially effective for membranes for which internal fouling is the main cause of loss in permeability. Nonetheless, we found out that for membranes with tight pores, both relaxation and backwash are equally effective. The critical flux decreases significantly for high-viscosity fluids, such as activated sludge. This effect is mainly caused by an intensified concentration polarization at the feed side rather than by internal fouling events. However, membrane permeability has been proven to rely more on the permeate viscosity than on th

关键词： Antibiotic   Mycophenolic acid   Penicillium brevicompactum   Fermentation  

摘要： Batch and fed-batch fermentation processes for the production of mycophenolic acid (MPA) were optimized and compared. MPA was produced using the microfungus Penicillium brevicompactwn. Different feeding strategies were assessed in fed-batch fermentations in a 14 L stirred bioreactor. A batch fermentation attained a maximum total (extracellular and intracellular) MPA concentration of 1.26 g/L after 288 h. The best fed-batch operation involving a constant-rate feeding of sorbitol (a feeding rate = 0.07 g/min, from 48 h to 240 h) and the pH controlled at 6, enhanced the total maximum MPA concentration to 3.26 g/L. The yield of MPA on substrate was 0.028 g/g, some 47% greater than in the aforementioned batch culture. The fermentation was highly aerobic. The fermentation temperature was 25 degrees C. Glucose could be used as an effective substrate instead of sorbitol, but the final total MPA concentration in a fed-batch fermentation using glucose was reduced to 2.72 g/L.

关键词： Single-use bioreactor   Stirred tank reactor   Heat transfer   Overall heat transfer coefficient   Scale up   Wilson plot method  

摘要： Stirred single-use bioreactors are present throughout the biopharmaceutical manufacturing of high-value cell products. Lots of work has been done determining relevant process engineering parameters to enable reliable scale-up on a physical foundation. However, heat transfer capabilities of such systems are not well described, yet. As processes are further intensified and microbial hosts offer interesting opportunities, heat transfer becomes increasingly relevant. The present work gives a comprehensive overview on the specific implications of a stirred, 50 L, single-use bioreactor by means of heat transfer. This includes the dependency of overall heat transfer coefficients on process parameters, i.e. stirring frequency and jacket flow, with a corresponding statistical analysis. Experimental results are compared against a theoretical approach, based on Nu numbers. Although a systematic discrepancy on the description of the jacket-side heat transfer is present, there already is a good agreement between experimental and literature derived values. The jacket-side impact on the overall performance is then analyzed in detail by the Wilson plot method, underlining the major influence of this aspect. Since the polymer-film layer represents a significant feature of single-use bioreactors, this effect has been investigated for two film types as well. Finally, a first comparison of the 50 L against a 200 L bioreactor was carried out to identify scale-dependencies.

关键词： Tilted panel   Activated sludge filtration   Membrane bioreactor   Membrane fouling   Multi-phases flow  

摘要： Membrane fouling is a major challenge in membrane bioreactors (MBRs) and its effective handling is the key to improve their competitiveness. Tilting panel system offers significant improvements for fouling control but is strictly limited to one-sided panel. In this study, we assess a two-way switch tilting panel system that enables two-sided membranes and project its implications on performance and energy footprint. Results show that tilting a panel improves permeance by up to 20% to reach a plateau flux thanks to better contacts between air bubbles and the membrane surface to scour-off the foulant. A plateau permeance could be achieved at aeration rate of as low as 0.901min(-1), a condition untenable by vertical panel even at twice of the aeration rate. Switching at short periods ( < 5min) can maintain the hydraulic performance as in no-switch (static system), enables application of a two-sided switching panel. A comparison of vertical panel under 1.801min(-1) aeration rate with a switching panel at a half of the rate, switched at 1 min period shows approximate to 1.0% higher permeance of the later. Since periodic switching consumes a very low energy (0.55% of the total of 0.276 kWh m(-3)), with reduction of aeration by 50%, the switching tilted panel offers 41% more energy efficient than a referenced full-scale MBR (0.390 kWh m(-3)). Overall results are very compelling and highly attractive for significant improvements of MBR technologies.